hotspot/src/share/vm/runtime/mutex.cpp
author mikael
Tue, 24 Dec 2013 11:48:39 -0800
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8029233: Update copyright year to match last edit in jdk8 hotspot repository for 2013 Summary: Copyright year updated for files modified during 2013 Reviewed-by: twisti, iveresov
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/*
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 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 *
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 * This code is free software; you can redistribute it and/or modify it
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 * under the terms of the GNU General Public License version 2 only, as
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 * published by the Free Software Foundation.
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 *
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * version 2 for more details (a copy is included in the LICENSE file that
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 * accompanied this code).
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 *
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 * You should have received a copy of the GNU General Public License version
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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 *
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 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * or visit www.oracle.com if you need additional information or have any
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 * questions.
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 *
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 */
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#include "precompiled.hpp"
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#include "runtime/mutex.hpp"
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#include "runtime/osThread.hpp"
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#include "runtime/thread.inline.hpp"
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#include "utilities/events.hpp"
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#ifdef TARGET_OS_FAMILY_linux
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# include "mutex_linux.inline.hpp"
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#endif
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#ifdef TARGET_OS_FAMILY_solaris
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# include "mutex_solaris.inline.hpp"
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#endif
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#ifdef TARGET_OS_FAMILY_windows
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# include "mutex_windows.inline.hpp"
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#endif
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#ifdef TARGET_OS_FAMILY_bsd
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# include "mutex_bsd.inline.hpp"
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#endif
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// o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o
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//
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// Native Monitor-Mutex locking - theory of operations
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//
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// * Native Monitors are completely unrelated to Java-level monitors,
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//   although the "back-end" slow-path implementations share a common lineage.
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//   See objectMonitor:: in synchronizer.cpp.
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//   Native Monitors do *not* support nesting or recursion but otherwise
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//   they're basically Hoare-flavor monitors.
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//
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// * A thread acquires ownership of a Monitor/Mutex by CASing the LockByte
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//   in the _LockWord from zero to non-zero.  Note that the _Owner field
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//   is advisory and is used only to verify that the thread calling unlock()
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//   is indeed the last thread to have acquired the lock.
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//
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// * Contending threads "push" themselves onto the front of the contention
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//   queue -- called the cxq -- with CAS and then spin/park.
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//   The _LockWord contains the LockByte as well as the pointer to the head
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//   of the cxq.  Colocating the LockByte with the cxq precludes certain races.
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//
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// * Using a separately addressable LockByte allows for CAS:MEMBAR or CAS:0
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//   idioms.  We currently use MEMBAR in the uncontended unlock() path, as
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//   MEMBAR often has less latency than CAS.  If warranted, we could switch to
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//   a CAS:0 mode, using timers to close the resultant race, as is done
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//   with Java Monitors in synchronizer.cpp.
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//
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//   See the following for a discussion of the relative cost of atomics (CAS)
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//   MEMBAR, and ways to eliminate such instructions from the common-case paths:
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//   -- http://blogs.sun.com/dave/entry/biased_locking_in_hotspot
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//   -- http://blogs.sun.com/dave/resource/MustangSync.pdf
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//   -- http://blogs.sun.com/dave/resource/synchronization-public2.pdf
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//   -- synchronizer.cpp
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//
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// * Overall goals - desiderata
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//   1. Minimize context switching
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//   2. Minimize lock migration
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//   3. Minimize CPI -- affinity and locality
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//   4. Minimize the execution of high-latency instructions such as CAS or MEMBAR
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//   5. Minimize outer lock hold times
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//   6. Behave gracefully on a loaded system
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//
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// * Thread flow and list residency:
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//
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//   Contention queue --> EntryList --> OnDeck --> Owner --> !Owner
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//   [..resident on monitor list..]
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//   [...........contending..................]
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//
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//   -- The contention queue (cxq) contains recently-arrived threads (RATs).
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//      Threads on the cxq eventually drain into the EntryList.
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//   -- Invariant: a thread appears on at most one list -- cxq, EntryList
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//      or WaitSet -- at any one time.
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//   -- For a given monitor there can be at most one "OnDeck" thread at any
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//      given time but if needbe this particular invariant could be relaxed.
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//
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// * The WaitSet and EntryList linked lists are composed of ParkEvents.
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//   I use ParkEvent instead of threads as ParkEvents are immortal and
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//   type-stable, meaning we can safely unpark() a possibly stale
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//   list element in the unlock()-path.  (That's benign).
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//
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// * Succession policy - providing for progress:
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//
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//   As necessary, the unlock()ing thread identifies, unlinks, and unparks
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//   an "heir presumptive" tentative successor thread from the EntryList.
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//   This becomes the so-called "OnDeck" thread, of which there can be only
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//   one at any given time for a given monitor.  The wakee will recontend
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//   for ownership of monitor.
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//
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//   Succession is provided for by a policy of competitive handoff.
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//   The exiting thread does _not_ grant or pass ownership to the
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//   successor thread.  (This is also referred to as "handoff" succession").
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//   Instead the exiting thread releases ownership and possibly wakes
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//   a successor, so the successor can (re)compete for ownership of the lock.
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//
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//   Competitive handoff provides excellent overall throughput at the expense
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//   of short-term fairness.  If fairness is a concern then one remedy might
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//   be to add an AcquireCounter field to the monitor.  After a thread acquires
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//   the lock it will decrement the AcquireCounter field.  When the count
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//   reaches 0 the thread would reset the AcquireCounter variable, abdicate
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//   the lock directly to some thread on the EntryList, and then move itself to the
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//   tail of the EntryList.
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//
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//   But in practice most threads engage or otherwise participate in resource
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//   bounded producer-consumer relationships, so lock domination is not usually
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//   a practical concern.  Recall too, that in general it's easier to construct
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//   a fair lock from a fast lock, but not vice-versa.
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//
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// * The cxq can have multiple concurrent "pushers" but only one concurrent
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//   detaching thread.  This mechanism is immune from the ABA corruption.
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//   More precisely, the CAS-based "push" onto cxq is ABA-oblivious.
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//   We use OnDeck as a pseudo-lock to enforce the at-most-one detaching
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//   thread constraint.
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//
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// * Taken together, the cxq and the EntryList constitute or form a
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//   single logical queue of threads stalled trying to acquire the lock.
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//   We use two distinct lists to reduce heat on the list ends.
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//   Threads in lock() enqueue onto cxq while threads in unlock() will
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//   dequeue from the EntryList.  (c.f. Michael Scott's "2Q" algorithm).
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//   A key desideratum is to minimize queue & monitor metadata manipulation
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//   that occurs while holding the "outer" monitor lock -- that is, we want to
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//   minimize monitor lock holds times.
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//
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//   The EntryList is ordered by the prevailing queue discipline and
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//   can be organized in any convenient fashion, such as a doubly-linked list or
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//   a circular doubly-linked list.  If we need a priority queue then something akin
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//   to Solaris' sleepq would work nicely.  Viz.,
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//   -- http://agg.eng/ws/on10_nightly/source/usr/src/uts/common/os/sleepq.c.
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//   -- http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/os/sleepq.c
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//   Queue discipline is enforced at ::unlock() time, when the unlocking thread
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//   drains the cxq into the EntryList, and orders or reorders the threads on the
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//   EntryList accordingly.
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//
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//   Barring "lock barging", this mechanism provides fair cyclic ordering,
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//   somewhat similar to an elevator-scan.
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//
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// * OnDeck
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//   --  For a given monitor there can be at most one OnDeck thread at any given
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//       instant.  The OnDeck thread is contending for the lock, but has been
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//       unlinked from the EntryList and cxq by some previous unlock() operations.
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//       Once a thread has been designated the OnDeck thread it will remain so
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//       until it manages to acquire the lock -- being OnDeck is a stable property.
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//   --  Threads on the EntryList or cxq are _not allowed to attempt lock acquisition.
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//   --  OnDeck also serves as an "inner lock" as follows.  Threads in unlock() will, after
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//       having cleared the LockByte and dropped the outer lock,  attempt to "trylock"
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//       OnDeck by CASing the field from null to non-null.  If successful, that thread
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//       is then responsible for progress and succession and can use CAS to detach and
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//       drain the cxq into the EntryList.  By convention, only this thread, the holder of
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//       the OnDeck inner lock, can manipulate the EntryList or detach and drain the
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//       RATs on the cxq into the EntryList.  This avoids ABA corruption on the cxq as
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//       we allow multiple concurrent "push" operations but restrict detach concurrency
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//       to at most one thread.  Having selected and detached a successor, the thread then
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//       changes the OnDeck to refer to that successor, and then unparks the successor.
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//       That successor will eventually acquire the lock and clear OnDeck.  Beware
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//       that the OnDeck usage as a lock is asymmetric.  A thread in unlock() transiently
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//       "acquires" OnDeck, performs queue manipulations, passes OnDeck to some successor,
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//       and then the successor eventually "drops" OnDeck.  Note that there's never
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//       any sense of contention on the inner lock, however.  Threads never contend
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//       or wait for the inner lock.
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//   --  OnDeck provides for futile wakeup throttling a described in section 3.3 of
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//       See http://www.usenix.org/events/jvm01/full_papers/dice/dice.pdf
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//       In a sense, OnDeck subsumes the ObjectMonitor _Succ and ObjectWaiter
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//       TState fields found in Java-level objectMonitors.  (See synchronizer.cpp).
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//
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// * Waiting threads reside on the WaitSet list -- wait() puts
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//   the caller onto the WaitSet.  Notify() or notifyAll() simply
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//   transfers threads from the WaitSet to either the EntryList or cxq.
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//   Subsequent unlock() operations will eventually unpark the notifyee.
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//   Unparking a notifee in notify() proper is inefficient - if we were to do so
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//   it's likely the notifyee would simply impale itself on the lock held
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//   by the notifier.
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//
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// * The mechanism is obstruction-free in that if the holder of the transient
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//   OnDeck lock in unlock() is preempted or otherwise stalls, other threads
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//   can still acquire and release the outer lock and continue to make progress.
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//   At worst, waking of already blocked contending threads may be delayed,
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//   but nothing worse.  (We only use "trylock" operations on the inner OnDeck
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//   lock).
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//
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// * Note that thread-local storage must be initialized before a thread
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//   uses Native monitors or mutexes.  The native monitor-mutex subsystem
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//   depends on Thread::current().
