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 "runtime/atomic.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 add_workers(true); 44 } 45 46 47 AbstractGangWorker* AbstractWorkGang::install_worker(uint worker_id) { 48 AbstractGangWorker* new_worker = allocate_worker(worker_id); 49 set_thread(worker_id, new_worker); 50 return new_worker; 51 } 52 53 void AbstractWorkGang::add_workers(bool initializing) { 54 add_workers(_active_workers, initializing); 55 } 56 57 void AbstractWorkGang::add_workers(uint active_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 uint previous_created_workers = _created_workers; 66 67 _created_workers = WorkerManager::add_workers(this, 68 active_workers, 69 _total_workers, 70 _created_workers, 71 worker_type, 72 initializing); 73 _active_workers = MIN2(_created_workers, _active_workers); 74 75 WorkerManager::log_worker_creation(this, previous_created_workers, _active_workers, _created_workers, initializing); 76 } 77 78 AbstractGangWorker* AbstractWorkGang::worker(uint i) const { 79 // Array index bounds checking. 80 AbstractGangWorker* result = NULL; 81 assert(_workers != NULL, "No workers for indexing"); 82 assert(i < total_workers(), "Worker index out of bounds"); 83 result = _workers[i]; 84 assert(result != NULL, "Indexing to null worker"); 85 return result; 86 } 87 88 void AbstractWorkGang::print_worker_threads_on(outputStream* st) const { 89 uint workers = created_workers(); 90 for (uint i = 0; i < workers; i++) { 91 worker(i)->print_on(st); 92 st->cr(); 93 } 94 } 95 96 void AbstractWorkGang::threads_do(ThreadClosure* tc) const { 97 assert(tc != NULL, "Null ThreadClosure"); 98 uint workers = created_workers(); 99 for (uint i = 0; i < workers; i++) { 100 tc->do_thread(worker(i)); 101 } 102 } 103 104 // WorkGang dispatcher implemented with semaphores. 105 // 106 // Semaphores don't require the worker threads to re-claim the lock when they wake up. 107 // This helps lowering the latency when starting and stopping the worker threads. 108 class SemaphoreGangTaskDispatcher : public GangTaskDispatcher { 109 // The task currently being dispatched to the GangWorkers. 110 AbstractGangTask* _task; 111 112 volatile uint _started; 113 volatile uint _not_finished; 114 115 // Semaphore used to start the GangWorkers. 116 Semaphore* _start_semaphore; 117 // Semaphore used to notify the coordinator that all workers are done. 118 Semaphore* _end_semaphore; 119 120 public: 121 SemaphoreGangTaskDispatcher() : 122 _task(NULL), 123 _started(0), 124 _not_finished(0), 125 _start_semaphore(new Semaphore()), 126 _end_semaphore(new Semaphore()) 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 assert(_not_finished == 0, "%d not finished workers?", _not_finished); 147 _task = NULL; 148 _started = 0; 149 150 } 151 152 WorkData worker_wait_for_task() { 153 // Wait for the coordinator to dispatch a task. 154 _start_semaphore->wait(); 155 156 uint num_started = Atomic::add(1u, &_started); 157 158 // Subtract one to get a zero-indexed worker id. 159 uint worker_id = num_started - 1; 160 161 return WorkData(_task, worker_id); 162 } 163 164 void worker_done_with_task() { 165 // Mark that the worker is done with the task. 166 // The worker is not allowed to read the state variables after this line. 167 uint not_finished = Atomic::sub(1u, &_not_finished); 168 169 // The last worker signals to the coordinator that all work is completed. 170 if (not_finished == 0) { 171 _end_semaphore->signal(); 172 } 173 } 174 }; 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 _started(0), 189 _finished(0), 190 _num_workers(0), 191 _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)) { 192 } 193 194 ~MutexGangTaskDispatcher() { 195 delete _monitor; 196 } 197 198 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) { 199 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag); 200 201 _task = task; 202 _num_workers = num_workers; 203 204 // Tell the workers to get to work. 205 _monitor->notify_all(); 206 207 // Wait for them to finish. 