1/*
2 * Copyright (c) 2001, 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/taskqueue.hpp"
27#include "gc/shared/owstTaskTerminator.hpp"
28#include "oops/oop.inline.hpp"
29#include "logging/log.hpp"
30#include "runtime/atomic.hpp"
31#include "runtime/os.hpp"
32#include "runtime/thread.inline.hpp"
33#include "utilities/debug.hpp"
34#include "utilities/stack.inline.hpp"
35
36#ifdef TRACESPINNING
37uint ParallelTaskTerminator::_total_yields = 0;
38uint ParallelTaskTerminator::_total_spins = 0;
39uint ParallelTaskTerminator::_total_peeks = 0;
40#endif
41
42#if TASKQUEUE_STATS
43const char * const TaskQueueStats::_names[last_stat_id] = {
44 "qpush", "qpop", "qpop-s", "qattempt", "qsteal", "opush", "omax"
45};
46
47TaskQueueStats & TaskQueueStats::operator +=(const TaskQueueStats & addend)
48{
49 for (unsigned int i = 0; i < last_stat_id; ++i) {
50 _stats[i] += addend._stats[i];
51 }
52 return *this;
53}
54
55void TaskQueueStats::print_header(unsigned int line, outputStream* const stream,
56 unsigned int width)
57{
58 // Use a width w: 1 <= w <= max_width
59 const unsigned int max_width = 40;
60 const unsigned int w = MAX2(MIN2(width, max_width), 1U);
61
62 if (line == 0) { // spaces equal in width to the header
63 const unsigned int hdr_width = w * last_stat_id + last_stat_id - 1;
64 stream->print("%*s", hdr_width, " ");
65 } else if (line == 1) { // labels
66 stream->print("%*s", w, _names[0]);
67 for (unsigned int i = 1; i < last_stat_id; ++i) {
68 stream->print(" %*s", w, _names[i]);
69 }
70 } else if (line == 2) { // dashed lines
71 char dashes[max_width + 1];
72 memset(dashes, '-', w);
73 dashes[w] = '\0';
74 stream->print("%s", dashes);
75 for (unsigned int i = 1; i < last_stat_id; ++i) {
76 stream->print(" %s", dashes);
77 }
78 }
79}
80
81void TaskQueueStats::print(outputStream* stream, unsigned int width) const
82{
83 #define FMT SIZE_FORMAT_W(*)
84 stream->print(FMT, width, _stats[0]);
85 for (unsigned int i = 1; i < last_stat_id; ++i) {
86 stream->print(" " FMT, width, _stats[i]);
87 }
88 #undef FMT
89}
90
91#ifdef ASSERT
92// Invariants which should hold after a TaskQueue has been emptied and is
93// quiescent; they do not hold at arbitrary times.
94void TaskQueueStats::verify() const
95{
96 assert(get(push) == get(pop) + get(steal),
97 "push=" SIZE_FORMAT " pop=" SIZE_FORMAT " steal=" SIZE_FORMAT,
98 get(push), get(pop), get(steal));
99 assert(get(pop_slow) <= get(pop),
100 "pop_slow=" SIZE_FORMAT " pop=" SIZE_FORMAT,
101 get(pop_slow), get(pop));
102 assert(get(steal) <= get(steal_attempt),
103 "steal=" SIZE_FORMAT " steal_attempt=" SIZE_FORMAT,
104 get(steal), get(steal_attempt));
105 assert(get(overflow) == 0 || get(push) != 0,
106 "overflow=" SIZE_FORMAT " push=" SIZE_FORMAT,
107 get(overflow), get(push));
108 assert(get(overflow_max_len) == 0 || get(overflow) != 0,
109 "overflow_max_len=" SIZE_FORMAT " overflow=" SIZE_FORMAT,
110 get(overflow_max_len), get(overflow));
111}
112#endif // ASSERT
113#endif // TASKQUEUE_STATS
114
115ParallelTaskTerminator::
116ParallelTaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set) :
117 _n_threads(n_threads),
118 _queue_set(queue_set),
119 _offered_termination(0) {}
120
121ParallelTaskTerminator::~ParallelTaskTerminator() {
122 assert(_offered_termination == 0 || !peek_in_queue_set(), "Precondition");
123 assert(_offered_termination == 0 || _offered_termination == _n_threads, "Terminated or aborted" );
124}
125
126bool ParallelTaskTerminator::peek_in_queue_set() {
127 return _queue_set->peek();
128}
129
130void ParallelTaskTerminator::yield() {
131 assert(_offered_termination <= _n_threads, "Invariant");
132 os::naked_yield();
133}
134
135void ParallelTaskTerminator::sleep(uint millis) {
136 assert(_offered_termination <= _n_threads, "Invariant");
137 os::sleep(Thread::current(), millis, false);
138}
139
140bool
141ParallelTaskTerminator::offer_termination(TerminatorTerminator* terminator) {
142 assert(_n_threads > 0, "Initialization is incorrect");
143 assert(_offered_termination < _n_threads, "Invariant");
144 Atomic::inc(&_offered_termination);
145
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 assert(_offered_termination <= _n_threads, "Invariant");
168 // Are all threads offering termination?