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//
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// * The monitor synchronization subsystem avoids the use of native
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//   synchronization primitives except for the narrow platform-specific
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//   park-unpark abstraction.  See the comments in os_solaris.cpp regarding
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//   the semantics of park-unpark.  Put another way, this monitor implementation
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//   depends only on atomic operations and park-unpark.  The monitor subsystem
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//   manages all RUNNING->BLOCKED and BLOCKED->READY transitions while the
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//   underlying OS manages the READY<->RUN transitions.
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//
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// * The memory consistency model provide by lock()-unlock() is at least as
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//   strong or stronger than the Java Memory model defined by JSR-133.
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//   That is, we guarantee at least entry consistency, if not stronger.
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//   See http://g.oswego.edu/dl/jmm/cookbook.html.
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//
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// * Thread:: currently contains a set of purpose-specific ParkEvents:
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//   _MutexEvent, _ParkEvent, etc.  A better approach might be to do away with
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//   the purpose-specific ParkEvents and instead implement a general per-thread
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//   stack of available ParkEvents which we could provision on-demand.  The
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//   stack acts as a local cache to avoid excessive calls to ParkEvent::Allocate()
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//   and ::Release().  A thread would simply pop an element from the local stack before it
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//   enqueued or park()ed.  When the contention was over the thread would
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//   push the no-longer-needed ParkEvent back onto its stack.
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//
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// * A slightly reduced form of ILock() and IUnlock() have been partially
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//   model-checked (Murphi) for safety and progress at T=1,2,3 and 4.
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//   It'd be interesting to see if TLA/TLC could be useful as well.
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//
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// * Mutex-Monitor is a low-level "leaf" subsystem.  That is, the monitor
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//   code should never call other code in the JVM that might itself need to
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//   acquire monitors or mutexes.  That's true *except* in the case of the
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//   ThreadBlockInVM state transition wrappers.  The ThreadBlockInVM DTOR handles
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//   mutator reentry (ingress) by checking for a pending safepoint in which case it will
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//   call SafepointSynchronize::block(), which in turn may call Safepoint_lock->lock(), etc.
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//   In that particular case a call to lock() for a given Monitor can end up recursively
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//   calling lock() on another monitor.   While distasteful, this is largely benign
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//   as the calls come from jacket that wraps lock(), and not from deep within lock() itself.
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//
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//   It's unfortunate that native mutexes and thread state transitions were convolved.
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//   They're really separate concerns and should have remained that way.  Melding
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//   them together was facile -- a bit too facile.   The current implementation badly
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//   conflates the two concerns.
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//
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// * TODO-FIXME:
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//
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//   -- Add DTRACE probes for contended acquire, contended acquired, contended unlock
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//      We should also add DTRACE probes in the ParkEvent subsystem for
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//      Park-entry, Park-exit, and Unpark.
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//
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//   -- We have an excess of mutex-like constructs in the JVM, namely:
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//      1. objectMonitors for Java-level synchronization (synchronizer.cpp)
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//      2. low-level muxAcquire and muxRelease
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//      3. low-level spinAcquire and spinRelease
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//      4. native Mutex:: and Monitor::
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//      5. jvm_raw_lock() and _unlock()
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//      6. JVMTI raw monitors -- distinct from (5) despite having a confusingly
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//         similar name.
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//
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// o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o-o
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// CASPTR() uses the canonical argument order that dominates in the literature.
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// Our internal cmpxchg_ptr() uses a bastardized ordering to accommodate Sun .il templates.
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#define CASPTR(a,c,s) intptr_t(Atomic::cmpxchg_ptr ((void *)(s),(void *)(a),(void *)(c)))
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#define UNS(x) (uintptr_t(x))
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#define TRACE(m) { static volatile int ctr = 0 ; int x = ++ctr ; if ((x & (x-1))==0) { ::printf ("%d:%s\n", x, #m); ::fflush(stdout); }}
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// Simplistic low-quality Marsaglia SHIFT-XOR RNG.
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// Bijective except for the trailing mask operation.
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// Useful for spin loops as the compiler can't optimize it away.
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static inline jint MarsagliaXORV (jint x) {
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  if (x == 0) x = 1|os::random() ;
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  x ^= x << 6;
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  x ^= ((unsigned)x) >> 21;
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  x ^= x << 7 ;
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  return x & 0x7FFFFFFF ;
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}
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static inline jint MarsagliaXOR (jint * const a) {
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  jint x = *a ;
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  if (x == 0) x = UNS(a)|1 ;
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  x ^= x << 6;
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  x ^= ((unsigned)x) >> 21;
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  x ^= x << 7 ;
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  *a = x ;
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  return x & 0x7FFFFFFF ;
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}
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static int Stall (int its) {
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  static volatile jint rv = 1 ;
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  volatile int OnFrame = 0 ;
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  jint v = rv ^ UNS(OnFrame) ;
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  while (--its >= 0) {
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    v = MarsagliaXORV (v) ;
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  }
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  // Make this impossible for the compiler to optimize away,
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  // but (mostly) avoid W coherency sharing on MP systems.
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  if (v == 0x12345) rv = v ;
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  return v ;
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}
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int Monitor::TryLock () {
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  intptr_t v = _LockWord.FullWord ;
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  for (;;) {
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    if ((v & _LBIT) != 0) return 0 ;
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    const intptr_t u = CASPTR (&_LockWord, v, v|_LBIT) ;
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    if (v == u) return 1 ;
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    v = u ;
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  }
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}
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int Monitor::TryFast () {
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  // Optimistic fast-path form ...
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  // Fast-path attempt for the common uncontended case.
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  // Avoid RTS->RTO $ coherence upgrade on typical SMP systems.
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  intptr_t v = CASPTR (&_LockWord, 0, _LBIT) ;  // agro ...
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  if (v == 0) return 1 ;
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  for (;;) {
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    if ((v & _LBIT) != 0) return 0 ;
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    const intptr_t u = CASPTR (&_LockWord, v, v|_LBIT) ;
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    if (v == u) return 1 ;
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    v = u ;
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  }
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}
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int Monitor::ILocked () {
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  const intptr_t w = _LockWord.FullWord & 0xFF ;
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  assert (w == 0 || w == _LBIT, "invariant") ;
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  return w == _LBIT ;
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}
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// Polite TATAS spinlock with exponential backoff - bounded spin.
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// Ideally we'd use processor cycles, time or vtime to control
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// the loop, but we currently use iterations.
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// All the constants within were derived empirically but work over
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// over the spectrum of J2SE reference platforms.
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// On Niagara-class systems the back-off is unnecessary but
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// is relatively harmless.  (At worst it'll slightly retard
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// acquisition times).  The back-off is critical for older SMP systems
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// where constant fetching of the LockWord would otherwise impair
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// scalability.
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//
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// Clamp spinning at approximately 1/2 of a context-switch round-trip.
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// See synchronizer.cpp for details and rationale.
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int Monitor::TrySpin (Thread * const Self) {
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  if (TryLock())    return 1 ;
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  if (!os::is_MP()) return 0 ;
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  int Probes  = 0 ;
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  int Delay   = 0 ;
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  int Steps   = 0 ;
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  int SpinMax = NativeMonitorSpinLimit ;
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  int flgs    = NativeMonitorFlags ;
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  for (;;) {
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    intptr_t v = _LockWord.FullWord;
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    if ((v & _LBIT) == 0) {
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   363
      if (CASPTR (&_LockWord, v, v|_LBIT) == v) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   364
        return 1 ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   365
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   366
      continue ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   367
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   368
489c9b5090e2 Initial load
duke
parents:
diff changeset
   369
    if ((flgs & 8) == 0) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   370
      SpinPause () ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   371
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   372
489c9b5090e2 Initial load
duke
parents:
diff changeset
   373
    // Periodically increase Delay -- variable Delay form
489c9b5090e2 Initial load
duke
parents:
diff changeset
   374
    // conceptually: delay *= 1 + 1/Exponent
489c9b5090e2 Initial load
duke
parents:
diff changeset
   375
    ++ Probes;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   376
    if (Probes > SpinMax) return 0 ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   377
489c9b5090e2 Initial load
duke
parents:
diff changeset
   378
    if ((Probes & 0x7) == 0) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   379
      Delay = ((Delay << 1)|1) & 0x7FF ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   380
      // CONSIDER: Delay += 1 + (Delay/4); Delay &= 0x7FF ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   381
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   382
489c9b5090e2 Initial load
duke
parents:
diff changeset
   383
    if (flgs & 2) continue ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   384
489c9b5090e2 Initial load
duke
parents:
diff changeset
   385
    // Consider checking _owner's schedctl state, if OFFPROC abort spin.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   386
    // If the owner is OFFPROC then it's unlike that the lock will be dropped
489c9b5090e2 Initial load
duke
parents:
diff changeset
   387
    // in a timely fashion, which suggests that spinning would not be fruitful
489c9b5090e2 Initial load
duke
parents:
diff changeset
   388
    // or profitable.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   389
489c9b5090e2 Initial load
duke
parents:
diff changeset
   390
    // Stall for "Delay" time units - iterations in the current implementation.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   391
    // Avoid generating coherency traffic while stalled.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   392
    // Possible ways to delay:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   393
    //   PAUSE, SLEEP, MEMBAR #sync, MEMBAR #halt,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   394
    //   wr %g0,%asi, gethrtime, rdstick, rdtick, rdtsc, etc. ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
   395
    // Note that on Niagara-class systems we want to minimize STs in the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   396
    // spin loop.  N1 and brethren write-around the L1$ over the xbar into the L2$.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   397
    // Furthermore, they don't have a W$ like traditional SPARC processors.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   398
    // We currently use a Marsaglia Shift-Xor RNG loop.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   399
    Steps += Delay ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   400
    if (Self != NULL) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   401
