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 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 = (uint) Atomic::add(1, (volatile jint*)&_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 = (uint) Atomic::add(-1, (volatile jint*)&_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 _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)), 193 _started(0), 194 _finished(0), 195 _num_workers(0) {} 196 197 ~MutexGangTaskDispatcher() { 198 delete _monitor; 199 } 200 201 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) { 202 MutexLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag); 203 204 _task = task; 205 _num_workers = num_workers; 206 207 // Tell the workers to get to work. 208 _monitor->notify_all(); 209 210 // Wait for them to finish. 211 while (_finished < _num_workers) { 212 _monitor->wait(/* no_safepoint_check */ true); 213 } 214 215 _task = NULL; 216 _num_workers = 0; 217 _started = 0; 218 _finished = 0; 219 } 220 221 WorkData worker_wait_for_task() { 222 MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag); 223 224 while (_num_workers == 0 || _started == _num_workers) { 225 _monitor->wait(/* no_safepoint_check */ true); 226 } 227 228 _started++; 229 230 // Subtract one to get a zero-indexed worker id. 231 uint worker_id = _started - 1; 232 233 return WorkData(_task, worker_id); 234 } 235 236 void worker_done_with_task() { 237 MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag); 238 239 _finished++; 240 241 if (_finished == _num_workers) { 242 // This will wake up all workers and not only the coordinator. 243 _monitor->notify_all(); 244 } 245 } 246 }; 247 248 static GangTaskDispatcher* create_dispatcher() { 249 if (UseSemaphoreGCThreadsSynchronization) { 250 return new SemaphoreGangTaskDispatcher(); 251 } 252 253 return new MutexGangTaskDispatcher(); 254 } 255 256 WorkGang::WorkGang(const char* name, 257 uint workers, 258 bool are_GC_task_threads, 259 bool are_ConcurrentGC_threads) : 260 AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads), 261 _dispatcher(create_dispatcher()) 262 { } 263 264 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) { 265 return new GangWorker(this, worker_id); 266 } 267 268 void WorkGang::run_task(AbstractGangTask* task) { 269 run_task(task, active_workers()); 270 } 271 272 void WorkGang::run_task(AbstractGangTask* task, uint num_workers) { 273 guarantee(num_workers <= total_workers(), 274 "Trying to execute task %s with %u workers which is more than the amount of total workers %u.", 275 task->name(), num_workers, total_workers()); 276 guarantee(num_workers > 0, "Trying to execute task %s with zero workers", task->name()); 277 add_workers(num_workers, false); 278 _dispatcher->coordinator_execute_on_workers(task, num_workers); 279 } 280 281 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) { 282 _gang = gang; 283 set_id(id); 284 set_name("%s#%d", gang->name(), id); 285 } 286 287 void AbstractGangWorker::run() { 288 initialize(); 289 loop(); 290 } 291 292 void AbstractGangWorker::initialize() { 293 this->record_stack_base_and_size(); 294 this->initialize_named_thread(); 295 assert(_gang != NULL, "No gang to run in"); 296 os::set_priority(this, NearMaxPriority); 297 log_develop_trace(gc, workgang)("Running gang worker for gang %s id %u", gang()->name(), id()); 298 // The VM thread should not execute here because MutexLocker's are used 299 // as (opposed to MutexLockerEx's). 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 WorkData GangWorker::wait_for_task() { 319 return gang()->dispatcher()->worker_wait_for_task(); 320 } 321 322 void GangWorker::signal_task_done() { 323 gang()->dispatcher()->worker_done_with_task(); 324 } 325 326 void GangWorker::run_task(WorkData data) { 327 GCIdMark gc_id_mark(data._task->gc_id()); 328 log_develop_trace(gc, workgang)("Running work gang: %s task: %s worker: %u", name(), data._task->name(), data._worker_id); 329 330 data._task->work(data._worker_id); 331 332 log_develop_trace(gc, workgang)("Finished work gang: %s task: %s worker: %u thread: " PTR_FORMAT, 333 name(), data._task->name(), data._worker_id, p2i(Thread::current())); 334 } 335 336 void GangWorker::loop() { 337 while (true) { 338 WorkData data = wait_for_task(); 339 340 run_task(data); 341 342 signal_task_done(); 343 } 344 } 345 346 // *** WorkGangBarrierSync 347 348 WorkGangBarrierSync::WorkGangBarrierSync() 349 : _monitor(Mutex::safepoint, "work gang barrier sync", true, 350 Monitor::_safepoint_check_never), 351 _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) { 352 } 353 354 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name) 355 : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never), 356 _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) { 357 } 358 359 void WorkGangBarrierSync::set_n_workers(uint n_workers) { 360 _n_workers = n_workers; 361 _n_completed = 0; 362 _should_reset = false; 363 _aborted = false; 364 } 365 366 bool WorkGangBarrierSync::enter() { 367 MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag); 368 if (should_reset()) { 369 // The should_reset() was set and we are the first worker to enter 370 // the sync barrier. We will zero the n_completed() count which 371 // effectively resets the barrier. 372 zero_completed(); 373 set_should_reset(false); 374 } 375 inc_completed(); 376 if (n_completed() == n_workers()) { 377 // At this point we would like to reset the barrier to be ready in 378 // case it is used again. However, we cannot set n_completed() to 379 // 0, even after the notify_all(), given that some other workers 380 // might still be waiting for n_completed() to become == 381 // n_workers(). So, if we set n_completed() to 0, those workers 382 // will get stuck (as they will wake up, see that n_completed() != 383 // n_workers() and go back to sleep). Instead, we raise the 384 // should_reset() flag and the barrier will be reset the first 385 // time a worker enters it again. 386 set_should_reset(true); 387 monitor()->notify_all(); 388 } else { 389 while (n_completed() != n_workers() && !aborted()) { 390 monitor()->wait(/* no_safepoint_check */ true); 391 } 392 } 393 return !aborted(); 394 } 395 396 void WorkGangBarrierSync::abort() { 397 MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag); 398 set_aborted(); 399 monitor()->notify_all(); 400 } 401 402 // SubTasksDone functions. 403 404 SubTasksDone::SubTasksDone(uint n) : 405 _n_tasks(n), _tasks(NULL) { 406 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal); 407 guarantee(_tasks != NULL, "alloc failure"); 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::is_task_claimed(uint t) { 426 assert(t < _n_tasks, "bad task id."); 427 uint old = _tasks[t]; 428 if (old == 0) { 429 old = Atomic::cmpxchg(1, &_tasks[t], 0); 430 } 431 assert(_tasks[t] == 1, "What else?"); 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((volatile jint*) &_claimed); 437 } 438 #endif 439 return res; 440 } 441 442 void SubTasksDone::all_tasks_completed(uint n_threads) { 443 jint observed = _threads_completed; 444 jint old; 445 do { 446 old = observed; 447 observed = Atomic::cmpxchg(old+1, &_threads_completed, old); 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 == (jint)adjusted_thread_count) { 452 clear(); 453 } 454 } 455 456 457 SubTasksDone::~SubTasksDone() { 458 if (_tasks != NULL) FREE_C_HEAP_ARRAY(jint, _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::is_task_claimed(uint& t) { 473 uint* n_claimed_ptr = &_n_claimed; 474 t = *n_claimed_ptr; 475 while (t < _n_tasks) { 476 jint res = Atomic::cmpxchg(t+1, n_claimed_ptr, t); 477 if (res == (jint)t) { 478 return false; 479 } 480 t = *n_claimed_ptr; 481 } 482 return true; 483 } 484 485 bool SequentialSubTasksDone::all_tasks_completed() { 486 uint* n_completed_ptr = &_n_completed; 487 uint complete = *n_completed_ptr; 488 while (true) { 489 uint res = Atomic::cmpxchg(complete+1, n_completed_ptr, complete); 490 if (res == complete) { 491 break; 492 } 493 complete = res; 494 } 495 if (complete+1 == _n_threads) { 496 clear(); 497 return true; 498 } 499 return false; 500 }