1 /*
2 * Copyright (c) 2001, 2015, 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/workgroup.hpp"
27 #include "memory/allocation.hpp"
28 #include "memory/allocation.inline.hpp"
29 #include "runtime/atomic.inline.hpp"
30 #include "runtime/os.hpp"
31 #include "runtime/thread.inline.hpp"
32 #include "utilities/semaphore.hpp"
33
34 // Definitions of WorkGang methods.
35
36 // The current implementation will exit if the allocation
37 // of any worker fails. Still, return a boolean so that
38 // a future implementation can possibly do a partial
39 // initialization of the workers and report such to the
40 // caller.
41 bool AbstractWorkGang::initialize_workers() {
42
43 if (TraceWorkGang) {
44 tty->print_cr("Constructing work gang %s with %d threads",
45 name(),
46 total_workers());
47 }
48 _workers = NEW_C_HEAP_ARRAY(AbstractGangWorker*, total_workers(), mtInternal);
49 if (_workers == NULL) {
50 vm_exit_out_of_memory(0, OOM_MALLOC_ERROR, "Cannot create GangWorker array.");
51 return false;
52 }
53 os::ThreadType worker_type;
54 if (are_ConcurrentGC_threads()) {
55 worker_type = os::cgc_thread;
56 } else {
57 worker_type = os::pgc_thread;
58 }
59 for (uint worker = 0; worker < total_workers(); worker += 1) {
60 AbstractGangWorker* new_worker = allocate_worker(worker);
61 assert(new_worker != NULL, "Failed to allocate GangWorker");
62 _workers[worker] = new_worker;
63 if (new_worker == NULL || !os::create_thread(new_worker, worker_type)) {
64 vm_exit_out_of_memory(0, OOM_MALLOC_ERROR,
65 "Cannot create worker GC thread. Out of system resources.");
66 return false;
67 }
68 if (!DisableStartThread) {
69 os::start_thread(new_worker);
70 }
71 }
72 return true;
73 }
74
75 AbstractGangWorker* AbstractWorkGang::worker(uint i) const {
76 // Array index bounds checking.
77 AbstractGangWorker* result = NULL;
78 assert(_workers != NULL, "No workers for indexing");
79 assert(i < total_workers(), "Worker index out of bounds");
80 result = _workers[i];
81 assert(result != NULL, "Indexing to null worker");
82 return result;
83 }
84
85 void AbstractWorkGang::print_worker_threads_on(outputStream* st) const {
86 uint workers = total_workers();
87 for (uint i = 0; i < workers; i++) {
88 worker(i)->print_on(st);
89 st->cr();
90 }
91 }
92
93 void AbstractWorkGang::threads_do(ThreadClosure* tc) const {
94 assert(tc != NULL, "Null ThreadClosure");
95 uint workers = total_workers();
96 for (uint i = 0; i < workers; i++) {
97 tc->do_thread(worker(i));
98 }
99 }
100
101 #if IMPLEMENTS_SEMAPHORE_CLASS
102
103 // WorkGang dispatcher implemented with semaphores.
104 //
105 // Semaphores don't require the worker threads to re-claim the lock when they wake up.
106 // This helps lowering the latency when starting and stopping the worker threads.
107 class SemaphoreGangTaskDispatcher : public GangTaskDispatcher {
108 // The task currently being dispatched to the GangWorkers.
109 AbstractGangTask* _task;
110
111 volatile uint _started;
112 volatile uint _not_finished;
113
114 // Semaphore used to start the GangWorkers.
115 Semaphore* _start_semaphore;
116 // Semaphore used to notify the coordinator that all workers are done.
117 Semaphore* _end_semaphore;
118
119 public:
120 SemaphoreGangTaskDispatcher(uint workers) :
121 _task(NULL),
122 _started(0),
123 _not_finished(0),
124 // Limit the semaphore value to the number of workers.
125 _start_semaphore(new Semaphore(0, workers)),
126 _end_semaphore(new Semaphore(0, workers))
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 _task = NULL;
147 _started = 0;
148 _not_finished = 0;
149 }
150
151 WorkData worker_wait_for_task() {
152 // Wait for the coordinator to dispatch a task.
153 _start_semaphore->wait();
154
155 uint num_started = (uint) Atomic::add(1, (volatile jint*)&_started);
156
157 // Subtract one to get a zero-indexed worker id.
158 uint worker_id = num_started - 1;
159
160 return WorkData(_task, worker_id);
161 }
162
163 void worker_done_with_task() {
164 // Mark that the worker is done with the task.
165 // The worker is not allowed to read the state variables after this line.
