1 /*
2 * Copyright (c) 2001, 2016, 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.inline.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 if (_workers == NULL) {
44 vm_exit_out_of_memory(0, OOM_MALLOC_ERROR, "Cannot create GangWorker array.");
45 }
46
47 add_workers(true);
48 }
49
50
51 AbstractGangWorker* AbstractWorkGang::install_worker(uint worker_id) {
52 AbstractGangWorker* new_worker = allocate_worker(worker_id);
53 set_thread(worker_id, new_worker);
54 return new_worker;
55 }
56
57 void AbstractWorkGang::add_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
66 _created_workers = WorkerManager::add_workers(this,
67 _active_workers,
68 _total_workers,
69 _created_workers,
70 worker_type,
71 initializing);
72 _active_workers = MIN2(_created_workers, _active_workers);
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 = created_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 = created_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 run_task(task, active_workers());
263 }
264
265 void WorkGang::run_task(AbstractGangTask* task, uint num_workers) {
266 guarantee(num_workers <= active_workers(),
267 "Trying to execute task %s with %u workers which is more than the amount of active workers %u.",
268 task->name(), num_workers, active_workers());
269 guarantee(num_workers > 0, "Trying to execute task %s with zero workers", task->name());
270 _dispatcher->coordinator_execute_on_workers(task, num_workers);
271 }
272
273 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) {
274 _gang = gang;
275 set_id(id);
276 set_name("%s#%d", gang->name(), id);
277 }
278
279 void AbstractGangWorker::run() {
280 initialize();
281 loop();
282 }
283
284 void AbstractGangWorker::initialize() {
285 this->record_stack_base_and_size();
286 this->initialize_named_thread();
287 assert(_gang != NULL, "No gang to run in");
288 os::set_priority(this, NearMaxPriority);
289 log_develop_trace(gc, workgang)("Running gang worker for gang %s id %u", gang()->name(), id());
290 // The VM thread should not execute here because MutexLocker's are used
291 // as (opposed to MutexLockerEx's).
292 assert(!Thread::current()->is_VM_thread(), "VM thread should not be part"
293 " of a work gang");
294 }
295
296 bool AbstractGangWorker::is_GC_task_thread() const {
297 return gang()->are_GC_task_threads();
298 }
299
300 bool AbstractGangWorker::is_ConcurrentGC_thread() const {
301 return gang()->are_ConcurrentGC_threads();
302 }
303
304 void AbstractGangWorker::print_on(outputStream* st) const {
305 st->print("\"%s\" ", name());
306 Thread::print_on(st);
307 st->cr();
308 }
309
310 WorkData GangWorker::wait_for_task() {
311 return gang()->dispatcher()->worker_wait_for_task();
312 }
313
314 void GangWorker::signal_task_done() {
315 gang()->dispatcher()->worker_done_with_task();
316 }
317
318 void GangWorker::run_task(WorkData data) {
319 GCIdMark gc_id_mark(data._task->gc_id());
320 log_develop_trace(gc, workgang)("Running work gang: %s task: %s worker: %u", name(), data._task->name(), data._worker_id);
321
322 data._task->work(data._worker_id);
323
324 log_develop_trace(gc, workgang)("Finished work gang: %s task: %s worker: %u thread: " PTR_FORMAT,
325 name(), data._task->name(), data._worker_id, p2i(Thread::current()));
326 }
327
328 void GangWorker::loop() {
329 while (true) {
330 WorkData data = wait_for_task();
331
332 run_task(data);
333
334 signal_task_done();
335 }
336 }
337
338 // *** WorkGangBarrierSync
339
340 WorkGangBarrierSync::WorkGangBarrierSync()
341 : _monitor(Mutex::safepoint, "work gang barrier sync", true,
342 Monitor::_safepoint_check_never),
343 _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) {
344 }
345
346 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name)
347 : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never),
348 _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) {
349 }
350
351 void WorkGangBarrierSync::set_n_workers(uint n_workers) {
352 _n_workers = n_workers;
353 _n_completed = 0;
354 _should_reset = false;
355 _aborted = false;
356 }
357
358 bool WorkGangBarrierSync::enter() {
359 MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag);
360 if (should_reset()) {
361 // The should_reset() was set and we are the first worker to enter
362 // the sync barrier. We will zero the n_completed() count which
363 // effectively resets the barrier.
