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/semaphore.hpp"
32 #include "runtime/thread.inline.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 // WorkGang dispatcher implemented with semaphores.
102 //
103 // Semaphores don't require the worker threads to re-claim the lock when they wake up.
104 // This helps lowering the latency when starting and stopping the worker threads.
105 class SemaphoreGangTaskDispatcher : public GangTaskDispatcher {
106 // The task currently being dispatched to the GangWorkers.
107 AbstractGangTask* _task;
108
109 volatile uint _started;
110 volatile uint _not_finished;
111
112 // Semaphore used to start the GangWorkers.
113 Semaphore* _start_semaphore;
114 // Semaphore used to notify the coordinator that all workers are done.
115 Semaphore* _end_semaphore;
116
117 public:
118 SemaphoreGangTaskDispatcher() :
119 _task(NULL),
120 _started(0),
121 _not_finished(0),
122 _start_semaphore(new Semaphore()),
123 _end_semaphore(new Semaphore())
124 { }
125
126 ~SemaphoreGangTaskDispatcher() {
127 delete _start_semaphore;
128 delete _end_semaphore;
129 }
130
131 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) {
132 // No workers are allowed to read the state variables until they have been signaled.
133 _task = task;
134 _not_finished = num_workers;
135
136 // Dispatch 'num_workers' number of tasks.
137 _start_semaphore->signal(num_workers);
138
139 // Wait for the last worker to signal the coordinator.
140 _end_semaphore->wait();
141
142 // No workers are allowed to read the state variables after the coordinator has been signaled.
143 assert(_not_finished == 0, "%d not finished workers?", _not_finished);
144 _task = NULL;
145 _started = 0;
146
147 }
148
149 WorkData worker_wait_for_task() {
150 // Wait for the coordinator to dispatch a task.
151 _start_semaphore->wait();
152
153 uint num_started = (uint) Atomic::add(1, (volatile jint*)&_started);
154
155 // Subtract one to get a zero-indexed worker id.
156 uint worker_id = num_started - 1;
157
158 return WorkData(_task, worker_id);
159 }
160
161 void worker_done_with_task() {
162 // Mark that the worker is done with the task.
163 // The worker is not allowed to read the state variables after this line.
164 uint not_finished = (uint) Atomic::add(-1, (volatile jint*)&_not_finished);
165
166 // The last worker signals to the coordinator that all work is completed.
167 if (not_finished == 0) {
168 _end_semaphore->signal();
169 }
170 }
171 };
172
173 class MutexGangTaskDispatcher : public GangTaskDispatcher {
174 AbstractGangTask* _task;
175
176 volatile uint _started;
177 volatile uint _finished;
178 volatile uint _num_workers;
179
180 Monitor* _monitor;
181
182 public:
183 MutexGangTaskDispatcher()
184 : _task(NULL),
185 _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)),
186 _started(0),
187 _finished(0),
188 _num_workers(0) {}
189
190 ~MutexGangTaskDispatcher() {
191 delete _monitor;
192 }
193
194 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) {
195 MutexLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag);
196
197 _task = task;
198 _num_workers = num_workers;
199
200 // Tell the workers to get to work.
201 _monitor->notify_all();
202
203 // Wait for them to finish.
204 while (_finished < _num_workers) {
205 _monitor->wait(/* no_safepoint_check */ true);
206 }
207
208 _task = NULL;
209 _num_workers = 0;
210 _started = 0;
211 _finished = 0;
212 }
213
214 WorkData worker_wait_for_task() {
215 MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag);
216
217 while (_num_workers == 0 || _started == _num_workers) {
218 _monitor->wait(/* no_safepoint_check */ true);
219 }
220
221 _started++;
222
223 // Subtract one to get a zero-indexed worker id.
224 uint worker_id = _started - 1;
225
226 return WorkData(_task, worker_id);
227 }
228
229 void worker_done_with_task() {
230 MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag);
231
232 _finished++;
233
234 if (_finished == _num_workers) {
235 // This will wake up all workers and not only the coordinator.
