1 /* 2 * Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "compiler/compileBroker.hpp" 27 #include "gc/shared/collectedHeap.hpp" 28 #include "jfr/jfrEvents.hpp" 29 #include "jfr/support/jfrThreadId.hpp" 30 #include "logging/log.hpp" 31 #include "logging/logStream.hpp" 32 #include "logging/logConfiguration.hpp" 33 #include "memory/resourceArea.hpp" 34 #include "memory/universe.hpp" 35 #include "oops/method.hpp" 36 #include "oops/oop.inline.hpp" 37 #include "oops/verifyOopClosure.hpp" 38 #include "runtime/handles.inline.hpp" 39 #include "runtime/interfaceSupport.inline.hpp" 40 #include "runtime/mutexLocker.hpp" 41 #include "runtime/os.hpp" 42 #include "runtime/safepoint.hpp" 43 #include "runtime/thread.inline.hpp" 44 #include "runtime/vmThread.hpp" 45 #include "runtime/vmOperations.hpp" 46 #include "services/runtimeService.hpp" 47 #include "utilities/dtrace.hpp" 48 #include "utilities/events.hpp" 49 #include "utilities/vmError.hpp" 50 #include "utilities/xmlstream.hpp" 51 52 VMOperationQueue::VMOperationQueue() { 53 // The queue is a circular doubled-linked list, which always contains 54 // one element (i.e., one element means empty). 55 for(int i = 0; i < nof_priorities; i++) { 56 _queue_length[i] = 0; 57 _queue_counter = 0; 58 _queue[i] = new VM_None("QueueHead"); 59 _queue[i]->set_next(_queue[i]); 60 _queue[i]->set_prev(_queue[i]); 61 } 62 _drain_list = NULL; 63 } 64 65 66 bool VMOperationQueue::queue_empty(int prio) { 67 // It is empty if there is exactly one element 68 bool empty = (_queue[prio] == _queue[prio]->next()); 69 assert( (_queue_length[prio] == 0 && empty) || 70 (_queue_length[prio] > 0 && !empty), "sanity check"); 71 return _queue_length[prio] == 0; 72 } 73 74 // Inserts an element to the right of the q element 75 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) { 76 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); 77 n->set_prev(q); 78 n->set_next(q->next()); 79 q->next()->set_prev(n); 80 q->set_next(n); 81 } 82 83 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) { 84 _queue_length[prio]++; 85 insert(_queue[prio]->next(), op); 86 } 87 88 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) { 89 _queue_length[prio]++; 90 insert(_queue[prio]->prev(), op); 91 } 92 93 94 void VMOperationQueue::unlink(VM_Operation* q) { 95 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); 96 q->prev()->set_next(q->next()); 97 q->next()->set_prev(q->prev()); 98 } 99 100 VM_Operation* VMOperationQueue::queue_remove_front(int prio) { 101 if (queue_empty(prio)) return NULL; 102 assert(_queue_length[prio] >= 0, "sanity check"); 103 _queue_length[prio]--; 104 VM_Operation* r = _queue[prio]->next(); 105 assert(r != _queue[prio], "cannot remove base element"); 106 unlink(r); 107 return r; 108 } 109 110 VM_Operation* VMOperationQueue::queue_drain(int prio) { 111 if (queue_empty(prio)) return NULL; 112 DEBUG_ONLY(int length = _queue_length[prio];); 113 assert(length >= 0, "sanity check"); 114 _queue_length[prio] = 0; 115 VM_Operation* r = _queue[prio]->next(); 116 assert(r != _queue[prio], "cannot remove base element"); 117 // remove links to base element from head and tail 118 r->set_prev(NULL); 119 _queue[prio]->prev()->set_next(NULL); 120 // restore queue to empty state 121 _queue[prio]->set_next(_queue[prio]); 122 _queue[prio]->set_prev(_queue[prio]); 123 assert(queue_empty(prio), "drain corrupted queue"); 124 #ifdef ASSERT 125 int len = 0; 126 VM_Operation* cur; 127 for(cur = r; cur != NULL; cur=cur->next()) len++; 128 assert(len == length, "drain lost some ops"); 129 #endif 130 return r; 131 } 132 133 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) { 134 VM_Operation* cur = _queue[queue]; 135 cur = cur->next(); 136 while (cur != _queue[queue]) { 137 cur->oops_do(f); 138 cur = cur->next(); 139 } 140 } 141 142 void VMOperationQueue::drain_list_oops_do(OopClosure* f) { 143 VM_Operation* cur = _drain_list; 144 while (cur != NULL) { 145 cur->oops_do(f); 146 cur = cur->next(); 147 } 148 } 149 150 //----------------------------------------------------------------- 151 // High-level interface 152 void VMOperationQueue::add(VM_Operation *op) { 153 154 HOTSPOT_VMOPS_REQUEST( 155 (char *) op->name(), strlen(op->name()), 156 op->evaluation_mode()); 157 158 // Encapsulates VM queue policy. Currently, that 159 // only involves putting them on the right list 160 queue_add_back(op->evaluate_at_safepoint() ? SafepointPriority : MediumPriority, op); 161 } 162 163 VM_Operation* VMOperationQueue::remove_next() { 164 // Assuming VMOperation queue is two-level priority queue. If there are 165 // more than two priorities, we need a different scheduling algorithm. 