208 while (_finished < _num_workers) { 209 ml.wait(); 210 } 211 212 _task = NULL; 213 _num_workers = 0; 214 _started = 0; 215 _finished = 0; 216 } 217 218 WorkData worker_wait_for_task() { 219 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag); 220 221 while (_num_workers == 0 || _started == _num_workers) { 222 _monitor->wait(); 223 } 224 225 _started++; 226 227 // Subtract one to get a zero-indexed worker id. 228 uint worker_id = _started - 1; 229 230 return WorkData(_task, worker_id); 231 } 232 233 void worker_done_with_task() { 234 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag); 235 236 _finished++; 237 238 if (_finished == _num_workers) { 239 // This will wake up all workers and not only the coordinator. 240 _monitor->notify_all(); 241 } 242 } 243 }; 244 245 static GangTaskDispatcher* create_dispatcher() { 246 if (UseSemaphoreGCThreadsSynchronization) { 247 return new SemaphoreGangTaskDispatcher(); 248 } 249 250 return new MutexGangTaskDispatcher(); 251 } 252 253 WorkGang::WorkGang(const char* name, 254 uint workers, 255 bool are_GC_task_threads, 256 bool are_ConcurrentGC_threads) : 257 AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads), 258 _dispatcher(create_dispatcher()) 259 { } 260 261 WorkGang::~WorkGang() { 262 delete _dispatcher; 263 } 264 265 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) { 266 return new GangWorker(this, worker_id); 267 } 268 269 void WorkGang::run_task(AbstractGangTask* task) { 270 run_task(task, active_workers()); 271 } 272 273 void WorkGang::run_task(AbstractGangTask* task, uint num_workers) { 274 guarantee(num_workers <= total_workers(), 275 "Trying to execute task %s with %u workers which is more than the amount of total workers %u.", 276 task->name(), num_workers, total_workers()); 277 guarantee(num_workers > 0, "Trying to execute task %s with zero workers", task->name()); 278 uint old_num_workers = _active_workers; 279 update_active_workers(num_workers); 280 _dispatcher->coordinator_execute_on_workers(task, num_workers); 281 update_active_workers(old_num_workers); 282 } 283 284 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) { 285 _gang = gang; 286 set_id(id); 287 set_name("%s#%d", gang->name(), id); 288 } 289 290 void AbstractGangWorker::run() { 291 initialize(); 292 loop(); 293 } 294 295 void AbstractGangWorker::initialize() { 296 assert(_gang != NULL, "No gang to run in"); 297 os::set_priority(this, NearMaxPriority); 298 log_develop_trace(gc, workgang)("Running gang worker for gang %s id %u", gang()->name(), id()); 299 assert(!Thread::current()->is_VM_thread(), "VM thread should not be part" 300 " of a work gang"); 301 } 302 303 bool AbstractGangWorker::is_GC_task_thread() const { 304 return gang()->are_GC_task_threads(); 305 } 306 307 bool AbstractGangWorker::is_ConcurrentGC_thread() const { 308 return gang()->are_ConcurrentGC_threads(); 309 } 310 311 void AbstractGangWorker::print_on(outputStream* st) const { 312 st->print("\"%s\" ", name()); 313 Thread::print_on(st); 314 st->cr(); 315 } 316 317 void AbstractGangWorker::print() const { print_on(tty); } 318 319 WorkData GangWorker::wait_for_task() { 320 return gang()->dispatcher()->worker_wait_for_task(); 321 } 322 323 void GangWorker::signal_task_done() { 324 gang()->dispatcher()->worker_done_with_task(); 325 } 326 327 void GangWorker::run_task(WorkData data) { 328 GCIdMark gc_id_mark(data._task->gc_id()); 329 log_develop_trace(gc, workgang)("Running work gang: %s task: %s worker: %u", name(), data._task->name(), data._worker_id); 330 331 data._task->work(data._worker_id); 332 333 log_develop_trace(gc, workgang)("Finished work gang: %s task: %s worker: %u thread: " PTR_FORMAT, 334 name(), data._task->name(), data._worker_id, p2i(Thread::current())); 335 } 336 337 void GangWorker::loop() { 338 while (true) { 339 WorkData data = wait_for_task(); 340 341 run_task(data); 342 343 signal_task_done(); 344 } 345 } 346 347 // *** WorkGangBarrierSync 348 349 WorkGangBarrierSync::WorkGangBarrierSync() 350 : _monitor(Mutex::safepoint, "work gang barrier sync", true, 351 Monitor::_safepoint_check_never), 352 _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) { 353 } 354 355 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name) 356 : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never), 357 _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) { 358 } 359 360 void WorkGangBarrierSync::set_n_workers(uint n_workers) { 361 _n_workers = n_workers; 362 _n_completed = 0; 363 _should_reset = false; 364 _aborted = false; 365 } 366 367 bool WorkGangBarrierSync::enter() { 368 MonitorLocker ml(monitor(), Mutex::_no_safepoint_check_flag); 369 if (should_reset()) { 370 // The should_reset() was set and we are the first worker to enter 371 // the sync barrier. We will zero the n_completed() count which 372 // effectively resets the barrier. 373 zero_completed(); 374 set_should_reset(false); 375 } 376 inc_completed(); 377 if (n_completed() == n_workers()) { 378 // At this point we would like to reset the barrier to be ready in 379 // case it is used again. However, we cannot set n_completed() to 380 // 0, even after the notify_all(), given that some other workers 381 // might still be waiting for n_completed() to become == 382 // n_workers(). So, if we set n_completed() to 0, those workers 383 // will get stuck (as they will wake up, see that n_completed() != 384 // n_workers() and go back to sleep). Instead, we raise the 385 // should_reset() flag and the barrier will be reset the first 386 // time a worker enters it again. 387 set_should_reset(true); 388 ml.notify_all(); 389 } else { 390 while (n_completed() != n_workers() && !aborted()) { 391 ml.wait(); 392 } 393 } 394 return !aborted(); 395 } 396 397 void WorkGangBarrierSync::abort() { 398 MutexLocker x(monitor(), Mutex::_no_safepoint_check_flag); 399 set_aborted(); 400 monitor()->notify_all(); 401 } 402 403 // SubTasksDone functions. 404 405 SubTasksDone::SubTasksDone(uint n) : 406 _tasks(NULL), _n_tasks(n), _threads_completed(0) { 407 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal); 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::try_claim_task(uint t) { 426 assert(t < _n_tasks, "bad task id."); 427 uint old = _tasks[t]; 428 if (old == 0) { 429 old = Atomic::cmpxchg(1u, &_tasks[t], 0u); 430 } 431 bool res = old == 0; 432 #ifdef ASSERT 433 if (res) { 434 assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?"); 435 Atomic::inc(&_claimed); 436 } 437 #endif 438 return res; 439 } 440 441 void SubTasksDone::all_tasks_completed(uint n_threads) { 442 uint observed = _threads_completed; 443 uint old; 444 do { 445 old = observed; 446 observed = Atomic::cmpxchg(old+1, &_threads_completed, old); 447 } while (observed != old); 448 // If this was the last thread checking in, clear the tasks. 449 uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads); 450 if (observed + 1 == adjusted_thread_count) { 451 clear(); 452 } 453 } 454 455 456 SubTasksDone::~SubTasksDone() { 457 FREE_C_HEAP_ARRAY(uint, _tasks); 458 } 459 460 // *** SequentialSubTasksDone 461 462 void SequentialSubTasksDone::clear() { 463 _n_tasks = _n_claimed = 0; 464 _n_threads = _n_completed = 0; 465 } 466 467 bool SequentialSubTasksDone::valid() { 468 return _n_threads > 0; 469 } 470 471 bool SequentialSubTasksDone::try_claim_task(uint& t) { 472 t = _n_claimed; 473 while (t < _n_tasks) { 474 uint res = Atomic::cmpxchg(t+1, &_n_claimed, t); 475 if (res == t) { 476 return true; 477 } 478 t = res; 479 } 480 return false; 481 } 482 483 bool SequentialSubTasksDone::all_tasks_completed() { 484 uint complete = _n_completed; 485 while (true) { 486 uint res = Atomic::cmpxchg(complete+1, &_n_completed, complete); 487 if (res == complete) { 488 break; 489 } 490 complete = res; 491 } 492 if (complete+1 == _n_threads) { 493 clear(); 494 return true; 495 } 496 return false; 497 }