1 /* 2 * Copyright (c) 2001, 2015, 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 "memory/allocation.hpp" 29 #include "memory/allocation.inline.hpp" 30 #include "runtime/atomic.inline.hpp" 31 #include "runtime/os.hpp" 32 #include "runtime/semaphore.hpp" 33 #include "runtime/thread.inline.hpp" 34 35 // Definitions of WorkGang methods. 36 37 // The current implementation will exit if the allocation 38 // of any worker fails. Still, return a boolean so that 39 // a future implementation can possibly do a partial 40 // initialization of the workers and report such to the 41 // caller. 42 bool AbstractWorkGang::initialize_workers() { 43 44 if (TraceWorkGang) { 45 tty->print_cr("Constructing work gang %s with %d threads", 46 name(), 47 total_workers()); 48 } 49 _workers = NEW_C_HEAP_ARRAY(AbstractGangWorker*, total_workers(), mtInternal); 50 if (_workers == NULL) { 51 vm_exit_out_of_memory(0, OOM_MALLOC_ERROR, "Cannot create GangWorker array."); 52 return false; 53 } 54 os::ThreadType worker_type; 55 if (are_ConcurrentGC_threads()) { 56 worker_type = os::cgc_thread; 57 } else { 58 worker_type = os::pgc_thread; 59 } 60 for (uint worker = 0; worker < total_workers(); worker += 1) { 61 AbstractGangWorker* new_worker = allocate_worker(worker); 62 assert(new_worker != NULL, "Failed to allocate GangWorker"); 63 _workers[worker] = new_worker; 64 if (new_worker == NULL || !os::create_thread(new_worker, worker_type)) { 65 vm_exit_out_of_memory(0, OOM_MALLOC_ERROR, 66 "Cannot create worker GC thread. Out of system resources."); 67 return false; 68 } 69 if (!DisableStartThread) { 70 os::start_thread(new_worker); 71 } 72 } 73 return true; 74 } 75 76 AbstractGangWorker* AbstractWorkGang::worker(uint i) const { 77 // Array index bounds checking. 78 AbstractGangWorker* result = NULL; 79 assert(_workers != NULL, "No workers for indexing"); 80 assert(i < total_workers(), "Worker index out of bounds"); 81 result = _workers[i]; 82 assert(result != NULL, "Indexing to null worker"); 83 return result; 84 } 85 86 void AbstractWorkGang::print_worker_threads_on(outputStream* st) const { 87 uint workers = total_workers(); 88 for (uint i = 0; i < workers; i++) { 89 worker(i)->print_on(st); 90 st->cr(); 91 } 92 } 93 94 void AbstractWorkGang::threads_do(ThreadClosure* tc) const { 95 assert(tc != NULL, "Null ThreadClosure"); 96 uint workers = total_workers(); 97 for (uint i = 0; i < workers; i++) { 98 tc->do_thread(worker(i)); 99 } 100 } 101 102 // WorkGang dispatcher implemented with semaphores. 103 // 104 // Semaphores don't require the worker threads to re-claim the lock when they wake up. 105 // This helps lowering the latency when starting and stopping the worker threads. 106 class SemaphoreGangTaskDispatcher : public GangTaskDispatcher { 107 // The task currently being dispatched to the GangWorkers. 108 AbstractGangTask* _task; 109 110 volatile uint _started; 111 volatile uint _not_finished; 112 113 // Semaphore used to start the GangWorkers. 114 Semaphore* _start_semaphore; 115 // Semaphore used to notify the coordinator that all workers are done. 116 Semaphore* _end_semaphore; 117 118 public: 119 SemaphoreGangTaskDispatcher() : 120 _task(NULL), 121 _started(0), 122 _not_finished(0), 123 _start_semaphore(new Semaphore()), 124 _end_semaphore(new Semaphore()) 125 { } 126 127 ~SemaphoreGangTaskDispatcher() { 128 delete _start_semaphore; 129 delete _end_semaphore; 130 } 131 132 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) { 133 // No workers are allowed to read the state variables until they have been signaled. 134 _task = task; 135 _not_finished = num_workers; 136 137 // Dispatch 'num_workers' number of tasks. 138 _start_semaphore->signal(num_workers); 139 140 // Wait for the last worker to signal the coordinator. 141 _end_semaphore->wait(); 142 143 // No workers are allowed to read the state variables after the coordinator has been signaled. 