      jint rv = Self->rng[0] ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   402
      for (int k = Delay ; --k >= 0; ) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   403
        rv = MarsagliaXORV (rv) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   404
        if ((flgs & 4) == 0 && SafepointSynchronize::do_call_back()) return 0 ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   405
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   406
      Self->rng[0] = rv ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   407
    } else {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   408
      Stall (Delay) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   409
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   410
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   411
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   412
489c9b5090e2 Initial load
duke
parents:
diff changeset
   413
static int ParkCommon (ParkEvent * ev, jlong timo) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   414
  // Diagnostic support - periodically unwedge blocked threads
489c9b5090e2 Initial load
duke
parents:
diff changeset
   415
  intx nmt = NativeMonitorTimeout ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   416
  if (nmt > 0 && (nmt < timo || timo <= 0)) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   417
     timo = nmt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   418
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   419
  int err = OS_OK ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   420
  if (0 == timo) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   421
    ev->park() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   422
  } else {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   423
    err = ev->park(timo) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   424
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   425
  return err ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   426
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   427
489c9b5090e2 Initial load
duke
parents:
diff changeset
   428
inline int Monitor::AcquireOrPush (ParkEvent * ESelf) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   429
  intptr_t v = _LockWord.FullWord ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   430
  for (;;) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   431
    if ((v & _LBIT) == 0) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   432
      const intptr_t u = CASPTR (&_LockWord, v, v|_LBIT) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   433
      if (u == v) return 1 ;        // indicate acquired
489c9b5090e2 Initial load
duke
parents:
diff changeset
   434
      v = u ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   435
    } else {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   436
      // Anticipate success ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
   437
      ESelf->ListNext = (ParkEvent *) (v & ~_LBIT) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   438
      const intptr_t u = CASPTR (&_LockWord, v, intptr_t(ESelf)|_LBIT) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   439
      if (u == v) return 0 ;        // indicate pushed onto cxq
489c9b5090e2 Initial load
duke
parents:
diff changeset
   440
      v = u ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   441
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   442
    // Interference - LockWord change - just retry
489c9b5090e2 Initial load
duke
parents:
diff changeset
   443
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   444
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   445
489c9b5090e2 Initial load
duke
parents:
diff changeset
   446
// ILock and IWait are the lowest level primitive internal blocking
489c9b5090e2 Initial load
duke
parents:
diff changeset
   447
// synchronization functions.  The callers of IWait and ILock must have
489c9b5090e2 Initial load
duke
parents:
diff changeset
   448
// performed any needed state transitions beforehand.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   449
// IWait and ILock may directly call park() without any concern for thread state.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   450
// Note that ILock and IWait do *not* access _owner.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   451
// _owner is a higher-level logical concept.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   452
489c9b5090e2 Initial load
duke
parents:
diff changeset
   453
void Monitor::ILock (Thread * Self) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   454
  assert (_OnDeck != Self->_MutexEvent, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   455
489c9b5090e2 Initial load
duke
parents:
diff changeset
   456
  if (TryFast()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   457
 Exeunt:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   458
    assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   459
    return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   460
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   461
489c9b5090e2 Initial load
duke
parents:
diff changeset
   462
  ParkEvent * const ESelf = Self->_MutexEvent ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   463
  assert (_OnDeck != ESelf, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   464
489c9b5090e2 Initial load
duke
parents:
diff changeset
   465
  // As an optimization, spinners could conditionally try to set ONDECK to _LBIT
489c9b5090e2 Initial load
duke
parents:
diff changeset
   466
  // Synchronizer.cpp uses a similar optimization.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   467
  if (TrySpin (Self)) goto Exeunt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   468
489c9b5090e2 Initial load
duke
parents:
diff changeset
   469
  // Slow-path - the lock is contended.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   470
  // Either Enqueue Self on cxq or acquire the outer lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   471
  // LockWord encoding = (cxq,LOCKBYTE)
489c9b5090e2 Initial load
duke
parents:
diff changeset
   472
  ESelf->reset() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   473
  OrderAccess::fence() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   474
489c9b5090e2 Initial load
duke
parents:
diff changeset
   475
  // Optional optimization ... try barging on the inner lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
   476
  if ((NativeMonitorFlags & 32) && CASPTR (&_OnDeck, NULL, UNS(Self)) == 0) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   477
    goto OnDeck_LOOP ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   478
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   479
489c9b5090e2 Initial load
duke
parents:
diff changeset
   480
  if (AcquireOrPush (ESelf)) goto Exeunt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   481
489c9b5090e2 Initial load
duke
parents:
diff changeset
   482
  // At any given time there is at most one ondeck thread.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   483
  // ondeck implies not resident on cxq and not resident on EntryList
489c9b5090e2 Initial load
duke
parents:
diff changeset
   484
  // Only the OnDeck thread can try to acquire -- contended for -- the lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   485
  // CONSIDER: use Self->OnDeck instead of m->OnDeck.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   486
  // Deschedule Self so that others may run.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   487
  while (_OnDeck != ESelf) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   488
    ParkCommon (ESelf, 0) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   489
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   490
489c9b5090e2 Initial load
duke
parents:
diff changeset
   491
  // Self is now in the ONDECK position and will remain so until it
489c9b5090e2 Initial load
duke
parents:
diff changeset
   492
  // manages to acquire the lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   493
 OnDeck_LOOP:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   494
  for (;;) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   495
    assert (_OnDeck == ESelf, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   496
    if (TrySpin (Self)) break ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   497
    // CONSIDER: if ESelf->TryPark() && TryLock() break ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
   498
    // It's probably wise to spin only if we *actually* blocked
489c9b5090e2 Initial load
duke
parents:
diff changeset
   499
    // CONSIDER: check the lockbyte, if it remains set then
489c9b5090e2 Initial load
duke
parents:
diff changeset
   500
    // preemptively drain the cxq into the EntryList.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   501
    // The best place and time to perform queue operations -- lock metadata --
489c9b5090e2 Initial load
duke
parents:
diff changeset
   502
    // is _before having acquired the outer lock, while waiting for the lock to drop.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   503
    ParkCommon (ESelf, 0) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   504
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   505
489c9b5090e2 Initial load
duke
parents:
diff changeset
   506
  assert (_OnDeck == ESelf, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   507
  _OnDeck = NULL ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   508
489c9b5090e2 Initial load
duke
parents:
diff changeset
   509
  // Note that we current drop the inner lock (clear OnDeck) in the slow-path
489c9b5090e2 Initial load
duke
parents:
diff changeset
   510
  // epilog immediately after having acquired the outer lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   511
  // But instead we could consider the following optimizations:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   512
  // A. Shift or defer dropping the inner lock until the subsequent IUnlock() operation.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   513
  //    This might avoid potential reacquisition of the inner lock in IUlock().
489c9b5090e2 Initial load
duke
parents:
diff changeset
   514
  // B. While still holding the inner lock, attempt to opportunistically select
489c9b5090e2 Initial load
duke
parents:
diff changeset
   515
  //    and unlink the next ONDECK thread from the EntryList.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   516
  //    If successful, set ONDECK to refer to that thread, otherwise clear ONDECK.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   517
  //    It's critical that the select-and-unlink operation run in constant-time as
489c9b5090e2 Initial load
duke
parents:
diff changeset
   518
  //    it executes when holding the outer lock and may artificially increase the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   519
  //    effective length of the critical section.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   520
  // Note that (A) and (B) are tantamount to succession by direct handoff for
489c9b5090e2 Initial load
duke
parents:
diff changeset
   521
  // the inner lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   522
  goto Exeunt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   523
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   524
489c9b5090e2 Initial load
duke
parents:
diff changeset
   525
void Monitor::IUnlock (bool RelaxAssert) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   526
  assert (ILocked(), "invariant") ;
11408
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   527
  // Conceptually we need a MEMBAR #storestore|#loadstore barrier or fence immediately
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   528
  // before the store that releases the lock.  Crucially, all the stores and loads in the
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   529
  // critical section must be globally visible before the store of 0 into the lock-word
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   530
  // that releases the lock becomes globally visible.  That is, memory accesses in the
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   531
  // critical section should not be allowed to bypass or overtake the following ST that
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   532
  // releases the lock.  As such, to prevent accesses within the critical section
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   533
  // from "leaking" out, we need a release fence between the critical section and the
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   534
  // store that releases the lock.  In practice that release barrier is elided on
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   535
  // platforms with strong memory models such as TSO.
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   536
  //
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   537
  // Note that the OrderAccess::storeload() fence that appears after unlock store
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   538
  // provides for progress conditions and succession and is _not related to exclusion
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   539
  // safety or lock release consistency.
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   540
  OrderAccess::release_store(&_LockWord.Bytes[_LSBINDEX], 0); // drop outer lock
3d678c27a7e2 7050298: ARM: SIGSEGV in JNIHandleBlock::allocate_handle
vladidan
parents: 10565
diff changeset
   541
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
   542
  OrderAccess::storeload ();
489c9b5090e2 Initial load
duke
parents:
diff changeset
   543
  ParkEvent * const w = _OnDeck ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   544
  assert (RelaxAssert || w != Thread::current()->_MutexEvent, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   545
  if (w != NULL) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   546
    // Either we have a valid ondeck thread or ondeck is transiently "locked"
489c9b5090e2 Initial load
duke
parents:
diff changeset
   547
    // by some exiting thread as it arranges for succession.  The LSBit of
489c9b5090e2 Initial load
duke
parents:
diff changeset
   548
    // OnDeck allows us to discriminate two cases.  If the latter, the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   549
    // responsibility for progress and succession lies with that other thread.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   550
    // For good performance, we also depend on the fact that redundant unpark()
489c9b5090e2 Initial load
duke
parents:
diff changeset
   551
    // operations are cheap.  That is, repeated Unpark()ing of the ONDECK thread
489c9b5090e2 Initial load
duke
parents:
diff changeset
   552
    // is inexpensive.  This approach provides implicit futile wakeup throttling.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   553
    // Note that the referent "w" might be stale with respect to the lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   554
    // In that case the following unpark() is harmless and the worst that'll happen
489c9b5090e2 Initial load
duke
parents:
diff changeset
   555
    // is a spurious return from a park() operation.  Critically, if "w" _is stale,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   556
    // then progress is known to have occurred as that means the thread associated
489c9b5090e2 Initial load
duke
parents:
diff changeset
   557
    // with "w" acquired the lock.  In that case this thread need take no further
489c9b5090e2 Initial load
duke
parents:
diff changeset
   558
    // action to guarantee progress.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   559
    if ((UNS(w) & _LBIT) == 0) w->unpark() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   560
    return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   561
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   562
489c9b5090e2 Initial load
duke
parents:
diff changeset
   563
  intptr_t cxq = _LockWord.FullWord ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   564
  if (((cxq & ~_LBIT)|UNS(_EntryList)) == 0) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   565
    return ;      // normal fast-path exit - cxq and EntryList both empty
489c9b5090e2 Initial load
duke
parents:
diff changeset
   566
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   567
  if (cxq & _LBIT) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   568
    // Optional optimization ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
   569
    // Some other thread acquired the lock in the window since this
489c9b5090e2 Initial load
duke
parents:
diff changeset
   570
    // thread released it.  Succession is now that thread's responsibility.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   571
    return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   572
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   573
489c9b5090e2 Initial load
duke
parents:
diff changeset
   574
 Succession:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   575
  // Slow-path exit - this thread must ensure succession and progress.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   576
  // OnDeck serves as lock to protect cxq and EntryList.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   577
  // Only the holder of OnDeck can manipulate EntryList or detach the RATs from cxq.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   578
  // Avoid ABA - allow multiple concurrent producers (enqueue via push-CAS)
489c9b5090e2 Initial load
duke
parents:
diff changeset
   579
  // but only one concurrent consumer (detacher of RATs).
