jdk8-mips64-public/hotspot: src/share/vm/runtime/park.cpp@63147986a428 (annotated)

src/share/vm/runtime/park.cpp@63147986a428 (annotated)

src/share/vm/runtime/park.cpp

Wed, 18 Sep 2013 07:02:10 -0700

author: dcubed
date: Wed, 18 Sep 2013 07:02:10 -0700
changeset 5743: 63147986a428
parent 5614: 9758d9f36299
child 6348: 0e6af9b390af
permissions: -rw-r--r--

8019835: Strings interned in different threads equal but does not ==
Summary: Add -XX:+VerifyStringTableAtExit option and code to verify StringTable invariants.
Reviewed-by: rdurbin, sspitsyn, coleenp

 /*
  * Copyright (c) 1997, 2013, 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.
  *
  */
 #include "precompiled.hpp"
 #include "runtime/thread.hpp"
 // Lifecycle management for TSM ParkEvents.
 // ParkEvents are type-stable (TSM).
 // In our particular implementation they happen to be immortal.
 //
 // We manage concurrency on the FreeList with a CAS-based
 // detach-modify-reattach idiom that avoids the ABA problems
 // that would otherwise be present in a simple CAS-based
 // push-pop implementation.   (push-one and pop-all)
 //
 // Caveat: Allocate() and Release() may be called from threads
 // other than the thread associated with the Event!
 // If we need to call Allocate() when running as the thread in
 // question then look for the PD calls to initialize native TLS.
 // Native TLS (Win32/Linux/Solaris) can only be initialized or
 // accessed by the associated thread.
 // See also pd_initialize().
 //
 // Note that we could defer associating a ParkEvent with a thread
 // until the 1st time the thread calls park().  unpark() calls to
 // an unprovisioned thread would be ignored.  The first park() call
 // for a thread would allocate and associate a ParkEvent and return
 // immediately.
 volatile int ParkEvent::ListLock = 0 ;
 ParkEvent * volatile ParkEvent::FreeList = NULL ;
 ParkEvent * ParkEvent::Allocate (Thread * t) {
   // In rare cases -- JVM_RawMonitor* operations -- we can find t == null.
   ParkEvent * ev ;
   // Start by trying to recycle an existing but unassociated
   // ParkEvent from the global free list.
   for (;;) {
     ev = FreeList ;
     if (ev == NULL) break ;
     // 1: Detach - sequester or privatize the list
     // Tantamount to ev = Swap (&FreeList, NULL)
     if (Atomic::cmpxchg_ptr (NULL, &FreeList, ev) != ev) {
        continue ;
     }
     // We've detached the list.  The list in-hand is now
     // local to this thread.   This thread can operate on the
     // list without risk of interference from other threads.
     // 2: Extract -- pop the 1st element from the list.
     ParkEvent * List = ev->FreeNext ;
     if (List == NULL) break ;
     for (;;) {
         // 3: Try to reattach the residual list
         guarantee (List != NULL, "invariant") ;
         ParkEvent * Arv =  (ParkEvent *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
         if (Arv == NULL) break ;
         // New nodes arrived.  Try to detach the recent arrivals.
         if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
             continue ;
         }
         guarantee (Arv != NULL, "invariant") ;
         // 4: Merge Arv into List
         ParkEvent * Tail = List ;
         while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
         Tail->FreeNext = Arv ;
     }
     break ;
   }
   if (ev != NULL) {
     guarantee (ev->AssociatedWith == NULL, "invariant") ;
   } else {
     // Do this the hard way -- materialize a new ParkEvent.
     // In rare cases an allocating thread might detach a long list --
     // installing null into FreeList -- and then stall or be obstructed.
     // A 2nd thread calling Allocate() would see FreeList == null.
     // The list held privately by the 1st thread is unavailable to the 2nd thread.
     // In that case the 2nd thread would have to materialize a new ParkEvent,
     // even though free ParkEvents existed in the system.  In this case we end up
     // with more ParkEvents in circulation than we need, but the race is
     // rare and the outcome is benign.  Ideally, the # of extant ParkEvents
     // is equal to the maximum # of threads that existed at any one time.
     // Because of the race mentioned above, segments of the freelist
     // can be transiently inaccessible.  At worst we may end up with the
     // # of ParkEvents in circulation slightly above the ideal.
     // Note that if we didn't have the TSM/immortal constraint, then
     // when reattaching, above, we could trim the list.
