rev 56635 : v2.00 -> v2.05 (CR5/v2.05/8-for-jdk13) patches combined into one; merge with 8229212.patch; merge with jdk-14+11; merge with 8230184.patch; merge with 8230876.patch; merge with jdk-14+15; merge with jdk-14+18.

   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/synchronizer.hpp"
  44 #include "runtime/thread.inline.hpp"
  45 #include "runtime/vmThread.hpp"
  46 #include "runtime/vmOperations.hpp"
  47 #include "services/runtimeService.hpp"
  48 #include "utilities/dtrace.hpp"
  49 #include "utilities/events.hpp"
  50 #include "utilities/vmError.hpp"
  51 #include "utilities/xmlstream.hpp"
  52 
  53 VMOperationQueue::VMOperationQueue() {
  54   // The queue is a circular doubled-linked list, which always contains
  55   // one element (i.e., one element means empty).
  56   for(int i = 0; i < nof_priorities; i++) {
  57     _queue_length[i] = 0;
  58     _queue_counter = 0;
  59     _queue[i] = new VM_None("QueueHead");
  60     _queue[i]->set_next(_queue[i]);
  61     _queue[i]->set_prev(_queue[i]);
  62   }
  63   _drain_list = NULL;
  64 }
  65 
  66 
  67 bool VMOperationQueue::queue_empty(int prio) {
  68   // It is empty if there is exactly one element
  69   bool empty = (_queue[prio] == _queue[prio]->next());
  70   assert( (_queue_length[prio] == 0 && empty) ||
  71           (_queue_length[prio] > 0  && !empty), "sanity check");
  72   return _queue_length[prio] == 0;
  73 }
  74 
  75 // Inserts an element to the right of the q element
  76 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
  77   assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
  78   n->set_prev(q);
  79   n->set_next(q->next());
  80   q->next()->set_prev(n);
  81   q->set_next(n);
  82 }
  83 
  84 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
  85   _queue_length[prio]++;
  86   insert(_queue[prio]->next(), op);
  87 }
  88 
  89 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
  90   _queue_length[prio]++;
  91   insert(_queue[prio]->prev(), op);
  92 }
  93 
  94 
  95 void VMOperationQueue::unlink(VM_Operation* q) {
  96   assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
  97   q->prev()->set_next(q->next());
  98   q->next()->set_prev(q->prev());
  99 }
 100 
 101 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
 102   if (queue_empty(prio)) return NULL;
 103   assert(_queue_length[prio] >= 0, "sanity check");
 104   _queue_length[prio]--;
 105   VM_Operation* r = _queue[prio]->next();
 106   assert(r != _queue[prio], "cannot remove base element");
 107   unlink(r);
 108   return r;
 109 }
 110 
 111 VM_Operation* VMOperationQueue::queue_drain(int prio) {
 112   if (queue_empty(prio)) return NULL;
 113   DEBUG_ONLY(int length = _queue_length[prio];);
 114   assert(length >= 0, "sanity check");
 115   _queue_length[prio] = 0;
 116   VM_Operation* r = _queue[prio]->next();
 117   assert(r != _queue[prio], "cannot remove base element");
 118   // remove links to base element from head and tail
 119   r->set_prev(NULL);
 120   _queue[prio]->prev()->set_next(NULL);
 121   // restore queue to empty state
 122   _queue[prio]->set_next(_queue[prio]);
 123   _queue[prio]->set_prev(_queue[prio]);
 124   assert(queue_empty(prio), "drain corrupted queue");
 125 #ifdef ASSERT
 126   int len = 0;
 127   VM_Operation* cur;
 128   for(cur = r; cur != NULL; cur=cur->next()) len++;
 129   assert(len == length, "drain lost some ops");
 130 #endif
 131   return r;
 132 }
 133 
 134 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
 135   VM_Operation* cur = _queue[queue];
 136   cur = cur->next();
 137   while (cur != _queue[queue]) {
 138     cur->oops_do(f);
 139     cur = cur->next();
 140   }
 141 }
 142 
 143 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
 144   VM_Operation* cur = _drain_list;
 145   while (cur != NULL) {
 146     cur->oops_do(f);
 147     cur = cur->next();
 148   }
 149 }
 150 
 151 //-----------------------------------------------------------------
 152 // High-level interface
 153 void VMOperationQueue::add(VM_Operation *op) {
 154 
 155   HOTSPOT_VMOPS_REQUEST(
 156                    (char *) op->name(), strlen(op->name()),
 157                    op->evaluation_mode());
 158 
 159   // Encapsulates VM queue policy. Currently, that
 160   // only involves putting them on the right list
 161   queue_add_back(op->evaluate_at_safepoint() ? SafepointPriority : MediumPriority, op);
 162 }
 163 
 164 VM_Operation* VMOperationQueue::remove_next() {
 165   // Assuming VMOperation queue is two-level priority queue. If there are
 166   // more than two priorities, we need a different scheduling algorithm.