489c9b5090e2 Initial load
duke
parents:
diff changeset
   580
  // Consider protecting this critical section with schedctl on Solaris.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   581
  // Unlike a normal lock, however, the exiting thread "locks" OnDeck,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   582
  // picks a successor and marks that thread as OnDeck.  That successor
489c9b5090e2 Initial load
duke
parents:
diff changeset
   583
  // thread will then clear OnDeck once it eventually acquires the outer lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   584
  if (CASPTR (&_OnDeck, NULL, _LBIT) != UNS(NULL)) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   585
    return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   586
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   587
489c9b5090e2 Initial load
duke
parents:
diff changeset
   588
  ParkEvent * List = _EntryList ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   589
  if (List != NULL) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   590
    // Transfer the head of the EntryList to the OnDeck position.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   591
    // Once OnDeck, a thread stays OnDeck until it acquires the lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   592
    // For a given lock there is at most OnDeck thread at any one instant.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   593
   WakeOne:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   594
    assert (List == _EntryList, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   595
    ParkEvent * const w = List ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   596
    assert (RelaxAssert || w != Thread::current()->_MutexEvent, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   597
    _EntryList = w->ListNext ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   598
    // as a diagnostic measure consider setting w->_ListNext = BAD
489c9b5090e2 Initial load
duke
parents:
diff changeset
   599
    assert (UNS(_OnDeck) == _LBIT, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   600
    _OnDeck = w ;           // pass OnDeck to w.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   601
                            // w will clear OnDeck once it acquires the outer lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
   602
489c9b5090e2 Initial load
duke
parents:
diff changeset
   603
    // Another optional optimization ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
   604
    // For heavily contended locks it's not uncommon that some other
489c9b5090e2 Initial load
duke
parents:
diff changeset
   605
    // thread acquired the lock while this thread was arranging succession.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   606
    // Try to defer the unpark() operation - Delegate the responsibility
489c9b5090e2 Initial load
duke
parents:
diff changeset
   607
    // for unpark()ing the OnDeck thread to the current or subsequent owners
489c9b5090e2 Initial load
duke
parents:
diff changeset
   608
    // That is, the new owner is responsible for unparking the OnDeck thread.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   609
    OrderAccess::storeload() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   610
    cxq = _LockWord.FullWord ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   611
    if (cxq & _LBIT) return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   612
489c9b5090e2 Initial load
duke
parents:
diff changeset
   613
    w->unpark() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   614
    return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   615
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   616
489c9b5090e2 Initial load
duke
parents:
diff changeset
   617
  cxq = _LockWord.FullWord ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   618
  if ((cxq & ~_LBIT) != 0) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   619
    // The EntryList is empty but the cxq is populated.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   620
    // drain RATs from cxq into EntryList
489c9b5090e2 Initial load
duke
parents:
diff changeset
   621
    // Detach RATs segment with CAS and then merge into EntryList
489c9b5090e2 Initial load
duke
parents:
diff changeset
   622
    for (;;) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   623
      // optional optimization - if locked, the owner is responsible for succession
489c9b5090e2 Initial load
duke
parents:
diff changeset
   624
      if (cxq & _LBIT) goto Punt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   625
      const intptr_t vfy = CASPTR (&_LockWord, cxq, cxq & _LBIT) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   626
      if (vfy == cxq) break ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   627
      cxq = vfy ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   628
      // Interference - LockWord changed - Just retry
489c9b5090e2 Initial load
duke
parents:
diff changeset
   629
      // We can see concurrent interference from contending threads
489c9b5090e2 Initial load
duke
parents:
diff changeset
   630
      // pushing themselves onto the cxq or from lock-unlock operations.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   631
      // From the perspective of this thread, EntryList is stable and
489c9b5090e2 Initial load
duke
parents:
diff changeset
   632
      // the cxq is prepend-only -- the head is volatile but the interior
489c9b5090e2 Initial load
duke
parents:
diff changeset
   633
      // of the cxq is stable.  In theory if we encounter interference from threads
489c9b5090e2 Initial load
duke
parents:
diff changeset
   634
      // pushing onto cxq we could simply break off the original cxq suffix and
489c9b5090e2 Initial load
duke
parents:
diff changeset
   635
      // move that segment to the EntryList, avoiding a 2nd or multiple CAS attempts
489c9b5090e2 Initial load
duke
parents:
diff changeset
   636
      // on the high-traffic LockWord variable.   For instance lets say the cxq is "ABCD"
489c9b5090e2 Initial load
duke
parents:
diff changeset
   637
      // when we first fetch cxq above.  Between the fetch -- where we observed "A"
489c9b5090e2 Initial load
duke
parents:
diff changeset
   638
      // -- and CAS -- where we attempt to CAS null over A -- "PQR" arrive,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   639
      // yielding cxq = "PQRABCD".  In this case we could simply set A.ListNext
489c9b5090e2 Initial load
duke
parents:
diff changeset
   640
      // null, leaving cxq = "PQRA" and transfer the "BCD" segment to the EntryList.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   641
      // Note too, that it's safe for this thread to traverse the cxq
489c9b5090e2 Initial load
duke
parents:
diff changeset
   642
      // without taking any special concurrency precautions.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   643
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   644
489c9b5090e2 Initial load
duke
parents:
diff changeset
   645
    // We don't currently reorder the cxq segment as we move it onto
489c9b5090e2 Initial load
duke
parents:
diff changeset
   646
    // the EntryList, but it might make sense to reverse the order
489c9b5090e2 Initial load
duke
parents:
diff changeset
   647
    // or perhaps sort by thread priority.  See the comments in
489c9b5090e2 Initial load
duke
parents:
diff changeset
   648
    // synchronizer.cpp objectMonitor::exit().
489c9b5090e2 Initial load
duke
parents:
diff changeset
   649
    assert (_EntryList == NULL, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   650
    _EntryList = List = (ParkEvent *)(cxq & ~_LBIT) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   651
    assert (List != NULL, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   652
    goto WakeOne ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   653
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   654
489c9b5090e2 Initial load
duke
parents:
diff changeset
   655
  // cxq|EntryList is empty.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   656
  // w == NULL implies that cxq|EntryList == NULL in the past.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   657
  // Possible race - rare inopportune interleaving.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   658
  // A thread could have added itself to cxq since this thread previously checked.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   659
  // Detect and recover by refetching cxq.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   660
 Punt:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   661
  assert (UNS(_OnDeck) == _LBIT, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   662
  _OnDeck = NULL ;            // Release inner lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   663
  OrderAccess::storeload();   // Dekker duality - pivot point
489c9b5090e2 Initial load
duke
parents:
diff changeset
   664
489c9b5090e2 Initial load
duke
parents:
diff changeset
   665
  // Resample LockWord/cxq to recover from possible race.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   666
  // For instance, while this thread T1 held OnDeck, some other thread T2 might
489c9b5090e2 Initial load
duke
parents:
diff changeset
   667
  // acquire the outer lock.  Another thread T3 might try to acquire the outer
489c9b5090e2 Initial load
duke
parents:
diff changeset
   668
  // lock, but encounter contention and enqueue itself on cxq.  T2 then drops the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   669
  // outer lock, but skips succession as this thread T1 still holds OnDeck.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   670
  // T1 is and remains responsible for ensuring succession of T3.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   671
  //
489c9b5090e2 Initial load
duke
parents:
diff changeset
   672
  // Note that we don't need to recheck EntryList, just cxq.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   673
  // If threads moved onto EntryList since we dropped OnDeck
489c9b5090e2 Initial load
duke
parents:
diff changeset
   674
  // that implies some other thread forced succession.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   675
  cxq = _LockWord.FullWord ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   676
  if ((cxq & ~_LBIT) != 0 && (cxq & _LBIT) == 0) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   677
    goto Succession ;         // potential race -- re-run succession
489c9b5090e2 Initial load
duke
parents:
diff changeset
   678
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   679
  return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   680
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   681
489c9b5090e2 Initial load
duke
parents:
diff changeset
   682
bool Monitor::notify() {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   683
  assert (_owner == Thread::current(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   684
  assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   685
  if (_WaitSet == NULL) return true ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   686
  NotifyCount ++ ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   687
489c9b5090e2 Initial load
duke
parents:
diff changeset
   688
  // Transfer one thread from the WaitSet to the EntryList or cxq.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   689
  // Currently we just unlink the head of the WaitSet and prepend to the cxq.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   690
  // And of course we could just unlink it and unpark it, too, but
489c9b5090e2 Initial load
duke
parents:
diff changeset
   691
  // in that case it'd likely impale itself on the reentry.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   692
  Thread::muxAcquire (_WaitLock, "notify:WaitLock") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   693
  ParkEvent * nfy = _WaitSet ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   694
  if (nfy != NULL) {                  // DCL idiom
489c9b5090e2 Initial load
duke
parents:
diff changeset
   695
    _WaitSet = nfy->ListNext ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   696
    assert (nfy->Notified == 0, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   697
    // push nfy onto the cxq
489c9b5090e2 Initial load
duke
parents:
diff changeset
   698
    for (;;) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   699
      const intptr_t v = _LockWord.FullWord ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   700
      assert ((v & 0xFF) == _LBIT, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   701
      nfy->ListNext = (ParkEvent *)(v & ~_LBIT);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   702
      if (CASPTR (&_LockWord, v, UNS(nfy)|_LBIT) == v) break;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   703
      // interference - _LockWord changed -- just retry
489c9b5090e2 Initial load
duke
parents:
diff changeset
   704
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   705
    // Note that setting Notified before pushing nfy onto the cxq is
489c9b5090e2 Initial load
duke
parents:
diff changeset
   706
    // also legal and safe, but the safety properties are much more
489c9b5090e2 Initial load
duke
parents:
diff changeset
   707
    // subtle, so for the sake of code stewardship ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
   708
    OrderAccess::fence() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   709
