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/workgroup.hpp"
  27 #include "memory/allocation.hpp"
  28 #include "memory/allocation.inline.hpp"
  29 #include "runtime/atomic.inline.hpp"
  30 #include "runtime/os.hpp"
  31 #include "runtime/thread.inline.hpp"
  32 #include "utilities/semaphore.hpp"
  33 
  34 // Definitions of WorkGang methods.
  35 
  36 // The current implementation will exit if the allocation
  37 // of any worker fails.  Still, return a boolean so that
  38 // a future implementation can possibly do a partial
  39 // initialization of the workers and report such to the
  40 // caller.
  41 bool AbstractWorkGang::initialize_workers() {
  42 
  43   if (TraceWorkGang) {
  44     tty->print_cr("Constructing work gang %s with %d threads",
  45                   name(),
  46                   total_workers());
  47   }
  48   _workers = NEW_C_HEAP_ARRAY(AbstractGangWorker*, total_workers(), mtInternal);
  49   if (_workers == NULL) {
  50     vm_exit_out_of_memory(0, OOM_MALLOC_ERROR, "Cannot create GangWorker array.");
  51     return false;
  52   }
  53   os::ThreadType worker_type;
  54   if (are_ConcurrentGC_threads()) {
  55     worker_type = os::cgc_thread;
  56   } else {
  57     worker_type = os::pgc_thread;
  58   }
  59   for (uint worker = 0; worker < total_workers(); worker += 1) {
  60     AbstractGangWorker* new_worker = allocate_worker(worker);
  61     assert(new_worker != NULL, "Failed to allocate GangWorker");
  62     _workers[worker] = new_worker;
  63     if (new_worker == NULL || !os::create_thread(new_worker, worker_type)) {
  64       vm_exit_out_of_memory(0, OOM_MALLOC_ERROR,
  65               "Cannot create worker GC thread. Out of system resources.");
  66       return false;
  67     }
  68     if (!DisableStartThread) {
  69       os::start_thread(new_worker);
  70     }
  71   }
  72   return true;
  73 }
  74 
  75 AbstractGangWorker* AbstractWorkGang::worker(uint i) const {
  76   // Array index bounds checking.
  77   AbstractGangWorker* result = NULL;
  78   assert(_workers != NULL, "No workers for indexing");
  79   assert(i < total_workers(), "Worker index out of bounds");
  80   result = _workers[i];
  81   assert(result != NULL, "Indexing to null worker");
  82   return result;
  83 }
  84 
  85 void AbstractWorkGang::print_worker_threads_on(outputStream* st) const {
  86   uint workers = total_workers();
  87   for (uint i = 0; i < workers; i++) {
  88     worker(i)->print_on(st);
  89     st->cr();
  90   }
  91 }
  92 
  93 void AbstractWorkGang::threads_do(ThreadClosure* tc) const {
  94   assert(tc != NULL, "Null ThreadClosure");
  95   uint workers = total_workers();
  96   for (uint i = 0; i < workers; i++) {
  97     tc->do_thread(worker(i));
  98   }
  99 }
 100 
 101 #if IMPLEMENTS_SEMAPHORE_CLASS
 102 
 103 // WorkGang dispatcher implemented with semaphores.
 104 //
 105 // Semaphores don't require the worker threads to re-claim the lock when they wake up.
 106 // This helps lowering the latency when starting and stopping the worker threads.
 107 class SemaphoreGangTaskDispatcher : public GangTaskDispatcher {
 108   // The task currently being dispatched to the GangWorkers.
 109   AbstractGangTask* _task;
 110 
 111   volatile uint _started;
 112   volatile uint _not_finished;
 113 
 114   // Semaphore used to start the GangWorkers.
 115   Semaphore* _start_semaphore;
 116   // Semaphore used to notify the coordinator that all workers are done.
 117   Semaphore* _end_semaphore;
 118 
 119 public:
 120   SemaphoreGangTaskDispatcher(uint workers) :
 121       _task(NULL),
 122       _started(0),
 123       _not_finished(0),
 124       // Limit the semaphore value to the number of workers.
