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/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/interfaceSupport.inline.hpp" 38 #include "runtime/mutexLocker.hpp" 39 #include "runtime/os.hpp" 40 #include "runtime/safepoint.hpp" 41 #include "runtime/thread.inline.hpp" 42 #include "runtime/vmThread.hpp" 43 #include "runtime/vmOperations.hpp" 44 #include "services/runtimeService.hpp" 45 #include "utilities/dtrace.hpp" 46 #include "utilities/events.hpp" 47 #include "utilities/vmError.hpp" 48 #include "utilities/xmlstream.hpp" 49 50 // Dummy VM operation to act as first element in our circular double-linked list 51 class VM_None: public VM_Operation { 52 VMOp_Type type() const { return VMOp_None; } 53 void doit() {}; 54 }; 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] = new VM_None(); 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_front(int prio, VM_Operation *op) { 88 _queue_length[prio]++; 89 insert(_queue[prio]->next(), op); 90 } 91 92 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) { 93 _queue_length[prio]++; 94 insert(_queue[prio]->prev(), op); 95 } 96 97 98 void VMOperationQueue::unlink(VM_Operation* q) { 99 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); 100 q->prev()->set_next(q->next()); 101 q->next()->set_prev(q->prev()); 102 } 103 104 VM_Operation* VMOperationQueue::queue_remove_front(int prio) { 105 if (queue_empty(prio)) return NULL; 106 assert(_queue_length[prio] >= 0, "sanity check"); 107 _queue_length[prio]--; 108 VM_Operation* r = _queue[prio]->next(); 109 assert(r != _queue[prio], "cannot remove base element"); 110 unlink(r); 111 return r; 112 } 113 114 VM_Operation* VMOperationQueue::queue_drain(int prio) { 115 if (queue_empty(prio)) return NULL; 116 DEBUG_ONLY(int length = _queue_length[prio];); 117 assert(length >= 0, "sanity check"); 118 _queue_length[prio] = 0; 119 VM_Operation* r = _queue[prio]->next(); 120 assert(r != _queue[prio], "cannot remove base element"); 121 // remove links to base element from head and tail 122 r->set_prev(NULL); 123 _queue[prio]->prev()->set_next(NULL); 124 // restore queue to empty state 125 _queue[prio]->set_next(_queue[prio]); 126 _queue[prio]->set_prev(_queue[prio]); 127 assert(queue_empty(prio), "drain corrupted queue"); 128 #ifdef ASSERT 129 int len = 0; 130 VM_Operation* cur; 131 for(cur = r; cur != NULL; cur=cur->next()) len++; 132 assert(len == length, "drain lost some ops"); 133 #endif 134 return r; 135 } 136 137 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) { 138 VM_Operation* cur = _queue[queue]; 139 cur = cur->next(); 140 while (cur != _queue[queue]) { 141 cur->oops_do(f); 142 cur = cur->next(); 143 } 144 } 145 146 void VMOperationQueue::drain_list_oops_do(OopClosure* f) { 147 VM_Operation* cur = _drain_list; 148 while (cur != NULL) { 149 cur->oops_do(f); 150 cur = cur->next(); 151 } 152 } 153 154 //----------------------------------------------------------------- 155 // High-level interface 156 bool VMOperationQueue::add(VM_Operation *op) { 157 158 HOTSPOT_VMOPS_REQUEST( 159 (char *) op->name(), strlen(op->name()), 160 op->evaluation_mode()); 161 162 // Encapsulates VM queue policy. Currently, that 163 // only involves putting them on the right list 164 if (op->evaluate_at_safepoint()) { 165 queue_add_back(SafepointPriority, op); 166 return true; 167 } 168 169 queue_add_back(MediumPriority, op); 170 return true; 171 } 172 173 VM_Operation* VMOperationQueue::remove_next() { 174 // Assuming VMOperation queue is two-level priority queue. If there are 175 // more than two priorities, we need a different scheduling algorithm. 176 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2, 177 "current algorithm does not work"); 178 179 // simple counter based scheduling to prevent starvation of lower priority 180 // queue. -- see 4390175 181 int high_prio, low_prio; 182 if (_queue_counter++ < 10) { 183 high_prio = SafepointPriority; 184 low_prio = MediumPriority; 185 } else { 186 _queue_counter = 0; 187 high_prio = MediumPriority; 188 low_prio = SafepointPriority; 189 } 190 191 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio); 192 } 193 194 void VMOperationQueue::oops_do(OopClosure* f) { 195 for(int i = 0; i < nof_priorities; i++) { 196 queue_oops_do(i, f); 197 } 198 drain_list_oops_do(f); 199 } 200 201 //------------------------------------------------------------------------------------------------------------------ 202 // Timeout machinery 203 204 void VMOperationTimeoutTask::task() { 205 assert(AbortVMOnVMOperationTimeout, "only if enabled"); 206 if (is_armed()) { 207 jlong delay = (os::javaTimeMillis() - _arm_time); 208 if (delay > AbortVMOnVMOperationTimeoutDelay) { 209 fatal("VM operation took too long: " SIZE_FORMAT " ms (timeout: " SIZE_FORMAT " ms)", 210 delay, AbortVMOnVMOperationTimeoutDelay); 211 } 212 } 213 } 214 215 bool VMOperationTimeoutTask::is_armed() { 216 return OrderAccess::load_acquire(&_armed) != 0; 217 } 218 219 void VMOperationTimeoutTask::arm() { 220 _arm_time = os::javaTimeMillis(); 221 OrderAccess::release_store_fence(&_armed, 1); 222 } 223 224 void VMOperationTimeoutTask::disarm() { 225 