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Java example source code file (park.cpp)
The park.cpp Java example source code/* * 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 ; } } Other Java examples (source code examples)Here is a short list of links related to this Java park.cpp source code file: |
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