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 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 add_workers(_active_workers, initializing); 59 } 60 61 void AbstractWorkGang::add_workers(uint active_workers, bool initializing) { 62 63 os::ThreadType worker_type; 64 if (are_ConcurrentGC_threads()) { 65 worker_type = os::cgc_thread; 66 } else { 67 worker_type = os::pgc_thread; 68 } 69 uint previous_created_workers = _created_workers; 70 71 _created_workers = WorkerManager::add_workers(this, 72 active_workers, 73 _total_workers, 74 _created_workers, 75 worker_type, 76 initializing); 77 _active_workers = MIN2(_created_workers, _active_workers); 78 79 WorkerManager::log_worker_creation(this, previous_created_workers, _active_workers, _created_workers, initializing); 80 } 81 82 AbstractGangWorker* AbstractWorkGang::worker(uint i) const { 83 // Array index bounds checking. 84 AbstractGangWorker* result = NULL; 85 assert(_workers != NULL, "No workers for indexing"); 86 assert(i < total_workers(), "Worker index out of bounds"); 87 result = _workers[i]; 88 assert(result != NULL, "Indexing to null worker"); 89 return result; 90 } 91 92 void AbstractWorkGang::print_worker_threads_on(outputStream* st) const { 93 uint workers = created_workers(); 94 for (uint i = 0; i < workers; i++) { 95 worker(i)->print_on(st); 96 st->cr(); 97 } 98 } 99 100 void AbstractWorkGang::threads_do(ThreadClosure* tc) const { 101 assert(tc != NULL, "Null ThreadClosure"); 102 uint workers = created_workers(); 103 for (uint i = 0; i < workers; i++) { 104 tc->do_thread(worker(i)); 105 } 106 } 107 108 // WorkGang dispatcher implemented with semaphores. 109 // 110 // Semaphores don't require the worker threads to re-claim the lock when they wake up. 111 // This helps lowering the latency when starting and stopping the worker threads. 112 class SemaphoreGangTaskDispatcher : public GangTaskDispatcher { 113 // The task currently being dispatched to the GangWorkers. 114 AbstractGangTask* _task; 115 116 volatile uint _started; 117 volatile uint _not_finished; 118 119 // Semaphore used to start the GangWorkers. 120 Semaphore* _start_semaphore; 121 // Semaphore used to notify the coordinator that all workers are done. 122 Semaphore* _end_semaphore; 123 124 public: 125 SemaphoreGangTaskDispatcher() : 126 _task(NULL), 127 _started(0), 128 _not_finished(0), 129 _start_semaphore(new Semaphore()), 130 _end_semaphore(new Semaphore()) 131 { } 132 133 ~SemaphoreGangTaskDispatcher() { 134 delete _start_semaphore; 135 delete _end_semaphore; 136 } 137 138 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) { 139 // No workers are allowed to read the state variables until they have been signaled. 140 _task = task; 141 _not_finished = num_workers; 142 143 // Dispatch 'num_workers' number of tasks. 144 _start_semaphore->signal(num_workers); 145 146 // Wait for the last worker to signal the coordinator. 147 _end_semaphore->wait(); 148 149 // No workers are allowed to read the state variables after the coordinator has been signaled. 150 assert(_not_finished == 0, "%d not finished workers?", _not_finished); 151 _task = NULL; 152 _started = 0; 153 154 } 155 156 WorkData worker_wait_for_task() { 157 // Wait for the coordinator to dispatch a task. 158 _start_semaphore->wait(); 159 160 uint num_started = Atomic::add(1u, &_started); 161 162 // Subtract one to get a zero-indexed worker id. 163 uint worker_id = num_started - 1; 164 165 return WorkData(_task, worker_id); 166 } 167 168 void worker_done_with_task() { 169 // Mark that the worker is done with the task. 170 // The worker is not allowed to read the state variables after this line. 171 uint not_finished = Atomic::sub(1u, &_not_finished); 172 173 // The last worker signals to the coordinator that all work is completed. 174 if (not_finished == 0) { 175 _end_semaphore->signal(); 176 } 177 } 178 }; 179 180 class MutexGangTaskDispatcher : public GangTaskDispatcher { 181 AbstractGangTask* _task; 182 183 volatile uint _started; 184 volatile uint _finished; 185 volatile uint _num_workers; 186 187 Monitor* _monitor; 188 189 public: 190 MutexGangTaskDispatcher() : 191 _task(NULL), 192 _started(0), 193 _finished(0), 194 _num_workers(0), 195 _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)) { 196 } 197 198 ~MutexGangTaskDispatcher() { 199 delete _monitor; 200 } 201 202 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) { 203 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag); 204 205 _task = task; 206 _num_workers = num_workers; 207 208 // Tell the workers to get to work. 209 _monitor->notify_all(); 210 211 // Wait for them to finish. 