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 70 _created_workers = WorkerManager::add_workers(this, 71 active_workers, 72 _total_workers, 73 _created_workers, 74 worker_type, 75 initializing); 76 _active_workers = MIN2(_created_workers, _active_workers); 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 = (uint) Atomic::add(1, (volatile jint*)&_started); 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 = (uint) Atomic::add(-1, (volatile jint*)&_not_finished); 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 _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)), 190 _started(0), 191 _finished(0), 192 _num_workers(0) {} 193 194 ~MutexGangTaskDispatcher() { 195 delete _monitor; 196 } 197 198 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) { 199 MutexLockerEx 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 _monitor->wait(/* no_safepoint_check */ true); 210 } 211 212 _task = NULL; 213 _num_workers = 0; 214 _started = 0; 215 _finished = 0; 216 } 217 218 WorkData worker_wait_for_task() { 219 MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag); 220 221 while (_num_workers == 0 || _started == _num_workers) { 222 _monitor->wait(/* no_safepoint_check */ true); 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 MonitorLockerEx 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 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) { 262 return new GangWorker(this, worker_id); 263 } 264 265 void WorkGang::run_task(AbstractGangTask* task) { 266 run_task(task, active_workers()); 267 } 268 269 void WorkGang::run_task(AbstractGangTask* task, uint num_workers) { 270 guarantee(num_workers <= total_workers(), 271 "Trying to execute task %s with %u workers which is more than the amount of total workers %u.", 272 task->name(), num_workers, total_workers()); 273 guarantee(num_workers > 0, "Trying to execute task %s with zero workers", task->name()); 274 add_workers(num_workers, false); 275 _dispatcher->coordinator_execute_on_workers(task, num_workers); 276 } 277 278 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) { 279 _gang = gang; 280 set_id(id); 281 set_name("%s#%d", gang->name(), id); 282 } 283 284 void AbstractGangWorker::run() { 285 initialize(); 286 loop(); 287 } 288 289 void AbstractGangWorker::initialize() { 290 this->record_stack_base_and_size(); 291 this->initialize_named_thread(); 292 assert(_gang != NULL, "No gang to run in"); 293 os::set_priority(this, NearMaxPriority); 294 log_develop_trace(gc, workgang)("Running gang worker for gang %s id %u", gang()->name(), id()); 295 // The VM thread should not execute here because MutexLocker's are used 296 // as (opposed to MutexLockerEx's). 297 assert(!Thread::current()->is_VM_thread(), "VM thread should not be part" 298 " of a work gang"); 299 } 300 301 bool AbstractGangWorker::is_GC_task_thread() const { 302 return gang()->are_GC_task_threads(); 303 } 304 305 bool AbstractGangWorker::is_ConcurrentGC_thread() const { 306 return gang()->are_ConcurrentGC_threads(); 307 } 308 309 void AbstractGangWorker::print_on(outputStream* st) const { 310 st->print("\"%s\" ", name()); 311 Thread::print_on(st); 312 st->cr(); 313 } 314 315 WorkData GangWorker::wait_for_task() { 316 return gang()->dispatcher()->worker_wait_for_task(); 317 } 318 319 void GangWorker::signal_task_done() { 320 gang()->dispatcher()->worker_done_with_task(); 321 } 322 323 void GangWorker::run_task(WorkData data) { 324 GCIdMark gc_id_mark(data._task->gc_id()); 325 log_develop_trace(gc, workgang)("Running work gang: %s task: %s worker: %u", name(), data._task->name(), data._worker_id); 326 327 data._task->work(data._worker_id); 328 329 log_develop_trace(gc, workgang)("Finished work gang: %s task: %s worker: %u thread: " PTR_FORMAT, 330 name(), data._task->name(), data._worker_id, p2i(Thread::current())); 331 } 332 333 void GangWorker::loop() { 334 while (true) { 335 WorkData data = wait_for_task(); 336 337 run_task(data); 338 339 signal_task_done(); 340 } 341 } 342 343 // *** WorkGangBarrierSync 344 345 WorkGangBarrierSync::WorkGangBarrierSync() 346 : _monitor(Mutex::safepoint, "work gang barrier sync", true, 347 Monitor::_safepoint_check_never), 