144 assert(_not_finished == 0, "%d not finished workers?", _not_finished); 145 _task = NULL; 146 _started = 0; 147 148 } 149 150 WorkData worker_wait_for_task() { 151 // Wait for the coordinator to dispatch a task. 152 _start_semaphore->wait(); 153 154 uint num_started = (uint) Atomic::add(1, (volatile jint*)&_started); 155 156 // Subtract one to get a zero-indexed worker id. 157 uint worker_id = num_started - 1; 158 159 return WorkData(_task, worker_id); 160 } 161 162 void worker_done_with_task() { 163 // Mark that the worker is done with the task. 164 // The worker is not allowed to read the state variables after this line. 165 uint not_finished = (uint) Atomic::add(-1, (volatile jint*)&_not_finished); 166 167 // The last worker signals to the coordinator that all work is completed. 168 if (not_finished == 0) { 169 _end_semaphore->signal(); 170 } 171 } 172 }; 173 174 class MutexGangTaskDispatcher : public GangTaskDispatcher { 175 AbstractGangTask* _task; 176 177 volatile uint _started; 178 volatile uint _finished; 179 volatile uint _num_workers; 180 181 Monitor* _monitor; 182 183 public: 184 MutexGangTaskDispatcher() 185 : _task(NULL), 186 _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)), 187 _started(0), 188 _finished(0), 189 _num_workers(0) {} 190 191 ~MutexGangTaskDispatcher() { 192 delete _monitor; 193 } 194 195 void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) { 196 MutexLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag); 197 198 _task = task; 199 _num_workers = num_workers; 200 201 // Tell the workers to get to work. 202 _monitor->notify_all(); 203 204 // Wait for them to finish. 205 while (_finished < _num_workers) { 206 _monitor->wait(/* no_safepoint_check */ true); 207 } 208 209 _task = NULL; 210 _num_workers = 0; 211 _started = 0; 212 _finished = 0; 213 } 214 215 WorkData worker_wait_for_task() { 216 MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag); 217 218 while (_num_workers == 0 || _started == _num_workers) { 219 _monitor->wait(/* no_safepoint_check */ true); 220 } 221 222 _started++; 223 224 // Subtract one to get a zero-indexed worker id. 225 uint worker_id = _started - 1; 226 227 return WorkData(_task, worker_id); 228 } 229 230 void worker_done_with_task() { 231 MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag); 232 233 _finished++; 234 235 if (_finished == _num_workers) { 236 // This will wake up all workers and not only the coordinator. 237 _monitor->notify_all(); 238 } 239 } 240 }; 241 242 static GangTaskDispatcher* create_dispatcher() { 243 if (UseSemaphoreGCThreadsSynchronization) { 244 return new SemaphoreGangTaskDispatcher(); 245 } 246 247 return new MutexGangTaskDispatcher(); 248 } 249 250 WorkGang::WorkGang(const char* name, 251 uint workers, 252 bool are_GC_task_threads, 253 bool are_ConcurrentGC_threads) : 254 AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads), 255 _dispatcher(create_dispatcher()) 256 { } 257 258 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) { 259 return new GangWorker(this, worker_id); 260 } 261 262 void WorkGang::run_task(AbstractGangTask* task) { 263 _dispatcher->coordinator_execute_on_workers(task, active_workers()); 264 } 265 266 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) { 267 _gang = gang; 268 set_id(id); 269 set_name("%s#%d", gang->name(), id); 270 } 271 272 void AbstractGangWorker::run() { 273 initialize(); 274 loop(); 275 } 276 277 void AbstractGangWorker::initialize() { 278 this->record_stack_base_and_size(); 279 this->initialize_named_thread(); 280 assert(_gang != NULL, "No gang to run in"); 281 os::set_priority(this, NearMaxPriority); 282 if (TraceWorkGang) { 283 tty->print_cr("Running gang worker for gang %s id %u", 284 gang()->name(), id()); 285 } 286 // The VM thread should not execute here because MutexLocker's are used 287 // as (opposed to MutexLockerEx's). 288 assert(!Thread::current()->is_VM_thread(), "VM thread should not be part" 289 " of a work gang"); 290 } 291 292 bool AbstractGangWorker::is_GC_task_thread() const { 293 return gang()->are_GC_task_threads(); 294 } 295 296 bool AbstractGangWorker::is_ConcurrentGC_thread() const { 297 return gang()->are_ConcurrentGC_threads(); 298 } 299 300 void AbstractGangWorker::print_on(outputStream* st) const { 301 st->print("\"%s\" ", name()); 302 Thread::print_on(st); 303 st->cr(); 304 } 305 306 WorkData GangWorker::wait_for_task() { 307 return gang()->dispatcher()->worker_wait_for_task(); 308 } 309 310 void GangWorker::signal_task_done() { 311 gang()->dispatcher()->worker_done_with_task(); 312 } 313 314 void GangWorker::print_task_started(WorkData