166 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2, 167 "current algorithm does not work"); 168 169 // simple counter based scheduling to prevent starvation of lower priority 170 // queue. -- see 4390175 171 int high_prio, low_prio; 172 if (_queue_counter++ < 10) { 173 high_prio = SafepointPriority; 174 low_prio = MediumPriority; 175 } else { 176 _queue_counter = 0; 177 high_prio = MediumPriority; 178 low_prio = SafepointPriority; 179 } 180 181 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio); 182 } 183 184 void VMOperationQueue::oops_do(OopClosure* f) { 185 for(int i = 0; i < nof_priorities; i++) { 186 queue_oops_do(i, f); 187 } 188 drain_list_oops_do(f); 189 } 190 191 //------------------------------------------------------------------------------------------------------------------ 192 // Timeout machinery 193 194 void VMOperationTimeoutTask::task() { 195 assert(AbortVMOnVMOperationTimeout, "only if enabled"); 196 if (is_armed()) { 197 jlong delay = (os::javaTimeMillis() - _arm_time); 198 if (delay > AbortVMOnVMOperationTimeoutDelay) { 199 fatal("VM operation took too long: " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)", 200 delay, AbortVMOnVMOperationTimeoutDelay); 201 } 202 } 203 } 204 205 bool VMOperationTimeoutTask::is_armed() { 206 return OrderAccess::load_acquire(&_armed) != 0; 207 } 208 209 void VMOperationTimeoutTask::arm() { 210 _arm_time = os::javaTimeMillis(); 211 OrderAccess::release_store_fence(&_armed, 1); 212 } 213 214 void VMOperationTimeoutTask::disarm() { 215 OrderAccess::release_store_fence(&_armed, 0); 216 } 217 218 //------------------------------------------------------------------------------------------------------------------ 219 // Implementation of VMThread stuff 220 221 bool VMThread::_should_terminate = false; 222 bool VMThread::_terminated = false; 223 Monitor* VMThread::_terminate_lock = NULL; 224 VMThread* VMThread::_vm_thread = NULL; 225 VM_Operation* VMThread::_cur_vm_operation = NULL; 226 VMOperationQueue* VMThread::_vm_queue = NULL; 227 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL; 228 uint64_t VMThread::_coalesced_count = 0; 229 VMOperationTimeoutTask* VMThread::_timeout_task = NULL; 230 231 232 void VMThread::create() { 233 assert(vm_thread() == NULL, "we can only allocate one VMThread"); 234 _vm_thread = new VMThread(); 235 236 if (AbortVMOnVMOperationTimeout) { 237 // Make sure we call the timeout task frequently enough, but not too frequent. 238 // Try to make the interval 10% of the timeout delay, so that we miss the timeout 239 // by those 10% at max. Periodic task also expects it to fit min/max intervals. 240 size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10; 241 interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran; 242 interval = MAX2<size_t>(interval, PeriodicTask::min_interval); 243 interval = MIN2<size_t>(interval, PeriodicTask::max_interval); 244 245 _timeout_task = new VMOperationTimeoutTask(interval); 246 _timeout_task->enroll(); 247 } else { 248 assert(_timeout_task == NULL, "sanity"); 249 } 250 251 // Create VM operation queue 252 _vm_queue = new VMOperationQueue(); 253 guarantee(_vm_queue != NULL, "just checking"); 254 255 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true, 256 Monitor::_safepoint_check_never); 257 258 if (UsePerfData) { 259 // jvmstat performance counters 260 Thread* THREAD = Thread::current(); 261 _perf_accumulated_vm_operation_time = 262 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime", 263 PerfData::U_Ticks, CHECK); 264 } 265 } 266 267 VMThread::VMThread() : NamedThread() { 268 set_name("VM Thread"); 269 } 270 271 void VMThread::destroy() { 272 _vm_thread = NULL; // VM thread is gone 273 } 274 275 static VM_None halt_op("Halt"); 276 277 void VMThread::run() { 278 assert(this == vm_thread(), "check"); 279 280 // Notify_lock wait checks on active_handles() to rewait in 281 // case of spurious wakeup, it should wait on the last 282 // value set prior to the notify 283 this->set_active_handles(JNIHandleBlock::allocate_block()); 284 285 { 286 MutexLocker ml(Notify_lock); 287 Notify_lock->notify(); 288 } 289 // Notify_lock is destroyed by Threads::create_vm() 290 291 int prio = (VMThreadPriority == -1) 292 ? os::java_to_os_priority[NearMaxPriority] 293 : VMThreadPriority; 294 // Note that I cannot call os::set_priority because it expects Java 295 // priorities and I am *explicitly* using OS priorities so that it's 296 // possible to set the VM thread priority higher than any Java thread. 