236 _monitor->notify_all();
237 }
238 }
239 };
240
241 static GangTaskDispatcher* create_dispatcher() {
242 if (UseSemaphoreGCThreadsSynchronization) {
243 return new SemaphoreGangTaskDispatcher();
244 }
245
246 return new MutexGangTaskDispatcher();
247 }
248
249 WorkGang::WorkGang(const char* name,
250 uint workers,
251 bool are_GC_task_threads,
252 bool are_ConcurrentGC_threads) :
253 AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads),
254 _dispatcher(create_dispatcher())
255 { }
256
257 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) {
258 return new GangWorker(this, worker_id);
259 }
260
261 void WorkGang::run_task(AbstractGangTask* task) {
262 _dispatcher->coordinator_execute_on_workers(task, active_workers());
263 }
264
265 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) {
266 _gang = gang;
267 set_id(id);
268 set_name("%s#%d", gang->name(), id);
269 }
270
271 void AbstractGangWorker::run() {
272 initialize();
273 loop();
274 }
275
276 void AbstractGangWorker::initialize() {
277 this->initialize_thread_local_storage();
278 this->record_stack_base_and_size();
279 this->initialize_named_thread();
280 assert(_gang != NULL, "No gang to run in");
281 os::set_priority(this, NearMaxPriority);
282 if (TraceWorkGang) {
283 tty->print_cr("Running gang worker for gang %s id %u",
284 gang()->name(), id());
285 }
286 // The VM thread should not execute here because MutexLocker's are used
287 // as (opposed to MutexLockerEx's).
288 assert(!Thread::current()->is_VM_thread(), "VM thread should not be part"
289 " of a work gang");
290 }
291
292 bool AbstractGangWorker::is_GC_task_thread() const {
293 return gang()->are_GC_task_threads();
294 }
295
296 bool AbstractGangWorker::is_ConcurrentGC_thread() const {
297 return gang()->are_ConcurrentGC_threads();
298 }
299
300 void AbstractGangWorker::print_on(outputStream* st) const {
301 st->print("\"%s\" ", name());
302 Thread::print_on(st);
303 st->cr();
304 }
305
306 WorkData GangWorker::wait_for_task() {
307 return gang()->dispatcher()->worker_wait_for_task();
308 }
309
310 void GangWorker::signal_task_done() {
311 gang()->dispatcher()->worker_done_with_task();
312 }
313
314 void GangWorker::print_task_started(WorkData data) {
315 if (TraceWorkGang) {
316 tty->print_cr("Running work gang %s task %s worker %u", name(), data._task->name(), data._worker_id);
317 }
318 }
319
320 void GangWorker::print_task_done(WorkData data) {
321 if (TraceWorkGang) {
322 tty->print_cr("\nFinished work gang %s task %s worker %u", name(), data._task->name(), data._worker_id);
323 Thread* me = Thread::current();
324 tty->print_cr(" T: " PTR_FORMAT " VM_thread: %d", p2i(me), me->is_VM_thread());
325 }
326 }
327
328 void GangWorker::run_task(WorkData data) {
329 print_task_started(data);
330
331 data._task->work(data._worker_id);
332
333 print_task_done(data);
334 }
335
336 void GangWorker::loop() {
337 while (true) {
338 WorkData data = wait_for_task();
339
340 run_task(data);
341
342 signal_task_done();
343 }
344 }
345
346 // *** WorkGangBarrierSync
347
348 WorkGangBarrierSync::WorkGangBarrierSync()
349 : _monitor(Mutex::safepoint, "work gang barrier sync", true,
350 Monitor::_safepoint_check_never),
351 _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) {
352 }
353
354 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name)
355 : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never),
356 _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) {
357 }
358
359 void WorkGangBarrierSync::set_n_workers(uint n_workers) {
360 _n_workers = n_workers;
361 _n_completed = 0;
362 _should_reset = false;
363 _aborted = false;
364 }
365
366 bool WorkGangBarrierSync::enter() {
367 MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag);
368 if (should_reset()) {
369 // The should_reset() was set and we are the first worker to enter
370 // the sync barrier. We will zero the n_completed() count which
371 // effectively resets the barrier.
