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/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 "runtime/atomic.hpp"
32 #include "runtime/os.hpp"
33 #include "runtime/semaphore.hpp"
34 #include "runtime/thread.inline.hpp"
35
36 // Definitions of WorkGang methods.
37
38 // The current implementation will exit if the allocation
39 // of any worker fails.
40 void AbstractWorkGang::initialize_workers() {
41 log_develop_trace(gc, workgang)("Constructing work gang %s with %u threads", name(), total_workers());
42 _workers = NEW_C_HEAP_ARRAY(AbstractGangWorker*, total_workers(), mtInternal);
43 add_workers(true);
44 }
45
46
47 AbstractGangWorker* AbstractWorkGang::install_worker(uint worker_id) {
48 AbstractGangWorker* new_worker = allocate_worker(worker_id);
49 set_thread(worker_id, new_worker);
50 return new_worker;
51 }
52
53 void AbstractWorkGang::add_workers(bool initializing) {
54 add_workers(_active_workers, initializing);
55 }
56
57 void AbstractWorkGang::add_workers(uint active_workers, bool initializing) {
58
59 os::ThreadType worker_type;
60 if (are_ConcurrentGC_threads()) {
61 worker_type = os::cgc_thread;
62 } else {
63 worker_type = os::pgc_thread;
64 }
65 uint previous_created_workers = _created_workers;
66
67 _created_workers = WorkerManager::add_workers(this,
68 active_workers,
69 _total_workers,
70 _created_workers,
71 worker_type,
72 initializing);
73 _active_workers = MIN2(_created_workers, _active_workers);
74
75 WorkerManager::log_worker_creation(this, previous_created_workers, _active_workers, _created_workers, initializing);
76 }
77
78 AbstractGangWorker* AbstractWorkGang::worker(uint i) const {
79 // Array index bounds checking.
80 AbstractGangWorker* result = NULL;
81 assert(_workers != NULL, "No workers for indexing");
82 assert(i < total_workers(), "Worker index out of bounds");
83 result = _workers[i];
84 assert(result != NULL, "Indexing to null worker");
85 return result;
86 }
87
88 void AbstractWorkGang::print_worker_threads_on(outputStream* st) const {
89 uint workers = created_workers();
90 for (uint i = 0; i < workers; i++) {
91 worker(i)->print_on(st);
92 st->cr();
93 }
94 }
95
96 void AbstractWorkGang::threads_do(ThreadClosure* tc) const {
97 assert(tc != NULL, "Null ThreadClosure");
98 uint workers = created_workers();
99 for (uint i = 0; i < workers; i++) {
100 tc->do_thread(worker(i));
101 }
102 }
103
104 // WorkGang dispatcher implemented with semaphores.
105 //
106 // Semaphores don't require the worker threads to re-claim the lock when they wake up.
107 // This helps lowering the latency when starting and stopping the worker threads.
108 class SemaphoreGangTaskDispatcher : public GangTaskDispatcher {
109 // The task currently being dispatched to the GangWorkers.
110 AbstractGangTask* _task;
111
112 volatile uint _started;
113 volatile uint _not_finished;
114
115 // Semaphore used to start the GangWorkers.
116 Semaphore* _start_semaphore;
117 // Semaphore used to notify the coordinator that all workers are done.
118 Semaphore* _end_semaphore;
119
120 public:
121 SemaphoreGangTaskDispatcher() :
122 _task(NULL),
123 _started(0),
124 _not_finished(0),
125 _start_semaphore(new Semaphore()),
126 _end_semaphore(new Semaphore())
127 { }
128
129 ~SemaphoreGangTaskDispatcher() {
130 delete _start_semaphore;
131 delete _end_semaphore;
132 }
133
134 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) {
135 // No workers are allowed to read the state variables until they have been signaled.
136 _task = task;
137 _not_finished = num_workers;
138
139 // Dispatch 'num_workers' number of tasks.
140 _start_semaphore->signal(num_workers);
141
142 // Wait for the last worker to signal the coordinator.
143 _end_semaphore->wait();
144
145 // No workers are allowed to read the state variables after the coordinator has been signaled.
146 assert(_not_finished == 0, "%d not finished workers?", _not_finished);
147 _task = NULL;
148 _started = 0;
149
150 }
151
152 WorkData worker_wait_for_task() {
153 // Wait for the coordinator to dispatch a task.
154 _start_semaphore->wait();
155
156 uint num_started = Atomic::add(1u, &_started);
157
158 // Subtract one to get a zero-indexed worker id.
159 uint worker_id = num_started - 1;
160
161 return WorkData(_task, worker_id);
162 }
163
164 void worker_done_with_task() {
165 // Mark that the worker is done with the task.
166 // The worker is not allowed to read the state variables after this line.
167 uint not_finished = Atomic::sub(1u, &_not_finished);
168
169 // The last worker signals to the coordinator that all work is completed.