297 os::set_native_priority( this, prio ); 298 299 // Wait for VM_Operations until termination 300 this->loop(); 301 302 // Note the intention to exit before safepointing. 303 // 6295565 This has the effect of waiting for any large tty 304 // outputs to finish. 305 if (xtty != NULL) { 306 ttyLocker ttyl; 307 xtty->begin_elem("destroy_vm"); 308 xtty->stamp(); 309 xtty->end_elem(); 310 assert(should_terminate(), "termination flag must be set"); 311 } 312 313 // 4526887 let VM thread exit at Safepoint 314 _cur_vm_operation = &halt_op; 315 SafepointSynchronize::begin(); 316 317 if (VerifyBeforeExit) { 318 HandleMark hm(VMThread::vm_thread()); 319 // Among other things, this ensures that Eden top is correct. 320 Universe::heap()->prepare_for_verify(); 321 // Silent verification so as not to pollute normal output, 322 // unless we really asked for it. 323 Universe::verify(); 324 } 325 326 CompileBroker::set_should_block(); 327 328 // wait for threads (compiler threads or daemon threads) in the 329 // _thread_in_native state to block. 330 VM_Exit::wait_for_threads_in_native_to_block(); 331 332 // signal other threads that VM process is gone 333 { 334 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows 335 // VM thread to enter any lock at Safepoint as long as its _owner is NULL. 336 // If that happens after _terminate_lock->wait() has unset _owner 337 // but before it actually drops the lock and waits, the notification below 338 // may get lost and we will have a hang. To avoid this, we need to use 339 // Mutex::lock_without_safepoint_check(). 340 MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 341 _terminated = true; 342 ml.notify(); 343 } 344 345 // We are now racing with the VM termination being carried out in 346 // another thread, so we don't "delete this". Numerous threads don't 347 // get deleted when the VM terminates 348 349 } 350 351 352 // Notify the VMThread that the last non-daemon JavaThread has terminated, 353 // and wait until operation is performed. 354 void VMThread::wait_for_vm_thread_exit() { 355 assert(Thread::current()->is_Java_thread(), "Should be a JavaThread"); 356 assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated"); 357 { MutexLocker mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); 358 _should_terminate = true; 359 VMOperationQueue_lock->notify(); 360 } 361 362 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint 363 // because this thread has been removed from the threads list. But anything 364 // that could get blocked by Safepoint should not be used after this point, 365 // otherwise we will hang, since there is no one can end the safepoint. 366 367 // Wait until VM thread is terminated 368 // Note: it should be OK to use Terminator_lock here. But this is called 369 // at a very delicate time (VM shutdown) and we are operating in non- VM 370 // thread at Safepoint. It's safer to not share lock with other threads. 371 { MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 372 while(!VMThread::is_terminated()) { 373 ml.wait(); 374 } 375 } 376 } 377 378 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) { 379 assert(event != NULL, "invariant"); 380 assert(event->should_commit(), "invariant"); 381 assert(op != NULL, "invariant"); 382 const bool is_concurrent = op->evaluate_concurrently(); 383 const bool evaluate_at_safepoint = op->evaluate_at_safepoint(); 384 event->set_operation(op->type()); 385 event->set_safepoint(evaluate_at_safepoint); 386 event->set_blocking(!is_concurrent); 387 // Only write caller thread information for non-concurrent vm operations. 388 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown. 389 // This is because the caller thread could have exited already. 