rev 57079 : imported patch 8234796

   1 /*
   2  * Copyright (c) 1998, 2019, 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 "compiler/compileBroker.hpp"
  27 #include "gc/shared/collectedHeap.hpp"
  28 #include "jfr/jfrEvents.hpp"
  29 #include "jfr/support/jfrThreadId.hpp"
  30 #include "logging/log.hpp"
  31 #include "logging/logStream.hpp"
  32 #include "logging/logConfiguration.hpp"
  33 #include "memory/resourceArea.hpp"
  34 #include "memory/universe.hpp"
  35 #include "oops/method.hpp"
  36 #include "oops/oop.inline.hpp"
  37 #include "oops/verifyOopClosure.hpp"
  38 #include "runtime/handles.inline.hpp"
  39 #include "runtime/interfaceSupport.inline.hpp"
  40 #include "runtime/mutexLocker.hpp"
  41 #include "runtime/os.hpp"
  42 #include "runtime/safepoint.hpp"
  43 #include "runtime/thread.inline.hpp"
  44 #include "runtime/vmThread.hpp"
  45 #include "runtime/vmOperations.hpp"
  46 #include "services/runtimeService.hpp"
  47 #include "utilities/dtrace.hpp"
  48 #include "utilities/events.hpp"
  49 #include "utilities/vmError.hpp"
  50 #include "utilities/xmlstream.hpp"
  51 
  52 VMOperationQueue::VMOperationQueue() {
  53   // The queue is a circular doubled-linked list, which always contains
  54   // one element (i.e., one element means empty).
  55   for(int i = 0; i < nof_priorities; i++) {
  56     _queue_length[i] = 0;
  57     _queue_counter = 0;
  58     _queue[i] = new VM_None("QueueHead");
  59     _queue[i]->set_next(_queue[i]);
  60     _queue[i]->set_prev(_queue[i]);
  61   }
  62   _drain_list = NULL;
  63 }
  64 
  65 
  66 bool VMOperationQueue::queue_empty(int prio) {
  67   // It is empty if there is exactly one element
  68   bool empty = (_queue[prio] == _queue[prio]->next());
  69   assert( (_queue_length[prio] == 0 && empty) ||
  70           (_queue_length[prio] > 0  && !empty), "sanity check");
  71   return _queue_length[prio] == 0;
  72 }
  73 
  74 // Inserts an element to the right of the q element
  75 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
  76   assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
  77   n->set_prev(q);
  78   n->set_next(q->next());
  79   q->next()->set_prev(n);
  80   q->set_next(n);
  81 }
  82 
  83 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
  84   _queue_length[prio]++;
  85   insert(_queue[prio]->next(), op);
  86 }
  87 
  88 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
  89   _queue_length[prio]++;
  90   insert(_queue[prio]->prev(), op);
  91 }
  92 
  93 
  94 void VMOperationQueue::unlink(VM_Operation* q) {
  95   assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
  96   q->prev()->set_next(q->next());
  97   q->next()->set_prev(q->prev());
  98 }
  99 
 100 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
 101   if (queue_empty(prio)) return NULL;
 102   assert(_queue_length[prio] >= 0, "sanity check");
 103   _queue_length[prio]--;
 104   VM_Operation* r = _queue[prio]->next();
 105   assert(r != _queue[prio], "cannot remove base element");
 106   unlink(r);
 107   return r;
 108 }
 109 
 110 VM_Operation* VMOperationQueue::queue_drain(int prio) {
 111   if (queue_empty(prio)) return NULL;
 112   DEBUG_ONLY(int length = _queue_length[prio];);
 113   assert(length >= 0, "sanity check");
 114   _queue_length[prio] = 0;
 115   VM_Operation* r = _queue[prio]->next();
 116   assert(r != _queue[prio], "cannot remove base element");
 117   // remove links to base element from head and tail
 118   r->set_prev(NULL);
 119   _queue[prio]->prev()->set_next(NULL);
 120   // restore queue to empty state
 121   _queue[prio]->set_next(_queue[prio]);
 122   _queue[prio]->set_prev(_queue[prio]);
 123   assert(queue_empty(prio), "drain corrupted queue");
 124 #ifdef ASSERT
 125   int len = 0;
 126   VM_Operation* cur;
 127   for(cur = r; cur != NULL; cur=cur->next()) len++;
 128   assert(len == length, "drain lost some ops");
 129 #endif
 130   return r;
 131 }
 132 