data) { 315 if (TraceWorkGang) { 316 tty->print_cr("Running work gang %s task %s worker %u", name(), data._task->name(), data._worker_id); 317 } 318 } 319 320 void GangWorker::print_task_done(WorkData data) { 321 if (TraceWorkGang) { 322 tty->print_cr("\nFinished work gang %s task %s worker %u", name(), data._task->name(), data._worker_id); 323 Thread* me = Thread::current(); 324 tty->print_cr(" T: " PTR_FORMAT " VM_thread: %d", p2i(me), me->is_VM_thread()); 325 } 326 } 327 328 void GangWorker::run_task(WorkData data) { 329 print_task_started(data); 330 331 GCIdMark gc_id_mark(data._task->gc_id()); 332 data._task->work(data._worker_id); 333 334 print_task_done(data); 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 MutexLockerEx x(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 monitor()->notify_all(); 389 } else { 390 while (n_completed() != n_workers() && !aborted()) { 391 monitor()->wait(/* no_safepoint_check */ true); 392 } 393 } 394 return !aborted(); 395 } 396 397 void WorkGangBarrierSync::abort() { 398 MutexLockerEx 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 _n_tasks(n), _tasks(NULL) { 407 _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal); 408 guarantee(_tasks != NULL, "alloc failure"); 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::is_task_claimed(uint t) { 427 assert(t < _n_tasks, "bad task id."); 428 uint old = _tasks[t]; 429 if (old == 0) { 430 old = Atomic::cmpxchg(1, &_tasks[t], 0); 431 } 432 assert(_tasks[t] == 1, "What else?"); 433 bool res = old != 0; 434 #ifdef ASSERT 435 if (!res) { 436 assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?"); 437 Atomic::inc((volatile jint*) &_claimed); 438 } 439 #endif 440 return res; 441 } 442 443 void SubTasksDone::all_tasks_completed(uint n_threads) { 444 jint observed = _threads_completed; 445 jint old; 446 do { 447 old = observed; 448 observed = Atomic::cmpxchg(old+1, &_threads_completed, old); 449 } while (observed != old); 450 // If this was the last thread checking in, clear the tasks. 451 uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads); 452 if (observed + 1 == (jint)adjusted_thread_count) { 453 clear(); 454 } 455 } 456 457 458 SubTasksDone::~SubTasksDone() { 459 if (_tasks != NULL) FREE_C_HEAP_ARRAY(jint, _tasks); 460 } 461 462 // *** SequentialSubTasksDone 463 464 void SequentialSubTasksDone::clear() { 465 _n_tasks = _n_claimed = 0; 466 _n_threads = _n_completed = 0; 467 } 468 469 bool SequentialSubTasksDone::valid() { 470 return _n_threads > 0; 471 } 472 473 bool SequentialSubTasksDone::is_task_claimed(uint& t) { 474 uint* n_claimed_ptr = &_n_claimed; 475 t = *n_claimed_ptr; 476 while (t < _n_tasks) { 477 jint res = Atomic::cmpxchg(t+1, n_claimed_ptr, t); 478 if (res == (jint)t) { 479 return false; 480 } 481 t = *n_claimed_ptr; 482 } 483 return true; 484 } 485 486 bool SequentialSubTasksDone::all_tasks_completed() { 487 uint* n_completed_ptr = &_n_completed; 488 uint complete = *n_completed_ptr; 489 while (true) { 490 uint res = Atomic::cmpxchg(complete+1, n_completed_ptr, complete); 491 if (res == complete) { 492 break; 493 } 494 complete = res; 495 } 496 if (complete+1 == _n_threads) { 497 clear(); 498 return true; 499 } 500 return false; 501 } 502 503 FreeIdSet::FreeIdSet(uint size, Monitor* mon) : 504 _size(size), _mon(mon), _hd(0), _waiters(0), _claimed(0) 505 { 506 guarantee(size != 0, "must be"); 507 _ids = NEW_C_HEAP_ARRAY(uint, size, mtGC); 508 for (uint i = 0; i < size - 1; i++) { 509 _ids[i] = i+1; 510 } 511 _ids[size-1] = end_of_list; // end of list. 512 } 513 514 FreeIdSet::~FreeIdSet() { 515 FREE_C_HEAP_ARRAY(uint, _ids); 516 } 517 518 uint FreeIdSet::claim_par_id() { 519 MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag); 520 while (_hd == end_of_list) { 521 _waiters++; 522 _mon->wait(Mutex::_no_safepoint_check_flag); 523 _waiters--; 524 } 525 uint res = _hd; 526 _hd = _ids[res]; 527 _ids[res] = claimed; // For debugging. 528 _claimed++; 529 return res; 530 } 531 532 void FreeIdSet::release_par_id(uint id) { 533 MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag); 534 assert(_ids[id] == claimed, "Precondition."); 535 _ids[id] = _hd; 536 _hd = id; 537 _claimed--; 538 if (_waiters > 0) { 539 _mon->notify_all(); 540 } 541 }