390 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread())); 391 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0); 392 event->commit(); 393 } 394 395 void VMThread::evaluate_operation(VM_Operation* op) { 396 ResourceMark rm; 397 398 { 399 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time()); 400 HOTSPOT_VMOPS_BEGIN( 401 (char *) op->name(), strlen(op->name()), 402 op->evaluation_mode()); 403 404 EventExecuteVMOperation event; 405 op->evaluate(); 406 if (event.should_commit()) { 407 post_vm_operation_event(&event, op); 408 } 409 410 HOTSPOT_VMOPS_END( 411 (char *) op->name(), strlen(op->name()), 412 op->evaluation_mode()); 413 } 414 415 // Last access of info in _cur_vm_operation! 416 bool c_heap_allocated = op->is_cheap_allocated(); 417 418 // Mark as completed 419 if (!op->evaluate_concurrently()) { 420 op->calling_thread()->increment_vm_operation_completed_count(); 421 } 422 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call, 423 // since if it is stack allocated the calling thread might have deallocated 424 if (c_heap_allocated) { 425 delete _cur_vm_operation; 426 } 427 } 428 429 static VM_None safepointALot_op("SafepointALot"); 430 static VM_Cleanup cleanup_op; 431 432 class HandshakeALotTC : public ThreadClosure { 433 public: 434 virtual void do_thread(Thread* thread) { 435 #ifdef ASSERT 436 assert(thread->is_Java_thread(), "must be"); 437 JavaThread* jt = (JavaThread*)thread; 438 jt->verify_states_for_handshake(); 439 #endif 440 } 441 }; 442 443 VM_Operation* VMThread::no_op_safepoint() { 444 // Check for handshakes first since we may need to return a VMop. 445 if (HandshakeALot) { 446 HandshakeALotTC haltc; 447 Handshake::execute(&haltc); 448 } 449 // Check for a cleanup before SafepointALot to keep stats correct. 450 long interval_ms = SafepointTracing::time_since_last_safepoint_ms(); 451 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && 452 (interval_ms >= GuaranteedSafepointInterval); 453 if (max_time_exceeded && SafepointSynchronize::is_cleanup_needed()) { 454 return &cleanup_op; 455 } 456 if (SafepointALot) { 457 return &safepointALot_op; 458 } 459 // Nothing to be done. 460 return NULL; 461 } 462 463 void VMThread::loop() { 464 assert(_cur_vm_operation == NULL, "no current one should be executing"); 465 466 SafepointSynchronize::init(_vm_thread); 467 468 while(true) { 469 VM_Operation* safepoint_ops = NULL; 470 // 471 // Wait for VM operation 472 // 473 // use no_safepoint_check to get lock without attempting to "sneak" 474 { MonitorLocker mu_queue(VMOperationQueue_lock, 475 Mutex::_no_safepoint_check_flag); 476 477 // Look for new operation 478 assert(_cur_vm_operation == NULL, "no current one should be executing"); 479 _cur_vm_operation = _vm_queue->remove_next(); 480 481 // Stall time tracking code 482 if (PrintVMQWaitTime && _cur_vm_operation != NULL && 483 !_cur_vm_operation->evaluate_concurrently()) { 484 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp(); 485 if (stall > 0) 486 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall); 487 } 488 489 while (!should_terminate() && _cur_vm_operation == NULL) { 490 // wait with a timeout to guarantee safepoints at regular intervals 491 bool timedout = 492 mu_queue.wait(GuaranteedSafepointInterval); 493 494 // Support for self destruction 495 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() && 496 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) { 497 tty->print_cr("VM self-destructed"); 498 exit(-1); 499 } 500 501 if (timedout) { 502 // Have to unlock VMOperationQueue_lock just in case no_op_safepoint() 503 // has to do a handshake. 504 MutexUnlocker mul(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); 505 if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) { 506 // Force a safepoint since we have not had one for at least 507 // 'GuaranteedSafepointInterval' milliseconds and we need to clean 508 // something. This will run all the clean-up processing that needs 509 // to be done at a safepoint. 