1 /* 2 * Copyright (c) 1998, 2014, 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_interface/collectedHeap.hpp" 28 #include "memory/resourceArea.hpp" 29 #include "oops/method.hpp" 30 #include "oops/oop.inline.hpp" 31 #include "runtime/interfaceSupport.hpp" 32 #include "runtime/mutexLocker.hpp" 33 #include "runtime/os.hpp" 34 #include "runtime/thread.inline.hpp" 35 #include "runtime/vmThread.hpp" 36 #include "runtime/vm_operations.hpp" 37 #include "services/runtimeService.hpp" 38 #include "trace/tracing.hpp" 39 #include "utilities/dtrace.hpp" 40 #include "utilities/events.hpp" 41 #include "utilities/xmlstream.hpp" 42 43 #ifndef USDT2 44 HS_DTRACE_PROBE_DECL3(hotspot, vmops__request, char *, uintptr_t, int); 45 HS_DTRACE_PROBE_DECL3(hotspot, vmops__begin, char *, uintptr_t, int); 46 HS_DTRACE_PROBE_DECL3(hotspot, vmops__end, char *, uintptr_t, int); 47 #endif /* !USDT2 */ 48 49 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC 50 51 // Dummy VM operation to act as first element in our circular double-linked list 52 class VM_Dummy: public VM_Operation { 53 VMOp_Type type() const { return VMOp_Dummy; } 54 void doit() {}; 55 }; 56 57 VMOperationQueue::VMOperationQueue() { 58 // The queue is a circular doubled-linked list, which always contains 59 // one element (i.e., one element means empty). 60 for(int i = 0; i < nof_priorities; i++) { 61 _queue_length[i] = 0; 62 _queue_counter = 0; 63 _queue[i] = new VM_Dummy(); 64 _queue[i]->set_next(_queue[i]); 65 _queue[i]->set_prev(_queue[i]); 66 } 67 _drain_list = NULL; 68 } 69 70 71 bool VMOperationQueue::queue_empty(int prio) { 72 // It is empty if there is exactly one element 73 bool empty = (_queue[prio] == _queue[prio]->next()); 74 assert( (_queue_length[prio] == 0 && empty) || 75 (_queue_length[prio] > 0 && !empty), "sanity check"); 76 return _queue_length[prio] == 0; 77 } 78 79 // Inserts an element to the right of the q element 80 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) { 81 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); 82 n->set_prev(q); 83 n->set_next(q->next()); 84 q->next()->set_prev(n); 85 q->set_next(n); 86 } 87 88 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) { 89 _queue_length[prio]++; 90 insert(_queue[prio]->next(), op); 91 } 92 93 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) { 94 _queue_length[prio]++; 95 insert(_queue[prio]->prev(), op); 96 } 97 98 99 void VMOperationQueue::unlink(VM_Operation* q) { 100 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); 101 q->prev()->set_next(q->next()); 102 q->next()->set_prev(q->prev()); 103 } 104 105 VM_Operation* VMOperationQueue::queue_remove_front(int prio) { 106 if (queue_empty(prio)) return NULL; 107 assert(_queue_length[prio] >= 0, "sanity check"); 108 _queue_length[prio]--; 109 VM_Operation* r = _queue[prio]->next(); 110 assert(r != _queue[prio], "cannot remove base element"); 111 unlink(r); 112 return r; 113 } 114 115 VM_Operation* VMOperationQueue::queue_drain(int prio) { 116 if (queue_empty(prio)) return NULL; 117 DEBUG_ONLY(int length = _queue_length[prio];); 118 assert(length >= 0, "sanity check"); 119 _queue_length[prio] = 0; 120 VM_Operation* r = _queue[prio]->next(); 121 assert(r != _queue[prio], "cannot remove base element"); 122 // remove links to base element from head and tail 123 r->set_prev(NULL); 124 _queue[prio]->prev()->set_next(NULL); 125 // restore queue to empty state 126 _queue[prio]->set_next(_queue[prio]); 127 _queue[prio]->set_prev(_queue[prio]); 128 assert(queue_empty(prio), "drain corrupted queue"); 129 #ifdef ASSERT 130 int len = 0; 131 VM_Operation* cur; 132 for(cur = r; cur != NULL; cur=cur->next()) len++; 133 assert(len == length, "drain lost some ops"); 134 #endif 135 return r; 136 } 137 138 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) { 139 VM_Operation* cur = _queue[queue]; 140 cur = cur->next(); 