 125       _start_semaphore(new Semaphore(0, workers)),
 126       _end_semaphore(new Semaphore(0, workers))
 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     _task         = NULL;
 147     _started      = 0;
 148     _not_finished = 0;
 149   }
 150 
 151   WorkData worker_wait_for_task() {
 152     // Wait for the coordinator to dispatch a task.
 153     _start_semaphore->wait();
 154 
 155     uint num_started = (uint) Atomic::add(1, (volatile jint*)&_started);
 156 
 157     // Subtract one to get a zero-indexed worker id.
 158     uint worker_id = num_started - 1;
 159 
 160     return WorkData(_task, worker_id);
 161   }
 162 
 163   void worker_done_with_task() {
 164     // Mark that the worker is done with the task.
 165     // The worker is not allowed to read the state variables after this line.
 166     uint not_finished = (uint) Atomic::add(-1, (volatile jint*)&_not_finished);
 167 
 168     // The last worker signals to the coordinator that all work is completed.
 169     if (not_finished == 0) {
 170       _end_semaphore->signal();
 171     }
 172   }
 173 };
 174 #endif // IMPLEMENTS_SEMAPHORE_CLASS
 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         _monitor(new Monitor(Monitor::leaf, "WorkGang dispatcher lock", false, Monitor::_safepoint_check_never)),
 189         _started(0),
 190         _finished(0),
 191         _num_workers(0) {}
 192 
 193   ~MutexGangTaskDispatcher() {
 194     delete _monitor;
 195   }
 196 
 197   void coordinator_execute_on_workers(AbstractGangTask* task, uint num_workers) {
 198     MutexLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag);
 199 
 200     _task        = task;
 201     _num_workers = num_workers;
 202 
 203     // Tell the workers to get to work.
 204     _monitor->notify_all();
 205 
 206     // Wait for them to finish.
 207     while (_finished < _num_workers) {
 208       _monitor->wait(/* no_safepoint_check */ true);
 209     }
 210 
 211     _task        = NULL;
 212     _num_workers = 0;
 213     _started     = 0;
 214     _finished    = 0;
 215   }
 216 
 217   WorkData worker_wait_for_task() {
 218     MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag);
 219 
 220     while (_num_workers == 0 || _started == _num_workers) {
 221       _monitor->wait(/* no_safepoint_check */ true);
 222     }
 223 
 224     _started++;
 225 
 226     // Subtract one to get a zero-indexed worker id.
 227     uint worker_id = _started - 1;
 228 
 229     return WorkData(_task, worker_id);
 230   }
 231 
 232   void worker_done_with_task() {
 233     MonitorLockerEx ml(_monitor, Mutex::_no_safepoint_check_flag);
 234 
 235     _finished++;
 236 
 237     if (_finished == _num_workers) {
 238       // This will wake up all workers and not only the coordinator.
 239       _monitor->notify_all();
 240     }
 241   }
 242 };
 243 
 244 static GangTaskDispatcher* create_dispatcher(uint workers) {
 245 #if IMPLEMENTS_SEMAPHORE_CLASS
 246   if (UseSemaphoreGCThreadsSynchronization) {
 247     return new SemaphoreGangTaskDispatcher(workers);
 248   }
 249 #endif
 250 
 251   return new MutexGangTaskDispatcher();
 252 }
 253 
 254 WorkGang::WorkGang(const char* name,
 255                    uint  workers,
 256                    bool  are_GC_task_threads,
 257                    bool  are_ConcurrentGC_threads,
 258                    GangTaskDispatcher* dispatcher) :
 259     AbstractWorkGang(name, workers, are_GC_task_threads, are_ConcurrentGC_threads),
 260     _dispatcher(dispatcher != NULL ? dispatcher: create_dispatcher(workers))
 261 { }
 262 
 263 AbstractGangWorker* WorkGang::allocate_worker(uint worker_id) {
 264   return new GangWorker(this, worker_id);
 265 }
 266 
 267 void WorkGang::run_task(AbstractGangTask* task) {
 268   _dispatcher->coordinator_execute_on_workers(task, active_workers());
 269 }
 270 
 271 AbstractGangWorker::AbstractGangWorker(AbstractWorkGang* gang, uint id) {
 272   _gang = gang;
 273   set_id(id);
 274   set_name("%s#%d", gang->name(), id);
 275 }
 276 
 277 void AbstractGangWorker::run() {
 278   initialize();
 279   loop();
 280 }
 281 
 282 void AbstractGangWorker::initialize() {
 283   this->initialize_thread_local_storage();
 284   this->record_stack_base_and_size();
 285   this->initialize_named_thread();
 286   assert(_gang != NULL, "No gang to run in");
 287   os::set_priority(this, NearMaxPriority);
 288   if (TraceWorkGang) {
 289     tty->print_cr("Running gang worker for gang %s id %u",
 290                   gang()->name(), id());
 291   }
 292   // The VM thread should not execute here because MutexLocker's are used
 293   // as (opposed to MutexLockerEx's).