     ev = new ParkEvent () ;
     guarantee ((intptr_t(ev) & 0xFF) == 0, "invariant") ;
   }
   ev->reset() ;                     // courtesy to caller
   ev->AssociatedWith = t ;          // Associate ev with t
   ev->FreeNext       = NULL ;
   return ev ;
 }
 void ParkEvent::Release (ParkEvent * ev) {
   if (ev == NULL) return ;
   guarantee (ev->FreeNext == NULL      , "invariant") ;
   ev->AssociatedWith = NULL ;
   for (;;) {
     // Push ev onto FreeList
     // The mechanism is "half" lock-free.
     ParkEvent * List = FreeList ;
     ev->FreeNext = List ;
     if (Atomic::cmpxchg_ptr (ev, &FreeList, List) == List) break ;
   }
 }
 // Override operator new and delete so we can ensure that the
 // least significant byte of ParkEvent addresses is 0.
 // Beware that excessive address alignment is undesirable
 // as it can result in D$ index usage imbalance as
 // well as bank access imbalance on Niagara-like platforms,
 // although Niagara's hash function should help.
 void * ParkEvent::operator new (size_t sz) throw() {
   return (void *) ((intptr_t (AllocateHeap(sz + 256, mtInternal, CALLER_PC)) + 256) & -256) ;
 }
 void ParkEvent::operator delete (void * a) {
   // ParkEvents are type-stable and immortal ...
   ShouldNotReachHere();
 }
 // 6399321 As a temporary measure we copied & modified the ParkEvent::
 // allocate() and release() code for use by Parkers.  The Parker:: forms
 // will eventually be removed as we consolide and shift over to ParkEvents
 // for both builtin synchronization and JSR166 operations.
 volatile int Parker::ListLock = 0 ;
 Parker * volatile Parker::FreeList = NULL ;
 Parker * Parker::Allocate (JavaThread * t) {
   guarantee (t != NULL, "invariant") ;
   Parker * p ;
   // Start by trying to recycle an existing but unassociated
   // Parker from the global free list.
   for (;;) {
     p = FreeList ;
     if (p  == NULL) break ;
     // 1: Detach
     // Tantamount to p = Swap (&FreeList, NULL)
     if (Atomic::cmpxchg_ptr (NULL, &FreeList, p) != p) {
        continue ;
     }
     // We've detached the list.  The list in-hand is now
     // local to this thread.   This thread can operate on the
     // list without risk of interference from other threads.
     // 2: Extract -- pop the 1st element from the list.
     Parker * List = p->FreeNext ;
     if (List == NULL) break ;
     for (;;) {
         // 3: Try to reattach the residual list
         guarantee (List != NULL, "invariant") ;
         Parker * Arv =  (Parker *) Atomic::cmpxchg_ptr (List, &FreeList, NULL) ;
         if (Arv == NULL) break ;
         // New nodes arrived.  Try to detach the recent arrivals.
         if (Atomic::cmpxchg_ptr (NULL, &FreeList, Arv) != Arv) {
             continue ;
         }
         guarantee (Arv != NULL, "invariant") ;
         // 4: Merge Arv into List
         Parker * Tail = List ;
         while (Tail->FreeNext != NULL) Tail = Tail->FreeNext ;
         Tail->FreeNext = Arv ;
     }
     break ;
   }
   if (p != NULL) {
     guarantee (p->AssociatedWith == NULL, "invariant") ;
   } else {
     // Do this the hard way -- materialize a new Parker..
     // In rare cases an allocating thread might detach
     // a long list -- installing null into FreeList --and
     // then stall.  Another thread calling Allocate() would see
     // FreeList == null and then invoke the ctor.  In this case we
     // end up with more Parkers in circulation than we need, but
     // the race is rare and the outcome is benign.
     // Ideally, the # of extant Parkers is equal to the
     // maximum # of threads that existed at any one time.
     // Because of the race mentioned above, segments of the
     // freelist can be transiently inaccessible.  At worst
     // we may end up with the # of Parkers in circulation
     // slightly above the ideal.
     p = new Parker() ;
   }
   p->AssociatedWith = t ;          // Associate p with t
   p->FreeNext       = NULL ;
   return p ;
 }
 void Parker::Release (Parker * p) {
   if (p == NULL) return ;
   guarantee (p->AssociatedWith != NULL, "invariant") ;
   guarantee (p->FreeNext == NULL      , "invariant") ;
   p->AssociatedWith = NULL ;
   for (;;) {
     // Push p onto FreeList
     Parker * List = FreeList ;
     p->FreeNext = List ;
     if (Atomic::cmpxchg_ptr (p, &FreeList, List) == List) break ;
   }
 }

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/runtime/park.cpp@63147986a428 (annotated)

src/share/vm/runtime/park.cpp