141 while (cur != _queue[queue]) { 142 cur->oops_do(f); 143 cur = cur->next(); 144 } 145 } 146 147 void VMOperationQueue::drain_list_oops_do(OopClosure* f) { 148 VM_Operation* cur = _drain_list; 149 while (cur != NULL) { 150 cur->oops_do(f); 151 cur = cur->next(); 152 } 153 } 154 155 //----------------------------------------------------------------- 156 // High-level interface 157 bool VMOperationQueue::add(VM_Operation *op) { 158 159 #ifndef USDT2 160 HS_DTRACE_PROBE3(hotspot, vmops__request, op->name(), strlen(op->name()), 161 op->evaluation_mode()); 162 #else /* USDT2 */ 163 HOTSPOT_VMOPS_REQUEST( 164 (char *) op->name(), strlen(op->name()), 165 op->evaluation_mode()); 166 #endif /* USDT2 */ 167 168 // Encapsulates VM queue policy. Currently, that 169 // only involves putting them on the right list 170 if (op->evaluate_at_safepoint()) { 171 queue_add_back(SafepointPriority, op); 172 return true; 173 } 174 175 queue_add_back(MediumPriority, op); 176 return true; 177 } 178 179 VM_Operation* VMOperationQueue::remove_next() { 180 // Assuming VMOperation queue is two-level priority queue. If there are 181 // more than two priorities, we need a different scheduling algorithm. 182 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2, 183 "current algorithm does not work"); 184 185 // simple counter based scheduling to prevent starvation of lower priority 186 // queue. -- see 4390175 187 int high_prio, low_prio; 188 if (_queue_counter++ < 10) { 189 high_prio = SafepointPriority; 190 low_prio = MediumPriority; 191 } else { 192 _queue_counter = 0; 193 high_prio = MediumPriority; 194 low_prio = SafepointPriority; 195 } 196 197 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio); 198 } 199 200 void VMOperationQueue::oops_do(OopClosure* f) { 201 for(int i = 0; i < nof_priorities; i++) { 202 queue_oops_do(i, f); 203 } 204 drain_list_oops_do(f); 205 } 206 207 208 //------------------------------------------------------------------------------------------------------------------ 209 // Implementation of VMThread stuff 210 211 bool VMThread::_should_terminate = false; 212 bool VMThread::_terminated = false; 213 Monitor* VMThread::_terminate_lock = NULL; 214 VMThread* VMThread::_vm_thread = NULL; 215 VM_Operation* VMThread::_cur_vm_operation = NULL; 216 VMOperationQueue* VMThread::_vm_queue = NULL; 217 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL; 218 219 220 void VMThread::create() { 221 assert(vm_thread() == NULL, "we can only allocate one VMThread"); 222 _vm_thread = new VMThread(); 223 224 // Create VM operation queue 225 _vm_queue = new VMOperationQueue(); 226 guarantee(_vm_queue != NULL, "just checking"); 227 228 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true); 229 230 if (UsePerfData) { 231 // jvmstat performance counters 232 Thread* THREAD = Thread::current(); 233 _perf_accumulated_vm_operation_time = 234 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime", 235 PerfData::U_Ticks, CHECK); 236 } 237 } 238 239 240 VMThread::VMThread() : NamedThread() { 241 set_name("VM Thread"); 242 } 243 244 void VMThread::destroy() { 245 if (_vm_thread != NULL) { 246 delete _vm_thread; 247 _vm_thread = NULL; // VM thread is gone 248 } 249 } 250 251 void VMThread::run() { 252 assert(this == vm_thread(), "check"); 253 254 this->initialize_thread_local_storage(); 255 this->record_stack_base_and_size(); 256 // Notify_lock wait checks on active_handles() to rewait in 257 // case of spurious wakeup, it should wait on the last 258 // value set prior to the notify 259 this->set_active_handles(JNIHandleBlock::allocate_block()); 260 261 { 262 MutexLocker ml(Notify_lock); 263 Notify_lock->notify(); 264 } 265 // Notify_lock is destroyed by Threads::create_vm() 266 267 int prio = (VMThreadPriority == -1) 268 ? os::java_to_os_priority[NearMaxPriority] 269 : VMThreadPriority; 270 // Note that I cannot call os::set_priority because it expects Java 271 // priorities and I am *explicitly* using OS priorities so that it's 272 // possible to set the VM thread priority higher than any Java thread. 