1 /*
2 * Copyright (c) 2001, 2020, 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.
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23 */
24
25 #include "precompiled.hpp"
26 #include "gc/shared/gcId.hpp"
27 #include "gc/shared/workgroup.hpp"
28 #include "gc/shared/workerManager.hpp"
29 #include "memory/allocation.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/iterator.hpp"
32 #include "runtime/atomic.hpp"
33 #include "runtime/os.hpp"
34 #include "runtime/semaphore.hpp"
35 #include "runtime/thread.inline.hpp"
36
37 // Definitions of WorkGang methods.
38
39 // The current implementation will exit if the allocation
40 // of any worker fails.
41 void AbstractWorkGang::initialize_workers() {
42 log_develop_trace(gc, workgang)("Constructing work gang %s with %u threads", name(), total_workers());
43 _workers = NEW_C_HEAP_ARRAY(AbstractGangWorker*, total_workers(), mtInternal);
44 add_workers(true);
45 }
46
47
48 AbstractGangWorker* AbstractWorkGang::install_worker(uint worker_id) {
49 AbstractGangWorker* new_worker = allocate_worker(worker_id);
50 set_thread(worker_id, new_worker);
51 return new_worker;
52 }
53
54 void AbstractWorkGang::add_workers(bool initializing) {
55 add_workers(_active_workers, initializing);
56 }
57
58 void AbstractWorkGang::add_workers(uint active_workers, bool initializing) {
59
60 os::ThreadType worker_type;
61 if (are_ConcurrentGC_threads()) {
62 worker_type = os::cgc_thread;
63 } else {
64 worker_type = os::pgc_thread;
65 }
66 uint previous_created_workers = _created_workers;
67
68 _created_workers = WorkerManager::add_workers(this,
69 active_workers,
70 _total_workers,
71 _created_workers,
72 worker_type,
73 initializing);
74 _active_workers = MIN2(_created_workers, _active_workers);
75
76 WorkerManager::log_worker_creation(this, previous_created_workers, _active_workers, _created_workers, initializing);
77 }
78
79 AbstractGangWorker* AbstractWorkGang::worker(uint i) const {
80 // Array index bounds checking.
81 AbstractGangWorker* result = NULL;
82 assert(_workers != NULL, "No workers for indexing");
83 assert(i < total_workers(), "Worker index out of bounds");
84 result = _workers[i];
85 assert(result != NULL, "Indexing to null worker");
86 return result;
87 }
88
89 void AbstractWorkGang::threads_do(ThreadClosure* tc) const {
90 assert(tc != NULL, "Null ThreadClosure");
91 uint workers = created_workers();
92 for (uint i = 0; i < workers; i++) {
93 tc->do_thread(worker(i));
94 }
95 }
96
97 static void run_foreground_task_if_needed(AbstractGangTask* task, uint num_workers,
98 bool add_foreground_work) {
99 if (add_foreground_work) {
100 log_develop_trace(gc, workgang)("Running work gang: %s task: %s worker: foreground",
101 Thread::current()->name(), task->name());
102 task->work(num_workers);
103 log_develop_trace(gc, workgang)("Finished work gang: %s task: %s worker: foreground "
104 "thread: " PTR_FORMAT, Thread::current()->name(), task->name(), p2i(Thread::current()));
105 }
106 }
107
108 // WorkGang dispatcher implemented with semaphores.
109 //
110 // Semaphores don't require the worker threads to re-claim the lock when they wake up.
111 // This helps lowering the latency when starting and stopping the worker threads.
112 class SemaphoreGangTaskDispatcher : public GangTaskDispatcher {
113 // The task currently being dispatched to the GangWorkers.
114 AbstractGangTask* _task;
115
116 volatile uint _started;
117 volatile uint _not_finished;
118
119 // Semaphore used to start the GangWorkers.
120 Semaphore* _start_semaphore;
121 // Semaphore used to notify the coordinator that all workers are done.
122 Semaphore* _end_semaphore;
123
124 public:
125 SemaphoreGangTaskDispatcher() :
126 _task(NULL),
127 _started(0),
128 _not_finished(0),
129 _start_semaphore(new Semaphore()),
130 _end_semaphore(new Semaphore())
131 { }
132
133 ~SemaphoreGangTaskDispatcher() {
134 delete _start_semaphore;
135 delete _end_semaphore;
136 }
137
138 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers, bool add_foreground_work) {
139 // No workers are allowed to read the state variables until they have been signaled.
140 _task = task;
141 _not_finished = num_workers;
142
143 // Dispatch 'num_workers' number of tasks.
