1798N/A * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved. 1798N/A * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 1798N/A * This code is free software; you can redistribute it and/or modify it 1798N/A * under the terms of the GNU General Public License version 2 only, as 1798N/A * published by the Free Software Foundation. 1798N/A * This code is distributed in the hope that it will be useful, but WITHOUT 1798N/A * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 1798N/A * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 1798N/A * version 2 for more details (a copy is included in the LICENSE file that 1798N/A * You should have received a copy of the GNU General Public License version 1798N/A * 2 along with this work; if not, write to the Free Software Foundation, 1798N/A * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 1798N/A * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 1798N/A// Lifecycle management for TSM ParkEvents. 1798N/A// ParkEvents are type-stable (TSM). 1798N/A// In our particular implementation they happen to be immortal. 1798N/A// We manage concurrency on the FreeList with a CAS-based 1798N/A// detach-modify-reattach idiom that avoids the ABA problems 1798N/A// that would otherwise be present in a simple CAS-based 1798N/A// push-pop implementation. (push-one and pop-all) 1798N/A// Caveat: Allocate() and Release() may be called from threads 1798N/A// other than the thread associated with the Event! 1798N/A// If we need to call Allocate() when running as the thread in 1798N/A// question then look for the PD calls to initialize native TLS. 1798N/A// accessed by the associated thread. 1798N/A// See also pd_initialize(). 1798N/A// Note that we could defer associating a ParkEvent with a thread 1798N/A// until the 1st time the thread calls park(). unpark() calls to 1798N/A// an unprovisioned thread would be ignored. The first park() call 1798N/A// for a thread would allocate and associate a ParkEvent and return 1798N/A // In rare cases -- JVM_RawMonitor* operations -- we can find t == null. 1798N/A // Start by trying to recycle an existing but unassociated 1798N/A // ParkEvent from the global free list. 1798N/A // 1: Detach - sequester or privatize the list 1798N/A // Tantamount to ev = Swap (&FreeList, NULL) 1798N/A // We've detached the list. The list in-hand is now 1798N/A // local to this thread. This thread can operate on the 1798N/A // list without risk of interference from other threads. 1798N/A // 2: Extract -- pop the 1st element from the list. 1798N/A // 3: Try to reattach the residual list 1798N/A // New nodes arrived. Try to detach the recent arrivals. 1798N/A // Do this the hard way -- materialize a new ParkEvent. 1798N/A // In rare cases an allocating thread might detach a long list -- 1798N/A // installing null into FreeList -- and then stall or be obstructed. 1798N/A // A 2nd thread calling Allocate() would see FreeList == null. 1798N/A // The list held privately by the 1st thread is unavailable to the 2nd thread. 1798N/A // In that case the 2nd thread would have to materialize a new ParkEvent, 1798N/A // even though free ParkEvents existed in the system. In this case we end up 1798N/A // with more ParkEvents in circulation than we need, but the race is 1798N/A // rare and the outcome is benign. Ideally, the # of extant ParkEvents 1798N/A // is equal to the maximum # of threads that existed at any one time. 1798N/A // Because of the race mentioned above, segments of the freelist 1798N/A // can be transiently inaccessible. At worst we may end up with the 1798N/A // # of ParkEvents in circulation slightly above the ideal. 1798N/A // when reattaching, above, we could trim the list. 1798N/A // The mechanism is "half" lock-free. 1798N/A// Override operator new and delete so we can ensure that the 1798N/A// least significant byte of ParkEvent addresses is 0. 1798N/A// Beware that excessive address alignment is undesirable 1798N/A// as it can result in D$ index usage imbalance as 1798N/A// well as bank access imbalance on Niagara-like platforms, 1798N/A// although Niagara's hash function should help. 1798N/A // ParkEvents are type-stable and immortal ... 1798N/A// 6399321 As a temporary measure we copied & modified the ParkEvent:: 1798N/A// allocate() and release() code for use by Parkers. The Parker:: forms 1798N/A// will eventually be removed as we consolide and shift over to ParkEvents 1798N/A// for both builtin synchronization and JSR166 operations. 1798N/A // Start by trying to recycle an existing but unassociated 1798N/A // Parker from the global free list. 1798N/A // Tantamount to p = Swap (&FreeList, NULL) 1798N/A // We've detached the list. The list in-hand is now 1798N/A // local to this thread. This thread can operate on the 1798N/A // list without risk of interference from other threads. 1798N/A // 2: Extract -- pop the 1st element from the list. 1798N/A // 3: Try to reattach the residual list 1798N/A // New nodes arrived. Try to detach the recent arrivals. 1798N/A // Do this the hard way -- materialize a new Parker.. 1798N/A // In rare cases an allocating thread might detach 1798N/A // a long list -- installing null into FreeList --and 1798N/A // then stall. Another thread calling Allocate() would see 1798N/A // FreeList == null and then invoke the ctor. In this case we 1798N/A // end up with more Parkers in circulation than we need, but 1798N/A // the race is rare and the outcome is benign. 1798N/A // Ideally, the # of extant Parkers is equal to the 1798N/A // maximum # of threads that existed at any one time. 1798N/A // Because of the race mentioned above, segments of the 1798N/A // freelist can be transiently inaccessible. At worst 1798N/A // we may end up with the # of Parkers in circulation 1798N/A // slightly above the ideal.