166 uint not_finished = (uint) Atomic::add(-1, (volatile jint*)&_not_finished);
167
168 // The last worker signals to the coordinator that all work is completed.
169 if (not_finished == 0) {
170 _end_semaphore->signal();
171 }
172 }
173 };
174 #endif // IMPLEMENTS_SEMAPHORE_CLASS
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 _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)),
189 _started(0),
190 _finished(0),
191 _num_workers(0) {}
192
193 ~MutexGangTaskDispatcher() {
194 delete _monitor;
195 }
196
197 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) {
198 MutexLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag);
199
200 _task = task;
201 _num_workers = num_workers;
202
203 // Tell the workers to get to work.
204 _monitor->notify_all();
205
206 // Wait for them to finish.
207 while (_finished < _num_workers) {
208 _monitor->wait(/* no_safepoint_check */ true);
209 }
210
211 _task = NULL;
212 _num_workers = 0;
213 _started = 0;
214 _finished = 0;
215 }
216
217 WorkData worker_wait_for_task() {
218 MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag);
219
220 while (_num_workers == 0 || _started == _num_workers) {
221 _monitor->wait(/* no_safepoint_check */ true);
222 }
223
224 _started++;
225
226 // Subtract one to get a zero-indexed worker id.
227 uint worker_id = _started - 1;
228
229 return WorkData(_task, worker_id);
230 }
231
232 void worker_done_with_task() {
233 MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag);
234
235 _finished++;
236
237 if (_finished == _num_workers) {
238 // This will wake up all workers and not only the coordinator.
239 _monitor->notify_all();
240 }
241 }
242 };
243
244 static GangTaskDispatcher* create_dispatcher(uint workers) {
245 #if IMPLEMENTS_SEMAPHORE_CLASS
246 if (UseSemaphoreGCThreadsSynchronization) {
247 return new SemaphoreGangTaskDispatcher(workers);
248 }
249 #endif
250
251 return new MutexGangTaskDispatcher();
252 }
253
254 WorkGang::WorkGang(const char* name,
255 uint workers,
256 bool are_GC_task_threads,
257 bool are_ConcurrentGC_threads) :
258 AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads),
259 _dispatcher(create_dispatcher(workers))
260 { }
261
262 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) {
263 return new GangWorker(this, worker_id);
264 }
265
266 void WorkGang::run_task(AbstractGangTask* task) {
267 _dispatcher->coordinator_execute_on_workers(task, active_workers());
268 }
269
270 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) {
271 _gang = gang;
272 set_id(id);
273 set_name("%s#%d", gang->name(), id);
274 }
275
276 void AbstractGangWorker::run() {
277 initialize();
278 loop();
279 }
280
281 void AbstractGangWorker::initialize() {
282 this->initialize_thread_local_storage();
283 this->record_stack_base_and_size();
284 this->initialize_named_thread();
285 assert(_gang != NULL, "No gang to run in");
286 os::set_priority(this, NearMaxPriority);
287 if (TraceWorkGang) {
288 tty->print_cr("Running gang worker for gang %s id %u",
289 gang()->name(), id());
290 }
291 // The VM thread should not execute here because MutexLocker's are used
292 // as (opposed to MutexLockerEx's).
293 assert(!Thread::current()->is_VM_thread(), "VM thread should not be part"
294 " of a work gang");
295 }
296
297 bool AbstractGangWorker::is_GC_task_thread() const {
298 return gang()->are_GC_task_threads();
299 }
300
301 bool AbstractGangWorker::is_ConcurrentGC_thread() const {
302 return gang()->are_ConcurrentGC_threads();
303 }
304
305 void AbstractGangWorker::print_on(outputStream* st) const {
306 st->print("\"%s\" ", name());
307 Thread::print_on(st);
308 st->cr();
309 }
310
311 WorkData GangWorker::wait_for_task() {
312 return gang()->dispatcher()->worker_wait_for_task();
313 }
314
315 void GangWorker::signal_task_done() {
316 gang()->dispatcher()->worker_done_with_task();
317 }
318
319 void GangWorker::print_task_started(WorkData data) {
320 if (TraceWorkGang) {
321 tty->print_cr("Running work gang %s task %s worker %u", name(), data._task->name(), data._worker_id);
322 }
323 }
324
325 void GangWorker::print_task_done(WorkData data) {
326 if (TraceWorkGang) {
327 tty->print_cr("\nFinished work gang %s task %s worker %u", name(), data._task->name(), data._worker_id);
328 Thread* me = Thread::current();
329 tty->print_cr(" T: " PTR_FORMAT " VM_thread: %d", p2i(me), me->is_VM_thread());
330 }
331 }
332
333 void GangWorker::run_task(WorkData data) {
334 print_task_started(data);
335
336 data._task->work(data._worker_id);
337
338 print_task_done(data);
339 }
340
341 void GangWorker::loop() {
342 while (true) {
343 WorkData data = wait_for_task();
344
345 run_task(data);
346
347 signal_task_done();
348 }
349 }
350
351 // *** WorkGangBarrierSync
352
353 WorkGangBarrierSync::WorkGangBarrierSync()
354 : _monitor(Mutex::safepoint, "work gang barrier sync", true,
355 Monitor::_safepoint_check_never),
356 _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) {
357 }
358
359 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name)
360 : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never),
361 _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) {
362 }
363
364 void WorkGangBarrierSync::set_n_workers(uint n_workers) {
365 _n_workers = n_workers;
366 _n_completed = 0;
367 _should_reset = false;
368 _aborted = false;
369 }
370
371 bool WorkGangBarrierSync::enter() {
372 MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag);
373 if (should_reset()) {
374 // The should_reset() was set and we are the first worker to enter
375 // the sync barrier. We will zero the n_completed() count which
376 // effectively resets the barrier.
