1 /*

     2  * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  *

    23  */

    24 

    25 

    26 # include "incls/_precompiled.incl"

    27 # include "incls/_park.cpp.incl"

    28 

    29 

    30 // Lifecycle management for TSM ParkEvents.

    31 // ParkEvents are type-stable (TSM).

    32 // In our particular implementation they happen to be immortal.

    33 //

    34 // We manage concurrency on the FreeList with a CAS-based

    35 // detach-modify-reattach idiom that avoids the ABA problems

    36 // that would otherwise be present in a simple CAS-based

    37 // push-pop implementation.   (push-one and pop-all)

    38 //

    39 // Caveat: Allocate() and Release() may be called from threads

    40 // other than the thread associated with the Event!

    41 // If we need to call Allocate() when running as the thread in

    42 // question then look for the PD calls to initialize native TLS.

    43 // Native TLS (Win32/Linux/Solaris) can only be initialized or

    44 // accessed by the associated thread.

    45 // See also pd_initialize().

    46 //

    47 // Note that we could defer associating a ParkEvent with a thread

    48 // until the 1st time the thread calls park().  unpark() calls to

    49 // an unprovisioned thread would be ignored.  The first park() call

    50 // for a thread would allocate and associate a ParkEvent and return

    51 // immediately.

    52 

    53 volatile int ParkEvent::ListLock = 0 ;

    54 ParkEvent * volatile ParkEvent::FreeList = NULL ;

    55 

    56 ParkEvent * ParkEvent::Allocate (Thread * t) {

    57   // In rare cases -- JVM_RawMonitor* operations -- we can find t == null.

    58   ParkEvent * ev ;

    59 

    60   // Start by trying to recycle an existing but unassociated

    61   // ParkEvent from the global free list.

    62   for (;;) {

    63     ev = FreeList ;

    64     if (ev == NULL) break ;

    65     // 1: Detach - sequester or privatize the list

    66     // Tantamount to ev = Swap (&FreeList, NULL)

    67     if (Atomic::cmpxchg_ptr (NULL, &FreeList, ev) != ev) {

    68        continue ;

    69     }

    70 

    71     // We've detached the list.  The list in-hand is now

    72     // local to this thread.   This thread can operate on the

    73     // list without risk of interference from other threads.

    74     // 2: Extract -- pop the 1st element from the list.

    75     ParkEvent * List = ev->FreeNext ;

    76     if (List == NULL) break ;

    77     for (;;) {

    78         // 3: Try to reattach the residual list

    79         guarantee (List != NULL, "invariant") ;

    80         ParkEvent * Arv =  (ParkEvent *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;

    81         if (Arv == NULL) break ;

    82 

    83         // New nodes arrived.  Try to detach the recent arrivals.

    84         if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {

    85             continue ;

    86         }

    87         guarantee (Arv != NULL, "invariant") ;

    88         // 4: Merge Arv into List

    89         ParkEvent * Tail = List ;

    90         while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;

    91         Tail->FreeNext = Arv ;

    92     }

    93     break ;

    94   }

    95 

    96   if (ev != NULL) {

    97     guarantee (ev->AssociatedWith == NULL, "invariant") ;

    98   } else {

    99     // Do this the hard way -- materialize a new ParkEvent.

   100     // In rare cases an allocating thread might detach a long list --

   101     // installing null into FreeList -- and then stall or be obstructed.

   102     // A 2nd thread calling Allocate() would see FreeList == null.

   103     // The list held privately by the 1st thread is unavailable to the 2nd thread.

   104     // In that case the 2nd thread would have to materialize a new ParkEvent,

   105     // even though free ParkEvents existed in the system.  In this case we end up

   106     // with more ParkEvents in circulation than we need, but the race is

   107     // rare and the outcome is benign.  Ideally, the # of extant ParkEvents

   108     // is equal to the maximum # of threads that existed at any one time.

   109     // Because of the race mentioned above, segments of the freelist

   110     // can be transiently inaccessible.  At worst we may end up with the

   111     // # of ParkEvents in circulation slightly above the ideal.

   112     // Note that if we didn't have the TSM/immortal constraint, then

   113     // when reattaching, above, we could trim the list.

   114     ev = new ParkEvent () ;

   115     guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ;

   116   }

   117   ev->reset() ;                     // courtesy to caller

   118   ev->AssociatedWith = t ;          // Associate ev with t

   119   ev->FreeNext       = NULL ;

   120   return ev ;

   121 }

   122 

   123 void ParkEvent::Release (ParkEvent * ev) {

   124   if (ev == NULL) return ;

   125   guarantee (ev->FreeNext == NULL      , "invariant") ;

   126   ev->AssociatedWith = NULL ;

   127   for (;;) {

   128     // Push ev onto FreeList

   129     // The mechanism is "half" lock-free.

