1 /* 2 * Copyright (c) 1998, 2018, 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/logConfiguration.hpp" 32 #include "memory/resourceArea.hpp" 33 #include "oops/method.hpp" 34 #include "oops/oop.inline.hpp" 35 #include "oops/verifyOopClosure.hpp" 36 #include "runtime/interfaceSupport.inline.hpp" 37 #include "runtime/mutexLocker.hpp" 38 #include "runtime/os.hpp" 39 #include "runtime/safepoint.hpp" 40 #include "runtime/thread.inline.hpp" 41 #include "runtime/vmThread.hpp" 42 #include "runtime/vm_operations.hpp" 43 #include "services/runtimeService.hpp" 44 #include "utilities/dtrace.hpp" 45 #include "utilities/events.hpp" 46 #include "utilities/vmError.hpp" 47 #include "utilities/xmlstream.hpp" 48 49 // Dummy VM operation to act as first element in our circular double-linked list 50 class VM_None: public VM_Operation { 51 VMOp_Type type() const { return VMOp_None; } 52 void doit() {}; 53 }; 54 55 VMOperationQueue::VMOperationQueue() { 56 // The queue is a circular doubled-linked list, which always contains 57 // one element (i.e., one element means empty). 58 for(int i = 0; i < nof_priorities; i++) { 59 _queue_length[i] = 0; 60 _queue_counter = 0; 61 _queue[i] = new VM_None(); 62 _queue[i]->set_next(_queue[i]); 63 _queue[i]->set_prev(_queue[i]); 64 } 65 _drain_list = NULL; 66 } 67 68 69 bool VMOperationQueue::queue_empty(int prio) { 70 // It is empty if there is exactly one element 71 bool empty = (_queue[prio] == _queue[prio]->next()); 72 assert( (_queue_length[prio] == 0 && empty) || 73 (_queue_length[prio] > 0 && !empty), "sanity check"); 74 return _queue_length[prio] == 0; 75 } 76 77 // Inserts an element to the right of the q element 78 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) { 79 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); 80 n->set_prev(q); 81 n->set_next(q->next()); 82 q->next()->set_prev(n); 83 q->set_next(n); 84 } 85 86 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) { 87 _queue_length[prio]++; 88 insert(_queue[prio]->next(), op); 89 } 90 91 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) { 92 _queue_length[prio]++; 93 insert(_queue[prio]->prev(), op); 94 } 95 96 97 void VMOperationQueue::unlink(VM_Operation* q) { 98 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); 99 q->prev()->set_next(q->next()); 100 q->next()->set_prev(q->prev()); 101 } 102 103 VM_Operation* VMOperationQueue::queue_remove_front(int prio) { 104 if (queue_empty(prio)) return NULL; 105 assert(_queue_length[prio] >= 0, "sanity check"); 106 _queue_length[prio]--; 107 VM_Operation* r = _queue[prio]->next(); 108 assert(r != _queue[prio], "cannot remove base element"); 109 unlink(r); 110 return r; 111 } 112 113 VM_Operation* VMOperationQueue::queue_drain(int prio) { 114 if (queue_empty(prio)) return NULL; 115 DEBUG_ONLY(int length = _queue_length[prio];); 116 assert(length >= 0, "sanity check"); 117 _queue_length[prio] = 0; 118 VM_Operation* r = _queue[prio]->next(); 119 assert(r != _queue[prio], "cannot remove base element"); 120 // remove links to base element from head and tail 121 r->set_prev(NULL); 122 _queue[prio]->prev()->set_next(NULL); 123 // restore queue to empty state 124 _queue[prio]->set_next(_queue[prio]); 125 _queue[prio]->set_prev(_queue[prio]); 126 assert(queue_empty(prio), "drain corrupted queue"); 127 #ifdef ASSERT 128 int len = 0; 129 VM_Operation* cur; 130 for(cur = r; cur != NULL; cur=cur->next()) len++; 131 assert(len == length, "drain lost some ops"); 132 #endif 133 return r; 134 } 135 136 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) { 137 VM_Operation* cur = _queue[queue]; 138 cur = cur->next(); 139 while (cur != _queue[queue]) { 140 cur->oops_do(f); 141 cur = cur->next(); 142 } 143 } 144 145 void VMOperationQueue::drain_list_oops_do(OopClosure* f) { 146 VM_Operation* cur = _drain_list; 147 while (cur != NULL) { 148 cur->oops_do(f); 149 cur = cur->next(); 150 } 151 } 152 153 //----------------------------------------------------------------- 154 // High-level interface 155 bool VMOperationQueue::add(VM_Operation *op) { 156 157 HOTSPOT_VMOPS_REQUEST( 158 (char *) op->name(), strlen(op->name()), 159 op->evaluation_mode()); 160 161 // Encapsulates VM queue policy. Currently, that 162 // only involves putting them on the right list 163 if (op->evaluate_at_safepoint()) { 164 queue_add_back(SafepointPriority, op); 165 return true; 166 } 167 168 queue_add_back(MediumPriority, op); 169 return true; 170 } 171 172 VM_Operation* VMOperationQueue::remove_next() { 173 // Assuming VMOperation queue is two-level priority queue. If there are 174 // more than two priorities, we need a different scheduling algorithm. 175 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2, 176 "current algorithm does not work"); 177 178 // simple counter based scheduling to prevent starvation of lower priority 179 // queue. -- see 4390175 180 int high_prio, low_prio; 181 if (_queue_counter++ < 10) { 182 high_prio = SafepointPriority; 183 low_prio = MediumPriority; 184 } else { 185 _queue_counter = 0; 186 high_prio = MediumPriority; 187 low_prio = SafepointPriority; 188 } 189 190 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio); 191 } 192 193 void VMOperationQueue::oops_do(OopClosure* f) { 194 for(int i = 0; i < nof_priorities; i++) { 195 queue_oops_do(i, f); 196 } 197 drain_list_oops_do(f); 198 } 199 200 201 //------------------------------------------------------------------------------------------------------------------ 202 // Implementation of VMThread stuff 203 204 bool VMThread::_should_terminate = false; 205 bool VMThread::_terminated = false; 206 Monitor* VMThread::_terminate_lock = NULL; 207 VMThread* VMThread::_vm_thread = NULL; 208 VM_Operation* VMThread::_cur_vm_operation = NULL; 209 VMOperationQueue* VMThread::_vm_queue = NULL; 210 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL; 211 const char* VMThread::_no_op_reason = NULL; 212 213 214 void VMThread::create() { 215 assert(vm_thread() == NULL, "we can only allocate one VMThread"); 216 _vm_thread = new VMThread(); 217 218 // Create VM operation queue 219 _vm_queue = new VMOperationQueue(); 220 guarantee(_vm_queue != NULL, "just checking"); 221 222 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true, 223 Monitor::_safepoint_check_never); 224 225 if (UsePerfData) { 226 // jvmstat performance counters 227 Thread* THREAD = Thread::current(); 228 _perf_accumulated_vm_operation_time = 229 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime", 230 PerfData::U_Ticks, CHECK); 231 } 232 } 233 234 VMThread::VMThread() : NamedThread() { 235 set_name("VM Thread"); 236 } 237 238 void VMThread::destroy() { 239 _vm_thread = NULL; // VM thread is gone 240 } 241 242 void VMThread::run() { 243 assert(this == vm_thread(), "check"); 244 245 this->initialize_named_thread(); 246 this->record_stack_base_and_size(); 247 // Notify_lock wait checks on active_handles() to rewait in 248 // case of spurious wakeup, it should wait on the last 249 // value set prior to the notify 250 this->set_active_handles(JNIHandleBlock::allocate_block()); 251 252 { 253 MutexLocker ml(Notify_lock); 254 Notify_lock->notify(); 255 } 256 // Notify_lock is destroyed by Threads::create_vm() 257 258 int prio = (VMThreadPriority == -1) 259 ? os::java_to_os_priority[NearMaxPriority] 260 : VMThreadPriority; 261 // Note that I cannot call os::set_priority because it expects Java 262 // priorities and I am *explicitly* using OS priorities so that it's 263 // possible to set the VM thread priority higher than any Java thread. 264 os::set_native_priority( this, prio ); 265 266 // Wait for VM_Operations until termination 267 this->loop(); 268 269 // Note the intention to exit before safepointing. 270 // 6295565 This has the effect of waiting for any large tty 271 // outputs to finish. 