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 "memory/iterator.hpp" 32 #include "runtime/atomic.hpp" 33 #include "runtime/os.hpp" 34 #include "runtime/semaphore.hpp" 35 #include "runtime/thread.inline.hpp" 36 37 // Definitions of WorkGang methods. 38 39 // The current implementation will exit if the allocation 40 // of any worker fails. 41 void AbstractWorkGang::initialize_workers() { 42 log_develop_trace(gc, workgang)("Constructing work gang %s with %u threads", name(), total_workers()); 43 _workers = NEW_C_HEAP_ARRAY(AbstractGangWorker*, total_workers(), mtInternal); 44 add_workers(true); 45 } 46 47 48 AbstractGangWorker* AbstractWorkGang::install_worker(uint worker_id) { 49 AbstractGangWorker* new_worker = allocate_worker(worker_id); 50 set_thread(worker_id, new_worker); 51 return new_worker; 52 } 53 54 void AbstractWorkGang::add_workers(bool initializing) { 55 add_workers(_active_workers, initializing); 56 } 57 58 void AbstractWorkGang::add_workers(uint active_workers, bool initializing) { 59 60 os::ThreadType worker_type; 61 if (are_ConcurrentGC_threads()) { 62 worker_type = os::cgc_thread; 63 } else { 64 worker_type = os::pgc_thread; 65 } 66 uint previous_created_workers = _created_workers; 67 68 _created_workers = WorkerManager::add_workers(this, 69 active_workers, 70 _total_workers, 71 _created_workers, 72 worker_type, 73 initializing); 74 _active_workers = MIN2(_created_workers, _active_workers); 75 76 WorkerManager::log_worker_creation(this, previous_created_workers, _active_workers, _created_workers, initializing); 77 } 78 79 AbstractGangWorker* AbstractWorkGang::worker(uint i) const { 80 // Array index bounds checking. 81 AbstractGangWorker* result = NULL; 82 assert(_workers != NULL, "No workers for indexing"); 83 assert(i < total_workers(), "Worker index out of bounds"); 84 result = _workers[i]; 85 assert(result != NULL, "Indexing to null worker"); 86 return result; 87 } 88 89 void AbstractWorkGang::print_worker_threads_on(outputStream* st) const { 90 uint workers = created_workers(); 91 for (uint i = 0; i < workers; i++) { 92 worker(i)->print_on(st); 93 st->cr(); 94 } 95 } 96 97 void AbstractWorkGang::threads_do(ThreadClosure* tc) const { 98 assert(tc != NULL, "Null ThreadClosure"); 99 uint workers = created_workers(); 100 for (uint i = 0; i < workers; i++) { 101 tc->do_thread(worker(i)); 102 } 103 } 104 105 // WorkGang dispatcher implemented with semaphores. 106 // 107 // Semaphores don't require the worker threads to re-claim the lock when they wake up. 108 // This helps lowering the latency when starting and stopping the worker threads. 109 class SemaphoreGangTaskDispatcher : public GangTaskDispatcher { 110 // The task currently being dispatched to the GangWorkers. 111 AbstractGangTask* _task; 112 113 volatile uint _started; 114 volatile uint _not_finished; 115 116 // Semaphore used to start the GangWorkers. 117 Semaphore* _start_semaphore; 118 // Semaphore used to notify the coordinator that all workers are done. 119 Semaphore* _end_semaphore; 120 121 public: 122 SemaphoreGangTaskDispatcher() : 123 _task(NULL), 124 _started(0), 125 _not_finished(0), 126 _start_semaphore(new Semaphore()), 127 _end_semaphore(new Semaphore()) 128 { } 129 130 ~SemaphoreGangTaskDispatcher() { 131 delete _start_semaphore; 132 delete _end_semaphore; 133 } 134 135 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) { 136 // No workers are allowed to read the state variables until they have been signaled. 137 _task = task; 138 _not_finished = num_workers; 139 140 // Dispatch 'num_workers' number of tasks. 141 _start_semaphore->signal(num_workers); 142 143 // Wait for the last worker to signal the coordinator. 144 _end_semaphore->wait(); 145 146 // No workers are allowed to read the state variables after the coordinator has been signaled. 147 assert(_not_finished == 0, "%d not finished workers?", _not_finished); 148 _task = NULL; 149 _started = 0; 150 151 } 152 153 WorkData worker_wait_for_task() { 154 // Wait for the coordinator to dispatch a task. 155 _start_semaphore->wait(); 156 157 uint num_started = Atomic::add(&_started, 1u); 158 159 // Subtract one to get a zero-indexed worker id. 160 uint worker_id = num_started - 1; 161 162 return WorkData(_task, worker_id); 163 } 164 165 void worker_done_with_task() { 166 // Mark that the worker is done with the task. 167 // The worker is not allowed to read the state variables after this line. 168 uint not_finished = Atomic::sub(&_not_finished, 1u); 169 170 // The last worker signals to the coordinator that all work is completed. 