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