 167   assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
 168          "current algorithm does not work");
 169 
 170   // simple counter based scheduling to prevent starvation of lower priority
 171   // queue. -- see 4390175
 172   int high_prio, low_prio;
 173   if (_queue_counter++ < 10) {
 174       high_prio = SafepointPriority;
 175       low_prio  = MediumPriority;
 176   } else {
 177       _queue_counter = 0;
 178       high_prio = MediumPriority;
 179       low_prio  = SafepointPriority;
 180   }
 181 
 182   return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
 183 }
 184 
 185 void VMOperationQueue::oops_do(OopClosure* f) {
 186   for(int i = 0; i < nof_priorities; i++) {
 187     queue_oops_do(i, f);
 188   }
 189   drain_list_oops_do(f);
 190 }
 191 
 192 //------------------------------------------------------------------------------------------------------------------
 193 // Timeout machinery
 194 
 195 void VMOperationTimeoutTask::task() {
 196   assert(AbortVMOnVMOperationTimeout, "only if enabled");
 197   if (is_armed()) {
 198     jlong delay = (os::javaTimeMillis() - _arm_time);
 199     if (delay > AbortVMOnVMOperationTimeoutDelay) {
 200       fatal("VM operation took too long: " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)",
 201             delay, AbortVMOnVMOperationTimeoutDelay);
 202     }
 203   }
 204 }
 205 
 206 bool VMOperationTimeoutTask::is_armed() {
 207   return OrderAccess::load_acquire(&_armed) != 0;
 208 }
 209 
 210 void VMOperationTimeoutTask::arm() {
 211   _arm_time = os::javaTimeMillis();
 212   OrderAccess::release_store_fence(&_armed, 1);
 213 }
 214 
 215 void VMOperationTimeoutTask::disarm() {
 216   OrderAccess::release_store_fence(&_armed, 0);
 217 }
 218 
 219 //------------------------------------------------------------------------------------------------------------------
 220 // Implementation of VMThread stuff
 221 
 222 bool              VMThread::_should_terminate   = false;
 223 bool              VMThread::_terminated         = false;
 224 Monitor*          VMThread::_terminate_lock     = NULL;
 225 VMThread*         VMThread::_vm_thread          = NULL;
 226 VM_Operation*     VMThread::_cur_vm_operation   = NULL;
 227 VMOperationQueue* VMThread::_vm_queue           = NULL;
 228 PerfCounter*      VMThread::_perf_accumulated_vm_operation_time = NULL;
 229 uint64_t          VMThread::_coalesced_count = 0;
 230 VMOperationTimeoutTask* VMThread::_timeout_task = NULL;
 231 
 232 
 233 void VMThread::create() {
 234   assert(vm_thread() == NULL, "we can only allocate one VMThread");
 235   _vm_thread = new VMThread();
 236 
 237   if (AbortVMOnVMOperationTimeout) {
 238     // Make sure we call the timeout task frequently enough, but not too frequent.
 239     // Try to make the interval 10% of the timeout delay, so that we miss the timeout
 240     // by those 10% at max. Periodic task also expects it to fit min/max intervals.