348 _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) { 349 } 350 351 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name) 352 : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never), 353 _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) { 354 } 355 356 void WorkGangBarrierSync::set_n_workers(uint n_workers) { 357 _n_workers = n_workers; 358 _n_completed = 0; 359 _should_reset = false; 360 _aborted = false; 361 } 362 363 bool WorkGangBarrierSync::enter() { 364 MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag); 365 if (should_reset()) { 366 // The should_reset() was set and we are the first worker to enter 367 // the sync barrier. We will zero the n_completed() count which 368 // effectively resets the barrier. 369 zero_completed(); 370 set_should_reset(false); 371 } 372 inc_completed(); 373 if (n_completed() == n_workers()) { 374 // At this point we would like to reset the barrier to be ready in 375 // case it is used again. However, we cannot set n_completed() to 376 // 0, even after the notify_all(), given that some other workers 377 // might still be waiting for n_completed() to become == 378 // n_workers(). So, if we set n_completed() to 0, those workers 379 // will get stuck (as they will wake up, see that n_completed() != 380 // n_workers() and go back to sleep). Instead, we raise the 381 // should_reset() flag and the barrier will be reset the first 382 // time a worker enters it again. 383 set_should_reset(true); 384 monitor()->notify_all(); 385 } else { 386 while (n_completed() != n_workers() && !aborted()) { 387 monitor()->wait(/* no_safepoint_check */ true); 388 } 389 } 390 return !aborted(); 391 } 392 393 void WorkGangBarrierSync::abort() { 394 MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag); 395 set_aborted(); 396 monitor()->notify_all(); 397 } 398 399 // SubTasksDone functions. 400 401 SubTasksDone::SubTasksDone(uint n) : 402 _n_tasks(n), _tasks(NULL) { 403 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal); 404 guarantee(_tasks != NULL, "alloc failure"); 405 clear(); 406 } 407 408 bool SubTasksDone::valid() { 409 return _tasks != NULL; 410 } 411 412 void SubTasksDone::clear() { 413 for (uint i = 0; i < _n_tasks; i++) { 414 _tasks[i] = 0; 415 } 416 _threads_completed = 0; 417 #ifdef ASSERT 418 _claimed = 0; 419 #endif 420 } 421 422 bool SubTasksDone::is_task_claimed(uint t) { 423 assert(t < _n_tasks, "bad task id."); 424 uint old = _tasks[t]; 425 if (old == 0) { 426 old = Atomic::cmpxchg(1, &_tasks[t], 0); 427 } 428 assert(_tasks[t] == 1, "What else?"); 429 bool res = old != 0; 430 #ifdef ASSERT 431 if (!res) { 432 assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?"); 433 Atomic::inc((volatile jint*) &_claimed); 434 } 435 #endif 436 return res; 437 } 438 439 void SubTasksDone::all_tasks_completed(uint n_threads) { 440 jint observed = _threads_completed; 441 jint old; 442 do { 443 old = observed; 444 observed = Atomic::cmpxchg(old+1, &_threads_completed, old); 445 } while (observed != old); 446 // If this was the last thread checking in, clear the tasks. 447 uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads); 448 if (observed + 1 == (jint)adjusted_thread_count) { 449 clear(); 450 } 451 } 452 453 454 SubTasksDone::~SubTasksDone() { 455 if (_tasks != NULL) FREE_C_HEAP_ARRAY(jint, _tasks); 456 } 457 458 // *** SequentialSubTasksDone 459 460 void SequentialSubTasksDone::clear() { 461 _n_tasks = _n_claimed = 0; 462 _n_threads = _n_completed = 0; 463 } 464 465 bool SequentialSubTasksDone::valid() { 466 return _n_threads > 0; 467 } 468 469 bool SequentialSubTasksDone::is_task_claimed(uint& t) { 470 uint* n_claimed_ptr = &_n_claimed; 471 t = *n_claimed_ptr; 472 while (t < _n_tasks) { 473 jint res = Atomic::cmpxchg(t+1, n_claimed_ptr, t); 474 if (res == (jint)t) { 475 return false; 476 } 477 t = *n_claimed_ptr; 478 } 479 return true; 480 } 481 482 bool SequentialSubTasksDone::all_tasks_completed() { 483 uint* n_completed_ptr = &_n_completed; 484 uint complete = *n_completed_ptr; 485 while (true) { 486 uint res = Atomic::cmpxchg(complete+1, n_completed_ptr, 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 }