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