 133 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
 134   VM_Operation* cur = _queue[queue];
 135   cur = cur->next();
 136   while (cur != _queue[queue]) {
 137     cur->oops_do(f);
 138     cur = cur->next();
 139   }
 140 }
 141 
 142 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
 143   VM_Operation* cur = _drain_list;
 144   while (cur != NULL) {
 145     cur->oops_do(f);
 146     cur = cur->next();
 147   }
 148 }
 149 
 150 //-----------------------------------------------------------------
 151 // High-level interface
 152 void VMOperationQueue::add(VM_Operation *op) {
 153 
 154   HOTSPOT_VMOPS_REQUEST(
 155                    (char *) op->name(), strlen(op->name()),
 156                    op->evaluation_mode());
 157 
 158   // Encapsulates VM queue policy. Currently, that
 159   // only involves putting them on the right list
 160   queue_add_back(op->evaluate_at_safepoint() ? SafepointPriority : MediumPriority, op);
 161 }
 162 
 163 VM_Operation* VMOperationQueue::remove_next() {
 164   // Assuming VMOperation queue is two-level priority queue. If there are
 165   // more than two priorities, we need a different scheduling algorithm.
 166   assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
 167          "current algorithm does not work");
 168 
 169   // simple counter based scheduling to prevent starvation of lower priority
 170   // queue. -- see 4390175
 171   int high_prio, low_prio;
 172   if (_queue_counter++ < 10) {
 173       high_prio = SafepointPriority;
 174       low_prio  = MediumPriority;
 175   } else {
 176       _queue_counter = 0;
 177       high_prio = MediumPriority;
 178       low_prio  = SafepointPriority;
 179   }
 180 
 181   return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
 182 }
 183 
 184 void VMOperationQueue::oops_do(OopClosure* f) {
 185   for(int i = 0; i < nof_priorities; i++) {
 186     queue_oops_do(i, f);
 187   }
 188   drain_list_oops_do(f);
 189 }
 190 
 191 //------------------------------------------------------------------------------------------------------------------
 192 // Timeout machinery
 193 
 194 void VMOperationTimeoutTask::task() {
 195   assert(AbortVMOnVMOperationTimeout, "only if enabled");
 196   if (is_armed()) {
 197     jlong delay = (os::javaTimeMillis() - _arm_time);
 198     if (delay > AbortVMOnVMOperationTimeoutDelay) {
 199       fatal("VM operation took too long: " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)",
 200             delay, AbortVMOnVMOperationTimeoutDelay);
 201     }
 202   }
 203 }
 204 
 205 bool VMOperationTimeoutTask::is_armed() {
 206   return OrderAccess::load_acquire(&_armed) != 0;
 207 }
 208 
 209 void VMOperationTimeoutTask::arm() {
 210   _arm_time = os::javaTimeMillis();
 211   OrderAccess::release_store_fence(&_armed, 1);
 212 }
 213 
 214 void VMOperationTimeoutTask::disarm() {
 215   OrderAccess::release_store_fence(&_armed, 0);
 216 }
 217 
 218 //------------------------------------------------------------------------------------------------------------------
 219 // Implementation of VMThread stuff
 220 
 221 bool              VMThread::_should_terminate   = false;
 222 bool              VMThread::_terminated         = false;
 223 Monitor*          VMThread::_terminate_lock     = NULL;
 224 VMThread*         VMThread::_vm_thread          = NULL;
 225 VM_Operation*     VMThread::_cur_vm_operation   = NULL;
 226 VMOperationQueue* VMThread::_vm_queue           = NULL;
 227 PerfCounter*      VMThread::_perf_accumulated_vm_operation_time = NULL;
 228 uint64_t          VMThread::_coalesced_count = 0;
 229 VMOperationTimeoutTask* VMThread::_timeout_task = NULL;
 230 
 231 
 232 void VMThread::create() {
 233   assert(vm_thread() == NULL, "we can only allocate one VMThread");
 234   _vm_thread = new VMThread();
 235 
 236   if (AbortVMOnVMOperationTimeout) {
 237     // Make sure we call the timeout task frequently enough, but not too frequent.