273 os::set_native_priority( this, prio ); 274 275 // Wait for VM_Operations until termination 276 this->loop(); 277 278 // Note the intention to exit before safepointing. 279 // 6295565 This has the effect of waiting for any large tty 280 // outputs to finish. 281 if (xtty != NULL) { 282 ttyLocker ttyl; 283 xtty->begin_elem("destroy_vm"); 284 xtty->stamp(); 285 xtty->end_elem(); 286 assert(should_terminate(), "termination flag must be set"); 287 } 288 289 // 4526887 let VM thread exit at Safepoint 290 SafepointSynchronize::begin(); 291 292 if (VerifyBeforeExit) { 293 HandleMark hm(VMThread::vm_thread()); 294 // Among other things, this ensures that Eden top is correct. 295 Universe::heap()->prepare_for_verify(); 296 os::check_heap(); 297 // Silent verification so as not to pollute normal output, 298 // unless we really asked for it. 299 Universe::verify(!(PrintGCDetails || Verbose) || VerifySilently); 300 } 301 302 CompileBroker::set_should_block(); 303 304 // wait for threads (compiler threads or daemon threads) in the 305 // _thread_in_native state to block. 306 VM_Exit::wait_for_threads_in_native_to_block(); 307 308 // signal other threads that VM process is gone 309 { 310 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows 311 // VM thread to enter any lock at Safepoint as long as its _owner is NULL. 312 // If that happens after _terminate_lock->wait() has unset _owner 313 // but before it actually drops the lock and waits, the notification below 314 // may get lost and we will have a hang. To avoid this, we need to use 315 // Mutex::lock_without_safepoint_check(). 316 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 317 _terminated = true; 318 _terminate_lock->notify(); 319 } 320 321 // Thread destructor usually does this. 322 ThreadLocalStorage::set_thread(NULL); 323 324 // Deletion must be done synchronously by the JNI DestroyJavaVM thread 325 // so that the VMThread deletion completes before the main thread frees 326 // up the CodeHeap. 327 328 } 329 330 331 // Notify the VMThread that the last non-daemon JavaThread has terminated, 332 // and wait until operation is performed. 333 void VMThread::wait_for_vm_thread_exit() { 334 { MutexLocker mu(VMOperationQueue_lock); 335 _should_terminate = true; 336 VMOperationQueue_lock->notify(); 337 } 338 339 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint 340 // because this thread has been removed from the threads list. But anything 341 // that could get blocked by Safepoint should not be used after this point, 342 // otherwise we will hang, since there is no one can end the safepoint. 343 344 // Wait until VM thread is terminated 345 // Note: it should be OK to use Terminator_lock here. But this is called 346 // at a very delicate time (VM shutdown) and we are operating in non- VM 347 // thread at Safepoint. It's safer to not share lock with other threads. 348 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 349 while(!VMThread::is_terminated()) { 350 _terminate_lock->wait(Mutex::_no_safepoint_check_flag); 351 } 352 } 353 } 354 355 void VMThread::print_on(outputStream* st) const { 356 st->print("\"%s\" ", name()); 357 Thread::print_on(st); 358 st->cr(); 359 } 360 361 void VMThread::evaluate_operation(VM_Operation* op) { 362 ResourceMark rm; 363 364 { 365 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time()); 366 #ifndef USDT2 367 HS_DTRACE_PROBE3(hotspot, vmops__begin, op->name(), strlen(op->name()), 368 op->evaluation_mode()); 369 #else /* USDT2 */ 370 HOTSPOT_VMOPS_BEGIN( 371 (char *) op->name(), strlen(op->name()), 372 op->evaluation_mode()); 373 #endif /* USDT2 */ 374 375 EventExecuteVMOperation event; 376 377 op->evaluate(); 378 379 if (event.should_commit()) { 380 bool is_concurrent = op->evaluate_concurrently(); 381 event.set_operation(op->type()); 382 event.set_safepoint(op->evaluate_at_safepoint()); 383 event.set_blocking(!is_concurrent); 384 // Only write caller thread information for non-concurrent vm operations. 