170 if (not_finished == 0) {
171 _end_semaphore->signal();
172 }
173 }
174 };
175
176 class MutexGangTaskDispatcher : public GangTaskDispatcher {
177 AbstractGangTask* _task;
178
179 volatile uint _started;
180 volatile uint _finished;
181 volatile uint _num_workers;
182
183 Monitor* _monitor;
184
185 public:
186 MutexGangTaskDispatcher() :
187 _task(NULL),
188 _started(0),
189 _finished(0),
190 _num_workers(0),
191 _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)) {
192 }
193
194 ~MutexGangTaskDispatcher() {
195 delete _monitor;
196 }
197
198 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) {
199 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag);
200
201 _task = task;
202 _num_workers = num_workers;
203
204 // Tell the workers to get to work.
205 _monitor->notify_all();
206
207 // Wait for them to finish.
208 while (_finished < _num_workers) {
209 ml.wait();
210 }
211
212 _task = NULL;
213 _num_workers = 0;
214 _started = 0;
215 _finished = 0;
216 }
217
218 WorkData worker_wait_for_task() {
219 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag);
220
221 while (_num_workers == 0 || _started == _num_workers) {
222 _monitor->wait();
223 }
224
225 _started++;
226
227 // Subtract one to get a zero-indexed worker id.
228 uint worker_id = _started - 1;
229
230 return WorkData(_task, worker_id);
231 }
232
233 void worker_done_with_task() {
234 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag);
235
236 _finished++;
237
238 if (_finished == _num_workers) {
239 // This will wake up all workers and not only the coordinator.
240 _monitor->notify_all();
241 }
242 }
243 };
244
245 static GangTaskDispatcher* create_dispatcher() {
246 if (UseSemaphoreGCThreadsSynchronization) {
247 return new SemaphoreGangTaskDispatcher();
248 }
249
250 return new MutexGangTaskDispatcher();
251 }
252
253 WorkGang::WorkGang(const char* name,
254 uint workers,
255 bool are_GC_task_threads,
256 bool are_ConcurrentGC_threads) :
257 AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads),
258 _dispatcher(create_dispatcher())
259 { }
260
261 WorkGang::~WorkGang() {
262 delete _dispatcher;
263 }
264
265 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) {
266 return new GangWorker(this, worker_id);
267 }
268
269 void WorkGang::run_task(AbstractGangTask* task) {
270 run_task(task, active_workers());
271 }
272
273 void WorkGang::run_task(AbstractGangTask* task, uint num_workers) {
274 guarantee(num_workers <= total_workers(),
275 "Trying to execute task %s with %u workers which is more than the amount of total workers %u.",
276 task->name(), num_workers, total_workers());
277 guarantee(num_workers > 0, "Trying to execute task %s with zero workers", task->name());
278 uint old_num_workers = _active_workers;
279 update_active_workers(num_workers);
280 _dispatcher->coordinator_execute_on_workers(task, num_workers);
281 update_active_workers(old_num_workers);
282 }
283
284 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) {
285 _gang = gang;
286 set_id(id);
287 set_name("%s#%d", gang->name(), id);
288 }
289
290 void AbstractGangWorker::run() {
291 initialize();
292 loop();
293 }
294
295 void AbstractGangWorker::initialize() {
296 assert(_gang != NULL, "No gang to run in");
297 os::set_priority(this, NearMaxPriority);
298 log_develop_trace(gc, workgang)("Running gang worker for gang %s id %u", gang()->name(), id());
299 assert(!Thread::current()->is_VM_thread(), "VM thread should not be part"
300 " of a work gang");
301 }
302
303 bool AbstractGangWorker::is_GC_task_thread() const {
304 return gang()->are_GC_task_threads();
305 }
306
307 bool AbstractGangWorker::is_ConcurrentGC_thread() const {
308 return gang()->are_ConcurrentGC_threads();
309 }
310
311 void AbstractGangWorker::print_on(outputStream* st) const {
312 st->print("\"%s\" ", name());
313 Thread::print_on(st);
314 st->cr();
315 }
316
317 void AbstractGangWorker::print() const { print_on(tty); }
318
319 WorkData GangWorker::wait_for_task() {
320 return gang()->dispatcher()->worker_wait_for_task();
321 }
322
323 void GangWorker::signal_task_done() {
324 gang()->dispatcher()->worker_done_with_task();
325 }
326
327 void GangWorker::run_task(WorkData data) {
328 GCIdMark gc_id_mark(data._task->gc_id());
329 log_develop_trace(gc, workgang)("Running work gang: %s task: %s worker: %u", name(), data._task->name(), data._worker_id);
330
331 data._task->work(data._worker_id);
332
333 log_develop_trace(gc, workgang)("Finished work gang: %s task: %s worker: %u thread: " PTR_FORMAT,
334 name(), data._task->name(), data._worker_id, p2i(Thread::current()));
335 }
336
337 void GangWorker::loop() {
338 while (true) {
339 WorkData data = wait_for_task();
340
341 run_task(data);
342
343 signal_task_done();
344 }
345 }
346
347 // *** WorkGangBarrierSync
348
349 WorkGangBarrierSync::WorkGangBarrierSync()
350 : _monitor(Mutex::safepoint, "work gang barrier sync", true,
351 Monitor::_safepoint_check_never),
352 _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) {
353 }
354
355 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name)
356 : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never),
357 _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) {
358 }
359
360 void WorkGangBarrierSync::set_n_workers(uint n_workers) {
361 _n_workers = n_workers;
362 _n_completed = 0;
363 _should_reset = false;
364 _aborted = false;
365 }
366
367 bool WorkGangBarrierSync::enter() {
368 MonitorLocker ml(monitor(), Mutex::_no_safepoint_check_flag);
369 if (should_reset()) {
370 // The should_reset() was set and we are the first worker to enter
371 // the sync barrier. We will zero the n_completed() count which
372 // effectively resets the barrier.
