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 "oops/method.hpp" 35 #include "oops/oop.inline.hpp" 36 #include "oops/verifyOopClosure.hpp" 37 #include "runtime/handles.inline.hpp" 38 #include "runtime/interfaceSupport.inline.hpp" 39 #include "runtime/mutexLocker.hpp" 40 #include "runtime/os.hpp" 41 #include "runtime/safepoint.hpp" 42 #include "runtime/thread.inline.hpp" 43 #include "runtime/vmThread.hpp" 44 #include "runtime/vmOperations.hpp" 45 #include "services/runtimeService.hpp" 46 #include "utilities/dtrace.hpp" 47 #include "utilities/events.hpp" 48 #include "utilities/vmError.hpp" 49 #include "utilities/xmlstream.hpp" 50 51 VMOperationQueue::VMOperationQueue() { 52 // The queue is a circular doubled-linked list, which always contains 53 // one element (i.e., one element means empty). 54 for(int i = 0; i < nof_priorities; i++) { 55 _queue_length[i] = 0; 56 _queue_counter = 0; 57 _queue[i] = new VM_None("QueueHead"); 58 _queue[i]->set_next(_queue[i]); 59 _queue[i]->set_prev(_queue[i]); 60 } 61 _drain_list = NULL; 62 } 63 64 65 bool VMOperationQueue::queue_empty(int prio) { 66 // It is empty if there is exactly one element 67 bool empty = (_queue[prio] == _queue[prio]->next()); 68 assert( (_queue_length[prio] == 0 && empty) || 69 (_queue_length[prio] > 0 && !empty), "sanity check"); 70 return _queue_length[prio] == 0; 71 } 72 73 // Inserts an element to the right of the q element 74 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) { 75 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); 76 n->set_prev(q); 77 n->set_next(q->next()); 78 q->next()->set_prev(n); 79 q->set_next(n); 80 } 81 82 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) { 83 _queue_length[prio]++; 84 insert(_queue[prio]->next(), op); 85 } 86 87 void VMOperationQueue::queue_add_back(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 bool VMOperationQueue::add(VM_Operation *op) { 152 153 HOTSPOT_VMOPS_REQUEST( 154 (char *) op->name(), strlen(op->name()), 155 op->evaluation_mode()); 156 157 // Encapsulates VM queue policy. Currently, that 158 // only involves putting them on the right list 159 if (op->evaluate_at_safepoint()) { 160 queue_add_back(SafepointPriority, op); 161 return true; 162 } 163 164 queue_add_back(MediumPriority, op); 165 return true; 166 } 167 168 VM_Operation* VMOperationQueue::remove_next() { 169 // Assuming VMOperation queue is two-level priority queue. If there are 170 // more than two priorities, we need a different scheduling algorithm. 171 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2, 172 "current algorithm does not work"); 173 174 // simple counter based scheduling to prevent starvation of lower priority 175 // queue. -- see 4390175 176 int high_prio, low_prio; 177 if (_queue_counter++ < 10) { 178 high_prio = SafepointPriority; 179 low_prio = MediumPriority; 180 } else { 181 _queue_counter = 0; 182 high_prio = MediumPriority; 183 low_prio = SafepointPriority; 184 } 185 186 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio); 187 } 188 189 void VMOperationQueue::oops_do(OopClosure* f) { 190 for(int i = 0; i < nof_priorities; i++) { 191 queue_oops_do(i, f); 192 } 193 drain_list_oops_do(f); 194 } 195 196 //------------------------------------------------------------------------------------------------------------------ 197 // Timeout machinery 198 199 void VMOperationTimeoutTask::task() { 200 assert(AbortVMOnVMOperationTimeout, "only if enabled"); 201 if (is_armed()) { 202 jlong delay = (os::javaTimeMillis() - _arm_time); 203 if (delay > AbortVMOnVMOperationTimeoutDelay) { 204 fatal("VM operation took too long: " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)", 205 delay, AbortVMOnVMOperationTimeoutDelay); 206 } 207 } 208 } 209 210 bool VMOperationTimeoutTask::is_armed() { 211 return OrderAccess::load_acquire(&_armed) != 0; 212 } 213 214 void VMOperationTimeoutTask::arm() { 215 _arm_time = os::javaTimeMillis(); 216 OrderAccess::release_store_fence(&_armed, 1); 217 } 218 219 void