 238     // Try to make the interval 10% of the timeout delay, so that we miss the timeout
 239     // by those 10% at max. Periodic task also expects it to fit min/max intervals.
 240     size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10;
 241     interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran;
 242     interval = MAX2<size_t>(interval, PeriodicTask::min_interval);
 243     interval = MIN2<size_t>(interval, PeriodicTask::max_interval);
 244 
 245     _timeout_task = new VMOperationTimeoutTask(interval);
 246     _timeout_task->enroll();
 247   } else {
 248     assert(_timeout_task == NULL, "sanity");
 249   }
 250 
 251   // Create VM operation queue
 252   _vm_queue = new VMOperationQueue();
 253   guarantee(_vm_queue != NULL, "just checking");
 254 
 255   _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
 256                                 Monitor::_safepoint_check_never);
 257 
 258   if (UsePerfData) {
 259     // jvmstat performance counters
 260     Thread* THREAD = Thread::current();
 261     _perf_accumulated_vm_operation_time =
 262                  PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
 263                                                  PerfData::U_Ticks, CHECK);
 264   }
 265 }
 266 
 267 VMThread::VMThread() : NamedThread() {
 268   set_name("VM Thread");
 269 }
 270 
 271 void VMThread::destroy() {
 272   _vm_thread = NULL;      // VM thread is gone
 273 }
 274 
 275 static VM_None halt_op("Halt");
 276 
 277 void VMThread::run() {
 278   assert(this == vm_thread(), "check");
 279 
 280   // Notify_lock wait checks on active_handles() to rewait in
 281   // case of spurious wakeup, it should wait on the last
 282   // value set prior to the notify
 283   this->set_active_handles(JNIHandleBlock::allocate_block());
 284 
 285   {
 286     MutexLocker ml(Notify_lock);
 287     Notify_lock->notify();
 288   }
 289   // Notify_lock is destroyed by Threads::create_vm()
 290 
 291   int prio = (VMThreadPriority == -1)
 292     ? os::java_to_os_priority[NearMaxPriority]
 293     : VMThreadPriority;
 294   // Note that I cannot call os::set_priority because it expects Java
 295   // priorities and I am *explicitly* using OS priorities so that it's
 296   // possible to set the VM thread priority higher than any Java thread.
 297   os::set_native_priority( this, prio );
 298 
 299   // Wait for VM_Operations until termination
 300   this->loop();
 301 
 302   // Note the intention to exit before safepointing.
 303   // 6295565  This has the effect of waiting for any large tty
 304   // outputs to finish.
 305   if (xtty != NULL) {
 306     ttyLocker ttyl;
 307     xtty->begin_elem("destroy_vm");
 308     xtty->stamp();
 309     xtty->end_elem();
 310     assert(should_terminate(), "termination flag must be set");
 311   }
 312 
 313   // 4526887 let VM thread exit at Safepoint
 314   _cur_vm_operation = &halt_op;
 315   SafepointSynchronize::begin();
 316 
 317   if (VerifyBeforeExit) {
 318     HandleMark hm(VMThread::vm_thread());
 319     // Among other things, this ensures that Eden top is correct.
 320     Universe::heap()->prepare_for_verify();
 321     // Silent verification so as not to pollute normal output,
 322     // unless we really asked for it.
 323     Universe::verify();
 324   }
 325 
 326   CompileBroker::set_should_block();
 327 
 328   // wait for threads (compiler threads or daemon threads) in the
 329   // _thread_in_native state to block.
 330   VM_Exit::wait_for_threads_in_native_to_block();
 331 
 332   // signal other threads that VM process is gone
 333   {
 334     // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
 335     // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
 336     // If that happens after _terminate_lock->wait() has unset _owner
 337     // but before it actually drops the lock and waits, the notification below
 338     // may get lost and we will have a hang. To avoid this, we need to use
 339     // Mutex::lock_without_safepoint_check().