    nfy->Notified = 1;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   710
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   711
  Thread::muxRelease (_WaitLock) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   712
  if (nfy != NULL && (NativeMonitorFlags & 16)) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   713
    // Experimental code ... light up the wakee in the hope that this thread (the owner)
489c9b5090e2 Initial load
duke
parents:
diff changeset
   714
    // will drop the lock just about the time the wakee comes ONPROC.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   715
    nfy->unpark() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   716
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   717
  assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   718
  return true ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   719
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   720
489c9b5090e2 Initial load
duke
parents:
diff changeset
   721
// Currently notifyAll() transfers the waiters one-at-a-time from the waitset
489c9b5090e2 Initial load
duke
parents:
diff changeset
   722
// to the cxq.  This could be done more efficiently with a single bulk en-mass transfer,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   723
// but in practice notifyAll() for large #s of threads is rare and not time-critical.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   724
// Beware too, that we invert the order of the waiters.  Lets say that the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   725
// waitset is "ABCD" and the cxq is "XYZ".  After a notifyAll() the waitset
489c9b5090e2 Initial load
duke
parents:
diff changeset
   726
// will be empty and the cxq will be "DCBAXYZ".  This is benign, of course.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   727
489c9b5090e2 Initial load
duke
parents:
diff changeset
   728
bool Monitor::notify_all() {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   729
  assert (_owner == Thread::current(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   730
  assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   731
  while (_WaitSet != NULL) notify() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   732
  return true ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   733
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   734
489c9b5090e2 Initial load
duke
parents:
diff changeset
   735
int Monitor::IWait (Thread * Self, jlong timo) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   736
  assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   737
489c9b5090e2 Initial load
duke
parents:
diff changeset
   738
  // Phases:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   739
  // 1. Enqueue Self on WaitSet - currently prepend
489c9b5090e2 Initial load
duke
parents:
diff changeset
   740
  // 2. unlock - drop the outer lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
   741
  // 3. wait for either notification or timeout
489c9b5090e2 Initial load
duke
parents:
diff changeset
   742
  // 4. lock - reentry - reacquire the outer lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
   743
489c9b5090e2 Initial load
duke
parents:
diff changeset
   744
  ParkEvent * const ESelf = Self->_MutexEvent ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   745
  ESelf->Notified = 0 ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   746
  ESelf->reset() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   747
  OrderAccess::fence() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   748
489c9b5090e2 Initial load
duke
parents:
diff changeset
   749
  // Add Self to WaitSet
489c9b5090e2 Initial load
duke
parents:
diff changeset
   750
  // Ideally only the holder of the outer lock would manipulate the WaitSet -
489c9b5090e2 Initial load
duke
parents:
diff changeset
   751
  // That is, the outer lock would implicitly protect the WaitSet.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   752
  // But if a thread in wait() encounters a timeout it will need to dequeue itself
489c9b5090e2 Initial load
duke
parents:
diff changeset
   753
  // from the WaitSet _before it becomes the owner of the lock.  We need to dequeue
489c9b5090e2 Initial load
duke
parents:
diff changeset
   754
  // as the ParkEvent -- which serves as a proxy for the thread -- can't reside
489c9b5090e2 Initial load
duke
parents:
diff changeset
   755
  // on both the WaitSet and the EntryList|cxq at the same time..  That is, a thread
489c9b5090e2 Initial load
duke
parents:
diff changeset
   756
  // on the WaitSet can't be allowed to compete for the lock until it has managed to
489c9b5090e2 Initial load
duke
parents:
diff changeset
   757
  // unlink its ParkEvent from WaitSet.  Thus the need for WaitLock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   758
  // Contention on the WaitLock is minimal.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   759
  //
489c9b5090e2 Initial load
duke
parents:
diff changeset
   760
  // Another viable approach would be add another ParkEvent, "WaitEvent" to the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   761
  // thread class.  The WaitSet would be composed of WaitEvents.  Only the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   762
  // owner of the outer lock would manipulate the WaitSet.  A thread in wait()
489c9b5090e2 Initial load
duke
parents:
diff changeset
   763
  // could then compete for the outer lock, and then, if necessary, unlink itself
489c9b5090e2 Initial load
duke
parents:
diff changeset
   764
  // from the WaitSet only after having acquired the outer lock.  More precisely,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   765
  // there would be no WaitLock.  A thread in in wait() would enqueue its WaitEvent
489c9b5090e2 Initial load
duke
parents:
diff changeset
   766
  // on the WaitSet; release the outer lock; wait for either notification or timeout;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   767
  // reacquire the inner lock; and then, if needed, unlink itself from the WaitSet.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   768
  //
489c9b5090e2 Initial load
duke
parents:
diff changeset
   769
  // Alternatively, a 2nd set of list link fields in the ParkEvent might suffice.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   770
  // One set would be for the WaitSet and one for the EntryList.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   771
  // We could also deconstruct the ParkEvent into a "pure" event and add a
489c9b5090e2 Initial load
duke
parents:
diff changeset
   772
  // new immortal/TSM "ListElement" class that referred to ParkEvents.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   773
  // In that case we could have one ListElement on the WaitSet and another
489c9b5090e2 Initial load
duke
parents:
diff changeset
   774
  // on the EntryList, with both referring to the same pure Event.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   775
489c9b5090e2 Initial load
duke
parents:
diff changeset
   776
  Thread::muxAcquire (_WaitLock, "wait:WaitLock:Add") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   777
  ESelf->ListNext = _WaitSet ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   778
  _WaitSet = ESelf ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   779
  Thread::muxRelease (_WaitLock) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   780
489c9b5090e2 Initial load
duke
parents:
diff changeset
   781
  // Release the outer lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
   782
  // We call IUnlock (RelaxAssert=true) as a thread T1 might
489c9b5090e2 Initial load
duke
parents:
diff changeset
   783
  // enqueue itself on the WaitSet, call IUnlock(), drop the lock,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   784
  // and then stall before it can attempt to wake a successor.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   785
  // Some other thread T2 acquires the lock, and calls notify(), moving
489c9b5090e2 Initial load
duke
parents:
diff changeset
   786
  // T1 from the WaitSet to the cxq.  T2 then drops the lock.  T1 resumes,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   787
  // and then finds *itself* on the cxq.  During the course of a normal
489c9b5090e2 Initial load
duke
parents:
diff changeset
   788
  // IUnlock() call a thread should _never find itself on the EntryList
489c9b5090e2 Initial load
duke
parents:
diff changeset
   789
  // or cxq, but in the case of wait() it's possible.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   790
  // See synchronizer.cpp objectMonitor::wait().
489c9b5090e2 Initial load
duke
parents:
diff changeset
   791
  IUnlock (true) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   792
489c9b5090e2 Initial load
duke
parents:
diff changeset
   793
  // Wait for either notification or timeout
489c9b5090e2 Initial load
duke
parents:
diff changeset
   794
  // Beware that in some circumstances we might propagate
489c9b5090e2 Initial load
duke
parents:
diff changeset
   795
  // spurious wakeups back to the caller.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   796
489c9b5090e2 Initial load
duke
parents:
diff changeset
   797
  for (;;) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   798
    if (ESelf->Notified) break ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   799
    int err = ParkCommon (ESelf, timo) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   800
    if (err == OS_TIMEOUT || (NativeMonitorFlags & 1)) break ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   801
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   802
489c9b5090e2 Initial load
duke
parents:
diff changeset
   803
  // Prepare for reentry - if necessary, remove ESelf from WaitSet
489c9b5090e2 Initial load
duke
parents:
diff changeset
   804
  // ESelf can be:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   805
  // 1. Still on the WaitSet.  This can happen if we exited the loop by timeout.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   806
  // 2. On the cxq or EntryList
489c9b5090e2 Initial load
duke
parents:
diff changeset
   807
  // 3. Not resident on cxq, EntryList or WaitSet, but in the OnDeck position.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   808
489c9b5090e2 Initial load
duke
parents:
diff changeset
   809
  OrderAccess::fence() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   810
  int WasOnWaitSet = 0 ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   811
  if (ESelf->Notified == 0) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   812
    Thread::muxAcquire (_WaitLock, "wait:WaitLock:remove") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   813
    if (ESelf->Notified == 0) {     // DCL idiom
489c9b5090e2 Initial load
duke
parents:
diff changeset
   814
      assert (_OnDeck != ESelf, "invariant") ;   // can't be both OnDeck and on WaitSet
489c9b5090e2 Initial load
duke
parents:
diff changeset
   815
      // ESelf is resident on the WaitSet -- unlink it.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   816
      // A doubly-linked list would be better here so we can unlink in constant-time.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   817
      // We have to unlink before we potentially recontend as ESelf might otherwise
489c9b5090e2 Initial load
duke
parents:
diff changeset
   818
      // end up on the cxq|EntryList -- it can't be on two lists at once.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   819
      ParkEvent * p = _WaitSet ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   820
      ParkEvent * q = NULL ;            // classic q chases p
489c9b5090e2 Initial load
duke
parents:
diff changeset
   821
      while (p != NULL && p != ESelf) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   822
        q = p ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   823
        p = p->ListNext ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   824
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   825
      assert (p == ESelf, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   826
      if (p == _WaitSet) {      // found at head
489c9b5090e2 Initial load
duke
parents:
diff changeset
   827
        assert (q == NULL, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   828
        _WaitSet = p->ListNext ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   829
      } else {                  // found in interior
489c9b5090e2 Initial load
duke
parents:
diff changeset
   830
        assert (q->ListNext == p, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   831
        q->ListNext = p->ListNext ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   832
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   833
      WasOnWaitSet = 1 ;        // We were *not* notified but instead encountered timeout
489c9b5090e2 Initial load
duke
parents:
diff changeset
   834
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   835
    Thread::muxRelease (_WaitLock) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   836
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   837
489c9b5090e2 Initial load
duke
parents:
diff changeset
   838
  // Reentry phase - reacquire the lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
   839
  if (WasOnWaitSet) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   840
    // ESelf was previously on the WaitSet but we just unlinked it above
489c9b5090e2 Initial load
duke
parents:
diff changeset
   841
