Mercurial > hg > graal-jvmci-8
diff src/share/vm/runtime/park.cpp @ 1878:fa83ab460c54
6988353: refactor contended sync subsystem
Summary: reduce complexity by factoring synchronizer.cpp
Reviewed-by: dholmes, never, coleenp
author | acorn |
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date | Fri, 22 Oct 2010 15:59:34 -0400 |
parents | |
children | f95d63e2154a |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/share/vm/runtime/park.cpp Fri Oct 22 15:59:34 2010 -0400 @@ -0,0 +1,237 @@ +/* + * Copyright (c) 1997, 2010, 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 "incls/_precompiled.incl" +# include "incls/_park.cpp.incl" + + +// 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) { + return (void *) ((intptr_t (CHeapObj::operator new (sz + 256)) + 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 ; + } +} +