1 /* 2 * Copyright (c) 2019, 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 #include "precompiled.hpp" 26 #include "runtime/atomic.hpp" 27 #include "runtime/orderAccess.hpp" 28 #include "runtime/os.hpp" 29 #include "utilities/waitBarrier_generic.hpp" 30 #include "utilities/spinYield.hpp" 31 32 void GenericWaitBarrier::arm(int barrier_tag) { 33 assert(_barrier_tag == 0, "Already armed"); 34 assert(_waiters == 0, "We left a thread hanging"); 35 _barrier_tag = barrier_tag; 36 _waiters = 0; 37 OrderAccess::fence(); 38 } 39 40 int GenericWaitBarrier::wake_if_needed() { 41 assert(_barrier_tag == 0, "Not disarmed"); 42 int w = _waiters; 43 if (w == 0) { 44 // Load of _barrier_threads in caller must not pass the load of _waiters. 45 OrderAccess::loadload(); 46 return 0; 47 } 48 assert(w > 0, "Bad counting"); 49 // We need an exact count which never goes below zero, 50 // otherwise the semaphore may be signalled too many times. 51 if (Atomic::cmpxchg(w - 1, &_waiters, w) == w) { 52 _sem_barrier.signal(); 53 return w - 1; 54 } 55 return w; 56 } 57 58 void GenericWaitBarrier::disarm() { 59 assert(_barrier_tag != 0, "Not armed"); 60 _barrier_tag = 0; 61 // Loads of _barrier_threads/_waiters must not float above disarm store and 62 // disarm store must not sink below. 63 OrderAccess::fence(); 64 int left; 65 SpinYield sp; 66 do { 67 left = GenericWaitBarrier::wake_if_needed(); 68 if (left == 0 && _barrier_threads > 0) { 69 // There is no thread to wake but we still have barrier threads. 70 sp.wait(); 71 } 72 // We must loop here until there are no waiters or potential waiters. 73 } while (left > 0 || _barrier_threads > 0); 74 // API specifies disarm() must provide a trailing fence. 75 OrderAccess::fence(); 76 } 77 78 void GenericWaitBarrier::wait(int barrier_tag) { 79 assert(barrier_tag != 0, "Trying to wait on disarmed value"); 80 if (barrier_tag != _barrier_tag) { 81 // API specifies wait() must provide a trailing fence. 82 OrderAccess::fence(); 83 return; 84 } 85 Atomic::add(1, &_barrier_threads); 86 if (barrier_tag != 0 && barrier_tag == _barrier_tag) { 87 Atomic::add(1, &_waiters); 88 _sem_barrier.wait(); 89 // We help out with posting, but we need to do so before we decrement the 90 // _barrier_threads otherwise we might wake threads up in next wait. 91 GenericWaitBarrier::wake_if_needed(); 92 } 93 Atomic::add(-1, &_barrier_threads); 94 }