385 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown. 386 // This is because the caller thread could have exited already. 387 event.set_caller(is_concurrent ? 0 : op->calling_thread()->osthread()->thread_id()); 388 event.commit(); 389 } 390 391 #ifndef USDT2 392 HS_DTRACE_PROBE3(hotspot, vmops__end, op->name(), strlen(op->name()), 393 op->evaluation_mode()); 394 #else /* USDT2 */ 395 HOTSPOT_VMOPS_END( 396 (char *) op->name(), strlen(op->name()), 397 op->evaluation_mode()); 398 #endif /* USDT2 */ 399 } 400 401 // Last access of info in _cur_vm_operation! 402 bool c_heap_allocated = op->is_cheap_allocated(); 403 404 // Mark as completed 405 if (!op->evaluate_concurrently()) { 406 op->calling_thread()->increment_vm_operation_completed_count(); 407 } 408 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call, 409 // since if it is stack allocated the calling thread might have deallocated 410 if (c_heap_allocated) { 411 delete _cur_vm_operation; 412 } 413 } 414 415 416 void VMThread::loop() { 417 assert(_cur_vm_operation == NULL, "no current one should be executing"); 418 419 while(true) { 420 VM_Operation* safepoint_ops = NULL; 421 // 422 // Wait for VM operation 423 // 424 // use no_safepoint_check to get lock without attempting to "sneak" 425 { MutexLockerEx mu_queue(VMOperationQueue_lock, 426 Mutex::_no_safepoint_check_flag); 427 428 // Look for new operation 429 assert(_cur_vm_operation == NULL, "no current one should be executing"); 430 _cur_vm_operation = _vm_queue->remove_next(); 431 432 // Stall time tracking code 433 if (PrintVMQWaitTime && _cur_vm_operation != NULL && 434 !_cur_vm_operation->evaluate_concurrently()) { 435 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp(); 436 if (stall > 0) 437 tty->print_cr("%s stall: %Ld", _cur_vm_operation->name(), stall); 438 } 439 440 while (!should_terminate() && _cur_vm_operation == NULL) { 441 // wait with a timeout to guarantee safepoints at regular intervals 442 bool timedout = 443 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag, 444 GuaranteedSafepointInterval); 445 446 // Support for self destruction 447 if ((SelfDestructTimer != 0) && !is_error_reported() && 448 (os::elapsedTime() > SelfDestructTimer * 60)) { 449 tty->print_cr("VM self-destructed"); 450 exit(-1); 451 } 452 453 if (timedout && (SafepointALot || 454 SafepointSynchronize::is_cleanup_needed())) { 455 MutexUnlockerEx mul(VMOperationQueue_lock, 456 Mutex::_no_safepoint_check_flag); 457 // Force a safepoint since we have not had one for at least 458 // 'GuaranteedSafepointInterval' milliseconds. This will run all 459 // the clean-up processing that needs to be done regularly at a 460 // safepoint 461 SafepointSynchronize::begin(); 462 #ifdef ASSERT 463 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot(); 464 #endif 465 SafepointSynchronize::end(); 466 } 467 _cur_vm_operation = _vm_queue->remove_next(); 468 469 // If we are at a safepoint we will evaluate all the operations that 470 // follow that also require a safepoint 471 if (_cur_vm_operation != NULL && 472 _cur_vm_operation->evaluate_at_safepoint()) { 473 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 474 } 475 } 476 477 if (should_terminate()) break; 478 } // Release mu_queue_lock 479 480 // 481 // Execute VM operation 482 // 483 { HandleMark hm(VMThread::vm_thread()); 484 485 EventMark em("Executing VM operation: %s", vm_operation()->name()); 486 assert(_cur_vm_operation != NULL, "we should have found an operation to execute"); 487 488 // Give the VM thread an extra quantum. Jobs tend to be bursty and this 489 // helps the VM thread to finish up the job. 490 // FIXME: When this is enabled and there are many threads, this can degrade 491 // performance significantly. 