 294   assert(!Thread::current()->is_VM_thread(), "VM thread should not be part"
 295          " of a work gang");
 296 }
 297 
 298 bool AbstractGangWorker::is_GC_task_thread() const {
 299   return gang()->are_GC_task_threads();
 300 }
 301 
 302 bool AbstractGangWorker::is_ConcurrentGC_thread() const {
 303   return gang()->are_ConcurrentGC_threads();
 304 }
 305 
 306 void AbstractGangWorker::print_on(outputStream* st) const {
 307   st->print("\"%s\" ", name());
 308   Thread::print_on(st);
 309   st->cr();
 310 }
 311 
 312 WorkData GangWorker::wait_for_task() {
 313   return gang()->dispatcher()->worker_wait_for_task();
 314 }
 315 
 316 void GangWorker::signal_task_done() {
 317   gang()->dispatcher()->worker_done_with_task();
 318 }
 319 
 320 void GangWorker::print_task_started(WorkData data) {
 321   if (TraceWorkGang) {
 322     tty->print_cr("Running work gang %s task %s worker %u", name(), data._task->name(), data._worker_id);
 323   }
 324 }
 325 
 326 void GangWorker::print_task_done(WorkData data) {
 327   if (TraceWorkGang) {
 328     tty->print_cr("\nFinished work gang %s task %s worker %u", name(), data._task->name(), data._worker_id);
 329     Thread* me = Thread::current();
 330     tty->print_cr("  T: " PTR_FORMAT "  VM_thread: %d", p2i(me), me->is_VM_thread());
 331   }
 332 }
 333 
 334 void GangWorker::run_task(WorkData data) {
 335   print_task_started(data);
 336 
 337   data._task->work(data._worker_id);
 338 
 339   print_task_done(data);
 340 }
 341 
 342 void GangWorker::loop() {
 343   while (true) {
 344     WorkData data = wait_for_task();
 345 
 346     run_task(data);
 347 
 348     signal_task_done();
 349   }
 350 }
 351 
 352 // *** WorkGangBarrierSync
 353 
 354 WorkGangBarrierSync::WorkGangBarrierSync()
 355   : _monitor(Mutex::safepoint, "work gang barrier sync", true,
 356              Monitor::_safepoint_check_never),
 357     _n_workers(0), _n_completed(0), _should_reset(false), _aborted(false) {
 358 }
 359 
 360 WorkGangBarrierSync::WorkGangBarrierSync(uint n_workers, const char* name)
 361   : _monitor(Mutex::safepoint, name, true, Monitor::_safepoint_check_never),
 362     _n_workers(n_workers), _n_completed(0), _should_reset(false), _aborted(false) {
 363 }
 364 
 365 void WorkGangBarrierSync::set_n_workers(uint n_workers) {
 366   _n_workers    = n_workers;
 367   _n_completed  = 0;
 368   _should_reset = false;
 369   _aborted      = false;
 370 }
 371 
 372 bool WorkGangBarrierSync::enter() {
 373   MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag);
 374   if (should_reset()) {
 375     // The should_reset() was set and we are the first worker to enter
 376     // the sync barrier. We will zero the n_completed() count which
 377     // effectively resets the barrier.