    // because of a timeout.  ESelf is not resident on any list and is not OnDeck
489c9b5090e2 Initial load
duke
parents:
diff changeset
   842
    assert (_OnDeck != ESelf, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   843
    ILock (Self) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   844
  } else {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   845
    // A prior notify() operation moved ESelf from the WaitSet to the cxq.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   846
    // ESelf is now on the cxq, EntryList or at the OnDeck position.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   847
    // The following fragment is extracted from Monitor::ILock()
489c9b5090e2 Initial load
duke
parents:
diff changeset
   848
    for (;;) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   849
      if (_OnDeck == ESelf && TrySpin(Self)) break ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   850
      ParkCommon (ESelf, 0) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   851
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   852
    assert (_OnDeck == ESelf, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   853
    _OnDeck = NULL ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   854
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   855
489c9b5090e2 Initial load
duke
parents:
diff changeset
   856
  assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   857
  return WasOnWaitSet != 0 ;        // return true IFF timeout
489c9b5090e2 Initial load
duke
parents:
diff changeset
   858
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   859
489c9b5090e2 Initial load
duke
parents:
diff changeset
   860
489c9b5090e2 Initial load
duke
parents:
diff changeset
   861
// ON THE VMTHREAD SNEAKING PAST HELD LOCKS:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   862
// In particular, there are certain types of global lock that may be held
489c9b5090e2 Initial load
duke
parents:
diff changeset
   863
// by a Java thread while it is blocked at a safepoint but before it has
489c9b5090e2 Initial load
duke
parents:
diff changeset
   864
// written the _owner field. These locks may be sneakily acquired by the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   865
// VM thread during a safepoint to avoid deadlocks. Alternatively, one should
489c9b5090e2 Initial load
duke
parents:
diff changeset
   866
// identify all such locks, and ensure that Java threads never block at
489c9b5090e2 Initial load
duke
parents:
diff changeset
   867
// safepoints while holding them (_no_safepoint_check_flag). While it
489c9b5090e2 Initial load
duke
parents:
diff changeset
   868
// seems as though this could increase the time to reach a safepoint
489c9b5090e2 Initial load
duke
parents:
diff changeset
   869
// (or at least increase the mean, if not the variance), the latter
489c9b5090e2 Initial load
duke
parents:
diff changeset
   870
// approach might make for a cleaner, more maintainable JVM design.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   871
//
489c9b5090e2 Initial load
duke
parents:
diff changeset
   872
// Sneaking is vile and reprehensible and should be excised at the 1st
489c9b5090e2 Initial load
duke
parents:
diff changeset
   873
// opportunity.  It's possible that the need for sneaking could be obviated
489c9b5090e2 Initial load
duke
parents:
diff changeset
   874
// as follows.  Currently, a thread might (a) while TBIVM, call pthread_mutex_lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
   875
// or ILock() thus acquiring the "physical" lock underlying Monitor/Mutex.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   876
// (b) stall at the TBIVM exit point as a safepoint is in effect.  Critically,
489c9b5090e2 Initial load
duke
parents:
diff changeset
   877
// it'll stall at the TBIVM reentry state transition after having acquired the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   878
// underlying lock, but before having set _owner and having entered the actual
489c9b5090e2 Initial load
duke
parents:
diff changeset
   879
// critical section.  The lock-sneaking facility leverages that fact and allowed the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   880
// VM thread to logically acquire locks that had already be physically locked by mutators
489c9b5090e2 Initial load
duke
parents:
diff changeset
   881
// but where mutators were known blocked by the reentry thread state transition.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   882
//
489c9b5090e2 Initial load
duke
parents:
diff changeset
   883
// If we were to modify the Monitor-Mutex so that TBIVM state transitions tightly
489c9b5090e2 Initial load
duke
parents:
diff changeset
   884
// wrapped calls to park(), then we could likely do away with sneaking.  We'd
489c9b5090e2 Initial load
duke
parents:
diff changeset
   885
// decouple lock acquisition and parking.  The critical invariant  to eliminating
489c9b5090e2 Initial load
duke
parents:
diff changeset
   886
// sneaking is to ensure that we never "physically" acquire the lock while TBIVM.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   887
// An easy way to accomplish this is to wrap the park calls in a narrow TBIVM jacket.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   888
// One difficulty with this approach is that the TBIVM wrapper could recurse and
489c9b5090e2 Initial load
duke
parents:
diff changeset
   889
// call lock() deep from within a lock() call, while the MutexEvent was already enqueued.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   890
// Using a stack (N=2 at minimum) of ParkEvents would take care of that problem.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   891
//
489c9b5090e2 Initial load
duke
parents:
diff changeset
   892
// But of course the proper ultimate approach is to avoid schemes that require explicit
489c9b5090e2 Initial load
duke
parents:
diff changeset
   893
// sneaking or dependence on any any clever invariants or subtle implementation properties
489c9b5090e2 Initial load
duke
parents:
diff changeset
   894
// of Mutex-Monitor and instead directly address the underlying design flaw.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   895
489c9b5090e2 Initial load
duke
parents:
diff changeset
   896
void Monitor::lock (Thread * Self) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   897
#ifdef CHECK_UNHANDLED_OOPS
489c9b5090e2 Initial load
duke
parents:
diff changeset
   898
  // Clear unhandled oops so we get a crash right away.  Only clear for non-vm
489c9b5090e2 Initial load
duke
parents:
diff changeset
   899
  // or GC threads.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   900
  if (Self->is_Java_thread()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   901
    Self->clear_unhandled_oops();
489c9b5090e2 Initial load
duke
parents:
diff changeset
   902
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   903
#endif // CHECK_UNHANDLED_OOPS
489c9b5090e2 Initial load
duke
parents:
diff changeset
   904
489c9b5090e2 Initial load
duke
parents:
diff changeset
   905
  debug_only(check_prelock_state(Self));
489c9b5090e2 Initial load
duke
parents:
diff changeset
   906
  assert (_owner != Self              , "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   907
  assert (_OnDeck != Self->_MutexEvent, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   908
489c9b5090e2 Initial load
duke
parents:
diff changeset
   909
  if (TryFast()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   910
 Exeunt:
489c9b5090e2 Initial load
duke
parents:
diff changeset
   911
    assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   912
    assert (owner() == NULL, "invariant");
489c9b5090e2 Initial load
duke
parents:
diff changeset
   913
    set_owner (Self);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   914
    return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   915
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   916
489c9b5090e2 Initial load
duke
parents:
diff changeset
   917
  // The lock is contended ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
   918
489c9b5090e2 Initial load
duke
parents:
diff changeset
   919
  bool can_sneak = Self->is_VM_thread() && SafepointSynchronize::is_at_safepoint();
489c9b5090e2 Initial load
duke
parents:
diff changeset
   920
  if (can_sneak && _owner == NULL) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   921
    // a java thread has locked the lock but has not entered the
489c9b5090e2 Initial load
duke
parents:
diff changeset
   922
    // critical region -- let's just pretend we've locked the lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
   923
    // and go on.  we note this with _snuck so we can also
489c9b5090e2 Initial load
duke
parents:
diff changeset
   924
    // pretend to unlock when the time comes.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   925
    _snuck = true;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   926
    goto Exeunt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   927
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   928
489c9b5090e2 Initial load
duke
parents:
diff changeset
   929
  // Try a brief spin to avoid passing thru thread state transition ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
   930
  if (TrySpin (Self)) goto Exeunt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   931
489c9b5090e2 Initial load
duke
parents:
diff changeset
   932
  check_block_state(Self);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   933
  if (Self->is_Java_thread()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   934
    // Horribile dictu - we suffer through a state transition
489c9b5090e2 Initial load
duke
parents:
diff changeset
   935
    assert(rank() > Mutex::special, "Potential deadlock with special or lesser rank mutex");
489c9b5090e2 Initial load
duke
parents:
diff changeset
   936
    ThreadBlockInVM tbivm ((JavaThread *) Self) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   937
    ILock (Self) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   938
  } else {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   939
    // Mirabile dictu
489c9b5090e2 Initial load
duke
parents:
diff changeset
   940
    ILock (Self) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   941
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   942
  goto Exeunt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   943
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   944
489c9b5090e2 Initial load
duke
parents:
diff changeset
   945
void Monitor::lock() {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   946
  this->lock(Thread::current());
489c9b5090e2 Initial load
duke
parents:
diff changeset
   947
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   948
489c9b5090e2 Initial load
duke
parents:
diff changeset
   949
// Lock without safepoint check - a degenerate variant of lock().
489c9b5090e2 Initial load
duke
parents:
diff changeset
   950
// Should ONLY be used by safepoint code and other code
489c9b5090e2 Initial load
duke
parents:
diff changeset
   951
// that is guaranteed not to block while running inside the VM. If this is called with
489c9b5090e2 Initial load
duke
parents:
diff changeset
   952
// thread state set to be in VM, the safepoint synchronization code will deadlock!
489c9b5090e2 Initial load
duke
parents:
diff changeset
   953
489c9b5090e2 Initial load
duke
parents:
diff changeset
   954
void Monitor::lock_without_safepoint_check (Thread * Self) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   955
  assert (_owner != Self, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   956
  ILock (Self) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   957
  assert (_owner == NULL, "invariant");
489c9b5090e2 Initial load
duke
parents:
diff changeset
   958
  set_owner (Self);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   959
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   960
489c9b5090e2 Initial load
duke
parents:
diff changeset
   961
void Monitor::lock_without_safepoint_check () {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   962
  lock_without_safepoint_check (Thread::current()) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   963
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   964
489c9b5090e2 Initial load
duke
parents:
diff changeset
   965
489c9b5090e2 Initial load
duke
parents:
diff changeset
   966
// Returns true if thread succeceed [sic] in grabbing the lock, otherwise false.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   967
489c9b5090e2 Initial load
duke
parents:
diff changeset
   968
bool Monitor::try_lock() {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   969
  Thread * const Self = Thread::current();
489c9b5090e2 Initial load
duke
parents:
diff changeset
   970
  debug_only(check_prelock_state(Self));
489c9b5090e2 Initial load
duke
parents:
diff changeset
   971
  // assert(!thread->is_inside_signal_handler(), "don't lock inside signal handler");
489c9b5090e2 Initial load
duke
parents:
diff changeset
   972
489c9b5090e2 Initial load
duke
parents:
diff changeset
   973
  // Special case, where all Java threads are stopped.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   974
  // The lock may have been acquired but _owner is not yet set.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   975
  // In that case the VM thread can safely grab the lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   976
  // It strikes me this should appear _after the TryLock() fails, below.