373 zero_completed();
374 set_should_reset(false);
375 }
376 inc_completed();
377 if (n_completed() == n_workers()) {
378 // At this point we would like to reset the barrier to be ready in
379 // case it is used again. However, we cannot set n_completed() to
380 // 0, even after the notify_all(), given that some other workers
381 // might still be waiting for n_completed() to become ==
382 // n_workers(). So, if we set n_completed() to 0, those workers
383 // will get stuck (as they will wake up, see that n_completed() !=
384 // n_workers() and go back to sleep). Instead, we raise the
385 // should_reset() flag and the barrier will be reset the first
386 // time a worker enters it again.
387 set_should_reset(true);
388 ml.notify_all();
389 } else {
390 while (n_completed() != n_workers() && !aborted()) {
391 ml.wait();
392 }
393 }
394 return !aborted();
395 }
396
397 void WorkGangBarrierSync::abort() {
398 MutexLocker x(monitor(), Mutex::_no_safepoint_check_flag);
399 set_aborted();
400 monitor()->notify_all();
401 }
402
403 // SubTasksDone functions.
404
405 SubTasksDone::SubTasksDone(uint n) :
406 _tasks(NULL), _n_tasks(n), _threads_completed(0) {
407 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal);
408 clear();
409 }
410
411 bool SubTasksDone::valid() {
412 return _tasks != NULL;
413 }
414
415 void SubTasksDone::clear() {
416 for (uint i = 0; i < _n_tasks; i++) {
417 _tasks[i] = 0;
418 }
419 _threads_completed = 0;
420 #ifdef ASSERT
421 _claimed = 0;
422 #endif
423 }
424
425 bool SubTasksDone::try_claim_task(uint t) {
426 assert(t < _n_tasks, "bad task id.");
427 uint old = _tasks[t];
428 if (old == 0) {
429 old = Atomic::cmpxchg(1u, &_tasks[t], 0u);
430 }
431 bool res = old == 0;
432 #ifdef ASSERT
433 if (res) {
434 assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?");
435 Atomic::inc(&_claimed);
436 }
437 #endif
438 return res;
439 }
440
441 void SubTasksDone::all_tasks_completed(uint n_threads) {
442 uint observed = _threads_completed;
443 uint old;
444 do {
445 old = observed;
446 observed = Atomic::cmpxchg(old+1, &_threads_completed, old);
447 } while (observed != old);
448 // If this was the last thread checking in, clear the tasks.
449 uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads);
450 if (observed + 1 == adjusted_thread_count) {
451 clear();
452 }
453 }
454
455
456 SubTasksDone::~SubTasksDone() {
457 if (_tasks != NULL) FREE_C_HEAP_ARRAY(uint, _tasks);
458 }
459
460 // *** SequentialSubTasksDone
461
462 void SequentialSubTasksDone::clear() {
463 _n_tasks = _n_claimed = 0;
464 _n_threads = _n_completed = 0;
465 }
466
467 bool SequentialSubTasksDone::valid() {
468 return _n_threads > 0;
469 }
470
471 bool SequentialSubTasksDone::try_claim_task(uint& t) {
472 t = _n_claimed;
473 while (t < _n_tasks) {
474 uint res = Atomic::cmpxchg(t+1, &_n_claimed, t);
475 if (res == t) {
476 return true;
477 }
478 t = res;
479 }
480 return false;
481 }
482
483 bool SequentialSubTasksDone::all_tasks_completed() {
484 uint complete = _n_completed;
485 while (true) {
486 uint res = Atomic::cmpxchg(complete+1, &_n_completed, complete);
487 if (res == complete) {
488 break;
489 }
490 complete = res;
491 }
492 if (complete+1 == _n_threads) {
493 clear();
494 return true;
495 }
496 return false;
497 }