--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/hotspot/share/runtime/park.hpp Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,166 @@
+/*
+ * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ *
+ */
+
+#ifndef SHARE_VM_RUNTIME_PARK_HPP
+#define SHARE_VM_RUNTIME_PARK_HPP
+
+#include "utilities/debug.hpp"
+#include "utilities/globalDefinitions.hpp"
+/*
+ * Per-thread blocking support for JSR166. See the Java-level
+ * Documentation for rationale. Basically, park acts like wait, unpark
+ * like notify.
+ *
+ * 6271289 --
+ * To avoid errors where an os thread expires but the JavaThread still
+ * exists, Parkers are immortal (type-stable) and are recycled across
+ * new threads. This parallels the ParkEvent implementation.
+ * Because park-unpark allow spurious wakeups it is harmless if an
+ * unpark call unparks a new thread using the old Parker reference.
+ *
+ * In the future we'll want to think about eliminating Parker and using
+ * ParkEvent instead. There's considerable duplication between the two
+ * services.
+ *
+ */
+
+class Parker : public os::PlatformParker {
+private:
+ volatile int _counter ;
+ Parker * FreeNext ;
+ JavaThread * AssociatedWith ; // Current association
+
+public:
+ Parker() : PlatformParker() {
+ _counter = 0 ;
+ FreeNext = NULL ;
+ AssociatedWith = NULL ;
+ }
+protected:
+ ~Parker() { ShouldNotReachHere(); }
+public:
+ // For simplicity of interface with Java, all forms of park (indefinite,
+ // relative, and absolute) are multiplexed into one call.
+ void park(bool isAbsolute, jlong time);
+ void unpark();
+
+ // Lifecycle operators
+ static Parker * Allocate (JavaThread * t) ;
+ static void Release (Parker * e) ;
+private:
+ static Parker * volatile FreeList ;
+ static volatile int ListLock ;
+
+};
+
+/////////////////////////////////////////////////////////////
+//
+// ParkEvents are type-stable and immortal.
+//
+// Lifecycle: Once a ParkEvent is associated with a thread that ParkEvent remains
+// associated with the thread for the thread's entire lifetime - the relationship is
+// stable. A thread will be associated at most one ParkEvent. When the thread
+// expires, the ParkEvent moves to the EventFreeList. New threads attempt to allocate from
+// the EventFreeList before creating a new Event. Type-stability frees us from
+// worrying about stale Event or Thread references in the objectMonitor subsystem.
+// (A reference to ParkEvent is always valid, even though the event may no longer be associated
+// with the desired or expected thread. A key aspect of this design is that the callers of
+// park, unpark, etc must tolerate stale references and spurious wakeups).
+//
+// Only the "associated" thread can block (park) on the ParkEvent, although
+// any other thread can unpark a reachable parkevent. Park() is allowed to
+// return spuriously. In fact park-unpark a really just an optimization to
+// avoid unbounded spinning and surrender the CPU to be a polite system citizen.
+// A degenerate albeit "impolite" park-unpark implementation could simply return.
+// See http://blogs.sun.com/dave for more details.
+//
+// Eventually I'd like to eliminate Events and ObjectWaiters, both of which serve as
+// thread proxies, and simply make the THREAD structure type-stable and persistent.
+// Currently, we unpark events associated with threads, but ideally we'd just
+// unpark threads.
+//
+// The base-class, PlatformEvent, is platform-specific while the ParkEvent is
+// platform-independent. PlatformEvent provides park(), unpark(), etc., and
+// is abstract -- that is, a PlatformEvent should never be instantiated except
+// as part of a ParkEvent.
+// Equivalently we could have defined a platform-independent base-class that
+// exported Allocate(), Release(), etc. The platform-specific class would extend
+// that base-class, adding park(), unpark(), etc.
+//
+// A word of caution: The JVM uses 2 very similar constructs:
+// 1. ParkEvent are used for Java-level "monitor" synchronization.
+// 2. Parkers are used by JSR166-JUC park-unpark.
+//
+// We'll want to eventually merge these redundant facilities and use ParkEvent.
+
+
+class ParkEvent : public os::PlatformEvent {
+ private:
+ ParkEvent * FreeNext ;
+
+ // Current association
+ Thread * AssociatedWith ;
+
+ public:
+ // MCS-CLH list linkage and Native Mutex/Monitor
+ ParkEvent * volatile ListNext ;
+ volatile intptr_t OnList ;
+ volatile int TState ;
+ volatile int Notified ; // for native monitor construct
+
+ private:
+ static ParkEvent * volatile FreeList ;
+ static volatile int ListLock ;
+
+ // It's prudent to mark the dtor as "private"
+ // ensuring that it's not visible outside the package.
+ // Unfortunately gcc warns about such usage, so
+ // we revert to the less desirable "protected" visibility.
+ // The other compilers accept private dtors.
+
+ protected: // Ensure dtor is never invoked
+ ~ParkEvent() { guarantee (0, "invariant") ; }
+
+ ParkEvent() : PlatformEvent() {
+ AssociatedWith = NULL ;
+ FreeNext = NULL ;
+ ListNext = NULL ;
+ OnList = 0 ;
+ TState = 0 ;
+ Notified = 0 ;
+ }
+
+ // We use placement-new to force ParkEvent instances to be
+ // aligned on 256-byte address boundaries. This ensures that the least
+ // significant byte of a ParkEvent address is always 0.
+
+ void * operator new (size_t sz) throw();
+ void operator delete (void * a) ;
+
+ public:
+ static ParkEvent * Allocate (Thread * t) ;
+ static void Release (ParkEvent * e) ;
+} ;
+
+#endif // SHARE_VM_RUNTIME_PARK_HPP