489c9b5090e2 Initial load
duke
parents:
diff changeset
   977
  bool can_sneak = Self->is_VM_thread() && SafepointSynchronize::is_at_safepoint();
489c9b5090e2 Initial load
duke
parents:
diff changeset
   978
  if (can_sneak && _owner == NULL) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   979
    set_owner(Self); // Do not need to be atomic, since we are at a safepoint
489c9b5090e2 Initial load
duke
parents:
diff changeset
   980
    _snuck = true;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   981
    return true;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   982
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   983
489c9b5090e2 Initial load
duke
parents:
diff changeset
   984
  if (TryLock()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   985
    // We got the lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
   986
    assert (_owner == NULL, "invariant");
489c9b5090e2 Initial load
duke
parents:
diff changeset
   987
    set_owner (Self);
489c9b5090e2 Initial load
duke
parents:
diff changeset
   988
    return true;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   989
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
   990
  return false;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   991
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
   992
489c9b5090e2 Initial load
duke
parents:
diff changeset
   993
void Monitor::unlock() {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   994
  assert (_owner  == Thread::current(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   995
  assert (_OnDeck != Thread::current()->_MutexEvent , "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   996
  set_owner (NULL) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
   997
  if (_snuck) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
   998
    assert(SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread(), "sneak");
489c9b5090e2 Initial load
duke
parents:
diff changeset
   999
    _snuck = false;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1000
    return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1001
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1002
  IUnlock (false) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1003
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1004
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1005
// Yet another degenerate version of Monitor::lock() or lock_without_safepoint_check()
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1006
// jvm_raw_lock() and _unlock() can be called by non-Java threads via JVM_RawMonitorEnter.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1007
//
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1008
// There's no expectation that JVM_RawMonitors will interoperate properly with the native
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1009
// Mutex-Monitor constructs.  We happen to implement JVM_RawMonitors in terms of
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1010
// native Mutex-Monitors simply as a matter of convenience.  A simple abstraction layer
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1011
// over a pthread_mutex_t would work equally as well, but require more platform-specific
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1012
// code -- a "PlatformMutex".  Alternatively, a simply layer over muxAcquire-muxRelease
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1013
// would work too.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1014
//
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1015
// Since the caller might be a foreign thread, we don't necessarily have a Thread.MutexEvent
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1016
// instance available.  Instead, we transiently allocate a ParkEvent on-demand if
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1017
// we encounter contention.  That ParkEvent remains associated with the thread
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1018
// until it manages to acquire the lock, at which time we return the ParkEvent
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1019
// to the global ParkEvent free list.  This is correct and suffices for our purposes.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1020
//
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1021
// Beware that the original jvm_raw_unlock() had a "_snuck" test but that
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1022
// jvm_raw_lock() didn't have the corresponding test.  I suspect that's an
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1023
// oversight, but I've replicated the original suspect logic in the new code ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1024
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1025
void Monitor::jvm_raw_lock() {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1026
  assert(rank() == native, "invariant");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1027
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1028
  if (TryLock()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1029
 Exeunt:
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1030
    assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1031
    assert (_owner == NULL, "invariant");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1032
    // This can potentially be called by non-java Threads. Thus, the ThreadLocalStorage
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1033
    // might return NULL. Don't call set_owner since it will break on an NULL owner
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1034
    // Consider installing a non-null "ANON" distinguished value instead of just NULL.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1035
    _owner = ThreadLocalStorage::thread();
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1036
    return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1037
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1038
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1039
  if (TrySpin(NULL)) goto Exeunt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1040
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1041
  // slow-path - apparent contention
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1042
  // Allocate a ParkEvent for transient use.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1043
  // The ParkEvent remains associated with this thread until
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1044
  // the time the thread manages to acquire the lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1045
  ParkEvent * const ESelf = ParkEvent::Allocate(NULL) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1046
  ESelf->reset() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1047
  OrderAccess::storeload() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1048
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1049
  // Either Enqueue Self on cxq or acquire the outer lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1050
  if (AcquireOrPush (ESelf)) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1051
    ParkEvent::Release (ESelf) ;      // surrender the ParkEvent
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1052
    goto Exeunt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1053
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1054
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1055
  // At any given time there is at most one ondeck thread.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1056
  // ondeck implies not resident on cxq and not resident on EntryList
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1057
  // Only the OnDeck thread can try to acquire -- contended for -- the lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1058
  // CONSIDER: use Self->OnDeck instead of m->OnDeck.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1059
  for (;;) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1060
    if (_OnDeck == ESelf && TrySpin(NULL)) break ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1061
    ParkCommon (ESelf, 0) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1062
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1063
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1064
  assert (_OnDeck == ESelf, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1065
  _OnDeck = NULL ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1066
  ParkEvent::Release (ESelf) ;      // surrender the ParkEvent
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1067
  goto Exeunt ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1068
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1069
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1070
void Monitor::jvm_raw_unlock() {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1071
  // Nearly the same as Monitor::unlock() ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1072
  // directly set _owner instead of using set_owner(null)
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1073
  _owner = NULL ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1074
  if (_snuck) {         // ???
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1075
    assert(SafepointSynchronize::is_at_safepoint() && Thread::current()->is_VM_thread(), "sneak");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1076
    _snuck = false;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1077
    return ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1078
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1079
  IUnlock(false) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1080
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1081
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1082
bool Monitor::wait(bool no_safepoint_check, long timeout, bool as_suspend_equivalent) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1083
  Thread * const Self = Thread::current() ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1084
  assert (_owner == Self, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1085
  assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1086
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1087
  // as_suspend_equivalent logically implies !no_safepoint_check
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1088
  guarantee (!as_suspend_equivalent || !no_safepoint_check, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1089
  // !no_safepoint_check logically implies java_thread
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1090
  guarantee (no_safepoint_check || Self->is_Java_thread(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1091
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1092
  #ifdef ASSERT
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1093
    Monitor * least = get_least_ranked_lock_besides_this(Self->owned_locks());
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1094
    assert(least != this, "Specification of get_least_... call above");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1095
    if (least != NULL && least->rank() <= special) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1096
      tty->print("Attempting to wait on monitor %s/%d while holding"
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1097
                 " lock %s/%d -- possible deadlock",
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1098
                 name(), rank(), least->name(), least->rank());
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1099
      assert(false, "Shouldn't block(wait) while holding a lock of rank special");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1100
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1101
  #endif // ASSERT
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1102
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1103
  int wait_status ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1104
  // conceptually set the owner to NULL in anticipation of
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1105
  // abdicating the lock in wait
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1106
  set_owner(NULL);
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1107
  if (no_safepoint_check) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1108
    wait_status = IWait (Self, timeout) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1109
  } else {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1110
    assert (Self->is_Java_thread(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1111
    JavaThread *jt = (JavaThread *)Self;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1112
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1113
    // Enter safepoint region - ornate and Rococo ...
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1114
    ThreadBlockInVM tbivm(jt);
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1115
    OSThreadWaitState osts(Self->osthread(), false /* not Object.wait() */);
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1116
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1117
    if (as_suspend_equivalent) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1118
      jt->set_suspend_equivalent();
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1119
      // cleared by handle_special_suspend_equivalent_condition() or
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1120
      // java_suspend_self()
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1121
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1122
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1123
    wait_status = IWait (Self, timeout) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1124
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1125
    // were we externally suspended while we were waiting?
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1126
    if (as_suspend_equivalent && jt->handle_special_suspend_equivalent_condition()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1127
      // Our event wait has finished and we own the lock, but
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1128
      // while we were waiting another thread suspended us. We don't
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1129
      // want to hold the lock while suspended because that
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1130
      // would surprise the thread that suspended us.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1131
      assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1132
      IUnlock (true) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1133
      jt->java_suspend_self();
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1134
      ILock (Self) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1135
      assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1136
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1137
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1138
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1139
  // Conceptually reestablish ownership of the lock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1140
  // The "real" lock -- the LockByte -- was reacquired by IWait().