272 if (xtty != NULL) { 273 ttyLocker ttyl; 274 xtty->begin_elem("destroy_vm"); 275 xtty->stamp(); 276 xtty->end_elem(); 277 assert(should_terminate(), "termination flag must be set"); 278 } 279 280 // 4526887 let VM thread exit at Safepoint 281 _no_op_reason = "Halt"; 282 SafepointSynchronize::begin(); 283 284 if (VerifyBeforeExit) { 285 HandleMark hm(VMThread::vm_thread()); 286 // Among other things, this ensures that Eden top is correct. 287 Universe::heap()->prepare_for_verify(); 288 // Silent verification so as not to pollute normal output, 289 // unless we really asked for it. 290 Universe::verify(); 291 } 292 293 CompileBroker::set_should_block(); 294 295 // wait for threads (compiler threads or daemon threads) in the 296 // _thread_in_native state to block. 297 VM_Exit::wait_for_threads_in_native_to_block(); 298 299 // signal other threads that VM process is gone 300 { 301 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows 302 // VM thread to enter any lock at Safepoint as long as its _owner is NULL. 303 // If that happens after _terminate_lock->wait() has unset _owner 304 // but before it actually drops the lock and waits, the notification below 305 // may get lost and we will have a hang. To avoid this, we need to use 306 // Mutex::lock_without_safepoint_check(). 307 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 308 _terminated = true; 309 _terminate_lock->notify(); 310 } 311 312 // We are now racing with the VM termination being carried out in 313 // another thread, so we don't "delete this". Numerous threads don't 314 // get deleted when the VM terminates 315 316 } 317 318 319 // Notify the VMThread that the last non-daemon JavaThread has terminated, 320 // and wait until operation is performed. 321 void VMThread::wait_for_vm_thread_exit() { 322 { MutexLocker mu(VMOperationQueue_lock); 323 _should_terminate = true; 324 VMOperationQueue_lock->notify(); 325 } 326 327 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint 328 // because this thread has been removed from the threads list. But anything 329 // that could get blocked by Safepoint should not be used after this point, 330 // otherwise we will hang, since there is no one can end the safepoint. 331 332 // Wait until VM thread is terminated 333 // Note: it should be OK to use Terminator_lock here. But this is called 334 // at a very delicate time (VM shutdown) and we are operating in non- VM 335 // thread at Safepoint. It's safer to not share lock with other threads. 336 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 337 while(!VMThread::is_terminated()) { 338 _terminate_lock->wait(Mutex::_no_safepoint_check_flag); 339 } 340 } 341 } 342 343 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) { 344 assert(event != NULL, "invariant"); 345 assert(event->should_commit(), "invariant"); 346 assert(op != NULL, "invariant"); 347 const bool is_concurrent = op->evaluate_concurrently(); 348 const bool evaluate_at_safepoint = op->evaluate_at_safepoint(); 349 event->set_operation(op->type()); 350 event->set_safepoint(evaluate_at_safepoint); 351 event->set_blocking(!is_concurrent); 352 // Only write caller thread information for non-concurrent vm operations. 353 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown. 354 // This is because the caller thread could have exited already. 355 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread())); 356 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0); 357 event->commit(); 358 } 359 360 void VMThread::evaluate_operation(VM_Operation* op) { 361 ResourceMark rm; 362 363 { 364 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time()); 365 HOTSPOT_VMOPS_BEGIN( 366 (char *) op->name(), strlen(op->name()), 367 op->evaluation_mode()); 368 369 EventExecuteVMOperation event; 370 op->evaluate(); 371 if (event.should_commit()) { 372 post_vm_operation_event(&event, op); 373 } 374 375 HOTSPOT_VMOPS_END( 376 (char *) op->name(), strlen(op->name()), 377 op->evaluation_mode()); 378 } 379 380 // Last access of info in _cur_vm_operation! 