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/vmOperations.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(); 246 247 // 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 assert(Thread::current()->is_Java_thread(), "Should be a JavaThread"); 323 assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated"); 324 { MutexLockerEx mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); 325 _should_terminate = true; 326 VMOperationQueue_lock->notify(); 327 } 328 329 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint 330 // because this thread has been removed from the threads list. But anything 331 // that could get blocked by Safepoint should not be used after this point, 332 // otherwise we will hang, since there is no one can end the safepoint. 333 334 // Wait until VM thread is terminated 335 // Note: it should be OK to use Terminator_lock here. But this is called 336 // at a very delicate time (VM shutdown) and we are operating in non- VM 337 // thread at Safepoint. It's safer to not share lock with other threads. 338 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 339 while(!VMThread::is_terminated()) { 340 _terminate_lock->wait(Mutex::_no_safepoint_check_flag); 341 } 342 } 343 } 344 345 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) { 346 assert(event != NULL, "invariant"); 347 assert(event->should_commit(), "invariant"); 348 assert(op != NULL, "invariant"); 349 const bool is_concurrent = op->evaluate_concurrently(); 350 const bool evaluate_at_safepoint = op->evaluate_at_safepoint(); 351 event->set_operation(op->type()); 352 event->set_safepoint(evaluate_at_safepoint); 353 event->set_blocking(!is_concurrent); 354 // Only write caller thread information for non-concurrent vm operations. 355 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown. 356 // This is because the caller thread could have exited already. 357 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread())); 358 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0); 359 event->commit(); 360 } 361 362 void VMThread::evaluate_operation(VM_Operation* op) { 363 ResourceMark rm; 364 365 { 366 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time()); 367 HOTSPOT_VMOPS_BEGIN( 368 (char *) op->name(), strlen(op->name()), 369 op->evaluation_mode()); 370 371 EventExecuteVMOperation event; 372 op->evaluate(); 373 if (event.should_commit()) { 374 post_vm_operation_event(&event, op); 375 } 376 377 HOTSPOT_VMOPS_END( 378 (char *) op->name(), strlen(op->name()), 379 op->evaluation_mode()); 380 } 381 382 // Last access of info in _cur_vm_operation! 383 bool c_heap_allocated = op->is_cheap_allocated(); 384 385 // Mark as completed 386 if (!op->evaluate_concurrently()) { 387 op->calling_thread()->increment_vm_operation_completed_count(); 388 } 389 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call, 390 // since if it is stack allocated the calling thread might have deallocated 391 if (c_heap_allocated) { 392 delete _cur_vm_operation; 393 } 394 } 395 396 bool VMThread::no_op_safepoint_needed(bool check_time) { 397 if (SafepointALot) { 398 _no_op_reason = "SafepointALot"; 399 return true; 400 } 401 if (!SafepointSynchronize::is_cleanup_needed()) { 402 return false; 403 } 404 if (check_time) { 405 long interval = SafepointSynchronize::last_non_safepoint_interval(); 406 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && 407 (interval > GuaranteedSafepointInterval); 408 if (!max_time_exceeded) { 409 return false; 410 } 411 } 412 _no_op_reason = "Cleanup"; 413 return true; 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) && !VMError::is_error_reported() && 448 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) { 449 tty->print_cr("VM self-destructed"); 450 exit(-1); 451 } 452 453 if (timedout && VMThread::no_op_safepoint_needed(false)) { 454 MutexUnlockerEx mul(VMOperationQueue_lock, 455 Mutex::_no_safepoint_check_flag); 456 // Force a safepoint since we have not had one for at least 457 // 'GuaranteedSafepointInterval' milliseconds. This will run all 458 // the clean-up processing that needs to be done regularly at a 459 // safepoint 460 SafepointSynchronize::begin(); 461 #ifdef ASSERT 462 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot(); 463 #endif 464 SafepointSynchronize::end(); 465 } 466 _cur_vm_operation = _vm_queue->remove_next(); 467 468 // If we are at