1 /*
2 * Copyright (c) 2018, 2019, Red Hat, Inc. All rights reserved.
3 * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #include "precompiled.hpp"
27
28 #include "gc/shared/taskTerminator.hpp"
29 #include "gc/shared/taskqueue.hpp"
30 #include "logging/log.hpp"
31
32 TaskTerminator::TaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set) :
33 _n_threads(n_threads),
34 _queue_set(queue_set),
35 _offered_termination(0),
36 _spin_master(NULL) {
37
38 _blocker = new Monitor(Mutex::leaf, "TaskTerminator", false, Monitor::_safepoint_check_never);
39 }
40
41 TaskTerminator::~TaskTerminator() {
42 assert(_offered_termination == 0 || !peek_in_queue_set(), "Precondition");
43 assert(_offered_termination == 0 || _offered_termination == _n_threads, "Terminated or aborted" );
44
45 assert(_spin_master == NULL, "Should have been reset");
46 assert(_blocker != NULL, "Can not be NULL");
47 delete _blocker;
48 }
49
50 #ifdef ASSERT
51 bool TaskTerminator::peek_in_queue_set() {
52 return _queue_set->peek();
53 }
54 #endif
55
56 void TaskTerminator::yield() {
57 assert(_offered_termination <= _n_threads, "Invariant");
58 os::naked_yield();
59 }
60
61 void TaskTerminator::reset_for_reuse() {
62 if (_offered_termination != 0) {
63 assert(_offered_termination == _n_threads,
64 "Terminator may still be in use");
65 _offered_termination = 0;
66 }
67 }
68
69 void TaskTerminator::reset_for_reuse(uint n_threads) {
70 reset_for_reuse();
71 _n_threads = n_threads;
72 }
73
74 bool TaskTerminator::exit_termination(size_t tasks, TerminatorTerminator* terminator) {
75 return tasks > 0 || (terminator != NULL && terminator->should_exit_termination());
76 }
77
78 size_t TaskTerminator::tasks_in_queue_set() const {
79 return _queue_set->tasks();
80 }
81
82 bool TaskTerminator::offer_termination(TerminatorTerminator* terminator) {
83 assert(_n_threads > 0, "Initialization is incorrect");
84 assert(_offered_termination < _n_threads, "Invariant");
85 assert(_blocker != NULL, "Invariant");
86
87 // Single worker, done
88 if (_n_threads == 1) {
89 _offered_termination = 1;
90 assert(!peek_in_queue_set(), "Precondition");
91 return true;
92 }
93
94 _blocker->lock_without_safepoint_check();
95 _offered_termination++;
96 // All arrived, done
97 if (_offered_termination == _n_threads) {
98 _blocker->notify_all();
99 _blocker->unlock();
100 assert(!peek_in_queue_set(), "Precondition");
101 return true;
102 }
103
104 Thread* the_thread = Thread::current();
105 while (true) {
106 if (_spin_master == NULL) {
107 _spin_master = the_thread;
108
109 _blocker->unlock();
110
111 if (do_spin_master_work(terminator)) {
112 assert(_offered_termination == _n_threads, "termination condition");
113 assert(!peek_in_queue_set(), "Precondition");
114 return true;
115 } else {
116 _blocker->lock_without_safepoint_check();
117 // There is possibility that termination is reached between dropping the lock
118 // before returning from do_spin_master_work() and acquiring lock above.
119 if (_offered_termination == _n_threads) {
120 _blocker->unlock();
121 assert(!peek_in_queue_set(), "Precondition");
122 return true;
123 }
124 }
125 } else {
126 _blocker->wait_without_safepoint_check(WorkStealingSleepMillis);
127
128 if (_offered_termination == _n_threads) {
129 _blocker->unlock();
130 assert(!peek_in_queue_set(), "Precondition");
131 return true;
132 }
133 }
134
135 size_t tasks = tasks_in_queue_set();
136 if (exit_termination(tasks, terminator)) {
137 assert_lock_strong(_blocker);
138 _offered_termination--;
139 _blocker->unlock();
140 return false;
141 }
142 }
143 }
144
145 bool TaskTerminator::do_spin_master_work(TerminatorTerminator* terminator) {
146 uint yield_count = 0;
147 // Number of hard spin loops done since last yield
148 uint hard_spin_count = 0;
149 // Number of iterations in the hard spin loop.
150 uint hard_spin_limit = WorkStealingHardSpins;
151
152 // If WorkStealingSpinToYieldRatio is 0, no hard spinning is done.
153 // If it is greater than 0, then start with a small number
154 // of spins and increase number with each turn at spinning until
155 // the count of hard spins exceeds WorkStealingSpinToYieldRatio.
156 // Then do a yield() call and start spinning afresh.
157 if (WorkStealingSpinToYieldRatio > 0) {
158 hard_spin_limit = WorkStealingHardSpins >> WorkStealingSpinToYieldRatio;
159 hard_spin_limit = MAX2(hard_spin_limit, 1U);
160 }
161 // Remember the initial spin limit.
162 uint hard_spin_start = hard_spin_limit;
163
164 // Loop waiting for all threads to offer termination or
165 // more work.
166 while (true) {
167 // Look for more work.
168 // Periodically sleep() instead of yield() to give threads
169 // waiting on the cores the chance to grab this code
170 if (yield_count <= WorkStealingYieldsBeforeSleep) {
171 // Do a yield or hardspin. For purposes of deciding whether
172 // to sleep, count this as a yield.
173 yield_count++;
174
175 // Periodically call yield() instead spinning
176 // After WorkStealingSpinToYieldRatio spins, do a yield() call
177 // and reset the counts and starting limit.
178 if (hard_spin_count > WorkStealingSpinToYieldRatio) {
179 yield();
180 hard_spin_count = 0;
181 hard_spin_limit = hard_spin_start;
182 } else {
183 // Hard spin this time
184 // Increase the hard spinning period but only up to a limit.
185 hard_spin_limit = MIN2(2*hard_spin_limit,
186 (uint) WorkStealingHardSpins);
187 for (uint j = 0; j < hard_spin_limit; j++) {
188 SpinPause();
189 }
190 hard_spin_count++;
191 }
192 } else {
193 log_develop_trace(gc, task)("TaskTerminator::do_spin_master_work() thread " PTR_FORMAT " sleeps after %u yields",
194 p2i(Thread::current()), yield_count);
195 yield_count = 0;
196
197 MonitorLocker locker(_blocker, Mutex::_no_safepoint_check_flag);
198 _spin_master = NULL;
199 locker.wait(WorkStealingSleepMillis);
200 if (_spin_master == NULL) {
201 _spin_master = Thread::current();
202 } else {
203 return false;
204 }
205 }
206
207 size_t tasks = tasks_in_queue_set();
208 bool exit = exit_termination(tasks, terminator);
209 {
210 MonitorLocker locker(_blocker, Mutex::_no_safepoint_check_flag);
211 // Termination condition reached
212 if (_offered_termination == _n_threads) {
213 _spin_master = NULL;
214 return true;
215 } else if (exit) {
216 if (tasks >= _offered_termination - 1) {
217 locker.notify_all();
218 } else {
219 for (; tasks > 1; tasks--) {
220 locker.notify();
221 }
222 }
223 _spin_master = NULL;
224 return false;
225 }
226 }
227 }
228 }