 340     MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
 341     _terminated = true;
 342     ml.notify();
 343   }
 344 
 345   // We are now racing with the VM termination being carried out in
 346   // another thread, so we don't "delete this". Numerous threads don't
 347   // get deleted when the VM terminates
 348 
 349 }
 350 
 351 
 352 // Notify the VMThread that the last non-daemon JavaThread has terminated,
 353 // and wait until operation is performed.
 354 void VMThread::wait_for_vm_thread_exit() {
 355   assert(Thread::current()->is_Java_thread(), "Should be a JavaThread");
 356   assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated");
 357   { MonitorLocker mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
 358     _should_terminate = true;
 359     mu.notify();
 360   }
 361 
 362   // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
 363   // because this thread has been removed from the threads list. But anything
 364   // that could get blocked by Safepoint should not be used after this point,
 365   // otherwise we will hang, since there is no one can end the safepoint.
 366 
 367   // Wait until VM thread is terminated
 368   // Note: it should be OK to use Terminator_lock here. But this is called
 369   // at a very delicate time (VM shutdown) and we are operating in non- VM
 370   // thread at Safepoint. It's safer to not share lock with other threads.
 371   { MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
 372     while(!VMThread::is_terminated()) {
 373       ml.wait();
 374     }
 375   }
 376 }
 377 
 378 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
 379   assert(event != NULL, "invariant");
 380   assert(event->should_commit(), "invariant");
 381   assert(op != NULL, "invariant");
 382   const bool is_concurrent = op->evaluate_concurrently();
 383   const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
 384   event->set_operation(op->type());
 385   event->set_safepoint(evaluate_at_safepoint);
 386   event->set_blocking(!is_concurrent);
 387   // Only write caller thread information for non-concurrent vm operations.
 388   // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
 389   // This is because the caller thread could have exited already.
 390   event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread()));
 391   event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0);
 392   event->commit();
 393 }
 394 
 395 void VMThread::evaluate_operation(VM_Operation* op) {
 396   ResourceMark rm;
 397 
 398   {
 399     PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
 400     HOTSPOT_VMOPS_BEGIN(
 401                      (char *) op->name(), strlen(op->name()),
 402                      op->evaluation_mode());
 403 
 404     EventExecuteVMOperation event;
 405     op->evaluate();
 406     if (event.should_commit()) {
 407       post_vm_operation_event(&event, op);
 408     }
 409 
 410     HOTSPOT_VMOPS_END(
 411                      (char *) op->name(), strlen(op->name()),
 412                      op->evaluation_mode());
 413   }
 414 
 415   // Last access of info in _cur_vm_operation!
 416   bool c_heap_allocated = op->is_cheap_allocated();
 417 
 418   // Mark as completed
 419   if (!op->evaluate_concurrently()) {
 420     op->calling_thread()->increment_vm_operation_completed_count();
 421   }
 422   // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
 423   // since if it is stack allocated the calling thread might have deallocated
 424   if (c_heap_allocated) {
 425     delete _cur_vm_operation;
 426   }
 427 }
 428 
 429 static VM_None    safepointALot_op("SafepointALot");
 430 static VM_Cleanup cleanup_op;
 431 
 432 class HandshakeALotHS : public HandshakeOperation {
 433  public:
 434   HandshakeALotHS() : HandshakeOperation("HandshakeALot") {}
 435   void do_thread(JavaThread* jt) {
 436 #ifdef ASSERT


 437     jt->verify_states_for_handshake();
 438 #endif
 439   }
 440 };
 441 
 442 VM_Operation* VMThread::no_op_safepoint() {
 443   // Check for handshakes first since we may need to return a VMop.
 444   if (HandshakeALot) {
 445     HandshakeALotHS halhs;
 446     Handshake::execute(&halhs);
 447   }
 448   // Check for a cleanup before SafepointALot to keep stats correct.
