1 /* 2 * Copyright (c) 2014, 2016, 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 "gc/g1/suspendibleThreadSet.hpp" 27 #include "runtime/mutexLocker.hpp" 28 #include "runtime/semaphore.hpp" 29 #include "runtime/thread.inline.hpp" 30 31 uint SuspendibleThreadSet::_nthreads = 0; 32 uint SuspendibleThreadSet::_nthreads_stopped = 0; 33 bool SuspendibleThreadSet::_suspend_all = false; 34 double SuspendibleThreadSet::_suspend_all_start = 0.0; 35 36 static Semaphore* _synchronize_wakeup = NULL; 37 38 void SuspendibleThreadSet_init() { 39 assert(_synchronize_wakeup == NULL, "STS already initialized"); 40 _synchronize_wakeup = new Semaphore(); 41 } 42 43 bool SuspendibleThreadSet::is_synchronized() { 44 assert_lock_strong(STS_lock); 45 assert(_nthreads_stopped <= _nthreads, "invariant"); 46 return _nthreads_stopped == _nthreads; 47 } 48 49 void SuspendibleThreadSet::join() { 50 assert(!Thread::current()->is_suspendible_thread(), "Thread already joined"); 51 MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag); 52 while (_suspend_all) { 53 ml.wait(Mutex::_no_safepoint_check_flag); 54 } 55 _nthreads++; 56 DEBUG_ONLY(Thread::current()->set_suspendible_thread();) 57 } 58 59 void SuspendibleThreadSet::leave() { 60 assert(Thread::current()->is_suspendible_thread(), "Thread not joined"); 61 MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag); 62 assert(_nthreads > 0, "Invalid"); 63 DEBUG_ONLY(Thread::current()->clear_suspendible_thread();) 64 _nthreads--; 65 if (_suspend_all && is_synchronized()) { 66 // This leave completes a request, so inform the requestor. 67 _synchronize_wakeup->signal(); 68 } 69 } 70 71 void SuspendibleThreadSet::yield() { 72 assert(Thread::current()->is_suspendible_thread(), "Must have joined"); 73 MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag); 74 if (_suspend_all) { 75 _nthreads_stopped++; 76 if (is_synchronized()) { 77 if (ConcGCYieldTimeout > 0) { 78 double now = os::elapsedTime(); 79 guarantee((now - _suspend_all_start) * 1000.0 < (double)ConcGCYieldTimeout, "Long delay"); 80 } 81 // This yield completes the request, so inform the requestor. 82 _synchronize_wakeup->signal(); 83 } 84 while (_suspend_all) { 85 ml.wait(Mutex::_no_safepoint_check_flag); 86 } 87 assert(_nthreads_stopped > 0, "Invalid"); 88 _nthreads_stopped--; 89 } 90 } 91 92 void SuspendibleThreadSet::synchronize() { 93 assert(Thread::current()->is_VM_thread(), "Must be the VM thread"); 94 if (ConcGCYieldTimeout > 0) { 95 _suspend_all_start = os::elapsedTime(); 96 } 97 { 98 MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag); 99 assert(!_suspend_all, "Only one at a time"); 100 _suspend_all = true; 101 if (is_synchronized()) { 102 return; 103 } 104 } // Release lock before semaphore wait. 105 106 // Semaphore initial count is zero. To reach here, there must be at 107 // least one not yielded thread in the set, e.g. is_synchronized() 108 // was false before the lock was released. A thread in the set will 109 // signal the semaphore iff it is the last to yield or leave while 110 // there is an active suspend request. So there will be exactly one 111 // signal, which will increment the semaphore count to one, which 112 // will then be consumed by this wait, returning it to zero. No 113 // thread can exit yield or enter the set until desynchronize is 114 // called, so there are no further opportunities for the semaphore 115 // being signaled until we get back here again for some later 116 // synchronize call. Hence, there is no need to re-check for 117 // is_synchronized after the wait; it will always be true there. 118 _synchronize_wakeup->wait(); 119 120 #ifdef ASSERT 121 MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag); 122 assert(_suspend_all, "STS not synchronizing"); 123 assert(is_synchronized(), "STS not synchronized"); 124 #endif 125 } 126 127 void SuspendibleThreadSet::desynchronize() { 128 assert(Thread::current()->is_VM_thread(), "Must be the VM thread"); 129 MonitorLockerEx ml(STS_lock, Mutex::_no_safepoint_check_flag); 130 assert(_suspend_all, "STS not synchronizing"); 131 assert(is_synchronized(), "STS not synchronized"); 132 _suspend_all = false; 133 ml.notify_all(); 134 }