492 if( VMThreadHintNoPreempt ) 493 os::hint_no_preempt(); 494 495 // If we are at a safepoint we will evaluate all the operations that 496 // follow that also require a safepoint 497 if (_cur_vm_operation->evaluate_at_safepoint()) { 498 499 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned 500 501 SafepointSynchronize::begin(); 502 evaluate_operation(_cur_vm_operation); 503 // now process all queued safepoint ops, iteratively draining 504 // the queue until there are none left 505 do { 506 _cur_vm_operation = safepoint_ops; 507 if (_cur_vm_operation != NULL) { 508 do { 509 // evaluate_operation deletes the op object so we have 510 // to grab the next op now 511 VM_Operation* next = _cur_vm_operation->next(); 512 _vm_queue->set_drain_list(next); 513 evaluate_operation(_cur_vm_operation); 514 _cur_vm_operation = next; 515 if (PrintSafepointStatistics) { 516 SafepointSynchronize::inc_vmop_coalesced_count(); 517 } 518 } while (_cur_vm_operation != NULL); 519 } 520 // There is a chance that a thread enqueued a safepoint op 521 // since we released the op-queue lock and initiated the safepoint. 522 // So we drain the queue again if there is anything there, as an 523 // optimization to try and reduce the number of safepoints. 524 // As the safepoint synchronizes us with JavaThreads we will see 525 // any enqueue made by a JavaThread, but the peek will not 526 // necessarily detect a concurrent enqueue by a GC thread, but 527 // that simply means the op will wait for the next major cycle of the 528 // VMThread - just as it would if the GC thread lost the race for 529 // the lock. 530 if (_vm_queue->peek_at_safepoint_priority()) { 531 // must hold lock while draining queue 532 MutexLockerEx mu_queue(VMOperationQueue_lock, 533 Mutex::_no_safepoint_check_flag); 534 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 535 } else { 536 safepoint_ops = NULL; 537 } 538 } while(safepoint_ops != NULL); 539 540 _vm_queue->set_drain_list(NULL); 541 542 // Complete safepoint synchronization 543 SafepointSynchronize::end(); 544 545 } else { // not a safepoint operation 546 if (TraceLongCompiles) { 547 elapsedTimer t; 548 t.start(); 549 evaluate_operation(_cur_vm_operation); 550 t.stop(); 551 double secs = t.seconds(); 552 if (secs * 1e3 > LongCompileThreshold) { 553 // XXX - _cur_vm_operation should not be accessed after 554 // the completed count has been incremented; the waiting 555 // thread may have already freed this memory. 556 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs); 557 } 558 } else { 559 evaluate_operation(_cur_vm_operation); 560 } 561 562 _cur_vm_operation = NULL; 563 } 564 } 565 566 // 567 // Notify (potential) waiting Java thread(s) - lock without safepoint 568 // check so that sneaking is not possible 569 { MutexLockerEx mu(VMOperationRequest_lock, 570 Mutex::_no_safepoint_check_flag); 571 VMOperationRequest_lock->notify_all(); 572 } 573 574 // 575 // We want to make sure that we get to a safepoint regularly. 576 // 577 if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) { 578 long interval = SafepointSynchronize::last_non_safepoint_interval(); 579 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval); 580 if (SafepointALot || max_time_exceeded) { 581 HandleMark hm(VMThread::vm_thread()); 582 SafepointSynchronize::begin(); 583 SafepointSynchronize::end(); 584 } 585 } 586 } 587 } 588 589 void VMThread::execute(VM_Operation* op) { 590 Thread* t = Thread::current(); 591 592 if (!t->is_VM_thread()) { 593 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot 594 // JavaThread or WatcherThread 595 bool concurrent = op->evaluate_concurrently(); 596 // only blocking VM operations need to verify the caller's safepoint state: 597 if (!concurrent) { 598 t->check_for_valid_safepoint_state(true); 599 } 600 601 // New request from Java thread, evaluate prologue 602 if (!op->doit_prologue()) { 603 return; // op was cancelled 604 } 605 606 // Setup VM_operations for execution 607 op->set_calling_thread(t, Thread::get_priority(t)); 608 609 // It does not make sense to execute the epilogue, if the VM operation object is getting 610 // deallocated by the VM thread. 