364 zero_completed();
365 set_should_reset(false);
366 }
367 inc_completed();
368 if (n_completed() == n_workers()) {
369 // At this point we would like to reset the barrier to be ready in
370 // case it is used again. However, we cannot set n_completed() to
371 // 0, even after the notify_all(), given that some other workers
372 // might still be waiting for n_completed() to become ==
373 // n_workers(). So, if we set n_completed() to 0, those workers
374 // will get stuck (as they will wake up, see that n_completed() !=
375 // n_workers() and go back to sleep). Instead, we raise the
376 // should_reset() flag and the barrier will be reset the first
377 // time a worker enters it again.
378 set_should_reset(true);
379 monitor()->notify_all();
380 } else {
381 while (n_completed() != n_workers() && !aborted()) {
382 monitor()->wait(/* no_safepoint_check */ true);
383 }
384 }
385 return !aborted();
386 }
387
388 void WorkGangBarrierSync::abort() {
389 MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag);
390 set_aborted();
391 monitor()->notify_all();
392 }
393
394 // SubTasksDone functions.
395
396 SubTasksDone::SubTasksDone(uint n) :
397 _n_tasks(n), _tasks(NULL) {
398 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal);
399 guarantee(_tasks != NULL, "alloc failure");
400 clear();
401 }
402
403 bool SubTasksDone::valid() {
404 return _tasks != NULL;
405 }
406
407 void SubTasksDone::clear() {
408 for (uint i = 0; i < _n_tasks; i++) {
409 _tasks[i] = 0;
410 }
411 _threads_completed = 0;
412 #ifdef ASSERT
413 _claimed = 0;
414 #endif
415 }
416
417 bool SubTasksDone::is_task_claimed(uint t) {
418 assert(t < _n_tasks, "bad task id.");
419 uint old = _tasks[t];
420 if (old == 0) {
421 old = Atomic::cmpxchg(1, &_tasks[t], 0);
422 }
423 assert(_tasks[t] == 1, "What else?");
424 bool res = old != 0;
425 #ifdef ASSERT
426 if (!res) {
427 assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?");
428 Atomic::inc((volatile jint*) &_claimed);
429 }
430 #endif
431 return res;
432 }
433
434 void SubTasksDone::all_tasks_completed(uint n_threads) {
435 jint observed = _threads_completed;
436 jint old;
437 do {
438 old = observed;
439 observed = Atomic::cmpxchg(old+1, &_threads_completed, old);
440 } while (observed != old);
441 // If this was the last thread checking in, clear the tasks.
442 uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads);
443 if (observed + 1 == (jint)adjusted_thread_count) {
444 clear();
445 }
446 }
447
448
449 SubTasksDone::~SubTasksDone() {
450 if (_tasks != NULL) FREE_C_HEAP_ARRAY(jint, _tasks);
451 }
452
453 // *** SequentialSubTasksDone
454
455 void SequentialSubTasksDone::clear() {
456 _n_tasks = _n_claimed = 0;
457 _n_threads = _n_completed = 0;
458 }
459
460 bool SequentialSubTasksDone::valid() {
461 return _n_threads > 0;
462 }
463
464 bool SequentialSubTasksDone::is_task_claimed(uint& t) {
465 uint* n_claimed_ptr = &_n_claimed;
466 t = *n_claimed_ptr;
467 while (t < _n_tasks) {
468 jint res = Atomic::cmpxchg(t+1, n_claimed_ptr, t);
469 if (res == (jint)t) {
470 return false;
471 }
472 t = *n_claimed_ptr;
473 }
474 return true;
475 }
476
477 bool SequentialSubTasksDone::all_tasks_completed() {
478 uint* n_completed_ptr = &_n_completed;
479 uint complete = *n_completed_ptr;
480 while (true) {
481 uint res = Atomic::cmpxchg(complete+1, n_completed_ptr, complete);
482 if (res == complete) {
483 break;
484 }
485 complete = res;
486 }
487 if (complete+1 == _n_threads) {
488 clear();
489 return true;
490 }
491 return false;
492 }