a safepoint we will evaluate all the operations that 469 // follow that also require a safepoint 470 if (_cur_vm_operation != NULL && 471 _cur_vm_operation->evaluate_at_safepoint()) { 472 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 473 } 474 } 475 476 if (should_terminate()) break; 477 } // Release mu_queue_lock 478 479 // 480 // Execute VM operation 481 // 482 { HandleMark hm(VMThread::vm_thread()); 483 484 EventMark em("Executing VM operation: %s", vm_operation()->name()); 485 assert(_cur_vm_operation != NULL, "we should have found an operation to execute"); 486 487 // If we are at a safepoint we will evaluate all the operations that 488 // follow that also require a safepoint 489 if (_cur_vm_operation->evaluate_at_safepoint()) { 490 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name()); 491 492 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned 493 494 SafepointSynchronize::begin(); 495 evaluate_operation(_cur_vm_operation); 496 // now process all queued safepoint ops, iteratively draining 497 // the queue until there are none left 498 do { 499 _cur_vm_operation = safepoint_ops; 500 if (_cur_vm_operation != NULL) { 501 do { 502 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name()); 503 // evaluate_operation deletes the op object so we have 504 // to grab the next op now 505 VM_Operation* next = _cur_vm_operation->next(); 506 _vm_queue->set_drain_list(next); 507 evaluate_operation(_cur_vm_operation); 508 _cur_vm_operation = next; 509 if (log_is_enabled(Debug, safepoint, stats)) { 510 SafepointSynchronize::inc_vmop_coalesced_count(); 511 } 512 } while (_cur_vm_operation != NULL); 513 } 514 // There is a chance that a thread enqueued a safepoint op 515 // since we released the op-queue lock and initiated the safepoint. 516 // So we drain the queue again if there is anything there, as an 517 // optimization to try and reduce the number of safepoints. 518 // As the safepoint synchronizes us with JavaThreads we will see 519 // any enqueue made by a JavaThread, but the peek will not 520 // necessarily detect a concurrent enqueue by a GC thread, but 521 // that simply means the op will wait for the next major cycle of the 522 // VMThread - just as it would if the GC thread lost the race for 523 // the lock. 524 if (_vm_queue->peek_at_safepoint_priority()) { 525 // must hold lock while draining queue 526 MutexLockerEx mu_queue(VMOperationQueue_lock, 527 Mutex::_no_safepoint_check_flag); 528 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 529 } else { 530 safepoint_ops = NULL; 531 } 532 } while(safepoint_ops != NULL); 533 534 _vm_queue->set_drain_list(NULL); 535 536 // Complete safepoint synchronization 537 SafepointSynchronize::end(); 538 539 } else { // not a safepoint operation 540 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name()); 541 if (TraceLongCompiles) { 542 elapsedTimer t; 543 t.start(); 544 evaluate_operation(_cur_vm_operation); 545 t.stop(); 546 double secs = t.seconds(); 547 if (secs * 1e3 > LongCompileThreshold) { 548 // XXX - _cur_vm_operation should not be accessed after 549 // the completed count has been incremented; the waiting 550 // thread may have already freed this memory. 551 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs); 552 } 553 } else { 554 evaluate_operation(_cur_vm_operation); 555 } 556 557 _cur_vm_operation = NULL; 558 } 559 } 560 561 // 562 // Notify (potential) waiting Java thread(s) - lock without safepoint 563 // check so that sneaking is not possible 564 { MutexLockerEx mu(VMOperationRequest_lock, 565 Mutex::_no_safepoint_check_flag); 566 VMOperationRequest_lock->notify_all(); 567 } 568 569 // 570 // We want to make sure that we get to a safepoint regularly. 571 // 572 if (VMThread::no_op_safepoint_needed(true)) { 573 HandleMark hm(VMThread::vm_thread()); 574 SafepointSynchronize::begin(); 575 SafepointSynchronize::end(); 576 } 577 } 578 } 579 580 // A SkipGCALot object is used to elide the usual effect of gc-a-lot 581 // over a section of execution by a thread. Currently, it's used only to 582 // prevent re-entrant calls to GC. 583 class SkipGCALot : public StackObj { 584 private: 585 bool _saved; 586 Thread* _t; 587 588 public: 589 #ifdef ASSERT 590 SkipGCALot(Thread* t) : _t(t) { 591 _saved = _t->skip_gcalot(); 592 _t->set_skip_gcalot(true); 593 } 594 595 ~SkipGCALot() { 596 assert(_t->skip_gcalot(), "Save-restore