VMOperationTimeoutTask::disarm() { 220 OrderAccess::release_store_fence(&_armed, 0); 221 } 222 223 //------------------------------------------------------------------------------------------------------------------ 224 // Implementation of VMThread stuff 225 226 bool VMThread::_should_terminate = false; 227 bool VMThread::_terminated = false; 228 Monitor* VMThread::_terminate_lock = NULL; 229 VMThread* VMThread::_vm_thread = NULL; 230 VM_Operation* VMThread::_cur_vm_operation = NULL; 231 VMOperationQueue* VMThread::_vm_queue = NULL; 232 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL; 233 uint64_t VMThread::_coalesced_count = 0; 234 VMOperationTimeoutTask* VMThread::_timeout_task = NULL; 235 236 237 void VMThread::create() { 238 assert(vm_thread() == NULL, "we can only allocate one VMThread"); 239 _vm_thread = new VMThread(); 240 241 if (AbortVMOnVMOperationTimeout) { 242 // Make sure we call the timeout task frequently enough, but not too frequent. 243 // Try to make the interval 10% of the timeout delay, so that we miss the timeout 244 // by those 10% at max. Periodic task also expects it to fit min/max intervals. 245 size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10; 246 interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran; 247 interval = MAX2<size_t>(interval, PeriodicTask::min_interval); 248 interval = MIN2<size_t>(interval, PeriodicTask::max_interval); 249 250 _timeout_task = new VMOperationTimeoutTask(interval); 251 _timeout_task->enroll(); 252 } else { 253 assert(_timeout_task == NULL, "sanity"); 254 } 255 256 // Create VM operation queue 257 _vm_queue = new VMOperationQueue(); 258 guarantee(_vm_queue != NULL, "just checking"); 259 260 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true, 261 Monitor::_safepoint_check_never); 262 263 if (UsePerfData) { 264 // jvmstat performance counters 265 Thread* THREAD = Thread::current(); 266 _perf_accumulated_vm_operation_time = 267 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime", 268 PerfData::U_Ticks, CHECK); 269 } 270 } 271 272 VMThread::VMThread() : NamedThread() { 273 set_name("VM Thread"); 274 } 275 276 void VMThread::destroy() { 277 _vm_thread = NULL; // VM thread is gone 278 } 279 280 static VM_None halt_op("Halt"); 281 282 void VMThread::run() { 283 assert(this == vm_thread(), "check"); 284 285 // Notify_lock wait checks on active_handles() to rewait in 286 // case of spurious wakeup, it should wait on the last 287 // value set prior to the notify 288 this->set_active_handles(JNIHandleBlock::allocate_block()); 289 290 { 291 MutexLocker ml(Notify_lock); 292 Notify_lock->notify(); 293 } 294 // Notify_lock is destroyed by Threads::create_vm() 295 296 int prio = (VMThreadPriority == -1) 297 ? os::java_to_os_priority[NearMaxPriority] 298 : VMThreadPriority; 299 // Note that I cannot call os::set_priority because it expects Java 300 // priorities and I am *explicitly* using OS priorities so that it's 301 // possible to set the VM thread priority higher than any Java thread. 302 os::set_native_priority( this, prio ); 303 304 // Wait for VM_Operations until termination 305 this->loop(); 306 307 // Note the intention to exit before safepointing. 308 // 6295565 This has the effect of waiting for any large tty 309 // outputs to finish. 310 if (xtty != NULL) { 311 ttyLocker ttyl; 312 xtty->begin_elem("destroy_vm"); 313 xtty->stamp(); 314 xtty->end_elem(); 315 assert(should_terminate(), "termination flag must be set"); 316 } 317 318 // 4526887 let VM thread exit at Safepoint 319 _cur_vm_operation = &halt_op; 320 SafepointSynchronize::begin(); 321 322 if (VerifyBeforeExit) { 323 HandleMark hm(VMThread::vm_thread()); 324 // Among other things, this ensures that Eden top is correct. 325 Universe::heap()->prepare_for_verify(); 326 // Silent verification so as not to pollute normal output, 327 // unless we really asked for it. 328 Universe::verify(); 329 } 330 331 CompileBroker::set_should_block(); 332 333 // wait for threads (compiler threads or daemon threads) in the 334 // _thread_in_native state to block. 