381 bool c_heap_allocated = op->is_cheap_allocated(); 382 383 // Mark as completed 384 if (!op->evaluate_concurrently()) { 385 op->calling_thread()->increment_vm_operation_completed_count(); 386 } 387 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call, 388 // since if it is stack allocated the calling thread might have deallocated 389 if (c_heap_allocated) { 390 delete _cur_vm_operation; 391 } 392 } 393 394 bool VMThread::no_op_safepoint_needed(bool check_time) { 395 if (SafepointALot) { 396 _no_op_reason = "SafepointALot"; 397 return true; 398 } 399 if (!SafepointSynchronize::is_cleanup_needed()) { 400 return false; 401 } 402 if (check_time) { 403 long interval = SafepointSynchronize::last_non_safepoint_interval(); 404 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && 405 (interval > GuaranteedSafepointInterval); 406 if (!max_time_exceeded) { 407 return false; 408 } 409 } 410 _no_op_reason = "Cleanup"; 411 return true; 412 } 413 414 void VMThread::loop() { 415 assert(_cur_vm_operation == NULL, "no current one should be executing"); 416 417 while(true) { 418 VM_Operation* safepoint_ops = NULL; 419 // 420 // Wait for VM operation 421 // 422 // use no_safepoint_check to get lock without attempting to "sneak" 423 { MutexLocker mu_queue(VMOperationQueue_lock); 424 425 // Look for new operation 426 assert(_cur_vm_operation == NULL, "no current one should be executing"); 427 _cur_vm_operation = _vm_queue->remove_next(); 428 429 // Stall time tracking code 430 if (PrintVMQWaitTime && _cur_vm_operation != NULL && 431 !_cur_vm_operation->evaluate_concurrently()) { 432 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp(); 433 if (stall > 0) 434 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall); 435 } 436 437 while (!should_terminate() && _cur_vm_operation == NULL) { 438 // wait with a timeout to guarantee safepoints at regular intervals 439 bool timedout = 440 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag, 441 GuaranteedSafepointInterval); 442 443 // Support for self destruction 444 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() && 445 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) { 446 tty->print_cr("VM self-destructed"); 447 exit(-1); 448 } 449 450 if (timedout && VMThread::no_op_safepoint_needed(false)) { 451 MutexUnlocker mul(VMOperationQueue_lock); 452 // Force a safepoint since we have not had one for at least 453 // 'GuaranteedSafepointInterval' milliseconds. This will run all 454 // the clean-up processing that needs to be done regularly at a 455 // safepoint 456 SafepointSynchronize::begin(); 457 #ifdef ASSERT 458 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot(); 459 #endif 460 SafepointSynchronize::end(); 461 } 462 _cur_vm_operation = _vm_queue->remove_next(); 463 464 // If we are at a safepoint we will evaluate all the operations that 465 // follow that also require a safepoint 466 if (_cur_vm_operation != NULL && 467 _cur_vm_operation->evaluate_at_safepoint()) { 468 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 469 } 470 } 471 472 if (should_terminate()) break; 473 } // Release mu_queue_lock 474 475 // 476 // Execute VM operation 477 // 478 { HandleMark hm(VMThread::vm_thread()); 479 480 EventMark em("Executing VM operation: %s", vm_operation()->name()); 481 assert(_cur_vm_operation != NULL, "we should have found an operation to execute"); 482 483 // If we are at a safepoint we will evaluate all the operations that 484 // follow that also require a safepoint 485 if (_cur_vm_operation->evaluate_at_safepoint()) { 486 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name()); 487 488 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned 489 490 SafepointSynchronize::begin(); 491 evaluate_operation(_cur_vm_operation); 492 // now process all queued safepoint ops, iteratively draining 493 // the queue until there are none left 494 do { 495 _cur_vm_operation = safepoint_ops; 496 if (_cur_vm_operation != NULL) { 497 do { 498 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name()); 499 // evaluate_operation deletes the op object so we have 500 // to grab the next op now 501 VM_Operation* next = _cur_vm_operation->next(); 502 _vm_queue->set_drain_list(next); 503 evaluate_operation(_cur_vm_operation); 504 _cur_vm_operation = next; 505 if (log_is_enabled(Debug, safepoint, stats)) { 506 SafepointSynchronize::inc_vmop_coalesced_count(); 507 } 508 } while (_cur_vm_operation != NULL); 509 } 510 // There is a chance that a thread enqueued a safepoint op 511 // since we released the op-queue lock and initiated the safepoint. 512 // So we drain the queue again if there is anything there, as an 513 // optimization to try and reduce the number of safepoints. 514 // As the safepoint synchronizes us with JavaThreads we will see 515 // any enqueue made by a JavaThread, but the peek will not 516 // necessarily detect a concurrent enqueue by a GC thread, but 517 // that simply means the op will wait for the next major cycle of the 518 // VMThread - just as it would if the GC thread lost the race for 519 // the lock. 520 if (_vm_queue->peek_at_safepoint_priority()) { 521 // must hold lock while draining queue 522 MutexLocker mu_queue(VMOperationQueue_lock); 523 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 524 } else { 525 safepoint_ops = NULL; 526 } 527 } while(safepoint_ops != NULL); 528 529 _vm_queue->set_drain_list(NULL); 530 531 // Complete safepoint synchronization 532 SafepointSynchronize::end(); 533 534 } else { // not a safepoint operation 535 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name()); 536 if (TraceLongCompiles) { 537 elapsedTimer t; 538 t.start(); 539 evaluate_operation(_cur_vm_operation); 540 t.stop(); 541 double secs = t.seconds(); 542 if (secs * 1e3 > LongCompileThreshold) { 543 // XXX - _cur_vm_operation should not be accessed after 544 // the completed count has been incremented; the waiting 545 // thread may have already freed this memory. 546 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs); 547 } 548 } else { 549 evaluate_operation(_cur_vm_operation); 550 } 551 552 _cur_vm_operation = NULL; 553 } 554 } 555 556 // 557 // Notify (potential) waiting Java thread(s) - lock without safepoint 558 // check so that sneaking is not possible 559 { MutexLockerEx mu(VMOperationRequest_lock); 560 VMOperationRequest_lock->notify_all(); 561 } 562 563 // 564 // We want to make sure that we get to a safepoint regularly. 565 // 566 if (VMThread::no_op_safepoint_needed(true)) { 567 HandleMark hm(VMThread::vm_thread()); 568 SafepointSynchronize::begin(); 569 SafepointSynchronize::end(); 570 } 571 } 572 } 573 574 // A SkipGCALot object is used to elide the usual effect of gc-a-lot 575 // over a section of execution by a thread. Currently, it's used only to 576 // prevent re-entrant calls to GC. 577 class SkipGCALot : public StackObj { 578 private: 579 bool _saved; 580 Thread* _t; 581 582 public: 583 #ifdef ASSERT 584 SkipGCALot(Thread* t) : _t(t) { 585 _saved = _t->skip_gcalot(); 586 _t->set_skip_gcalot(true); 587 } 588 589 ~SkipGCALot() { 590 assert(_t->skip_gcalot(), "Save-restore protocol invariant"); 591 _t->set_skip_gcalot(_saved); 592 } 593 #else 594 SkipGCALot(Thread* t) { } 595 ~SkipGCALot() { } 596 #endif 597 }; 598 599 void VMThread::execute(VM_Operation* op) { 600 Thread* t = Thread::current(); 601 602 if (!t->is_VM_thread()) { 603 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot 604 // JavaThread or WatcherThread 605 bool concurrent = op->evaluate_concurrently(); 606 // only blocking VM operations need to verify the caller's safepoint state: 607 if (!concurrent) { 608 t->check_for_valid_safepoint_state(true); 609 } 610 611 // New request from Java thread, evaluate prologue 612 if (!op->doit_prologue()) { 613 return; // op was cancelled 614 } 615 616 // Setup VM_operations for execution 617 op->set_calling_thread(t, Thread::get_priority(t)); 618 619 // It does not make sense to execute the epilogue, if the VM operation object is getting 620 // deallocated by the VM thread. 