 241     size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10;
 242     interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran;
 243     interval = MAX2<size_t>(interval, PeriodicTask::min_interval);
 244     interval = MIN2<size_t>(interval, PeriodicTask::max_interval);
 245 
 246     _timeout_task = new VMOperationTimeoutTask(interval);
 247     _timeout_task->enroll();
 248   } else {
 249     assert(_timeout_task == NULL, "sanity");
 250   }
 251 
 252   // Create VM operation queue
 253   _vm_queue = new VMOperationQueue();
 254   guarantee(_vm_queue != NULL, "just checking");
 255 
 256   _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
 257                                 Monitor::_safepoint_check_never);
 258 
 259   if (UsePerfData) {
 260     // jvmstat performance counters
 261     Thread* THREAD = Thread::current();
 262     _perf_accumulated_vm_operation_time =
 263                  PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
 264                                                  PerfData::U_Ticks, CHECK);
 265   }
 266 }
 267 
 268 VMThread::VMThread() : NamedThread() {
 269   set_name("VM Thread");
 270 }
 271 
 272 void VMThread::destroy() {
 273   _vm_thread = NULL;      // VM thread is gone
 274 }
 275 
 276 static VM_None halt_op("Halt");
 277 
 278 void VMThread::run() {
 279   assert(this == vm_thread(), "check");
 280 
 281   // Notify_lock wait checks on active_handles() to rewait in
 282   // case of spurious wakeup, it should wait on the last
 283   // value set prior to the notify
 284   this->set_active_handles(JNIHandleBlock::allocate_block());
 285 
 286   {
 287     MutexLocker ml(Notify_lock);
 288     Notify_lock->notify();
 289   }
 290   // Notify_lock is destroyed by Threads::create_vm()
 291 
 292   int prio = (VMThreadPriority == -1)
 293     ? os::java_to_os_priority[NearMaxPriority]
 294     : VMThreadPriority;
 295   // Note that I cannot call os::set_priority because it expects Java
 296   // priorities and I am *explicitly* using OS priorities so that it's
 297   // possible to set the VM thread priority higher than any Java thread.
 298   os::set_native_priority( this, prio );
 299 
 300   // Wait for VM_Operations until termination
 301   this->loop();
 302 
 303   // Note the intention to exit before safepointing.
 304   // 6295565  This has the effect of waiting for any large tty
 305   // outputs to finish.
 306   if (xtty != NULL) {
 307     ttyLocker ttyl;
 308     xtty->begin_elem("destroy_vm");
 309     xtty->stamp();
 310     xtty->end_elem();
 311     assert(should_terminate(), "termination flag must be set");
 312   }
 313 
 314   if (AsyncDeflateIdleMonitors && log_is_enabled(Info, monitorinflation)) {
 315     // AsyncDeflateIdleMonitors does a special deflation at the final
 316     // safepoint in order to reduce the in-use monitor population that
 317     // is reported by ObjectSynchronizer::log_in_use_monitor_details()
 318     // at VM exit.
 319     ObjectSynchronizer::set_is_special_deflation_requested(true);
 320   }
 321 
 322   // 4526887 let VM thread exit at Safepoint
 323   _cur_vm_operation = &halt_op;
 324   SafepointSynchronize::begin();
 325 
 326   if (VerifyBeforeExit) {
 327     HandleMark hm(VMThread::vm_thread());
 328     // Among other things, this ensures that Eden top is correct.
 329     Universe::heap()->prepare_for_verify();
 330     // Silent verification so as not to pollute normal output,
 331     // unless we really asked for it.
 332     Universe::verify();
 333   }
 334 
 335   CompileBroker::set_should_block();
 336 
 337   // wait for threads (compiler threads or daemon threads) in the
 338   // _thread_in_native state to block.
 339   VM_Exit::wait_for_threads_in_native_to_block();
 340 
 341   // signal other threads that VM process is gone
 342   {
 343     // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
 344     // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
 345     // If that happens after _terminate_lock->wait() has unset _owner
 346     // but before it actually drops the lock and waits, the notification below
 347     // may get lost and we will have a hang. To avoid this, we need to use
 348     // Mutex::lock_without_safepoint_check().