377 zero_completed();
378 set_should_reset(false);
379 }
380 inc_completed();
381 if (n_completed() == n_workers()) {
382 // At this point we would like to reset the barrier to be ready in
383 // case it is used again. However, we cannot set n_completed() to
384 // 0, even after the notify_all(), given that some other workers
385 // might still be waiting for n_completed() to become ==
386 // n_workers(). So, if we set n_completed() to 0, those workers
387 // will get stuck (as they will wake up, see that n_completed() !=
388 // n_workers() and go back to sleep). Instead, we raise the
389 // should_reset() flag and the barrier will be reset the first
390 // time a worker enters it again.
391 set_should_reset(true);
392 monitor()->notify_all();
393 } else {
394 while (n_completed() != n_workers() && !aborted()) {
395 monitor()->wait(/* no_safepoint_check */ true);
396 }
397 }
398 return !aborted();
399 }
400
401 void WorkGangBarrierSync::abort() {
402 MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag);
403 set_aborted();
404 monitor()->notify_all();
405 }
406
407 // SubTasksDone functions.
408
409 SubTasksDone::SubTasksDone(uint n) :
410 _n_tasks(n), _tasks(NULL) {
411 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal);
412 guarantee(_tasks != NULL, "alloc failure");
413 clear();
414 }
415
416 bool SubTasksDone::valid() {
417 return _tasks != NULL;
418 }
419
420 void SubTasksDone::clear() {
421 for (uint i = 0; i < _n_tasks; i++) {
422 _tasks[i] = 0;
423 }
424 _threads_completed = 0;
425 #ifdef ASSERT
426 _claimed = 0;
427 #endif
428 }
429
430 bool SubTasksDone::is_task_claimed(uint t) {
431 assert(t < _n_tasks, "bad task id.");
432 uint old = _tasks[t];
433 if (old == 0) {
434 old = Atomic::cmpxchg(1, &_tasks[t], 0);
435 }
436 assert(_tasks[t] == 1, "What else?");
437 bool res = old != 0;
438 #ifdef ASSERT
439 if (!res) {
440 assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?");
441 Atomic::inc((volatile jint*) &_claimed);
442 }
443 #endif
444 return res;
445 }
446
447 void SubTasksDone::all_tasks_completed(uint n_threads) {
448 jint observed = _threads_completed;
449 jint old;
450 do {
451 old = observed;
452 observed = Atomic::cmpxchg(old+1, &_threads_completed, old);
453 } while (observed != old);
454 // If this was the last thread checking in, clear the tasks.