621 bool execute_epilog = !op->is_cheap_allocated(); 622 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated"); 623 624 // Get ticket number for non-concurrent VM operations 625 int ticket = 0; 626 if (!concurrent) { 627 ticket = t->vm_operation_ticket(); 628 } 629 630 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the 631 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests 632 // to be queued up during a safepoint synchronization. 633 { 634 VMOperationQueue_lock->lock(); 635 log_debug(vmthread)("Adding VM operation: %s", op->name()); 636 bool ok = _vm_queue->add(op); 637 op->set_timestamp(os::javaTimeMillis()); 638 VMOperationQueue_lock->notify(); 639 VMOperationQueue_lock->unlock(); 640 // VM_Operation got skipped 641 if (!ok) { 642 assert(concurrent, "can only skip concurrent tasks"); 643 if (op->is_cheap_allocated()) delete op; 644 return; 645 } 646 } 647 648 if (!concurrent) { 649 // Wait for completion of request (non-concurrent) 650 // Note: only a JavaThread triggers the safepoint check when locking 651 MutexLocker mu(VMOperationRequest_lock); 652 while(t->vm_operation_completed_count() < ticket) { 653 VMOperationRequest_lock->wait(!t->is_Java_thread()); 654 } 655 } 656 657 if (execute_epilog) { 658 op->doit_epilogue(); 659 } 660 } else { 661 // invoked by VM thread; usually nested VM operation 662 assert(t->is_VM_thread(), "must be a VM thread"); 663 VM_Operation* prev_vm_operation = vm_operation(); 664 if (prev_vm_operation != NULL) { 665 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler 666 // does not allow nested scavenges or compiles. 667 if (!prev_vm_operation->allow_nested_vm_operations()) { 668 fatal("Nested VM operation %s requested by operation %s", 669 op->name(), vm_operation()->name()); 670 } 671 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority()); 672 } 673 674 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name()); 675 676 // Release all internal handles after operation is evaluated 677 HandleMark hm(t); 678 _cur_vm_operation = op; 679 680 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) { 681 SafepointSynchronize::begin(); 682 op->evaluate(); 683 SafepointSynchronize::end(); 684 } else { 685 op->evaluate(); 686 } 687 688 // Free memory if needed 689 if (op->is_cheap_allocated()) delete op; 690 691 _cur_vm_operation = prev_vm_operation; 692 } 693 } 694 695 696 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) { 697 Thread::oops_do(f, cf); 698 _vm_queue->oops_do(f); 699 } 700 701 //------------------------------------------------------------------------------------------------------------------ 702 #ifndef PRODUCT 703 704 void VMOperationQueue::verify_queue(int prio) { 705 // Check that list is correctly linked 706 int length = _queue_length[prio]; 707 VM_Operation *cur = _queue[prio]; 708 int i; 709 710 // Check forward links 711 for(i = 0; i < length; i++) { 712 cur = cur->next(); 713 assert(cur != _queue[prio], "list to short (forward)"); 714 } 715 assert(cur->next() == _queue[prio], "list to long (forward)"); 716 717 // Check backwards links 718 cur = _queue[prio]; 719 for(i = 0; i < length; i++) { 720 cur = cur->prev(); 721 assert(cur != _queue[prio], "list to short (backwards)"); 722 } 723 assert(cur->prev() == _queue[prio], "list to long (backwards)"); 724 } 725 726 #endif 727 728 void VMThread::verify() { 729 oops_do(&VerifyOopClosure::verify_oop, NULL); 730 }