 349     MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
 350     _terminated = true;
 351     ml.notify();
 352   }
 353 
 354   // We are now racing with the VM termination being carried out in
 355   // another thread, so we don't "delete this". Numerous threads don't
 356   // get deleted when the VM terminates
 357 
 358 }
 359 
 360 
 361 // Notify the VMThread that the last non-daemon JavaThread has terminated,
 362 // and wait until operation is performed.
 363 void VMThread::wait_for_vm_thread_exit() {
 364   assert(Thread::current()->is_Java_thread(), "Should be a JavaThread");
 365   assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated");
 366   { MonitorLocker mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
 367     _should_terminate = true;
 368     mu.notify();
 369   }
 370 
 371   // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
 372   // because this thread has been removed from the threads list. But anything
 373   // that could get blocked by Safepoint should not be used after this point,
 374   // otherwise we will hang, since there is no one can end the safepoint.
 375 
 376   // Wait until VM thread is terminated
 377   // Note: it should be OK to use Terminator_lock here. But this is called
 378   // at a very delicate time (VM shutdown) and we are operating in non- VM
 379   // thread at Safepoint. It's safer to not share lock with other threads.
 380   { MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
 381     while(!VMThread::is_terminated()) {
 382       ml.wait();
 383     }
 384   }
 385 }
 386 
 387 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
 388   assert(event != NULL, "invariant");
 389   assert(event->should_commit(), "invariant");
 390   assert(op != NULL, "invariant");
 391   const bool is_concurrent = op->evaluate_concurrently();
 392   const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
 393   event->set_operation(op->type());
 394   event->set_safepoint(evaluate_at_safepoint);
 395   event->set_blocking(!is_concurrent);
 396   // Only write caller thread information for non-concurrent vm operations.
 397   // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
 398   // This is because the caller thread could have exited already.
 399   event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread()));
 400   event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0);
 401   event->commit();
 402 }
 403 
 404 void VMThread::evaluate_operation(VM_Operation* op) {
 405   ResourceMark rm;
 406 
 407   {
 408     PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
 409     HOTSPOT_VMOPS_BEGIN(
 410                      (char *) op->name(), strlen(op->name()),
 411                      op->evaluation_mode());
 412 
 413     EventExecuteVMOperation event;
 414     op->evaluate();
 415     if (event.should_commit()) {
 416       post_vm_operation_event(&event, op);
 417     }
 418 
 419     HOTSPOT_VMOPS_END(
 420                      (char *) op->name(), strlen(op->name()),
 421                      op->evaluation_mode());
 422   }
 423 
 424   // Last access of info in _cur_vm_operation!
 425   bool c_heap_allocated = op->is_cheap_allocated();
 426 
 427   // Mark as completed
 428   if (!op->evaluate_concurrently()) {
 429     op->calling_thread()->increment_vm_operation_completed_count();
 430   }
 431   // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
 432   // since if it is stack allocated the calling thread might have deallocated
 433   if (c_heap_allocated) {
 434     delete _cur_vm_operation;
 435   }
 436 }
 437 
 438 static VM_None    safepointALot_op("SafepointALot");
 439 static VM_Cleanup cleanup_op;
 440 
 441 class HandshakeALotTC : public ThreadClosure {
 442  public:
 443   virtual void do_thread(Thread* thread) {
 444 #ifdef ASSERT
 445     assert(thread->is_Java_thread(), "must be");
 446     JavaThread* jt = (JavaThread*)thread;
 447     jt->verify_states_for_handshake();
 448 #endif
 449   }
 450 };
 451 
 452 VM_Operation* VMThread::no_op_safepoint() {
 453   // Check for handshakes first since we may need to return a VMop.
 454   if (HandshakeALot) {
 455     HandshakeALotTC haltc;
 456     Handshake::execute(&haltc);
 457   }
 458   // Check for a cleanup before SafepointALot to keep stats correct.