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1141
  assert (ILocked(), "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1142
  assert (_owner == NULL, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1143
  set_owner (Self) ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1144
  return wait_status != 0 ;          // return true IFF timeout
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1145
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1146
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1147
Monitor::~Monitor() {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1148
  assert ((UNS(_owner)|UNS(_LockWord.FullWord)|UNS(_EntryList)|UNS(_WaitSet)|UNS(_OnDeck)) == 0, "") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1149
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1150
228
69939fa91efd 6610420: Debug VM crashes during monitor lock rank checking
xlu
parents: 1
diff changeset
  1151
void Monitor::ClearMonitor (Monitor * m, const char *name) {
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1152
  m->_owner             = NULL ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1153
  m->_snuck             = false ;
228
69939fa91efd 6610420: Debug VM crashes during monitor lock rank checking
xlu
parents: 1
diff changeset
  1154
  if (name == NULL) {
69939fa91efd 6610420: Debug VM crashes during monitor lock rank checking
xlu
parents: 1
diff changeset
  1155
    strcpy(m->_name, "UNKNOWN") ;
69939fa91efd 6610420: Debug VM crashes during monitor lock rank checking
xlu
parents: 1
diff changeset
  1156
  } else {
69939fa91efd 6610420: Debug VM crashes during monitor lock rank checking
xlu
parents: 1
diff changeset
  1157
    strncpy(m->_name, name, MONITOR_NAME_LEN - 1);
69939fa91efd 6610420: Debug VM crashes during monitor lock rank checking
xlu
parents: 1
diff changeset
  1158
    m->_name[MONITOR_NAME_LEN - 1] = '\0';
69939fa91efd 6610420: Debug VM crashes during monitor lock rank checking
xlu
parents: 1
diff changeset
  1159
  }
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1160
  m->_LockWord.FullWord = 0 ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1161
  m->_EntryList         = NULL ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1162
  m->_OnDeck            = NULL ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1163
  m->_WaitSet           = NULL ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1164
  m->_WaitLock[0]       = 0 ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1165
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1166
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1167
Monitor::Monitor() { ClearMonitor(this); }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1168
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1169
Monitor::Monitor (int Rank, const char * name, bool allow_vm_block) {
228
69939fa91efd 6610420: Debug VM crashes during monitor lock rank checking
xlu
parents: 1
diff changeset
  1170
  ClearMonitor (this, name) ;
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1171
#ifdef ASSERT
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1172
  _allow_vm_block  = allow_vm_block;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1173
  _rank            = Rank ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1174
#endif
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1175
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1176
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1177
Mutex::~Mutex() {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1178
  assert ((UNS(_owner)|UNS(_LockWord.FullWord)|UNS(_EntryList)|UNS(_WaitSet)|UNS(_OnDeck)) == 0, "") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1179
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1180
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1181
Mutex::Mutex (int Rank, const char * name, bool allow_vm_block) {
228
69939fa91efd 6610420: Debug VM crashes during monitor lock rank checking
xlu
parents: 1
diff changeset
  1182
  ClearMonitor ((Monitor *) this, name) ;
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1183
#ifdef ASSERT
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1184
 _allow_vm_block   = allow_vm_block;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1185
 _rank             = Rank ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1186
#endif
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1187
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1188
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1189
bool Monitor::owned_by_self() const {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1190
  bool ret = _owner == Thread::current();
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1191
  assert (!ret || _LockWord.Bytes[_LSBINDEX] != 0, "invariant") ;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1192
  return ret;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1193
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1194
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1195
void Monitor::print_on_error(outputStream* st) const {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1196
  st->print("[" PTR_FORMAT, this);
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1197
  st->print("] %s", _name);
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1198
  st->print(" - owner thread: " PTR_FORMAT, _owner);
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1199
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1200
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1201
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1202
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1203
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1204
// ----------------------------------------------------------------------------------
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1205
// Non-product code
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1206
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1207
#ifndef PRODUCT
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1208
void Monitor::print_on(outputStream* st) const {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1209
  st->print_cr("Mutex: [0x%lx/0x%lx] %s - owner: 0x%lx", this, _LockWord.FullWord, _name, _owner);
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1210
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1211
#endif
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1212
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1213
#ifndef PRODUCT
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1214
#ifdef ASSERT
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1215
Monitor * Monitor::get_least_ranked_lock(Monitor * locks) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1216
  Monitor *res, *tmp;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1217
  for (res = tmp = locks; tmp != NULL; tmp = tmp->next()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1218
    if (tmp->rank() < res->rank()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1219
      res = tmp;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1220
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1221
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1222
  if (!SafepointSynchronize::is_at_safepoint()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1223
    // In this case, we expect the held locks to be
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1224
    // in increasing rank order (modulo any native ranks)
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1225
    for (tmp = locks; tmp != NULL; tmp = tmp->next()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1226
      if (tmp->next() != NULL) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1227
        assert(tmp->rank() == Mutex::native ||
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1228
               tmp->rank() <= tmp->next()->rank(), "mutex rank anomaly?");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1229
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1230
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1231
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1232
  return res;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1233
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1234
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1235
Monitor* Monitor::get_least_ranked_lock_besides_this(Monitor* locks) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1236
  Monitor *res, *tmp;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1237
  for (res = NULL, tmp = locks; tmp != NULL; tmp = tmp->next()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1238
    if (tmp != this && (res == NULL || tmp->rank() < res->rank())) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1239
      res = tmp;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1240
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1241
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1242
  if (!SafepointSynchronize::is_at_safepoint()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1243
    // In this case, we expect the held locks to be
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1244
    // in increasing rank order (modulo any native ranks)
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1245
    for (tmp = locks; tmp != NULL; tmp = tmp->next()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1246
      if (tmp->next() != NULL) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1247
        assert(tmp->rank() == Mutex::native ||
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1248
               tmp->rank() <= tmp->next()->rank(), "mutex rank anomaly?");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1249
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1250
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1251
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1252
  return res;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1253
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1254
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1255
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1256
bool Monitor::contains(Monitor* locks, Monitor * lock) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1257
  for (; locks != NULL; locks = locks->next()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1258
    if (locks == lock)
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1259
      return true;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1260
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1261
  return false;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1262
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1263
#endif
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1264
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1265
// Called immediately after lock acquisition or release as a diagnostic
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1266
// to track the lock-set of the thread and test for rank violations that
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1267
// might indicate exposure to deadlock.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1268
// Rather like an EventListener for _owner (:>).
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1269
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1270
void Monitor::set_owner_implementation(Thread *new_owner) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1271
  // This function is solely responsible for maintaining
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1272
  // and checking the invariant that threads and locks
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1273
  // are in a 1/N relation, with some some locks unowned.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1274
  // It uses the Mutex::_owner, Mutex::_next, and
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1275
  // Thread::_owned_locks fields, and no other function
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1276
  // changes those fields.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1277
  // It is illegal to set the mutex from one non-NULL
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1278
  // owner to another--it must be owned by NULL as an
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1279
  // intermediate state.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1280
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1281
  if (new_owner != NULL) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1282
    // the thread is acquiring this lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1283
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1284
    assert(new_owner == Thread::current(), "Should I be doing this?");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1285
    assert(_owner == NULL, "setting the owner thread of an already owned mutex");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1286
    _owner = new_owner; // set the owner
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1287
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1288
    // link "this" into the owned locks list
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1289
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1290
    #ifdef ASSERT  // Thread::_owned_locks is under the same ifdef
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1291
      Monitor* locks = get_least_ranked_lock(new_owner->owned_locks());
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1292
                    // Mutex::set_owner_implementation is a friend of Thread
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1293
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1294
      assert(this->rank() >= 0, "bad lock rank");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1295
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1296
      // Deadlock avoidance rules require us to acquire Mutexes only in
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1297
      // a global total order. For example m1 is the lowest ranked mutex
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1298
      // that the thread holds and m2 is the mutex the thread is trying
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1299
      // to acquire, then  deadlock avoidance rules require that the rank
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1300
      // of m2 be less  than the rank of m1.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1301
      // The rank Mutex::native  is an exception in that it is not subject
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1302
      // to the verification rules.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1303
      // Here are some further notes relating to mutex acquisition anomalies:
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1304
      // . under Solaris, the interrupt lock gets acquired when doing
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1305
      //   profiling, so any lock could be held.
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1306
      // . it is also ok to acquire Safepoint_lock at the very end while we
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1307
      //   already hold Terminator_lock - may happen because of periodic safepoints
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1308
      if (this->rank() != Mutex::native &&
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1309
          this->rank() != Mutex::suspend_resume &&
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1310
          locks != NULL && locks->rank() <= this->rank() &&
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1311
          !SafepointSynchronize::is_at_safepoint() &&
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1312
          this != Interrupt_lock && this != ProfileVM_lock &&
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1313
          !(this == Safepoint_lock && contains(locks, Terminator_lock) &&
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1314
            SafepointSynchronize::is_synchronizing())) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1315
        new_owner->print_owned_locks();
5403
6b0dd9c75dde 6888954: argument formatting for assert() and friends
jcoomes
parents: 670
diff changeset
  1316
        fatal(err_msg("acquiring lock %s/%d out of order with lock %s/%d -- "
6b0dd9c75dde 6888954: argument formatting for assert() and friends
jcoomes
parents: 670
diff changeset
  1317
                      "possible deadlock", this->name(), this->rank(),
6b0dd9c75dde 6888954: argument formatting for assert() and friends
jcoomes
parents: 670
diff changeset
  1318
                      locks->name(), locks->rank()));
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1319
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1320
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1321
      this->_next = new_owner->_owned_locks;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1322
      new_owner->_owned_locks = this;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1323
    #endif
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1324
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1325
  } else {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1326
    // the thread is releasing this lock
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1327
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1328
    Thread* old_owner = _owner;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1329
    debug_only(_last_owner = old_owner);
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1330
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1331
    assert(old_owner != NULL, "removing the owner thread of an unowned mutex");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1332
    assert(old_owner == Thread::current(), "removing the owner thread of an unowned mutex");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1333
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1334
    _owner = NULL; // set the owner
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1335
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1336
    #ifdef ASSERT
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1337
      Monitor *locks = old_owner->owned_locks();
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1338
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1339
      // remove "this" from the owned locks list
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1340
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1341
      Monitor *prev = NULL;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1342
      bool found = false;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1343
      for (; locks != NULL; prev = locks, locks = locks->next()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1344
        if (locks == this) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1345
          found = true;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1346
          break;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1347
        }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1348
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1349
      assert(found, "Removing a lock not owned");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1350
      if (prev == NULL) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1351
        old_owner->_owned_locks = _next;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1352
      } else {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1353
        prev->_next = _next;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1354
      }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1355
      _next = NULL;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1356
    #endif
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1357
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1358
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1359
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1360
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1361
// Factored out common sanity checks for locking mutex'es. Used by lock() and try_lock()
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1362
void Monitor::check_prelock_state(Thread *thread) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1363
  assert((!thread->is_Java_thread() || ((JavaThread *)thread)->thread_state() == _thread_in_vm)
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1364
         || rank() == Mutex::special, "wrong thread state for using locks");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1365
  if (StrictSafepointChecks) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1366
    if (thread->is_VM_thread() && !allow_vm_block()) {
5403
6b0dd9c75dde 6888954: argument formatting for assert() and friends
jcoomes
parents: 670
diff changeset
  1367
      fatal(err_msg("VM thread using lock %s (not allowed to block on)",
6b0dd9c75dde 6888954: argument formatting for assert() and friends
jcoomes
parents: 670
diff changeset
  1368
                    name()));
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1369
    }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1370
    debug_only(if (rank() != Mutex::special) \
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1371
      thread->check_for_valid_safepoint_state(false);)
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1372
  }
18943
7d0ef675e808 8020701: Avoid crashes in WatcherThread
rbackman
parents: 14583
diff changeset
  1373
  if (thread->is_Watcher_thread()) {
7d0ef675e808 8020701: Avoid crashes in WatcherThread
rbackman
parents: 14583
diff changeset
  1374
    assert(!WatcherThread::watcher_thread()->has_crash_protection(),
7d0ef675e808 8020701: Avoid crashes in WatcherThread
rbackman
parents: 14583
diff changeset
  1375
        "locking not allowed when crash protection is set");
7d0ef675e808 8020701: Avoid crashes in WatcherThread
rbackman
parents: 14583
diff changeset
  1376
  }
1
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1377
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1378
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1379
void Monitor::check_block_state(Thread *thread) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1380
  if (!_allow_vm_block && thread->is_VM_thread()) {
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1381
    warning("VM thread blocked on lock");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1382
    print();
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1383
    BREAKPOINT;
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1384
  }
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1385
  assert(_owner != thread, "deadlock: blocking on monitor owned by current thread");
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1386
}
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1387
489c9b5090e2 Initial load
duke
parents:
diff changeset
  1388
#endif // PRODUCT