510 SafepointSynchronize::begin(); 511 #ifdef ASSERT 512 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot(); 513 #endif 514 SafepointSynchronize::end(); 515 _cur_vm_operation = NULL; 516 } 517 } 518 _cur_vm_operation = _vm_queue->remove_next(); 519 520 // If we are at a safepoint we will evaluate all the operations that 521 // follow that also require a safepoint 522 if (_cur_vm_operation != NULL && 523 _cur_vm_operation->evaluate_at_safepoint()) { 524 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 525 } 526 } 527 528 if (should_terminate()) break; 529 } // Release mu_queue_lock 530 531 // 532 // Execute VM operation 533 // 534 { HandleMark hm(VMThread::vm_thread()); 535 536 EventMark em("Executing VM operation: %s", vm_operation()->name()); 537 assert(_cur_vm_operation != NULL, "we should have found an operation to execute"); 538 539 // If we are at a safepoint we will evaluate all the operations that 540 // follow that also require a safepoint 541 if (_cur_vm_operation->evaluate_at_safepoint()) { 542 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name()); 543 544 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned 545 546 SafepointSynchronize::begin(); 547 548 if (_timeout_task != NULL) { 549 _timeout_task->arm(); 550 } 551 552 evaluate_operation(_cur_vm_operation); 553 // now process all queued safepoint ops, iteratively draining 554 // the queue until there are none left 555 do { 556 _cur_vm_operation = safepoint_ops; 557 if (_cur_vm_operation != NULL) { 558 do { 559 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name()); 560 // evaluate_operation deletes the op object so we have 561 // to grab the next op now 562 VM_Operation* next = _cur_vm_operation->next(); 563 _vm_queue->set_drain_list(next); 564 evaluate_operation(_cur_vm_operation); 565 _cur_vm_operation = next; 566 _coalesced_count++; 567 } while (_cur_vm_operation != NULL); 568 } 569 // There is a chance that a thread enqueued a safepoint op 570 // since we released the op-queue lock and initiated the safepoint. 571 // So we drain the queue again if there is anything there, as an 572 // optimization to try and reduce the number of safepoints. 573 // As the safepoint synchronizes us with JavaThreads we will see 574 // any enqueue made by a JavaThread, but the peek will not 575 // necessarily detect a concurrent enqueue by a GC thread, but 576 // that simply means the op will wait for the next major cycle of the 577 // VMThread - just as it would if the GC thread lost the race for 578 // the lock. 579 if (_vm_queue->peek_at_safepoint_priority()) { 580 // must hold lock while draining queue 581 MutexLocker mu_queue(VMOperationQueue_lock, 582 Mutex::_no_safepoint_check_flag); 583 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 584 } else { 585 safepoint_ops = NULL; 586 } 587 } while(safepoint_ops != NULL); 588 589 _vm_queue->set_drain_list(NULL); 590 591 if (_timeout_task != NULL) { 592 _timeout_task->disarm(); 593 } 594 595 // Complete safepoint synchronization 596 SafepointSynchronize::end(); 597 598 } else { // not a safepoint operation 599 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name()); 600 if (TraceLongCompiles) { 601 elapsedTimer t; 602 t.start(); 603 evaluate_operation(_cur_vm_operation); 604 t.stop(); 605 double secs = t.seconds(); 606 if (secs * 1e3 > LongCompileThreshold) { 607 // XXX - _cur_vm_operation should not be accessed after 608 // the completed count has been incremented; the waiting 609 // thread may have already freed this memory. 610 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs); 611 } 612 } else { 613 evaluate_operation(_cur_vm_operation); 614 } 615 616 _cur_vm_operation = NULL; 617 } 618 } 619 620 // 621 // Notify (potential) waiting Java thread(s) 622 { MutexLocker mu(VMOperationRequest_lock, Mutex::_no_safepoint_check_flag); 623 VMOperationRequest_lock->notify_all(); 624 } 625 626 // We want to make sure that we get to a safepoint regularly 627 // even when executing VMops that don't require safepoints. 