335 VM_Exit::wait_for_threads_in_native_to_block(); 336 337 // signal other threads that VM process is gone 338 { 339 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows 340 // VM thread to enter any lock at Safepoint as long as its _owner is NULL. 341 // If that happens after _terminate_lock->wait() has unset _owner 342 // but before it actually drops the lock and waits, the notification below 343 // may get lost and we will have a hang. To avoid this, we need to use 344 // Mutex::lock_without_safepoint_check(). 345 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 346 _terminated = true; 347 _terminate_lock->notify(); 348 } 349 350 // We are now racing with the VM termination being carried out in 351 // another thread, so we don't "delete this". Numerous threads don't 352 // get deleted when the VM terminates 353 354 } 355 356 357 // Notify the VMThread that the last non-daemon JavaThread has terminated, 358 // and wait until operation is performed. 359 void VMThread::wait_for_vm_thread_exit() { 360 assert(Thread::current()->is_Java_thread(), "Should be a JavaThread"); 361 assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated"); 362 { MutexLockerEx mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); 363 _should_terminate = true; 364 VMOperationQueue_lock->notify(); 365 } 366 367 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint 368 // because this thread has been removed from the threads list. But anything 369 // that could get blocked by Safepoint should not be used after this point, 370 // otherwise we will hang, since there is no one can end the safepoint. 371 372 // Wait until VM thread is terminated 373 // Note: it should be OK to use Terminator_lock here. But this is called 374 // at a very delicate time (VM shutdown) and we are operating in non- VM 375 // thread at Safepoint. It's safer to not share lock with other threads. 376 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 377 while(!VMThread::is_terminated()) { 378 _terminate_lock->wait(Mutex::_no_safepoint_check_flag); 379 } 380 } 381 } 382 383 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) { 384 assert(event != NULL, "invariant"); 385 assert(event->should_commit(), "invariant"); 386 assert(op != NULL, "invariant"); 387 const bool is_concurrent = op->evaluate_concurrently(); 388 const bool evaluate_at_safepoint = op->evaluate_at_safepoint(); 389 event->set_operation(op->type()); 390 event->set_safepoint(evaluate_at_safepoint); 391 event->set_blocking(!is_concurrent); 392 // Only write caller thread information for non-concurrent vm operations. 393 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown. 394 // This is because the caller thread could have exited already. 395 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread())); 396 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0); 397 event->commit(); 398 } 399 400 void VMThread::evaluate_operation(VM_Operation* op) { 401 ResourceMark rm; 402 403 { 404 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time()); 405 HOTSPOT_VMOPS_BEGIN( 406 (char *) op->name(), strlen(op->name()), 407 op->evaluation_mode()); 408 409 EventExecuteVMOperation event; 410 op->evaluate(); 411 if (event.should_commit()) { 412 post_vm_operation_event(&event, op); 413 } 414 415 HOTSPOT_VMOPS_END( 416 (char *) op->name(), strlen(op->name()), 417 op->evaluation_mode()); 418 } 419 420 // Last access of info in _cur_vm_operation! 