 378     zero_completed();
 379     set_should_reset(false);
 380   }
 381   inc_completed();
 382   if (n_completed() == n_workers()) {
 383     // At this point we would like to reset the barrier to be ready in
 384     // case it is used again. However, we cannot set n_completed() to
 385     // 0, even after the notify_all(), given that some other workers
 386     // might still be waiting for n_completed() to become ==
 387     // n_workers(). So, if we set n_completed() to 0, those workers
 388     // will get stuck (as they will wake up, see that n_completed() !=
 389     // n_workers() and go back to sleep). Instead, we raise the
 390     // should_reset() flag and the barrier will be reset the first
 391     // time a worker enters it again.
 392     set_should_reset(true);
 393     monitor()->notify_all();
 394   } else {
 395     while (n_completed() != n_workers() && !aborted()) {
 396       monitor()->wait(/* no_safepoint_check */ true);
 397     }
 398   }
 399   return !aborted();
 400 }
 401 
 402 void WorkGangBarrierSync::abort() {
 403   MutexLockerEx x(monitor(), Mutex::_no_safepoint_check_flag);
 404   set_aborted();
 405   monitor()->notify_all();
 406 }
 407 
 408 // SubTasksDone functions.
 409 
 410 SubTasksDone::SubTasksDone(uint n) :
 411   _n_tasks(n), _tasks(NULL) {
 412   _tasks = NEW_C_HEAP_ARRAY(uint, n, mtInternal);
 413   guarantee(_tasks != NULL, "alloc failure");
 414   clear();
 415 }
 416 
 417 bool SubTasksDone::valid() {
 418   return _tasks != NULL;
 419 }
 420 
 421 void SubTasksDone::clear() {
 422   for (uint i = 0; i < _n_tasks; i++) {
 423     _tasks[i] = 0;
 424   }
 425   _threads_completed = 0;
 426 #ifdef ASSERT
 427   _claimed = 0;
 428 #endif
 429 }
 430 
 431 bool SubTasksDone::is_task_claimed(uint t) {
 432   assert(t < _n_tasks, "bad task id.");
 433   uint old = _tasks[t];
 434   if (old == 0) {
 435     old = Atomic::cmpxchg(1, &_tasks[t], 0);
 436   }
 437   assert(_tasks[t] == 1, "What else?");
 438   bool res = old != 0;
 439 #ifdef ASSERT
 440   if (!res) {
 441     assert(_claimed < _n_tasks, "Too many tasks claimed; missing clear?");
 442     Atomic::inc((volatile jint*) &_claimed);
 443   }
 444 #endif
 445   return res;
 446 }
 447 
 448 void SubTasksDone::all_tasks_completed(uint n_threads) {
 449   jint observed = _threads_completed;
 450   jint old;
 451   do {
 452     old = observed;
 453     observed = Atomic::cmpxchg(old+1, &_threads_completed, old);
 454   } while (observed != old);
 455   // If this was the last thread checking in, clear the tasks.