212 while (_finished < _num_workers) { 213 ml.wait(); 214 } 215 216 _task = NULL; 217 _num_workers = 0; 218 _started = 0; 219 _finished = 0; 220 } 221 222 WorkData worker_wait_for_task() { 223 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag); 224 225 while (_num_workers == 0 || _started == _num_workers) { 226 _monitor->wait(); 227 } 228 229 _started++; 230 231 // Subtract one to get a zero-indexed worker id. 232 uint worker_id = _started - 1; 233 234 return WorkData(_task, worker_id); 235 } 236 237 void worker_done_with_task() { 238 MonitorLocker ml(_monitor, Mutex::_no_safepoint_check_flag); 239 240 _finished++; 241 242 if (_finished == _num_workers) { 243 // This will wake up all workers and not only the coordinator. 244 _monitor->notify_all(); 245 } 246 } 247 }; 248 249 static GangTaskDispatcher* create_dispatcher() { 250 if (UseSemaphoreGCThreadsSynchronization) { 251 return new SemaphoreGangTaskDispatcher(); 252 } 253 254 return new MutexGangTaskDispatcher(); 255 } 256 257 WorkGang::WorkGang(const char* name, 258 uint workers, 259 bool are_GC_task_threads, 260 bool are_ConcurrentGC_threads) : 261 AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads), 262 _dispatcher(create_dispatcher()) 263 { } 264 265 WorkGang::~WorkGang() { 266 delete _dispatcher; 267 } 268 269 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) { 270 return new GangWorker(this, worker_id); 271 } 272 273 void WorkGang::run_task(AbstractGangTask* task) { 274 run_task(task, active_workers()); 275 } 276 277 void WorkGang::run_task(AbstractGangTask* task, uint num_workers) { 278 guarantee(num_workers <= total_workers(), 279 "Trying to execute task %s with %u workers which is more than the amount of total workers %u.", 280 task->name(), num_workers, total_workers()); 281 guarantee(num_workers > 0, "Trying to execute task %s with zero workers", task->name()); 282 uint old_num_workers = _active_workers; 283 update_active_workers(num_workers); 284 _dispatcher->coordinator_execute_on_workers(task, num_workers); 285 update_active_workers(old_num_workers); 286 } 287 288 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) { 289 _gang = gang; 290 set_id(id); 291 set_name("%s#%d", gang->name(), id); 292 } 293 294 void AbstractGangWorker::run() { 295 initialize(); 296 loop(); 297 } 298 299 void AbstractGangWorker::initialize() { 300 assert(_gang != NULL, "No gang to run in"); 301 os::set_priority(this, NearMaxPriority); 302 log_develop_trace(gc, workgang)("Running gang worker for gang %s id %u", gang()->name(), id()); 303 assert(!Thread::current()->is_VM_thread(), "VM thread should not be part" 304 " of a work gang"); 305 } 306 307 bool AbstractGangWorker::is_GC_task_thread() const { 308 return gang()->are_GC_task_threads(); 309 } 310 311 bool AbstractGangWorker::is_ConcurrentGC_thread() const { 312 return gang()->are_ConcurrentGC_threads(); 313 } 314 315 void AbstractGangWorker::print_on(outputStream* st) const { 316 st->print("\"%s\" ", name()); 317 Thread::print_on(st); 318 st->cr(); 319 } 320 321 void AbstractGangWorker::print() const { print_on(tty); } 322 323 WorkData GangWorker::wait_for_task() { 324 return gang()->dispatcher()->worker_wait_for_task(); 325 } 326 327 void GangWorker::signal_task_done() { 328 gang()->dispatcher()->worker_done_with_task(); 329 } 330 331 void GangWorker::run_task(WorkData data) { 332 GCIdMark gc_id_mark(data._task->gc_id()); 333 log_develop_trace(gc, workgang)("Running work gang: %s task: %s worker: %u", name(), data._task->name(), data._worker_id); 334 335 data._task->work(data._worker_id); 336 337 log_develop_trace(gc, workgang)("Finished work gang: %s task: %s worker: %u thread: " PTR_FORMAT, 338 name(), data._task->name(), data._worker_id, p2i(Thread::current())); 339 } 340 341 void GangWorker::loop() { 342 while (true) { 343 WorkData data = wait_for_task(); 344 345 run_task(data); 346 347 signal_task_done(); 348 } 349 } 350 351 // *** WorkGangBarrierSync 352 353 WorkGangBarrierSync::WorkGangBarrierSync() 354 : _monitor(Mutex::safepoint, "work gang barrier sync", true, 355 Monitor::_safepoint_check_never), 356 _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) { 357 } 358 359 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name) 360 : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never), 361 _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) { 362 } 363 364 void WorkGangBarrierSync::set_n_workers(uint n_workers) { 365 _n_workers = n_workers; 366 _n_completed = 0; 367 _should_reset = false; 368 _aborted = false; 369 } 370 371 bool WorkGangBarrierSync::enter() { 372 MonitorLocker ml(monitor(), Mutex::_no_safepoint_check_flag); 373 if (should_reset()) { 374 // The should_reset() was set and we are the first worker to enter 375 // the sync barrier. We will zero the n_completed() count which 376 // effectively resets the barrier. 377 zero_completed(); 378 set_should_reset(false); 379 } 380 inc_completed(); 381 if (n_completed() == n_workers()) { 382 // At this point we would like to reset the barrier to be ready in 383 // case it is used again. However, we cannot set n_completed() to 384 // 0, even after the notify_all(), given that some other workers 385 // might still be waiting for n_completed() to become == 386 // n_workers(). So, if we set n_completed() to 0, those workers 387 // will get stuck (as they will wake up, see that n_completed() != 388 // n_workers() and go back to sleep). Instead, we raise the 389 // should_reset() flag and the barrier will be reset the first 390 // time a worker enters it again. 391 set_should_reset(true); 392 ml.notify_all(); 393 } else { 394 while (n_completed() != n_workers() && !aborted()) { 395 ml.wait(); 396 } 397 } 398 return !aborted(); 399 } 400 401 void WorkGangBarrierSync::abort() { 402 MutexLocker x(monitor(), Mutex::_no_safepoint_check_flag); 403 set_aborted(); 404 monitor()->notify_all(); 405 } 406 407 // SubTasksDone functions. 408 409 SubTasksDone::SubTasksDone(uint n) : 410 _tasks(NULL), _n_tasks(n), _threads_completed(0) { 411 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal); 412 guarantee(_tasks != NULL, "alloc failure"); 413 clear(); 414 } 415 416 bool SubTasksDone::valid() { 417 return _tasks != NULL; 418 } 419 420 void SubTasksDone::clear() { 421 for (uint i = 0; i < _n_tasks; i++) { 422 _tasks[i] = 0; 423 } 424 _threads_completed = 0; 425 #ifdef ASSERT 426 _claimed = 0; 427 #endif 428 } 429 430 bool SubTasksDone::try_claim_task(uint t) { 431 assert(t < _n_tasks, "bad task id."); 432 uint old = _tasks[t]; 433 if (old == 0) { 434 old = Atomic::cmpxchg(1u, &_tasks[t], 0u); 435 } 436 bool res = old == 0; 437 #ifdef ASSERT 438 if (res) { 439 assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?"); 440 Atomic::inc(&_claimed); 441 } 442 #endif 443 return res; 444 } 445 446 void SubTasksDone::all_tasks_completed(uint n_threads) { 447 uint observed = _threads_completed; 448 uint old; 449 do { 450 old = observed; 451 observed = Atomic::cmpxchg(old+1, &_threads_completed, old); 452 } while (observed != old); 453 // If this was the last thread checking in, clear the tasks. 454 uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads); 455 if (observed + 1 == adjusted_thread_count) { 456 clear(); 457 } 458 } 459 460 461 SubTasksDone::~SubTasksDone() { 462 if (_tasks != NULL) FREE_C_HEAP_ARRAY(uint, _tasks); 463 } 464 465 // *** SequentialSubTasksDone 466 467 void SequentialSubTasksDone::clear() { 468 _n_tasks = _n_claimed = 0; 469 _n_threads = _n_completed = 0; 470 } 471 472 bool SequentialSubTasksDone::valid() { 473 return _n_threads > 0; 474 } 475 476 bool SequentialSubTasksDone::try_claim_task(uint& t) { 477 t = _n_claimed; 478 while (t < _n_tasks) { 479 uint res = Atomic::cmpxchg(t+1, &_n_claimed, t); 480 if (res == t) { 481 return true; 482 } 483 t = res; 484 } 485 return false; 486 } 487 488 bool SequentialSubTasksDone::all_tasks_completed() { 489 uint complete = _n_completed; 490 while (true) { 491 uint res = Atomic::cmpxchg(complete+1, &_n_completed, complete); 492 if (res == complete) { 493 break; 494 } 495 complete = res; 496 } 497 if (complete+1 == _n_threads) { 498 clear(); 499 return true; 500 } 501 return false; 502 }