144 _start_semaphore->signal(num_workers);
145
146 run_foreground_task_if_needed(task, num_workers, add_foreground_work);
147
148 // Wait for the last worker to signal the coordinator.
149 _end_semaphore->wait();
150
151 // No workers are allowed to read the state variables after the coordinator has been signaled.
152 assert(_not_finished == 0, "%d not finished workers?", _not_finished);
153 _task = NULL;
154 _started = 0;
155
156 }
157
158 WorkData worker_wait_for_task() {
159 // Wait for the coordinator to dispatch a task.
160 _start_semaphore->wait();
161
162 uint num_started = Atomic::add(&_started, 1u);
163
164 // Subtract one to get a zero-indexed worker id.
165 uint worker_id = num_started - 1;
166
167 return WorkData(_task, worker_id);
168 }
169
170 void worker_done_with_task() {
171 // Mark that the worker is done with the task.
172 // The worker is not allowed to read the state variables after this line.
173 uint not_finished = Atomic::sub(&_not_finished, 1u);
174
175 // The last worker signals to the coordinator that all work is completed.
176 if (not_finished == 0) {
177 _end_semaphore->signal();
178 }
179 }
180 };
181
182 WorkGang::WorkGang(const char* name,
183 uint workers,
184 bool are_GC_task_threads,
185 bool are_ConcurrentGC_threads) :
186 AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads),
187 _dispatcher(new SemaphoreGangTaskDispatcher())
188 { }
189
190 WorkGang::~WorkGang() {
191 delete _dispatcher;
192 }
193
194 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) {
195 return new GangWorker(this, worker_id);
196 }
197
198 void WorkGang::run_task(AbstractGangTask* task) {
199 run_task(task, active_workers());
200 }
201
202 void WorkGang::run_task(AbstractGangTask* task, uint num_workers, bool add_foreground_work) {
203 guarantee(num_workers <= total_workers(),
204 "Trying to execute task %s with %u workers which is more than the amount of total workers %u.",
205 task->name(), num_workers, total_workers());
206 guarantee(num_workers > 0, "Trying to execute task %s with zero workers", task->name());
207 uint old_num_workers = _active_workers;
208 update_active_workers(num_workers);
209 _dispatcher->coordinator_execute_on_workers(task, num_workers, add_foreground_work);
210 update_active_workers(old_num_workers);
211 }
212
213 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) {
214 _gang = gang;
215 set_id(id);
216 set_name("%s#%d", gang->name(), id);
217 }
218
219 void AbstractGangWorker::run() {
220 initialize();
221 loop();
222 }
223
224 void AbstractGangWorker::initialize() {
225 assert(_gang != NULL, "No gang to run in");
226 os::set_priority(this, NearMaxPriority);
227 log_develop_trace(gc, workgang)("Running gang worker for gang %s id %u", gang()->name(), id());
228 assert(!Thread::current()->is_VM_thread(), "VM thread should not be part"
229 " of a work gang");
230 }
231
232 bool AbstractGangWorker::is_GC_task_thread() const {
233 return gang()->are_GC_task_threads();
234 }
235
236 bool AbstractGangWorker::is_ConcurrentGC_thread() const {
237 return gang()->are_ConcurrentGC_threads();
238 }
239
240 void AbstractGangWorker::print_on(outputStream* st) const {
241 st->print("\"%s\" ", name());
242 Thread::print_on(st);
243 st->cr();
244 }
245
246 void AbstractGangWorker::print() const { print_on(tty); }
247
248 WorkData GangWorker::wait_for_task() {
249 return gang()->dispatcher()->worker_wait_for_task();
250 }
251
252 void GangWorker::signal_task_done() {
253 gang()->dispatcher()->worker_done_with_task();
254 }
255
256 void GangWorker::run_task(WorkData data) {
257 GCIdMark gc_id_mark(data._task->gc_id());
258 log_develop_trace(gc, workgang)("Running work gang: %s task: %s worker: %u", name(), data._task->name(), data._worker_id);
259
260 data._task->work(data._worker_id);
261
262 log_develop_trace(gc, workgang)("Finished work gang: %s task: %s worker: %u thread: " PTR_FORMAT,
263 name(), data._task->name(), data._worker_id, p2i(Thread::current()));
264 }
265
266 void GangWorker::loop() {
267 while (true) {
268 WorkData data = wait_for_task();
269
270 run_task(data);
271
272 signal_task_done();
273 }
274 }
275
276 // *** WorkGangBarrierSync
277
278 WorkGangBarrierSync::WorkGangBarrierSync()
279 : _monitor(Mutex::safepoint, "work gang barrier sync", true,
280 Monitor::_safepoint_check_never),
281 _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) {
282 }
283
284 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name)
285 : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never),
286 _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) {
287 }
288
289 void WorkGangBarrierSync::set_n_workers(uint n_workers) {
290 _n_workers = n_workers;
291 _n_completed = 0;
292 _should_reset = false;
293 _aborted = false;
294 }
295
296 bool WorkGangBarrierSync::enter() {
297 MonitorLocker ml(monitor(), Mutex::_no_safepoint_check_flag);
298 if (should_reset()) {
299 // The should_reset() was set and we are the first worker to enter
300 // the sync barrier. We will zero the n_completed() count which
301 // effectively resets the barrier.