421 bool c_heap_allocated = op->is_cheap_allocated(); 422 423 // Mark as completed 424 if (!op->evaluate_concurrently()) { 425 op->calling_thread()->increment_vm_operation_completed_count(); 426 } 427 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call, 428 // since if it is stack allocated the calling thread might have deallocated 429 if (c_heap_allocated) { 430 delete _cur_vm_operation; 431 } 432 } 433 434 static VM_None safepointALot_op("SafepointALot"); 435 static VM_Cleanup cleanup_op; 436 437 class HandshakeALotTC : public ThreadClosure { 438 public: 439 virtual void do_thread(Thread* thread) { 440 #ifdef ASSERT 441 assert(thread->is_Java_thread(), "must be"); 442 JavaThread* jt = (JavaThread*)thread; 443 jt->verify_states_for_handshake(); 444 #endif 445 } 446 }; 447 448 VM_Operation* VMThread::no_op_safepoint() { 449 // Check for handshakes first since we may need to return a VMop. 450 if (HandshakeALot) { 451 HandshakeALotTC haltc; 452 Handshake::execute(&haltc); 453 } 454 // Check for a cleanup before SafepointALot to keep stats correct. 455 long interval_ms = SafepointTracing::time_since_last_safepoint_ms(); 456 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && 457 (interval_ms >= GuaranteedSafepointInterval); 458 if (max_time_exceeded && SafepointSynchronize::is_cleanup_needed()) { 459 return &cleanup_op; 460 } 461 if (SafepointALot) { 462 return &safepointALot_op; 463 } 464 // Nothing to be done. 465 return NULL; 466 } 467 468 void VMThread::loop() { 469 assert(_cur_vm_operation == NULL, "no current one should be executing"); 470 471 SafepointSynchronize::init(_vm_thread); 472 473 while(true) { 474 VM_Operation* safepoint_ops = NULL; 475 // 476 // Wait for VM operation 477 // 478 // use no_safepoint_check to get lock without attempting to "sneak" 479 { MutexLockerEx mu_queue(VMOperationQueue_lock, 480 Mutex::_no_safepoint_check_flag); 481 482 // Look for new operation 483 assert(_cur_vm_operation == NULL, "no current one should be executing"); 484 _cur_vm_operation = _vm_queue->remove_next(); 485 486 // Stall time tracking code 487 if (PrintVMQWaitTime && _cur_vm_operation != NULL && 488 !_cur_vm_operation->evaluate_concurrently()) { 489 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp(); 490 if (stall > 0) 491 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall); 492 } 493 494 while (!should_terminate() && _cur_vm_operation == NULL) { 495 // wait with a timeout to guarantee safepoints at regular intervals 496 bool timedout = 497 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag, 498 GuaranteedSafepointInterval); 499 500 // Support for self destruction 501 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() && 502 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) { 503 tty->print_cr("VM self-destructed"); 504 exit(-1); 505 } 506 507 { 508 // Have to unlock VMOperationQueue_lock just in case no_op_safepoint() 509 // has to do a handshake. 510 MutexUnlockerEx mul(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); 511 if (timedout && (_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) { 512 // Force a safepoint since we have not had one for at least 513 // 'GuaranteedSafepointInterval' milliseconds and we need to clean 514 // something. This will run all the clean-up processing that needs 515 // to be done at a safepoint. 516 SafepointSynchronize::begin(); 517 #ifdef ASSERT 518 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot(); 519 #endif 520 SafepointSynchronize::end(); 521 _cur_vm_operation = NULL; 522 } 523 } 524 _cur_vm_operation = _vm_queue->remove_next(); 525 526 // If we are at a safepoint we will evaluate all the operations that 527 // follow that also require a safepoint 528 if (_cur_vm_operation != NULL && 529 _cur_vm_operation->evaluate_at_safepoint()) { 530 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 531 } 532 } 533 534 if (should_terminate()) break; 535 } // Release mu_queue_lock 536 537 // 538 // Execute VM operation 539 // 540 { HandleMark hm(VMThread::vm_thread()); 541 542 EventMark em("Executing VM operation: %s", vm_operation()->name()); 543 assert(_cur_vm_operation != NULL, "we should have found an operation to execute"); 544 545 // If we are at a safepoint we will evaluate all the operations that 546 // follow that also require a safepoint 547 if (_cur_vm_operation->evaluate_at_safepoint()) { 548 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name()); 549 550 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned 551 552 