 449   long interval_ms = SafepointTracing::time_since_last_safepoint_ms();
 450   bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
 451                            (interval_ms >= GuaranteedSafepointInterval);
 452   if (max_time_exceeded && SafepointSynchronize::is_cleanup_needed()) {
 453     return &cleanup_op;
 454   }
 455   if (SafepointALot) {
 456     return &safepointALot_op;
 457   }
 458   // Nothing to be done.
 459   return NULL;
 460 }
 461 
 462 void VMThread::loop() {
 463   assert(_cur_vm_operation == NULL, "no current one should be executing");
 464 
 465   SafepointSynchronize::init(_vm_thread);
 466 
 467   while(true) {
 468     VM_Operation* safepoint_ops = NULL;
 469     //
 470     // Wait for VM operation
 471     //
 472     // use no_safepoint_check to get lock without attempting to "sneak"
 473     { MonitorLocker mu_queue(VMOperationQueue_lock,
 474                              Mutex::_no_safepoint_check_flag);
 475 
 476       // Look for new operation
 477       assert(_cur_vm_operation == NULL, "no current one should be executing");
 478       _cur_vm_operation = _vm_queue->remove_next();
 479 
 480       // Stall time tracking code
 481       if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
 482           !_cur_vm_operation->evaluate_concurrently()) {
 483         long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
 484         if (stall > 0)
 485           tty->print_cr("%s stall: %ld",  _cur_vm_operation->name(), stall);
 486       }
 487 
 488       while (!should_terminate() && _cur_vm_operation == NULL) {
 489         // wait with a timeout to guarantee safepoints at regular intervals
 490         bool timedout =
 491           mu_queue.wait(GuaranteedSafepointInterval);
 492 
 493         // Support for self destruction
 494         if ((SelfDestructTimer != 0) && !VMError::is_error_reported() &&
 495             (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
 496           tty->print_cr("VM self-destructed");
 497           exit(-1);
 498         }
 499 
 500         if (timedout) {
 501           // Have to unlock VMOperationQueue_lock just in case no_op_safepoint()
 502           // has to do a handshake.
 503           MutexUnlocker mul(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
 504           if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
 505             // Force a safepoint since we have not had one for at least
 506             // 'GuaranteedSafepointInterval' milliseconds and we need to clean
 507             // something. This will run all the clean-up processing that needs
 508             // to be done at a safepoint.
 509             SafepointSynchronize::begin();
 510             #ifdef ASSERT
 511             if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
 512             #endif
 513             SafepointSynchronize::end();
 514             _cur_vm_operation = NULL;
 515           }
 516         }
 517         _cur_vm_operation = _vm_queue->remove_next();
 518 
 519         // If we are at a safepoint we will evaluate all the operations that
 520         // follow that also require a safepoint
 521         if (_cur_vm_operation != NULL &&
 522             _cur_vm_operation->evaluate_at_safepoint()) {
 523           safepoint_ops = _vm_queue->drain_at_safepoint_priority();
 524         }
 525       }
 526 
 527       if (should_terminate()) break;
 528     } // Release mu_queue_lock
 529 
 530     //
 531     // Execute VM operation
 532     //
 533     { HandleMark hm(VMThread::vm_thread());
 534 
 535       EventMark em("Executing VM operation: %s", vm_operation()->name());
 536       assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
 537 
 538       // If we are at a safepoint we will evaluate all the operations that
 539       // follow that also require a safepoint
 540       if (_cur_vm_operation->evaluate_at_safepoint()) {
 541         log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name());
 542 
 543         _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
 544 
 545         SafepointSynchronize::begin();
 546 
 547         if (_timeout_task != NULL) {
 548           _timeout_task->arm();
 549         }
 550 
 551         evaluate_operation(_cur_vm_operation);
 552         // now process all queued safepoint ops, iteratively draining
 553         // the queue until there are none left
 554         do {
 555           _cur_vm_operation = safepoint_ops;
 556           if (_cur_vm_operation != NULL) {
 557             do {
 558               EventMark em("Executing coalesced safepoint VM operation: %s", _cur_vm_operation->name());
 559               log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name());
 560               // evaluate_operation deletes the op object so we have
 561               // to grab the next op now
 562               VM_Operation* next = _cur_vm_operation->next();
 563               _vm_queue->set_drain_list(next);
 564               evaluate_operation(_cur_vm_operation);
 565               _cur_vm_operation = next;
 566               _coalesced_count++;
 567             } while (_cur_vm_operation != NULL);
 568           }
 569           // There is a chance that a thread enqueued a safepoint op
 570           // since we released the op-queue lock and initiated the safepoint.
