1 /*
2 * Copyright (c) 2014, 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 "gc/shared/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
SuspendibleThreadSet_init()38 void SuspendibleThreadSet_init() {
39 assert(_synchronize_wakeup == NULL, "STS already initialized");
40 _synchronize_wakeup = new Semaphore();
41 }
42
is_synchronized()43 bool SuspendibleThreadSet::is_synchronized() {
44 assert_lock_strong(STS_lock);
45 assert(_nthreads_stopped <= _nthreads, "invariant");
46 return _nthreads_stopped == _nthreads;
47 }
48
join()49 void SuspendibleThreadSet::join() {
50 assert(!Thread::current()->is_suspendible_thread(), "Thread already joined");
51 MonitorLocker ml(STS_lock, Mutex::_no_safepoint_check_flag);
52 while (_suspend_all) {
53 ml.wait();
54 }
55 _nthreads++;
56 DEBUG_ONLY(Thread::current()->set_suspendible_thread();)
57 }
58
leave()59 void SuspendibleThreadSet::leave() {
60 assert(Thread::current()->is_suspendible_thread(), "Thread not joined");
61 MonitorLocker 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
yield()71 void SuspendibleThreadSet::yield() {
72 assert(Thread::current()->is_suspendible_thread(), "Must have joined");
73 MonitorLocker 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();
86 }
87 assert(_nthreads_stopped > 0, "Invalid");
88 _nthreads_stopped--;
89 }
90 }
91
synchronize()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 MonitorLocker 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 MonitorLocker 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
desynchronize()127 void SuspendibleThreadSet::desynchronize() {
128 assert(Thread::current()->is_VM_thread(), "Must be the VM thread");
129 MonitorLocker 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 }
135