 459   long interval_ms = SafepointTracing::time_since_last_safepoint_ms();
 460   bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
 461                            (interval_ms >= GuaranteedSafepointInterval);
 462   if (max_time_exceeded && SafepointSynchronize::is_cleanup_needed()) {
 463     return &cleanup_op;
 464   }
 465   if (SafepointALot) {
 466     return &safepointALot_op;
 467   }
 468   // Nothing to be done.
 469   return NULL;
 470 }
 471 
 472 void VMThread::loop() {
 473   assert(_cur_vm_operation == NULL, "no current one should be executing");
 474 
 475   SafepointSynchronize::init(_vm_thread);
 476 
 477   while(true) {
 478     VM_Operation* safepoint_ops = NULL;
 479     //
 480     // Wait for VM operation
 481     //
 482     // use no_safepoint_check to get lock without attempting to "sneak"
 483     { MonitorLocker mu_queue(VMOperationQueue_lock,
 484                              Mutex::_no_safepoint_check_flag);
 485 
 486       // Look for new operation
 487       assert(_cur_vm_operation == NULL, "no current one should be executing");
 488       _cur_vm_operation = _vm_queue->remove_next();
 489 
 490       // Stall time tracking code
 491       if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
 492           !_cur_vm_operation->evaluate_concurrently()) {
 493         long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
 494         if (stall > 0)
 495           tty->print_cr("%s stall: %ld",  _cur_vm_operation->name(), stall);
 496       }
 497 
 498       while (!should_terminate() && _cur_vm_operation == NULL) {
 499         // wait with a timeout to guarantee safepoints at regular intervals
 500         bool timedout =
 501           mu_queue.wait(GuaranteedSafepointInterval);
 502 
 503         // Support for self destruction
 504         if ((SelfDestructTimer != 0) && !VMError::is_error_reported() &&
 505             (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
 506           tty->print_cr("VM self-destructed");
 507           exit(-1);
 508         }
 509 
 510         if (timedout) {
 511           // Have to unlock VMOperationQueue_lock just in case no_op_safepoint()
 512           // has to do a handshake.
 513           MutexUnlocker mul(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
 514           if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
 515             // Force a safepoint since we have not had one for at least
 516             // 'GuaranteedSafepointInterval' milliseconds and we need to clean
 517             // something. This will run all the clean-up processing that needs
 518             // to be done at a safepoint.
 519             SafepointSynchronize::begin();
 520             #ifdef ASSERT
 521             if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
 522             #endif
 523             SafepointSynchronize::end();
 524             _cur_vm_operation = NULL;
 525           }
 526         }
 527         _cur_vm_operation = _vm_queue->remove_next();
 528 
 529         // If we are at a safepoint we will evaluate all the operations that
 530         // follow that also require a safepoint
 531         if (_cur_vm_operation != NULL &&
 532             _cur_vm_operation->evaluate_at_safepoint()) {
 533           safepoint_ops = _vm_queue->drain_at_safepoint_priority();
 534         }
 535       }
 536 
 537       if (should_terminate()) break;
 538     } // Release mu_queue_lock
 539 
 540     //
 541     // Execute VM operation
 542     //
 543     { HandleMark hm(VMThread::vm_thread());
 544 
 545       EventMark em("Executing VM operation: %s", vm_operation()->name());
 546       assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
 547 
 548       // If we are at a safepoint we will evaluate all the operations that
 549       // follow that also require a safepoint
 550       if (_cur_vm_operation->evaluate_at_safepoint()) {
 551         log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name());
 552 
 553         _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
 554 
 555         SafepointSynchronize::begin();
 556 
 557         if (_timeout_task != NULL) {
 558           _timeout_task->arm();
 559         }
 560 
 561         evaluate_operation(_cur_vm_operation);
 562         // now process all queued safepoint ops, iteratively draining
 563         // the queue until there are none left
 564         do {
 565           _cur_vm_operation = safepoint_ops;
 566           if (_cur_vm_operation != NULL) {
 567             do {
 568               EventMark em("Executing coalesced safepoint VM operation: %s", _cur_vm_operation->name());
 569               log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name());
 570               // evaluate_operation deletes the op object so we have
 571               // to grab the next op now
 572               VM_Operation* next = _cur_vm_operation->next();
 573               _vm_queue->set_drain_list(next);
 574               evaluate_operation(_cur_vm_operation);
 575               _cur_vm_operation = next;
 576               _coalesced_count++;
 577             } while (_cur_vm_operation != NULL);
 578           }
 579           // There is a chance that a thread enqueued a safepoint op
 580           // since we released the op-queue lock and initiated the safepoint.