611 bool execute_epilog = !op->is_cheap_allocated(); 612 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated"); 613 614 // Get ticket number for non-concurrent VM operations 615 int ticket = 0; 616 if (!concurrent) { 617 ticket = t->vm_operation_ticket(); 618 } 619 620 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the 621 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests 622 // to be queued up during a safepoint synchronization. 623 { 624 VMOperationQueue_lock->lock_without_safepoint_check(); 625 bool ok = _vm_queue->add(op); 626 op->set_timestamp(os::javaTimeMillis()); 627 VMOperationQueue_lock->notify(); 628 VMOperationQueue_lock->unlock(); 629 // VM_Operation got skipped 630 if (!ok) { 631 assert(concurrent, "can only skip concurrent tasks"); 632 if (op->is_cheap_allocated()) delete op; 633 return; 634 } 635 } 636 637 if (!concurrent) { 638 // Wait for completion of request (non-concurrent) 639 // Note: only a JavaThread triggers the safepoint check when locking 640 MutexLocker mu(VMOperationRequest_lock); 641 while(t->vm_operation_completed_count() < ticket) { 642 VMOperationRequest_lock->wait(!t->is_Java_thread()); 643 } 644 } 645 646 if (execute_epilog) { 647 op->doit_epilogue(); 648 } 649 } else { 650 // invoked by VM thread; usually nested VM operation 651 assert(t->is_VM_thread(), "must be a VM thread"); 652 VM_Operation* prev_vm_operation = vm_operation(); 653 if (prev_vm_operation != NULL) { 654 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler 655 // does not allow nested scavenges or compiles. 656 if (!prev_vm_operation->allow_nested_vm_operations()) { 657 fatal(err_msg("Nested VM operation %s requested by operation %s", 658 op->name(), vm_operation()->name())); 659 } 660 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority()); 661 } 662 663 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name()); 664 665 // Release all internal handles after operation is evaluated 666 HandleMark hm(t); 667 _cur_vm_operation = op; 668 669 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) { 670 SafepointSynchronize::begin(); 671 op->evaluate(); 672 SafepointSynchronize::end(); 673 } else { 674 op->evaluate(); 675 } 676 677 // Free memory if needed 678 if (op->is_cheap_allocated()) delete op; 679 680 _cur_vm_operation = prev_vm_operation; 681 } 682 } 683 684 685 void VMThread::oops_do(OopClosure* f, CLDClosure* cld_f, CodeBlobClosure* cf) { 686 Thread::oops_do(f, cld_f, cf); 687 _vm_queue->oops_do(f); 688 } 689 690 //------------------------------------------------------------------------------------------------------------------ 691 #ifndef PRODUCT 692 693 void VMOperationQueue::verify_queue(int prio) { 694 // Check that list is correctly linked 695 int length = _queue_length[prio]; 696 VM_Operation *cur = _queue[prio]; 697 int i; 698 699 // Check forward links 700 for(i = 0; i < length; i++) { 701 cur = cur->next(); 702 assert(cur != _queue[prio], "list to short (forward)"); 703 } 704 assert(cur->next() == _queue[prio], "list to long (forward)"); 705 706 // Check backwards links 707 cur = _queue[prio]; 708 for(i = 0; i < length; i++) { 709 cur = cur->prev(); 710 assert(cur != _queue[prio], "list to short (backwards)"); 711 } 712 assert(cur->prev() == _queue[prio], "list to long (backwards)"); 713 } 714 715 #endif 716 717 void VMThread::verify() { 718 oops_do(&VerifyOopClosure::verify_oop, NULL, NULL); 719 }