372 zero_completed();
373 set_should_reset(false);
374 }
375 inc_completed();
376 if (n_completed() == n_workers()) {
377 // At this point we would like to reset the barrier to be ready in
378 // case it is used again. However, we cannot set n_completed() to
379 // 0, even after the notify_all(), given that some other workers
380 // might still be waiting for n_completed() to become ==
381 // n_workers(). So, if we set n_completed() to 0, those workers
382 // will get stuck (as they will wake up, see that n_completed() !=
383 // n_workers() and go back to sleep). Instead, we raise the
384 // should_reset() flag and the barrier will be reset the first
385 // time a worker enters it again.
386 set_should_reset(true);
387 monitor()->notify_all();
388 } else {
389 while (n_completed() != n_workers() && !aborted()) {
390 monitor()->wait(/* no_safepoint_check */ true);
391 }
392 }
393 return !aborted();
394 }
395
396 void WorkGangBarrierSync::abort() {
397 MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag);
398 set_aborted();
399 monitor()->notify_all();
400 }
401
402 // SubTasksDone functions.
403
404 SubTasksDone::SubTasksDone(uint n) :
405 _n_tasks(n), _tasks(NULL) {
406 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal);
407 guarantee(_tasks != NULL, "alloc failure");
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::is_task_claimed(uint t) {
426 assert(t < _n_tasks, "bad task id.");
427 uint old = _tasks[t];
428 if (old == 0) {
429 old = Atomic::cmpxchg(1, &_tasks[t], 0);
430 }
431 assert(_tasks[t] == 1, "What else?");
432 bool res = old != 0;
433 #ifdef ASSERT
434 if (!res) {
435 assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?");
436 Atomic::inc((volatile jint*) &_claimed);
437 }
438 #endif
439 return res;
440 }
441
442 void SubTasksDone::all_tasks_completed(uint n_threads) {
443 jint observed = _threads_completed;
444 jint old;
445 do {
446 old = observed;
447 observed = Atomic::cmpxchg(old+1, &_threads_completed, old);
448 } while (observed != old);
449 // If this was the last thread checking in, clear the tasks.
450 uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads);
451 if (observed + 1 == (jint)adjusted_thread_count) {
452 clear();
453 }
454 }
455
456
457 SubTasksDone::~SubTasksDone() {
458 if (_tasks != NULL) FREE_C_HEAP_ARRAY(jint, _tasks);
459 }
460
461 // *** SequentialSubTasksDone
462
463 void SequentialSubTasksDone::clear() {
464 _n_tasks = _n_claimed = 0;
465 _n_threads = _n_completed = 0;
466 }
467
468 bool SequentialSubTasksDone::valid() {
469 return _n_threads > 0;
470 }
471
472 bool SequentialSubTasksDone::is_task_claimed(uint& t) {
473 uint* n_claimed_ptr = &_n_claimed;
474 t = *n_claimed_ptr;
475 while (t < _n_tasks) {
476 jint res = Atomic::cmpxchg(t+1, n_claimed_ptr, t);
477 if (res == (jint)t) {
478 return false;
479 }
480 t = *n_claimed_ptr;
481 }
482 return true;
483 }
484
485 bool SequentialSubTasksDone::all_tasks_completed() {
486 uint* n_completed_ptr = &_n_completed;
487 uint complete = *n_completed_ptr;
488 while (true) {
489 uint res = Atomic::cmpxchg(complete+1, n_completed_ptr, complete);
490 if (res == complete) {
491 break;
492 }
493 complete = res;
494 }
495 if (complete+1 == _n_threads) {
496 clear();
497 return true;
498 }
499 return false;
500 }
501
502 bool FreeIdSet::_stat_init = false;
503 FreeIdSet* FreeIdSet::_sets[NSets];
504 bool FreeIdSet::_safepoint;
505
506 FreeIdSet::FreeIdSet(int sz, Monitor* mon) :
507 _sz(sz), _mon(mon), _hd(0), _waiters(0), _index(-1), _claimed(0)
508 {
509 _ids = NEW_C_HEAP_ARRAY(int, sz, mtInternal);
510 for (int i = 0; i < sz; i++) _ids[i] = i+1;
511 _ids[sz-1] = end_of_list; // end of list.