169 if (_offered_termination == _n_threads) {
170 assert(!peek_in_queue_set(), "Precondition");
171 return true;
172 } else {
173 // Look for more work.
174 // Periodically sleep() instead of yield() to give threads
175 // waiting on the cores the chance to grab this code
176 if (yield_count <= WorkStealingYieldsBeforeSleep) {
177 // Do a yield or hardspin. For purposes of deciding whether
178 // to sleep, count this as a yield.
179 yield_count++;
180
181 // Periodically call yield() instead spinning
182 // After WorkStealingSpinToYieldRatio spins, do a yield() call
183 // and reset the counts and starting limit.
184 if (hard_spin_count > WorkStealingSpinToYieldRatio) {
185 yield();
186 hard_spin_count = 0;
187 hard_spin_limit = hard_spin_start;
188#ifdef TRACESPINNING
189 _total_yields++;
190#endif
191 } else {
192 // Hard spin this time
193 // Increase the hard spinning period but only up to a limit.
194 hard_spin_limit = MIN2(2*hard_spin_limit,
195 (uint) WorkStealingHardSpins);
196 for (uint j = 0; j < hard_spin_limit; j++) {
197 SpinPause();
198 }
199 hard_spin_count++;
200#ifdef TRACESPINNING
201 _total_spins++;
202#endif
203 }
204 } else {
205 log_develop_trace(gc, task)("ParallelTaskTerminator::offer_termination() thread " PTR_FORMAT " sleeps after %u yields",
206 p2i(Thread::current()), yield_count);
207 yield_count = 0;
208 // A sleep will cause this processor to seek work on another processor's
209 // runqueue, if it has nothing else to run (as opposed to the yield
210 // which may only move the thread to the end of the this processor's
211 // runqueue).
212 sleep(WorkStealingSleepMillis);
213 }
214
215#ifdef TRACESPINNING
216 _total_peeks++;
217#endif
218 if (peek_in_queue_set() ||
219 (terminator != NULL && terminator->should_exit_termination())) {
220 return complete_or_exit_termination();
221 }
222 }
223 }
224}
225
226#ifdef TRACESPINNING
227void ParallelTaskTerminator::print_termination_counts() {
228 log_trace(gc, task)("ParallelTaskTerminator Total yields: %u"
229 " Total spins: %u Total peeks: %u",
230 total_yields(),
231 total_spins(),
232 total_peeks());
233}
234#endif
235
236bool ParallelTaskTerminator::complete_or_exit_termination() {
237 // If termination is ever reached, terminator should stay in such state,
238 // so that all threads see the same state
239 uint current_offered = _offered_termination;
240 uint expected_value;
241 do {
242 if (current_offered == _n_threads) {
243 assert(!peek_in_queue_set(), "Precondition");
244 return true;
245 }
246 expected_value = current_offered;
247 } while ((current_offered = Atomic::cmpxchg(current_offered - 1, &_offered_termination, current_offered)) != expected_value);
248
249 assert(_offered_termination < _n_threads, "Invariant");
250 return false;
251}
252
253void ParallelTaskTerminator::reset_for_reuse() {
254 if (_offered_termination != 0) {
255 assert(_offered_termination == _n_threads,
256 "Terminator may still be in use");
257 _offered_termination = 0;
258 }
259}
260
261#ifdef ASSERT
262bool ObjArrayTask::is_valid() const {
263 return _obj != NULL && _obj->is_objArray() && _index >= 0 &&
264 _index < objArrayOop(_obj)->length();
265}
266#endif // ASSERT
267
268void ParallelTaskTerminator::reset_for_reuse(uint n_threads) {
269 reset_for_reuse();
270 _n_threads = n_threads;
271}
272
273TaskTerminator::TaskTerminator(uint n_threads, TaskQueueSetSuper* queue_set) :
274 _terminator(UseOWSTTaskTerminator ? new OWSTTaskTerminator(n_threads, queue_set)
275 : new ParallelTaskTerminator(n_threads, queue_set)) {
276}
277
278TaskTerminator::~TaskTerminator() {
279 if (_terminator != NULL) {
280 delete _terminator;
281 }
282}
283
284