 571           // So we drain the queue again if there is anything there, as an
 572           // optimization to try and reduce the number of safepoints.
 573           // As the safepoint synchronizes us with JavaThreads we will see
 574           // any enqueue made by a JavaThread, but the peek will not
 575           // necessarily detect a concurrent enqueue by a GC thread, but
 576           // that simply means the op will wait for the next major cycle of the
 577           // VMThread - just as it would if the GC thread lost the race for
 578           // the lock.
 579           if (_vm_queue->peek_at_safepoint_priority()) {
 580             // must hold lock while draining queue
 581             MutexLocker mu_queue(VMOperationQueue_lock,
 582                                  Mutex::_no_safepoint_check_flag);
 583             safepoint_ops = _vm_queue->drain_at_safepoint_priority();
 584           } else {
 585             safepoint_ops = NULL;
 586           }
 587         } while(safepoint_ops != NULL);
 588 
 589         _vm_queue->set_drain_list(NULL);
 590 
 591         if (_timeout_task != NULL) {
 592           _timeout_task->disarm();
 593         }
 594 
 595         // Complete safepoint synchronization
 596         SafepointSynchronize::end();
 597 
 598       } else {  // not a safepoint operation
 599         log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name());
 600         if (TraceLongCompiles) {
 601           elapsedTimer t;
 602           t.start();
 603           evaluate_operation(_cur_vm_operation);
 604           t.stop();
 605           double secs = t.seconds();
 606           if (secs * 1e3 > LongCompileThreshold) {
 607             // XXX - _cur_vm_operation should not be accessed after
 608             // the completed count has been incremented; the waiting
 609             // thread may have already freed this memory.
 610             tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
 611           }
 612         } else {
 613           evaluate_operation(_cur_vm_operation);
 614         }
 615 
 616         _cur_vm_operation = NULL;
 617       }
 618     }
 619 
 620     //
 621     //  Notify (potential) waiting Java thread(s)
 622     { MonitorLocker mu(VMOperationRequest_lock, Mutex::_no_safepoint_check_flag);
 623       mu.notify_all();
 624     }
 625 
 626     // We want to make sure that we get to a safepoint regularly
 627     // even when executing VMops that don't require safepoints.
 628     if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
 629       HandleMark hm(VMThread::vm_thread());
 630       SafepointSynchronize::begin();
 631       SafepointSynchronize::end();
 632       _cur_vm_operation = NULL;
 633     }
 634   }
 635 }
 636 
 637 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
 638 // over a section of execution by a thread. Currently, it's used only to
 639 // prevent re-entrant calls to GC.
 640 class SkipGCALot : public StackObj {
 641   private:
 642    bool _saved;
 643    Thread* _t;
 644 
 645   public:
 646 #ifdef ASSERT
 647     SkipGCALot(Thread* t) : _t(t) {
 648       _saved = _t->skip_gcalot();
 649       _t->set_skip_gcalot(true);
 650     }
 651 
 652     ~SkipGCALot() {
 653       assert(_t->skip_gcalot(), "Save-restore protocol invariant");
 654       _t->set_skip_gcalot(_saved);
 655     }
 656 #else
 657     SkipGCALot(Thread* t) { }
 658     ~SkipGCALot() { }
 659 #endif
 660 };
 661 
 662 void VMThread::execute(VM_Operation* op) {
 663   Thread* t = Thread::current();
 664 
 665   if (!t->is_VM_thread()) {
 666     SkipGCALot sgcalot(t);    // avoid re-entrant attempts to gc-a-lot
 667     // JavaThread or WatcherThread
 668     bool concurrent = op->evaluate_concurrently();
 669     // only blocking VM operations need to verify the caller's safepoint state:
 670     if (!concurrent) {
 671       t->check_for_valid_safepoint_state();
 672     }
 673 
 674     // New request from Java thread, evaluate prologue
 675     if (!op->doit_prologue()) {
 676       return;   // op was cancelled
 677     }
 678 
 679     // Setup VM_operations for execution
 680     op->set_calling_thread(t);
 681 
 682     // It does not make sense to execute the epilogue, if the VM operation object is getting
 683     // deallocated by the VM thread.