 581           // So we drain the queue again if there is anything there, as an
 582           // optimization to try and reduce the number of safepoints.
 583           // As the safepoint synchronizes us with JavaThreads we will see
 584           // any enqueue made by a JavaThread, but the peek will not
 585           // necessarily detect a concurrent enqueue by a GC thread, but
 586           // that simply means the op will wait for the next major cycle of the
 587           // VMThread - just as it would if the GC thread lost the race for
 588           // the lock.
 589           if (_vm_queue->peek_at_safepoint_priority()) {
 590             // must hold lock while draining queue
 591             MutexLocker mu_queue(VMOperationQueue_lock,
 592                                  Mutex::_no_safepoint_check_flag);
 593             safepoint_ops = _vm_queue->drain_at_safepoint_priority();
 594           } else {
 595             safepoint_ops = NULL;
 596           }
 597         } while(safepoint_ops != NULL);
 598 
 599         _vm_queue->set_drain_list(NULL);
 600 
 601         if (_timeout_task != NULL) {
 602           _timeout_task->disarm();
 603         }
 604 
 605         // Complete safepoint synchronization
 606         SafepointSynchronize::end();
 607 
 608       } else {  // not a safepoint operation
 609         log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name());
 610         if (TraceLongCompiles) {
 611           elapsedTimer t;
 612           t.start();
 613           evaluate_operation(_cur_vm_operation);
 614           t.stop();
 615           double secs = t.seconds();
 616           if (secs * 1e3 > LongCompileThreshold) {
 617             // XXX - _cur_vm_operation should not be accessed after
 618             // the completed count has been incremented; the waiting
 619             // thread may have already freed this memory.
 620             tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
 621           }
 622         } else {
 623           evaluate_operation(_cur_vm_operation);
 624         }
 625 
 626         _cur_vm_operation = NULL;
 627       }
 628     }
 629 
 630     //
 631     //  Notify (potential) waiting Java thread(s)
 632     { MonitorLocker mu(VMOperationRequest_lock, Mutex::_no_safepoint_check_flag);
 633       mu.notify_all();
 634     }
 635 
 636     // We want to make sure that we get to a safepoint regularly
 637     // even when executing VMops that don't require safepoints.
 638     if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
 639       HandleMark hm(VMThread::vm_thread());
 640       SafepointSynchronize::begin();
 641       SafepointSynchronize::end();
 642       _cur_vm_operation = NULL;
 643     }
 644   }
 645 }
 646 
 647 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
 648 // over a section of execution by a thread. Currently, it's used only to
 649 // prevent re-entrant calls to GC.
 650 class SkipGCALot : public StackObj {
 651   private:
 652    bool _saved;
 653    Thread* _t;
 654 
 655   public:
 656 #ifdef ASSERT
 657     SkipGCALot(Thread* t) : _t(t) {
 658       _saved = _t->skip_gcalot();
 659       _t->set_skip_gcalot(true);
 660     }
 661 
 662     ~SkipGCALot() {
 663       assert(_t->skip_gcalot(), "Save-restore protocol invariant");
 664       _t->set_skip_gcalot(_saved);
 665     }
 666 #else
 667     SkipGCALot(Thread* t) { }
 668     ~SkipGCALot() { }
 669 #endif
 670 };
 671 
 672 void VMThread::execute(VM_Operation* op) {
 673   Thread* t = Thread::current();
 674 
 675   if (!t->is_VM_thread()) {
 676     SkipGCALot sgcalot(t);    // avoid re-entrant attempts to gc-a-lot
 677     // JavaThread or WatcherThread
 678     bool concurrent = op->evaluate_concurrently();
 679     // only blocking VM operations need to verify the caller's safepoint state:
 680     if (!concurrent) {
 681       t->check_for_valid_safepoint_state();
 682     }
 683 
 684     // New request from Java thread, evaluate prologue
 685     if (!op->doit_prologue()) {
 686       return;   // op was cancelled
 687     }
 688 
 689     // Setup VM_operations for execution
 690     op->set_calling_thread(t);
 691 
 692     // It does not make sense to execute the epilogue, if the VM operation object is getting
 693     // deallocated by the VM thread.