SafepointSynchronize::begin(); 553 554 if (_timeout_task != NULL) { 555 _timeout_task->arm(); 556 } 557 558 evaluate_operation(_cur_vm_operation); 559 // now process all queued safepoint ops, iteratively draining 560 // the queue until there are none left 561 do { 562 _cur_vm_operation = safepoint_ops; 563 if (_cur_vm_operation != NULL) { 564 do { 565 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name()); 566 // evaluate_operation deletes the op object so we have 567 // to grab the next op now 568 VM_Operation* next = _cur_vm_operation->next(); 569 _vm_queue->set_drain_list(next); 570 evaluate_operation(_cur_vm_operation); 571 _cur_vm_operation = next; 572 _coalesced_count++; 573 } while (_cur_vm_operation != NULL); 574 } 575 // There is a chance that a thread enqueued a safepoint op 576 // since we released the op-queue lock and initiated the safepoint. 577 // So we drain the queue again if there is anything there, as an 578 // optimization to try and reduce the number of safepoints. 579 // As the safepoint synchronizes us with JavaThreads we will see 580 // any enqueue made by a JavaThread, but the peek will not 581 // necessarily detect a concurrent enqueue by a GC thread, but 582 // that simply means the op will wait for the next major cycle of the 583 // VMThread - just as it would if the GC thread lost the race for 584 // the lock. 585 if (_vm_queue->peek_at_safepoint_priority()) { 586 // must hold lock while draining queue 587 MutexLockerEx mu_queue(VMOperationQueue_lock, 588 Mutex::_no_safepoint_check_flag); 589 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 590 } else { 591 safepoint_ops = NULL; 592 } 593 } while(safepoint_ops != NULL); 594 595 _vm_queue->set_drain_list(NULL); 596 597 if (_timeout_task != NULL) { 598 _timeout_task->disarm(); 599 } 600 601 // Complete safepoint synchronization 602 SafepointSynchronize::end(); 603 604 } else { // not a safepoint operation 605 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name()); 606 if (TraceLongCompiles) { 607 elapsedTimer t; 608 t.start(); 609 evaluate_operation(_cur_vm_operation); 610 t.stop(); 611 double secs = t.seconds(); 612 if (secs * 1e3 > LongCompileThreshold) { 613 // XXX - _cur_vm_operation should not be accessed after 614 // the completed count has been incremented; the waiting 615 // thread may have already freed this memory. 616 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs); 617 } 618 } else { 619 evaluate_operation(_cur_vm_operation); 620 } 621 622 _cur_vm_operation = NULL; 623 } 624 } 625 626 // 627 // Notify (potential) waiting Java thread(s) - lock without safepoint 628 // check so that sneaking is not possible 629 { MutexLockerEx mu(VMOperationRequest_lock, 630 Mutex::_no_safepoint_check_flag); 631 VMOperationRequest_lock->notify_all(); 632 } 633 634 // We want to make sure that we get to a safepoint regularly 635 // even when executing VMops that don't require safepoints. 636 if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) { 637 HandleMark hm(VMThread::vm_thread()); 638 SafepointSynchronize::begin(); 639 SafepointSynchronize::end(); 640 _cur_vm_operation = NULL; 641 } 642 } 643 } 644 645 // A SkipGCALot object is used to elide the usual effect of gc-a-lot 646 // over a section of execution by a thread. Currently, it's used only to 647 // prevent re-entrant calls to GC. 648 class SkipGCALot : public StackObj { 649 private: 650 bool _saved; 651 Thread* _t; 652 653 public: 654 #ifdef ASSERT 655 SkipGCALot(Thread* t) : _t(t) { 656 _saved = _t->skip_gcalot(); 657 _t->set_skip_gcalot(true); 658 } 659 660 ~SkipGCALot() { 661 assert(_t->skip_gcalot(), "Save-restore protocol invariant"); 662 _t->set_skip_gcalot(_saved); 663 } 664 #else 665 SkipGCALot(Thread* t) { } 666 ~SkipGCALot() { } 667 #endif 668 }; 669 670 void VMThread::execute(VM_Operation* op) { 671 Thread* t = Thread::current(); 672 673 if (!t->is_VM_thread()) { 674 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot 675 // JavaThread or WatcherThread 676 bool concurrent = op->evaluate_concurrently(); 677 // only blocking VM operations need to verify the caller's safepoint state: 678 if (!concurrent) { 679 t->check_for_valid_safepoint_state(true); 680 } 681 682 // New request from Java thread, evaluate prologue 683 if (!op->doit_prologue()) { 684 return; // op was cancelled 685 } 686 687 // Setup VM_operations for execution 688 op->set_calling_thread(t, Thread::get_priority(t)); 689 690 // It does not make sense to execute the epilogue, if the VM operation object is getting 691 // deallocated by the VM thread. 