455 uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads);
456 if (observed + 1 == (jint)adjusted_thread_count) {
457 clear();
458 }
459 }
460
461
462 SubTasksDone::~SubTasksDone() {
463 if (_tasks != NULL) FREE_C_HEAP_ARRAY(jint, _tasks);
464 }
465
466 // *** SequentialSubTasksDone
467
468 void SequentialSubTasksDone::clear() {
469 _n_tasks = _n_claimed = 0;
470 _n_threads = _n_completed = 0;
471 }
472
473 bool SequentialSubTasksDone::valid() {
474 return _n_threads > 0;
475 }
476
477 bool SequentialSubTasksDone::is_task_claimed(uint& t) {
478 uint* n_claimed_ptr = &_n_claimed;
479 t = *n_claimed_ptr;
480 while (t < _n_tasks) {
481 jint res = Atomic::cmpxchg(t+1, n_claimed_ptr, t);
482 if (res == (jint)t) {
483 return false;
484 }
485 t = *n_claimed_ptr;
486 }
487 return true;
488 }
489
490 bool SequentialSubTasksDone::all_tasks_completed() {
491 uint* n_completed_ptr = &_n_completed;
492 uint complete = *n_completed_ptr;
493 while (true) {
494 uint res = Atomic::cmpxchg(complete+1, n_completed_ptr, complete);
495 if (res == complete) {
496 break;
497 }
498 complete = res;
499 }
500 if (complete+1 == _n_threads) {
501 clear();
502 return true;
503 }
504 return false;
505 }
506
507 bool FreeIdSet::_stat_init = false;
508 FreeIdSet* FreeIdSet::_sets[NSets];
509 bool FreeIdSet::_safepoint;
510
511 FreeIdSet::FreeIdSet(int sz, Monitor* mon) :
512 _sz(sz), _mon(mon), _hd(0), _waiters(0), _index(-1), _claimed(0)
513 {
514 _ids = NEW_C_HEAP_ARRAY(int, sz, mtInternal);
515 for (int i = 0; i < sz; i++) _ids[i] = i+1;
516 _ids[sz-1] = end_of_list; // end of list.
517 if (_stat_init) {
518 for (int j = 0; j < NSets; j++) _sets[j] = NULL;
519 _stat_init = true;
520 }
521 // Add to sets. (This should happen while the system is still single-threaded.)
522 for (int j = 0; j < NSets; j++) {
523 if (_sets[j] == NULL) {
524 _sets[j] = this;
525 _index = j;
526 break;
527 }
528 }
529 guarantee(_index != -1, "Too many FreeIdSets in use!");
530 }
531
532 FreeIdSet::~FreeIdSet() {
533 _sets[_index] = NULL;
534 FREE_C_HEAP_ARRAY(int, _ids);
535 }
536
537 void FreeIdSet::set_safepoint(bool b) {
538 _safepoint = b;
539 if (b) {
540 for (int j = 0; j < NSets; j++) {
541 if (_sets[j] != NULL && _sets[j]->_waiters > 0) {
542 Monitor* mon = _sets[j]->_mon;
543 mon->lock_without_safepoint_check();
544 mon->notify_all();
545 mon->unlock();
546 }
547 }
548 }
549 }
550
551 #define FID_STATS 0
552
553 int FreeIdSet::claim_par_id() {
554 #if FID_STATS
555 thread_t tslf = thr_self();
556 tty->print("claim_par_id[%d]: sz = %d, claimed = %d\n", tslf, _sz, _claimed);
557 #endif
558 MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag);
559 while (!_safepoint && _hd == end_of_list) {
560 _waiters++;
561 #if FID_STATS
562 if (_waiters > 5) {
563 tty->print("claim_par_id waiting[%d]: %d waiters, %d claimed.\n",
564 tslf, _waiters, _claimed);
565 }
566 #endif
567 _mon->wait(Mutex::_no_safepoint_check_flag);
568 _waiters--;
569 }
570 if (_hd == end_of_list) {
571 #if FID_STATS
572 tty->print("claim_par_id[%d]: returning EOL.\n", tslf);
573 #endif
574 return -1;
575 } else {
576 int res = _hd;
577 _hd = _ids[res];
578 _ids[res] = claimed; // For debugging.
579 _claimed++;
580 #if FID_STATS
581 tty->print("claim_par_id[%d]: returning %d, claimed = %d.\n",
582 tslf, res, _claimed);
583 #endif
584 return res;
585 }
586 }
587
588 bool FreeIdSet::claim_perm_id(int i) {
589 assert(0 <= i && i < _sz, "Out of range.");
590 MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag);
591 int prev = end_of_list;
592 int cur = _hd;
593 while (cur != end_of_list) {
594 if (cur == i) {
595 if (prev == end_of_list) {
596 _hd = _ids[cur];
597 } else {
598 _ids[prev] = _ids[cur];
599 }
600 _ids[cur] = claimed;
601 _claimed++;
602 return true;
603 } else {
604 prev = cur;
605 cur = _ids[cur];
606 }
607 }
608 return false;
609
610 }
611
612 void FreeIdSet::release_par_id(int id) {
613 MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag);
614 assert(_ids[id] == claimed, "Precondition.");
615 _ids[id] = _hd;
616 _hd = id;
617 _claimed--;
618 #if FID_STATS
619 tty->print("[%d] release_par_id(%d), waiters =%d, claimed = %d.\n",
620 thr_self(), id, _waiters, _claimed);
621 #endif
622 if (_waiters > 0)
623 // Notify all would be safer, but this is OK, right?
624 _mon->notify_all();
625 }