 684     bool execute_epilog = !op->is_cheap_allocated();
 685     assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
 686 
 687     // Get ticket number for non-concurrent VM operations
 688     int ticket = 0;
 689     if (!concurrent) {
 690       ticket = t->vm_operation_ticket();
 691     }
 692 
 693     // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
 694     // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
 695     // to be queued up during a safepoint synchronization.
 696     {
 697       MonitorLocker ml(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
 698       log_debug(vmthread)("Adding VM operation: %s", op->name());
 699       _vm_queue->add(op);
 700       op->set_timestamp(os::javaTimeMillis());
 701       ml.notify();
 702     }
 703 
 704     if (!concurrent) {
 705       // Wait for completion of request (non-concurrent)
 706       // Note: only a JavaThread triggers the safepoint check when locking
 707       MonitorLocker ml(VMOperationRequest_lock,
 708                        t->is_Java_thread() ? Mutex::_safepoint_check_flag : Mutex::_no_safepoint_check_flag);
 709       while(t->vm_operation_completed_count() < ticket) {
 710         ml.wait();
 711       }
 712     }
 713 
 714     if (execute_epilog) {
 715       op->doit_epilogue();
 716     }
 717   } else {
 718     // invoked by VM thread; usually nested VM operation
 719     assert(t->is_VM_thread(), "must be a VM thread");
 720     VM_Operation* prev_vm_operation = vm_operation();
 721     if (prev_vm_operation != NULL) {
 722       // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
 723       // does not allow nested scavenges or compiles.
 724       if (!prev_vm_operation->allow_nested_vm_operations()) {
 725         fatal("Nested VM operation %s requested by operation %s",
 726               op->name(), vm_operation()->name());
 727       }
 728       op->set_calling_thread(prev_vm_operation->calling_thread());
 729     }
 730 
 731     EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
 732 
 733     // Release all internal handles after operation is evaluated
 734     HandleMark hm(t);
 735     _cur_vm_operation = op;
 736 
 737     if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
 738       SafepointSynchronize::begin();
 739       op->evaluate();
 740       SafepointSynchronize::end();
 741     } else {
 742       op->evaluate();
 743     }
 744 
 745     // Free memory if needed
 746     if (op->is_cheap_allocated()) delete op;
 747 
 748     _cur_vm_operation = prev_vm_operation;
 749   }
 750 }
 751 
 752 
 753 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
 754   Thread::oops_do(f, cf);
 755   _vm_queue->oops_do(f);
 756 }
 757 
 758 //------------------------------------------------------------------------------------------------------------------
 759 #ifndef PRODUCT
 760 
 761 void VMOperationQueue::verify_queue(int prio) {
 762   // Check that list is correctly linked
 763   int length = _queue_length[prio];
 764   VM_Operation *cur = _queue[prio];
 765   int i;
 766 
 767   // Check forward links
 768   for(i = 0; i < length; i++) {
 769     cur = cur->next();
 770     assert(cur != _queue[prio], "list to short (forward)");
 771   }
 772   assert(cur->next() == _queue[prio], "list to long (forward)");
 773 
 774   // Check backwards links
 775   cur = _queue[prio];
 776   for(i = 0; i < length; i++) {
 777     cur = cur->prev();
 778     assert(cur != _queue[prio], "list to short (backwards)");
 779   }
 780   assert(cur->prev() == _queue[prio], "list to long (backwards)");
 781 }
 782 
 783 #endif
 784 
 785 void VMThread::verify() {
 786   oops_do(&VerifyOopClosure::verify_oop, NULL);
 787 }
--- EOF ---