512 if (_stat_init) {
513 for (int j = 0; j < NSets; j++) _sets[j] = NULL;
514 _stat_init = true;
515 }
516 // Add to sets. (This should happen while the system is still single-threaded.)
517 for (int j = 0; j < NSets; j++) {
518 if (_sets[j] == NULL) {
519 _sets[j] = this;
520 _index = j;
521 break;
522 }
523 }
524 guarantee(_index != -1, "Too many FreeIdSets in use!");
525 }
526
527 FreeIdSet::~FreeIdSet() {
528 _sets[_index] = NULL;
529 FREE_C_HEAP_ARRAY(int, _ids);
530 }
531
532 void FreeIdSet::set_safepoint(bool b) {
533 _safepoint = b;
534 if (b) {
535 for (int j = 0; j < NSets; j++) {
536 if (_sets[j] != NULL && _sets[j]->_waiters > 0) {
537 Monitor* mon = _sets[j]->_mon;
538 mon->lock_without_safepoint_check();
539 mon->notify_all();
540 mon->unlock();
541 }
542 }
543 }
544 }
545
546 #define FID_STATS 0
547
548 int FreeIdSet::claim_par_id() {
549 #if FID_STATS
550 thread_t tslf = thr_self();
551 tty->print("claim_par_id[%d]: sz = %d, claimed = %d\n", tslf, _sz, _claimed);
552 #endif
553 MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag);
554 while (!_safepoint && _hd == end_of_list) {
555 _waiters++;
556 #if FID_STATS
557 if (_waiters > 5) {
558 tty->print("claim_par_id waiting[%d]: %d waiters, %d claimed.\n",
559 tslf, _waiters, _claimed);
560 }
561 #endif
562 _mon->wait(Mutex::_no_safepoint_check_flag);
563 _waiters--;
564 }
565 if (_hd == end_of_list) {
566 #if FID_STATS
567 tty->print("claim_par_id[%d]: returning EOL.\n", tslf);
568 #endif
569 return -1;
570 } else {
571 int res = _hd;
572 _hd = _ids[res];
573 _ids[res] = claimed; // For debugging.
574 _claimed++;
575 #if FID_STATS
576 tty->print("claim_par_id[%d]: returning %d, claimed = %d.\n",
577 tslf, res, _claimed);
578 #endif
579 return res;
580 }
581 }
582
583 bool FreeIdSet::claim_perm_id(int i) {
584 assert(0 <= i && i < _sz, "Out of range.");
585 MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag);
586 int prev = end_of_list;
587 int cur = _hd;
588 while (cur != end_of_list) {
589 if (cur == i) {
590 if (prev == end_of_list) {
591 _hd = _ids[cur];
592 } else {
593 _ids[prev] = _ids[cur];
594 }
595 _ids[cur] = claimed;
596 _claimed++;
597 return true;
598 } else {
599 prev = cur;
600 cur = _ids[cur];
601 }
602 }
603 return false;
604
605 }
606
607 void FreeIdSet::release_par_id(int id) {
608 MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag);
609 assert(_ids[id] == claimed, "Precondition.");
610 _ids[id] = _hd;
611 _hd = id;
612 _claimed--;
613 #if FID_STATS
614 tty->print("[%d] release_par_id(%d), waiters =%d, claimed = %d.\n",
615 thr_self(), id, _waiters, _claimed);
616 #endif
617 if (_waiters > 0)
618 // Notify all would be safer, but this is OK, right?
619 _mon->notify_all();
620 }