692 bool execute_epilog = !op->is_cheap_allocated(); 693 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated"); 694 695 // Get ticket number for non-concurrent VM operations 696 int ticket = 0; 697 if (!concurrent) { 698 ticket = t->vm_operation_ticket(); 699 } 700 701 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the 702 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests 703 // to be queued up during a safepoint synchronization. 704 { 705 VMOperationQueue_lock->lock_without_safepoint_check(); 706 log_debug(vmthread)("Adding VM operation: %s", op->name()); 707 bool ok = _vm_queue->add(op); 708 op->set_timestamp(os::javaTimeMillis()); 709 VMOperationQueue_lock->notify(); 710 VMOperationQueue_lock->unlock(); 711 // VM_Operation got skipped 712 if (!ok) { 713 assert(concurrent, "can only skip concurrent tasks"); 714 if (op->is_cheap_allocated()) delete op; 715 return; 716 } 717 } 718 719 if (!concurrent) { 720 // Wait for completion of request (non-concurrent) 721 // Note: only a JavaThread triggers the safepoint check when locking 722 MutexLocker mu(VMOperationRequest_lock); 723 while(t->vm_operation_completed_count() < ticket) { 724 VMOperationRequest_lock->wait(!t->is_Java_thread()); 725 } 726 } 727 728 if (execute_epilog) { 729 op->doit_epilogue(); 730 } 731 } else { 732 // invoked by VM thread; usually nested VM operation 733 assert(t->is_VM_thread(), "must be a VM thread"); 734 VM_Operation* prev_vm_operation = vm_operation(); 735 if (prev_vm_operation != NULL) { 736 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler 737 // does not allow nested scavenges or compiles. 738 if (!prev_vm_operation->allow_nested_vm_operations()) { 739 fatal("Nested VM operation %s requested by operation %s", 740 op->name(), vm_operation()->name()); 741 } 742 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority()); 743 } 744 745 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name()); 746 747 // Release all internal handles after operation is evaluated 748 HandleMark hm(t); 749 _cur_vm_operation = op; 750 751 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) { 752 SafepointSynchronize::begin(); 753 op->evaluate(); 754 SafepointSynchronize::end(); 755 } else { 756 op->evaluate(); 757 } 758 759 // Free memory if needed 760 if (op->is_cheap_allocated()) delete op; 761 762 _cur_vm_operation = prev_vm_operation; 763 } 764 } 765 766 767 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) { 768 Thread::oops_do(f, cf); 769 _vm_queue->oops_do(f); 770 } 771 772 //------------------------------------------------------------------------------------------------------------------ 773 #ifndef PRODUCT 774 775 void VMOperationQueue::verify_queue(int prio) { 776 // Check that list is correctly linked 777 int length = _queue_length[prio]; 778 VM_Operation *cur = _queue[prio]; 779 int i; 780 781 // Check forward links 782 for(i = 0; i < length; i++) { 783 cur = cur->next(); 784 assert(cur != _queue[prio], "list to short (forward)"); 785 } 786 assert(cur->next() == _queue[prio], "list to long (forward)"); 787 788 // Check backwards links 789 cur = _queue[prio]; 790 for(i = 0; i < length; i++) { 791 cur = cur->prev(); 792 assert(cur != _queue[prio], "list to short (backwards)"); 793 } 794 assert(cur->prev() == _queue[prio], "list to long (backwards)"); 795 } 796 797 #endif 798 799 void VMThread::verify() { 800 oops_do(&VerifyOopClosure::verify_oop, NULL); 801 }