171 if (not_finished == 0) { 172 _end_semaphore->signal(); 173 } 174 } 175 }; 176 177 class MutexGangTaskDispatcher : public GangTaskDispatcher { 178 AbstractGangTask* _task; 179 180 volatile uint _started; 181 volatile uint _finished; 182 volatile uint _num_workers; 183 184 Monitor* _monitor; 185 186 public: 187 MutexGangTaskDispatcher() : 188 _task(NULL), 189 _started(0), 190 _finished(0), 191 _num_workers(0), 192 _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)) { 193 } 194 195 ~MutexGangTaskDispatcher() { 196 delete _monitor; 197 } 198 199 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) { 200 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag); 201 202 _task = task; 203 _num_workers = num_workers; 204 205 // Tell the workers to get to work. 206 _monitor->notify_all(); 207 208 // Wait for them to finish. 209 while (_finished < _num_workers) { 210 ml.wait(); 211 } 212 213 _task = NULL; 214 _num_workers = 0; 215 _started = 0; 216 _finished = 0; 217 } 218 219 WorkData worker_wait_for_task() { 220 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag); 221 222 while (_num_workers == 0 || _started == _num_workers) { 223 _monitor->wait(); 224 } 225 226 _started++; 227 228 // Subtract one to get a zero-indexed worker id. 229 uint worker_id = _started - 1; 230 231 return WorkData(_task, worker_id); 232 } 233 234 void worker_done_with_task() { 235 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag); 236 237 _finished++; 238 239 if (_finished == _num_workers) { 240 // This will wake up all workers and not only the coordinator. 241 _monitor->notify_all(); 242 } 243 } 244 }; 245 246 static GangTaskDispatcher* create_dispatcher() { 247 if (UseSemaphoreGCThreadsSynchronization) { 248 return new SemaphoreGangTaskDispatcher(); 249 } 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()) 260 { } 261 262 WorkGang::~WorkGang() { 263 delete _dispatcher; 264 } 265 266 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) { 267 return new GangWorker(this, worker_id); 268 } 269 270 void WorkGang::run_task(AbstractGangTask* task) { 271 run_task(task, active_workers()); 272 } 273 274 void WorkGang::run_task(AbstractGangTask* task, uint num_workers) { 275 guarantee(num_workers <= total_workers(), 276 "Trying to execute task %s with %u workers which is more than the amount of total workers %u.", 277 task->name(), num_workers, total_workers()); 278 guarantee(num_workers > 0, "Trying to execute task %s with zero workers", task->name()); 279 uint old_num_workers = _active_workers; 280 update_active_workers(num_workers); 281 _dispatcher->coordinator_execute_on_workers(task, num_workers); 282 update_active_workers(old_num_workers); 283 } 284 285 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) { 286 _gang = gang; 287 set_id(id); 288 set_name("%s#%d", gang->name(), id); 289 } 290 291 void AbstractGangWorker::run() { 292 initialize(); 293 loop(); 294 } 295 296 void AbstractGangWorker::initialize() { 297 assert(_gang != NULL, "No gang to run in"); 298 os::set_priority(this, NearMaxPriority); 299 log_develop_trace(gc, workgang)("Running gang worker for gang %s id %u", gang()->name(), id()); 300 assert(!Thread::current()->is_VM_thread(), "VM thread should not be part" 301 " of a work gang"); 302 } 303 304 bool AbstractGangWorker::is_GC_task_thread() const { 305 return gang()->are_GC_task_threads(); 306 } 307 308 bool AbstractGangWorker::is_ConcurrentGC_thread() const { 309 return gang()->are_ConcurrentGC_threads(); 310 } 311 312 void AbstractGangWorker::print_on(outputStream* st) const { 313 st->print("\"%s\" ", name()); 314 Thread::print_on(st); 315 st->cr(); 316 } 317 318 void AbstractGangWorker::print() const { print_on(tty); } 319 320 WorkData GangWorker::wait_for_task() { 321 return gang()->dispatcher()->worker_wait_for_task(); 322 } 323 324 void GangWorker::signal_task_done() { 325 gang()->dispatcher()->worker_done_with_task(); 326 } 327 328 void GangWorker::run_task(WorkData data) { 329 GCIdMark gc_id_mark(data._task->gc_id()); 