302 zero_completed();
303 set_should_reset(false);
304 }
305 inc_completed();
306 if (n_completed() == n_workers()) {
307 // At this point we would like to reset the barrier to be ready in
308 // case it is used again. However, we cannot set n_completed() to
309 // 0, even after the notify_all(), given that some other workers
310 // might still be waiting for n_completed() to become ==
311 // n_workers(). So, if we set n_completed() to 0, those workers
312 // will get stuck (as they will wake up, see that n_completed() !=
313 // n_workers() and go back to sleep). Instead, we raise the
314 // should_reset() flag and the barrier will be reset the first
315 // time a worker enters it again.
316 set_should_reset(true);
317 ml.notify_all();
318 } else {
319 while (n_completed() != n_workers() && !aborted()) {
320 ml.wait();
321 }
322 }
323 return !aborted();
324 }
325
326 void WorkGangBarrierSync::abort() {
327 MutexLocker x(monitor(), Mutex::_no_safepoint_check_flag);
328 set_aborted();
329 monitor()->notify_all();
330 }
331
332 // SubTasksDone functions.
333
334 SubTasksDone::SubTasksDone(uint n) :
335 _tasks(NULL), _n_tasks(n), _threads_completed(0) {
336 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal);
337 clear();
338 }
339
340 bool SubTasksDone::valid() {
341 return _tasks != NULL;
342 }
343
344 void SubTasksDone::clear() {
345 for (uint i = 0; i < _n_tasks; i++) {
346 _tasks[i] = 0;
347 }
348 _threads_completed = 0;
349 #ifdef ASSERT
350 _claimed = 0;
351 #endif
352 }
353
354 bool SubTasksDone::try_claim_task(uint t) {
355 assert(t < _n_tasks, "bad task id.");
356 uint old = _tasks[t];
357 if (old == 0) {
358 old = Atomic::cmpxchg(&_tasks[t], 0u, 1u);
359 }
360 bool res = old == 0;
361 #ifdef ASSERT
362 if (res) {
363 assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?");
364 Atomic::inc(&_claimed);
365 }
366 #endif
367 return res;
368 }
369
370 void SubTasksDone::all_tasks_completed(uint n_threads) {
371 uint observed = _threads_completed;
372 uint old;
373 do {
374 old = observed;
375 observed = Atomic::cmpxchg(&_threads_completed, old, old+1);
376 } while (observed != old);
377 // If this was the last thread checking in, clear the tasks.
378 uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads);
379 if (observed + 1 == adjusted_thread_count) {
380 clear();
381 }
382 }
383
384
385 SubTasksDone::~SubTasksDone() {
386 FREE_C_HEAP_ARRAY(uint, _tasks);
387 }
388
389 // *** SequentialSubTasksDone
390
391 void SequentialSubTasksDone::clear() {
392 _n_tasks = _n_claimed = 0;
393 _n_threads = _n_completed = 0;
394 }
395
396 bool SequentialSubTasksDone::valid() {
397 return _n_threads > 0;
398 }
399
400 bool SequentialSubTasksDone::try_claim_task(uint& t) {
401 t = _n_claimed;
402 while (t < _n_tasks) {
403 uint res = Atomic::cmpxchg(&_n_claimed, t, t+1);
404 if (res == t) {
405 return true;
406 }
407 t = res;
408 }
409 return false;
410 }
411
412 bool SequentialSubTasksDone::all_tasks_completed() {
413 uint complete = _n_completed;
414 while (true) {
415 uint res = Atomic::cmpxchg(&_n_completed, complete, complete+1);
416 if (res == complete) {
417 break;
418 }
419 complete = res;
420 }
421 if (complete+1 == _n_threads) {
422 clear();
423 return true;
424 }
425 return false;
426 }