protocol invariant"); 597 _t->set_skip_gcalot(_saved); 598 } 599 #else 600 SkipGCALot(Thread* t) { } 601 ~SkipGCALot() { } 602 #endif 603 }; 604 605 void VMThread::execute(VM_Operation* op) { 606 Thread* t = Thread::current(); 607 608 if (!t->is_VM_thread()) { 609 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot 610 // JavaThread or WatcherThread 611 bool concurrent = op->evaluate_concurrently(); 612 // only blocking VM operations need to verify the caller's safepoint state: 613 if (!concurrent) { 614 t->check_for_valid_safepoint_state(true); 615 } 616 617 // New request from Java thread, evaluate prologue 618 if (!op->doit_prologue()) { 619 return; // op was cancelled 620 } 621 622 // Setup VM_operations for execution 623 op->set_calling_thread(t, Thread::get_priority(t)); 624 625 // It does not make sense to execute the epilogue, if the VM operation object is getting 626 // deallocated by the VM thread. 627 bool execute_epilog = !op->is_cheap_allocated(); 628 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated"); 629 630 // Get ticket number for non-concurrent VM operations 631 int ticket = 0; 632 if (!concurrent) { 633 ticket = t->vm_operation_ticket(); 634 } 635 636 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the 637 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests 638 // to be queued up during a safepoint synchronization. 639 { 640 VMOperationQueue_lock->lock_without_safepoint_check(); 641 log_debug(vmthread)("Adding VM operation: %s", op->name()); 642 bool ok = _vm_queue->add(op); 643 op->set_timestamp(os::javaTimeMillis()); 644 VMOperationQueue_lock->notify(); 645 VMOperationQueue_lock->unlock(); 646 // VM_Operation got skipped 647 if (!ok) { 648 assert(concurrent, "can only skip concurrent tasks"); 649 if (op->is_cheap_allocated()) delete op; 650 return; 651 } 652 } 653 654 if (!concurrent) { 655 // Wait for completion of request (non-concurrent) 656 // Note: only a JavaThread triggers the safepoint check when locking 657 MutexLocker mu(VMOperationRequest_lock); 658 while(t->vm_operation_completed_count() < ticket) { 659 VMOperationRequest_lock->wait(!t->is_Java_thread()); 660 } 661 } 662 663 if (execute_epilog) { 664 op->doit_epilogue(); 665 } 666 } else { 667 // invoked by VM thread; usually nested VM operation 668 assert(t->is_VM_thread(), "must be a VM thread"); 669 VM_Operation* prev_vm_operation = vm_operation(); 670 if (prev_vm_operation != NULL) { 671 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler 672 // does not allow nested scavenges or compiles. 673 if (!prev_vm_operation->allow_nested_vm_operations()) { 674 fatal("Nested VM operation %s requested by operation %s", 675 op->name(), vm_operation()->name()); 676 } 677 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority()); 678 } 679 680 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name()); 681 682 // Release all internal handles after operation is evaluated 683 HandleMark hm(t); 684 _cur_vm_operation = op; 685 686 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) { 687 SafepointSynchronize::begin(); 688 op->evaluate(); 689 SafepointSynchronize::end(); 690 } else { 691 op->evaluate(); 692 } 693 694 // Free memory if needed 695 if (op->is_cheap_allocated()) delete op; 696 697 _cur_vm_operation = prev_vm_operation; 698 } 699 } 700 701 702 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) { 703 Thread::oops_do(f, cf); 704 _vm_queue->oops_do(f); 705 } 706 707 //------------------------------------------------------------------------------------------------------------------ 708 #ifndef PRODUCT 709 710 void VMOperationQueue::verify_queue(int prio) { 711 // Check that list is correctly linked 712 int length = _queue_length[prio]; 713 VM_Operation *cur = _queue[prio]; 714 int i; 715 716 // Check forward links 717 for(i = 0; i < length; i++) { 718 cur = cur->next(); 719 assert(cur != _queue[prio], "list to short (forward)"); 720 } 721 assert(cur->next() == _queue[prio], "list to long (forward)"); 722 723 // Check backwards links 724 cur = _queue[prio]; 725 for(i = 0; i < length; i++) { 726 cur = cur->prev(); 727 assert(cur != _queue[prio], "list to short (backwards)"); 728 } 729 assert(cur->prev() == _queue[prio], "list to long (backwards)"); 730 } 731 732 #endif 733 734 void VMThread::verify() { 735 oops_do(&VerifyOopClosure::verify_oop, NULL); 736 }