 456   uint adjusted_thread_count = (n_threads == 0 ? 1 : n_threads);
 457   if (observed + 1 == (jint)adjusted_thread_count) {
 458     clear();
 459   }
 460 }
 461 
 462 
 463 SubTasksDone::~SubTasksDone() {
 464   if (_tasks != NULL) FREE_C_HEAP_ARRAY(jint, _tasks);
 465 }
 466 
 467 // *** SequentialSubTasksDone
 468 
 469 void SequentialSubTasksDone::clear() {
 470   _n_tasks   = _n_claimed   = 0;
 471   _n_threads = _n_completed = 0;
 472 }
 473 
 474 bool SequentialSubTasksDone::valid() {
 475   return _n_threads > 0;
 476 }
 477 
 478 bool SequentialSubTasksDone::is_task_claimed(uint& t) {
 479   uint* n_claimed_ptr = &_n_claimed;
 480   t = *n_claimed_ptr;
 481   while (t < _n_tasks) {
 482     jint res = Atomic::cmpxchg(t+1, n_claimed_ptr, t);
 483     if (res == (jint)t) {
 484       return false;
 485     }
 486     t = *n_claimed_ptr;
 487   }
 488   return true;
 489 }
 490 
 491 bool SequentialSubTasksDone::all_tasks_completed() {
 492   uint* n_completed_ptr = &_n_completed;
 493   uint  complete        = *n_completed_ptr;
 494   while (true) {
 495     uint res = Atomic::cmpxchg(complete+1, n_completed_ptr, complete);
 496     if (res == complete) {
 497       break;
 498     }
 499     complete = res;
 500   }
 501   if (complete+1 == _n_threads) {
 502     clear();
 503     return true;
 504   }
 505   return false;
 506 }
 507 
 508 bool FreeIdSet::_stat_init = false;
 509 FreeIdSet* FreeIdSet::_sets[NSets];
 510 bool FreeIdSet::_safepoint;
 511 
 512 FreeIdSet::FreeIdSet(int sz, Monitor* mon) :
 513   _sz(sz), _mon(mon), _hd(0), _waiters(0), _index(-1), _claimed(0)
 514 {
 515   _ids = NEW_C_HEAP_ARRAY(int, sz, mtInternal);
 516   for (int i = 0; i < sz; i++) _ids[i] = i+1;
 517   _ids[sz-1] = end_of_list; // end of list.
 518   if (_stat_init) {
 519     for (int j = 0; j < NSets; j++) _sets[j] = NULL;
 520     _stat_init = true;
 521   }
 522   // Add to sets.  (This should happen while the system is still single-threaded.)
 523   for (int j = 0; j < NSets; j++) {
 524     if (_sets[j] == NULL) {
 525       _sets[j] = this;
 526       _index = j;
 527       break;
 528     }
 529   }
 530   guarantee(_index != -1, "Too many FreeIdSets in use!");
 531 }
 532 
 533 FreeIdSet::~FreeIdSet() {
 534   _sets[_index] = NULL;
 535   FREE_C_HEAP_ARRAY(int, _ids);
 536 }
 537 
 538 void FreeIdSet::set_safepoint(bool b) {
 539   _safepoint = b;
 540   if (b) {
 541     for (int j = 0; j < NSets; j++) {
 542       if (_sets[j] != NULL && _sets[j]->_waiters > 0) {
 543         Monitor* mon = _sets[j]->_mon;
 544         mon->lock_without_safepoint_check();
 545         mon->notify_all();
 546         mon->unlock();
 547       }
 548     }
 549   }
 550 }
 551 
 552 #define FID_STATS 0
 553 
 554 int FreeIdSet::claim_par_id() {
 555 #if FID_STATS
 556   thread_t tslf = thr_self();
 557   tty->print("claim_par_id[%d]: sz = %d, claimed = %d\n", tslf, _sz, _claimed);
 558 #endif
 559   MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag);
 560   while (!_safepoint && _hd == end_of_list) {
 561     _waiters++;
 562 #if FID_STATS
 563     if (_waiters > 5) {
 564       tty->print("claim_par_id waiting[%d]: %d waiters, %d claimed.\n",
 565                  tslf, _waiters, _claimed);
 566     }
 567 #endif
 568     _mon->wait(Mutex::_no_safepoint_check_flag);
 569     _waiters--;
 570   }
 571   if (_hd == end_of_list) {
 572 #if FID_STATS
 573     tty->print("claim_par_id[%d]: returning EOL.\n", tslf);
 574 #endif
 575     return -1;
 576   } else {
 577     int res = _hd;
 578     _hd = _ids[res];
 579     _ids[res] = claimed;  // For debugging.