330 log_develop_trace(gc, workgang)("Running work gang: %s task: %s worker: %u", name(), data._task->name(), data._worker_id); 331 332 data._task->work(data._worker_id); 333 334 log_develop_trace(gc, workgang)("Finished work gang: %s task: %s worker: %u thread: " PTR_FORMAT, 335 name(), data._task->name(), data._worker_id, p2i(Thread::current())); 336 } 337 338 void GangWorker::loop() { 339 while (true) { 340 WorkData data = wait_for_task(); 341 342 run_task(data); 343 344 signal_task_done(); 345 } 346 } 347 348 // *** WorkGangBarrierSync 349 350 WorkGangBarrierSync::WorkGangBarrierSync() 351 : _monitor(Mutex::safepoint, "work gang barrier sync", true, 352 Monitor::_safepoint_check_never), 353 _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) { 354 } 355 356 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name) 357 : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never), 358 _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) { 359 } 360 361 void WorkGangBarrierSync::set_n_workers(uint n_workers) { 362 _n_workers = n_workers; 363 _n_completed = 0; 364 _should_reset = false; 365 _aborted = false; 366 } 367 368 bool WorkGangBarrierSync::enter() { 369 MonitorLocker ml(monitor(), Mutex::_no_safepoint_check_flag); 370 if (should_reset()) { 371 // The should_reset() was set and we are the first worker to enter 372 // the sync barrier. We will zero the n_completed() count which 373 // effectively resets the barrier. 374 zero_completed(); 375 set_should_reset(false); 376 } 377 inc_completed(); 378 if (n_completed() == n_workers()) { 379 // At this point we would like to reset the barrier to be ready in 380 // case it is used again. However, we cannot set n_completed() to 381 // 0, even after the notify_all(), given that some other workers 382 // might still be waiting for n_completed() to become == 383 // n_workers(). So, if we set n_completed() to 0, those workers 384 // will get stuck (as they will wake up, see that n_completed() != 385 // n_workers() and go back to sleep). Instead, we raise the 386 // should_reset() flag and the barrier will be reset the first 387 // time a worker enters it again. 388 set_should_reset(true); 389 ml.notify_all(); 390 } else { 391 while (n_completed() != n_workers() && !aborted()) { 392 ml.wait(); 393 } 394 } 395 return !aborted(); 396 } 397 398 void WorkGangBarrierSync::abort() { 399 MutexLocker x(monitor(), Mutex::_no_safepoint_check_flag); 400 set_aborted(); 401 monitor()->notify_all(); 402 } 403 404 // SubTasksDone functions. 405 406 SubTasksDone::SubTasksDone(uint n) : 407 _tasks(NULL), _n_tasks(n), _threads_completed(0) { 408 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal); 409 clear(); 410 } 411 412 bool SubTasksDone::valid() { 413 return _tasks != NULL; 414 } 415 416 void SubTasksDone::clear() { 417 for (uint i = 0; i < _n_tasks; i++) { 418 _tasks[i] = 0; 419 } 420 _threads_completed = 0; 421 #ifdef ASSERT 422 _claimed = 0; 423 #endif 424 } 425 426 bool SubTasksDone::try_claim_task(uint t) { 427 assert(t < _n_tasks, "bad task id."); 428 uint old = _tasks[t]; 429 if (old == 0) { 430 old = Atomic::cmpxchg(&_tasks[t], 0u, 1u); 431 } 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(&_claimed); 437 } 438 #endif 439 return res; 440 } 441 442 void SubTasksDone::all_tasks_completed(uint n_threads) { 443 uint observed = _threads_completed; 444 uint old; 445 do { 446 old = observed; 447 observed = Atomic::cmpxchg(&_threads_completed, old, old+1); 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 == adjusted_thread_count) { 452 clear(); 453 } 454 } 455 456 457 SubTasksDone::~SubTasksDone() { 458 FREE_C_HEAP_ARRAY(uint, _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::try_claim_task(uint& t) { 473 t = _n_claimed; 474 while (t < _n_tasks) { 475 uint res = Atomic::cmpxchg(&_n_claimed, t, t+1); 476 if (res == t) { 477 return true; 478 } 479 t = res; 480 } 481 return false; 482 } 483 484 bool SequentialSubTasksDone::all_tasks_completed() { 485 uint complete = _n_completed; 486 while (true) { 487 uint res = Atomic::cmpxchg(&_n_completed, complete, complete+1); 488 if (res == complete) { 489 break; 490 } 491 complete = res; 492 } 493 if (complete+1 == _n_threads) { 494 clear(); 495 return true; 496 } 497 return false; 498 }