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 if (_offered_termination != 0) {
43 assert(_offered_termination == _n_threads, "Must be terminated or aborted");
44 assert_queue_set_empty();
45 }
46
47 assert(_spin_master == NULL, "Should have been reset");
48 assert(_blocker != NULL, "Can not be NULL");
49 delete _blocker;
50 }
51
52 #ifdef ASSERT
53 void TaskTerminator::assert_queue_set_empty() const {
54 _queue_set->assert_empty();
55 }
56 #endif
57
58 void TaskTerminator::yield() {
59 assert(_offered_termination <= _n_threads, "Invariant");
60 os::naked_yield();
61 }
62
63 void TaskTerminator::reset_for_reuse() {
64 if (_offered_termination != 0) {
65 assert(_offered_termination == _n_threads,
66 "Terminator may still be in use");
67 _offered_termination = 0;
68 }
69 }
70
71 void TaskTerminator::reset_for_reuse(uint n_threads) {
72 reset_for_reuse();
73 _n_threads = n_threads;
74 }
75
76 bool TaskTerminator::exit_termination(size_t tasks, TerminatorTerminator* terminator) {
77 return tasks > 0 || (terminator != NULL && terminator->should_exit_termination());
78 }
79
80 size_t TaskTerminator::tasks_in_queue_set() const {
81 return _queue_set->tasks();
82 }
83
84 bool TaskTerminator::offer_termination(TerminatorTerminator* terminator) {
85 assert(_n_threads > 0, "Initialization is incorrect");
86 assert(_offered_termination < _n_threads, "Invariant");
87 assert(_blocker != NULL, "Invariant");
88
89 // Single worker, done
90 if (_n_threads == 1) {
91 _offered_termination = 1;
92 assert_queue_set_empty();
93 return true;
94 }
95
96 _blocker->lock_without_safepoint_check();
97 _offered_termination++;
98 // All arrived, done
99 if (_offered_termination == _n_threads) {
100 _blocker->notify_all();
101 _blocker->unlock();
102 assert_queue_set_empty();
103 return true;
104 }
105
106 Thread* the_thread = Thread::current();
107 while (true) {
108 if (_spin_master == NULL) {
109 _spin_master = the_thread;
110
111 _blocker->unlock();
112
113 if (do_spin_master_work(terminator)) {
114 assert(_offered_termination == _n_threads, "termination condition");
115 assert_queue_set_empty();
116 return true;
117 } else {
118 _blocker->lock_without_safepoint_check();
119 // There is possibility that termination is reached between dropping the lock
120 // before returning from do_spin_master_work() and acquiring lock above.
121 if (_offered_termination == _n_threads) {
122 _blocker->unlock();
123 assert_queue_set_empty();
124 return true;
125 }
126 }
127 } else {
128 _blocker->wait_without_safepoint_check(WorkStealingSleepMillis);
129
130 if (_offered_termination == _n_threads) {
131 _blocker->unlock();
132 assert_queue_set_empty();
133 return true;
134 }
135 }
136
137 size_t tasks = tasks_in_queue_set();
138 if (exit_termination(tasks, terminator)) {
139 assert_lock_strong(_blocker);
140 _offered_termination--;
141 _blocker->unlock();
142 return false;
143 }
144 }
145 }
146
147 bool TaskTerminator::do_spin_master_work(TerminatorTerminator* terminator) {
148 uint yield_count = 0;
149 // Number of hard spin loops done since last yield
150 uint hard_spin_count = 0;
151 // Number of iterations in the hard spin loop.
152 uint hard_spin_limit = WorkStealingHardSpins;
153
154 // If WorkStealingSpinToYieldRatio is 0, no hard spinning is done.
155 // If it is greater than 0, then start with a small number
156 // of spins and increase number with each turn at spinning until
157 // the count of hard spins exceeds WorkStealingSpinToYieldRatio.
158 // Then do a yield() call and start spinning afresh.
159 if (WorkStealingSpinToYieldRatio > 0) {
160 hard_spin_limit = WorkStealingHardSpins >> WorkStealingSpinToYieldRatio;
161 hard_spin_limit = MAX2(hard_spin_limit, 1U);
162 }
163 // Remember the initial spin limit.
164 uint hard_spin_start = hard_spin_limit;
165
166 // Loop waiting for all threads to offer termination or
167 // more work.
168 while (true) {
169 // Look for more work.
170 // Periodically sleep() instead of yield() to give threads
171 // waiting on the cores the chance to grab this code
172 if (yield_count <= WorkStealingYieldsBeforeSleep) {
173 // Do a yield or hardspin. For purposes of deciding whether
174 // to sleep, count this as a yield.
175 yield_count++;
176
177 // Periodically call yield() instead spinning
178 // After WorkStealingSpinToYieldRatio spins, do a yield() call
179 // and reset the counts and starting limit.
180 if (hard_spin_count > WorkStealingSpinToYieldRatio) {
181 yield();
182 hard_spin_count = 0;
183 hard_spin_limit = hard_spin_start;
184 } else {
185 // Hard spin this time
186 // Increase the hard spinning period but only up to a limit.
187 hard_spin_limit = MIN2(2*hard_spin_limit,
188 (uint) WorkStealingHardSpins);
189 for (uint j = 0; j < hard_spin_limit; j++) {
190 SpinPause();
191 }
192 hard_spin_count++;
193 }
194 } else {
195 log_develop_trace(gc, task)("TaskTerminator::do_spin_master_work() thread " PTR_FORMAT " sleeps after %u yields",
196 p2i(Thread::current()), yield_count);
197 yield_count = 0;
198
199 MonitorLocker locker(_blocker, Mutex::_no_safepoint_check_flag);
200 _spin_master = NULL;
201 locker.wait(WorkStealingSleepMillis);
202 if (_spin_master == NULL) {
203 _spin_master = Thread::current();
204 } else {
205 return false;
206 }
207 }
208
209 size_t tasks = tasks_in_queue_set();
210 bool exit = exit_termination(tasks, terminator);
211 {
212 MonitorLocker locker(_blocker, Mutex::_no_safepoint_check_flag);
213 // Termination condition reached
214 if (_offered_termination == _n_threads) {
215 _spin_master = NULL;
216 return true;
217 } else if (exit) {
218 if (tasks >= _offered_termination - 1) {
219 locker.notify_all();
220 } else {
221 for (; tasks > 1; tasks--) {
222 locker.notify();
223 }
224 }
225 _spin_master = NULL;
226 return false;
227 }
228 }
229 }
230 }