 694     bool execute_epilog = !op->is_cheap_allocated();
 695     assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
 696 
 697     // Get ticket number for non-concurrent VM operations
 698     int ticket = 0;
 699     if (!concurrent) {
 700       ticket = t->vm_operation_ticket();
 701     }
 702 
 703     // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
 704     // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
 705     // to be queued up during a safepoint synchronization.
 706     {
 707       MonitorLocker ml(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
 708       log_debug(vmthread)("Adding VM operation: %s", op->name());
 709       _vm_queue->add(op);
 710       op->set_timestamp(os::javaTimeMillis());
 711       ml.notify();
 712     }
 713 
 714     if (!concurrent) {
 715       // Wait for completion of request (non-concurrent)
 716       // Note: only a JavaThread triggers the safepoint check when locking
 717       MonitorLocker ml(VMOperationRequest_lock,
 718                        t->is_Java_thread() ? Mutex::_safepoint_check_flag : Mutex::_no_safepoint_check_flag);
 719       while(t->vm_operation_completed_count() < ticket) {
 720         ml.wait();
 721       }
 722     }
 723 
 724     if (execute_epilog) {
 725       op->doit_epilogue();
 726     }
 727   } else {
 728     // invoked by VM thread; usually nested VM operation
 729     assert(t->is_VM_thread(), "must be a VM thread");
 730     VM_Operation* prev_vm_operation = vm_operation();
 731     if (prev_vm_operation != NULL) {
 732       // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
 733       // does not allow nested scavenges or compiles.
 734       if (!prev_vm_operation->allow_nested_vm_operations()) {
 735         fatal("Nested VM operation %s requested by operation %s",
 736               op->name(), vm_operation()->name());
 737       }
 738       op->set_calling_thread(prev_vm_operation->calling_thread());
 739     }
 740 
 741     EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
 742 
 743     // Release all internal handles after operation is evaluated
 744     HandleMark hm(t);
 745     _cur_vm_operation = op;
 746 
 747     if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
 748       SafepointSynchronize::begin();
 749       op->evaluate();
 750       SafepointSynchronize::end();
 751     } else {
 752       op->evaluate();
 753     }
 754 
 755     // Free memory if needed
 756     if (op->is_cheap_allocated()) delete op;
 757 
 758     _cur_vm_operation = prev_vm_operation;
 759   }
 760 }
 761 
 762 
 763 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
 764   Thread::oops_do(f, cf);
 765   _vm_queue->oops_do(f);
 766 }
 767 
 768 //------------------------------------------------------------------------------------------------------------------
 769 #ifndef PRODUCT
 770 
 771 void VMOperationQueue::verify_queue(int prio) {
 772   // Check that list is correctly linked
 773   int length = _queue_length[prio];
 774   VM_Operation *cur = _queue[prio];
 775   int i;
 776 
 777   // Check forward links
 778   for(i = 0; i < length; i++) {
 779     cur = cur->next();
 780     assert(cur != _queue[prio], "list to short (forward)");
 781   }
 782   assert(cur->next() == _queue[prio], "list to long (forward)");
 783 
 784   // Check backwards links
 785   cur = _queue[prio];
 786   for(i = 0; i < length; i++) {
 787     cur = cur->prev();
 788     assert(cur != _queue[prio], "list to short (backwards)");
 789   }
 790   assert(cur->prev() == _queue[prio], "list to long (backwards)");
 791 }
 792 
 793 #endif
 794 
 795 void VMThread::verify() {
 796   oops_do(&VerifyOopClosure::verify_oop, NULL);
 797 }
--- EOF ---