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 }