   130     ParkEvent * List = FreeList ;

   131     ev->FreeNext = List ;

   132     if (Atomic::cmpxchg_ptr (ev, &FreeList, List) == List) break ;

   133   }

   134 }

   135 

   136 // Override operator new and delete so we can ensure that the

   137 // least significant byte of ParkEvent addresses is 0.

   138 // Beware that excessive address alignment is undesirable

   139 // as it can result in D$ index usage imbalance as

   140 // well as bank access imbalance on Niagara-like platforms,

   141 // although Niagara's hash function should help.

   142 

   143 void * ParkEvent::operator new (size_t sz) {

   144   return (void *) ((intptr_t (CHeapObj::operator new (sz + 256)) + 256) & -256) ;

   145 }

   146 

   147 void ParkEvent::operator delete (void * a) {

   148   // ParkEvents are type-stable and immortal ...

   149   ShouldNotReachHere();

   150 }

   151 

   152 

   153 // 6399321 As a temporary measure we copied & modified the ParkEvent::

   154 // allocate() and release() code for use by Parkers.  The Parker:: forms

   155 // will eventually be removed as we consolide and shift over to ParkEvents

   156 // for both builtin synchronization and JSR166 operations.

   157 

   158 volatile int Parker::ListLock = 0 ;

   159 Parker * volatile Parker::FreeList = NULL ;

   160 

   161 Parker * Parker::Allocate (JavaThread * t) {

   162   guarantee (t != NULL, "invariant") ;

   163   Parker * p ;

   164 

   165   // Start by trying to recycle an existing but unassociated

   166   // Parker from the global free list.

   167   for (;;) {

   168     p = FreeList ;

   169     if (p  == NULL) break ;

   170     // 1: Detach

   171     // Tantamount to p = Swap (&FreeList, NULL)

   172     if (Atomic::cmpxchg_ptr (NULL, &FreeList, p) != p) {

   173        continue ;

   174     }

   175 

   176     // We've detached the list.  The list in-hand is now

   177     // local to this thread.   This thread can operate on the

   178     // list without risk of interference from other threads.

   179     // 2: Extract -- pop the 1st element from the list.

   180     Parker * List = p->FreeNext ;

   181     if (List == NULL) break ;

   182     for (;;) {

   183         // 3: Try to reattach the residual list

   184         guarantee (List != NULL, "invariant") ;

   185         Parker * Arv =  (Parker *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;

   186         if (Arv == NULL) break ;

   187 

   188         // New nodes arrived.  Try to detach the recent arrivals.

   189         if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {

   190             continue ;

   191         }

   192         guarantee (Arv != NULL, "invariant") ;

   193         // 4: Merge Arv into List

   194         Parker * Tail = List ;

   195         while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;

   196         Tail->FreeNext = Arv ;

   197     }

   198     break ;

   199   }

   200 

   201   if (p != NULL) {

   202     guarantee (p->AssociatedWith == NULL, "invariant") ;

   203   } else {

   204     // Do this the hard way -- materialize a new Parker..

   205     // In rare cases an allocating thread might detach

   206     // a long list -- installing null into FreeList --and

   207     // then stall.  Another thread calling Allocate() would see

   208     // FreeList == null and then invoke the ctor.  In this case we

   209     // end up with more Parkers in circulation than we need, but

   210     // the race is rare and the outcome is benign.

   211     // Ideally, the # of extant Parkers is equal to the

   212     // maximum # of threads that existed at any one time.

   213     // Because of the race mentioned above, segments of the

   214     // freelist can be transiently inaccessible.  At worst

   215     // we may end up with the # of Parkers in circulation

   216     // slightly above the ideal.

   217     p = new Parker() ;

   218   }

   219   p->AssociatedWith = t ;          // Associate p with t

   220   p->FreeNext       = NULL ;

   221   return p ;

   222 }

   223 

   224 

   225 void Parker::Release (Parker * p) {

   226   if (p == NULL) return ;

   227   guarantee (p->AssociatedWith != NULL, "invariant") ;

   228   guarantee (p->FreeNext == NULL      , "invariant") ;

   229   p->AssociatedWith = NULL ;

   230   for (;;) {

   231     // Push p onto FreeList

   232     Parker * List = FreeList ;

   233     p->FreeNext = List ;

   234     if (Atomic::cmpxchg_ptr (p, &FreeList, List) == List) break ;

   235   }

   236 }

   237