 580     _claimed++;
 581 #if FID_STATS
 582     tty->print("claim_par_id[%d]: returning %d, claimed = %d.\n",
 583                tslf, res, _claimed);
 584 #endif
 585     return res;
 586   }
 587 }
 588 
 589 bool FreeIdSet::claim_perm_id(int i) {
 590   assert(0 <= i && i < _sz, "Out of range.");
 591   MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag);
 592   int prev = end_of_list;
 593   int cur = _hd;
 594   while (cur != end_of_list) {
 595     if (cur == i) {
 596       if (prev == end_of_list) {
 597         _hd = _ids[cur];
 598       } else {
 599         _ids[prev] = _ids[cur];
 600       }
 601       _ids[cur] = claimed;
 602       _claimed++;
 603       return true;
 604     } else {
 605       prev = cur;
 606       cur = _ids[cur];
 607     }
 608   }
 609   return false;
 610 
 611 }
 612 
 613 void FreeIdSet::release_par_id(int id) {
 614   MutexLockerEx x(_mon, Mutex::_no_safepoint_check_flag);
 615   assert(_ids[id] == claimed, "Precondition.");
 616   _ids[id] = _hd;
 617   _hd = id;
 618   _claimed--;
 619 #if FID_STATS
 620   tty->print("[%d] release_par_id(%d), waiters =%d,  claimed = %d.\n",
 621              thr_self(), id, _waiters, _claimed);
 622 #endif
 623   if (_waiters > 0)
 624     // Notify all would be safer, but this is OK, right?
 625     _mon->notify_all();
 626 }
 627 
 628 /////////////// Unit tests ///////////////
 629 
 630 #ifndef PRODUCT
 631 
 632 class CountTask : public AbstractGangTask {
 633   volatile jint _count;
 634   bool _sleep;
 635  public:
 636   CountTask(bool sleep) : AbstractGangTask("CountTask"), _sleep(sleep), _count(0) {}
 637   virtual void work(uint worker_id) {
 638     if (_sleep) {
 639       // Sleep a while, to delay the task to allow the coordinator to run.
 640       os::sleep(Thread::current(), 100, false);
 641     }
 642 
 643     // Count number of times executed.
 644     Atomic::inc(&_count);
 645   }
 646   uint count() { return _count; }
 647 };
 648 
 649 
 650 static void test_workgang_dispatch(bool use_semaphore,
 651                                    uint total_workers,
 652                                    uint active_workers,
 653                                    bool sleep) {
 654 
 655   GangTaskDispatcher* dispatcher = use_semaphore
 656       ? (GangTaskDispatcher*) new SemGangTaskDispatcher(total_workers)
 657       : (GangTaskDispatcher*) new MutexGangTaskDispatcher();
 658 
 659   // Intentionally leaking WorkGang, since there's no support to delete WorkGangs.
 660   WorkGang* gang = new WorkGang("Test WorkGang", total_workers, false, false, dispatcher);
 661   gang->initialize_workers();
 662 
 663   gang->set_active_workers(active_workers);
 664 
 665   CountTask task(sleep);
 666 
 667   gang->run_task(&task);
 668 
 669   uint task_count = task.count();
 670 
 671   assert(task_count == active_workers, err_msg("Expected count: %u got: %u", active_workers, task_count));
 672 }
 673 
 674 static void test_workgang_dispatch(bool use_semaphore) {
 675   const bool sleep = true;
 676   const uint total_workers = 8;
 677   for (uint active_workers = 1; active_workers <= 4; active_workers++) {
 678     test_workgang_dispatch(use_semaphore, total_workers, active_workers, sleep);
 679     test_workgang_dispatch(use_semaphore, total_workers, active_workers, !sleep);
 680   }
 681 }
 682 
 683 static void test_workgang_dispatch_mutex() {
 684   test_workgang_dispatch(false);
 685 }
 686 
 687 static void test_workgang_dispatch_semaphore() {
 688   test_workgang_dispatch(true);
 689 }
 690 
 691 void test_workgang() {
 692   // Needed to use dynamic number of active workers.
 693   FlagSetting fs(UseDynamicNumberOfGCThreads, true);
 694 
 695   test_workgang_dispatch_semaphore();
 696   test_workgang_dispatch_mutex();
 697 }
 698 
 699 #endif // PRODUCT