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