628 if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) { 629 HandleMark hm(VMThread::vm_thread()); 630 SafepointSynchronize::begin(); 631 SafepointSynchronize::end(); 632 _cur_vm_operation = NULL; 633 } 634 } 635 } 636 637 // A SkipGCALot object is used to elide the usual effect of gc-a-lot 638 // over a section of execution by a thread. Currently, it's used only to 639 // prevent re-entrant calls to GC. 640 class SkipGCALot : public StackObj { 641 private: 642 bool _saved; 643 Thread* _t; 644 645 public: 646 #ifdef ASSERT 647 SkipGCALot(Thread* t) : _t(t) { 648 _saved = _t->skip_gcalot(); 649 _t->set_skip_gcalot(true); 650 } 651 652 ~SkipGCALot() { 653 assert(_t->skip_gcalot(), "Save-restore protocol invariant"); 654 _t->set_skip_gcalot(_saved); 655 } 656 #else 657 SkipGCALot(Thread* t) { } 658 ~SkipGCALot() { } 659 #endif 660 }; 661 662 void VMThread::execute(VM_Operation* op) { 663 Thread* t = Thread::current(); 664 665 if (!t->is_VM_thread()) { 666 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot 667 // JavaThread or WatcherThread 668 bool concurrent = op->evaluate_concurrently(); 669 // only blocking VM operations need to verify the caller's safepoint state: 670 if (!concurrent) { 671 t->check_for_valid_safepoint_state(true); 672 } 673 674 // New request from Java thread, evaluate prologue 675 if (!op->doit_prologue()) { 676 return; // op was cancelled 677 } 678 679 // Setup VM_operations for execution 680 op->set_calling_thread(t); 681 682 // It does not make sense to execute the epilogue, if the VM operation object is getting 683 // deallocated by the VM thread. 684 bool execute_epilog = !op->is_cheap_allocated(); 685 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated"); 686 687 // Get ticket number for non-concurrent VM operations 688 int ticket = 0; 689 if (!concurrent) { 690 ticket = t->vm_operation_ticket(); 691 } 692 693 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the 694 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests 695 // to be queued up during a safepoint synchronization. 696 { 697 VMOperationQueue_lock->lock_without_safepoint_check(); 698 log_debug(vmthread)("Adding VM operation: %s", op->name()); 699 _vm_queue->add(op); 700 op->set_timestamp(os::javaTimeMillis()); 701 VMOperationQueue_lock->notify(); 702 VMOperationQueue_lock->unlock(); 703 } 704 705 if (!concurrent) { 706 // Wait for completion of request (non-concurrent) 707 // Note: only a JavaThread triggers the safepoint check when locking 708 MonitorLocker ml(VMOperationRequest_lock, 709 t->is_Java_thread() ? Mutex::_safepoint_check_flag : Mutex::_no_safepoint_check_flag); 710 while(t->vm_operation_completed_count() < ticket) { 711 ml.wait(); 712 } 713 } 714 715 if (execute_epilog) { 716 op->doit_epilogue(); 717 } 718 } else { 719 // invoked by VM thread; usually nested VM operation 720 assert(t->is_VM_thread(), "must be a VM thread"); 721 VM_Operation* prev_vm_operation = vm_operation(); 722 if (prev_vm_operation != NULL) { 723 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler 724 // does not allow nested scavenges or compiles. 725 if (!prev_vm_operation->allow_nested_vm_operations()) { 726 fatal("Nested VM operation %s requested by operation %s", 727 op->name(), vm_operation()->name()); 728 } 729 op->set_calling_thread(prev_vm_operation->calling_thread()); 730 } 731 732 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name()); 733 734 // Release all internal handles after operation is evaluated 735 HandleMark hm(t); 736 _cur_vm_operation = op; 737 738 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) { 739 SafepointSynchronize::begin(); 740 op->evaluate(); 741 SafepointSynchronize::end(); 742 } else { 743 op->evaluate(); 744 } 745 746 // Free memory if needed 747 if (op->is_cheap_allocated()) delete op; 748 749 _cur_vm_operation = prev_vm_operation; 750 } 751 } 752 753 754 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) { 755 Thread::oops_do(f, cf); 756 _vm_queue->oops_do(f); 757 } 758 759 //------------------------------------------------------------------------------------------------------------------ 760 #ifndef PRODUCT 761 762 void VMOperationQueue::verify_queue(int prio) { 763 // Check that list is correctly linked 764 int length = _queue_length[prio]; 765 VM_Operation *cur = _queue[prio]; 766 int i; 767 768 // Check forward links 769 for(i = 0; i < length; i++) { 770 cur = cur->next(); 771 assert(cur != _queue[prio], "list to short (forward)"); 772 } 773 assert(cur->next() == _queue[prio], "list to long (forward)"); 774 775 // Check backwards links 776 cur = _queue[prio]; 777 for(i = 0; i < length; i++) { 778 cur = cur->prev(); 779 assert(cur != _queue[prio], "list to short (backwards)"); 780 } 781 assert(cur->prev() == _queue[prio], "list to long (backwards)"); 782 } 783 784 #endif 785 786 void VMThread::verify() { 787 oops_do(&VerifyOopClosure::verify_oop, NULL); 788 }