OrderAccess::release_store_fence(&_armed, 0); 226 } 227 228 //------------------------------------------------------------------------------------------------------------------ 229 // Implementation of VMThread stuff 230 231 bool VMThread::_should_terminate = false; 232 bool VMThread::_terminated = false; 233 Monitor* VMThread::_terminate_lock = NULL; 234 VMThread* VMThread::_vm_thread = NULL; 235 VM_Operation* VMThread::_cur_vm_operation = NULL; 236 VMOperationQueue* VMThread::_vm_queue = NULL; 237 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL; 238 const char* VMThread::_no_op_reason = NULL; 239 VMOperationTimeoutTask* VMThread::_timeout_task = NULL; 240 241 242 void VMThread::create() { 243 assert(vm_thread() == NULL, "we can only allocate one VMThread"); 244 _vm_thread = new VMThread(); 245 246 if (AbortVMOnVMOperationTimeout) { 247 // Make sure we call the timeout task frequently enough, but not too frequent. 248 // Try to make the interval 10% of the timeout delay, so that we miss the timeout 249 // by those 10% at max. Periodic task also expects it to fit min/max intervals. 250 size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10; 251 interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran; 252 interval = MAX2<size_t>(interval, PeriodicTask::min_interval); 253 interval = MIN2<size_t>(interval, PeriodicTask::max_interval); 254 255 _timeout_task = new VMOperationTimeoutTask(interval); 256 _timeout_task->enroll(); 257 } else { 258 assert(_timeout_task == NULL, "sanity"); 259 } 260 261 // Create VM operation queue 262 _vm_queue = new VMOperationQueue(); 263 guarantee(_vm_queue != NULL, "just checking"); 264 265 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true, 266 Monitor::_safepoint_check_never); 267 268 if (UsePerfData) { 269 // jvmstat performance counters 270 Thread* THREAD = Thread::current(); 271 _perf_accumulated_vm_operation_time = 272 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime", 273 PerfData::U_Ticks, CHECK); 274 } 275 } 276 277 VMThread::VMThread() : NamedThread() { 278 set_name("VM Thread"); 279 } 280 281 void VMThread::destroy() { 282 _vm_thread = NULL; // VM thread is gone 283 } 284 285 void VMThread::run() { 286 assert(this == vm_thread(), "check"); 287 288 this->initialize_named_thread(); 289 290 // Notify_lock wait checks on active_handles() to rewait in 291 // case of spurious wakeup, it should wait on the last 292 // value set prior to the notify 293 this->set_active_handles(JNIHandleBlock::allocate_block()); 294 295 { 296 MutexLocker ml(Notify_lock); 297 Notify_lock->notify(); 298 } 299 // Notify_lock is destroyed by Threads::create_vm() 300 301 int prio = (VMThreadPriority == -1) 302 ? os::java_to_os_priority[NearMaxPriority] 303 : VMThreadPriority; 304 // Note that I cannot call os::set_priority because it expects Java 305 // priorities and I am *explicitly* using OS priorities so that it's 306 // possible to set the VM thread priority higher than any Java thread. 307 os::set_native_priority( this, prio ); 308 309 // Wait for VM_Operations until termination 310 this->loop(); 311 312 // Note the intention to exit before safepointing. 313 // 6295565 This has the effect of waiting for any large tty 314 // outputs to finish. 315 if (xtty != NULL) { 316 ttyLocker ttyl; 317 xtty->begin_elem("destroy_vm"); 318 xtty->stamp(); 319 xtty->end_elem(); 320 assert(should_terminate(), "termination flag must be set"); 321 } 322 323 // 4526887 let VM thread exit at Safepoint 324 _no_op_reason = "Halt"; 325 SafepointSynchronize::begin(); 326 327 if (VerifyBeforeExit) { 328 HandleMark hm(VMThread::vm_thread()); 329 // Among other things, this ensures that Eden top is correct. 330 Universe::heap()->prepare_for_verify(); 331 // Silent verification so as not to pollute normal output, 332 // unless we really asked for it. 333 Universe::verify(); 334 } 335 336 CompileBroker::set_should_block(); 337 338 // wait for threads (compiler threads or daemon threads) in the 339 // _thread_in_native state to block. 340 VM_Exit::wait_for_threads_in_native_to_block(); 341 342 // signal other threads that VM process is gone 343 { 344 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows 345 // VM thread to enter any lock at Safepoint as long as its _owner is NULL. 346 // If that happens after _terminate_lock->wait() has unset _owner 347 // but before it actually drops the lock and waits, the notification below 348 // may get lost and we will have a hang. To avoid this, we need to use 349 // Mutex::lock_without_safepoint_check(). 350 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 351 _terminated = true; 352 _terminate_lock->notify(); 353 } 354 355 // We are now racing with the VM termination being carried out in 356 // another thread, so we don't "delete this". Numerous threads don't 357 // get deleted when the VM terminates 358 359 } 360 361 362 // Notify the VMThread that the last non-daemon JavaThread has terminated, 363 // and wait until operation is performed. 364 void VMThread::wait_for_vm_thread_exit() { 365 assert(Thread::current()->is_Java_thread(), "Should be a JavaThread"); 366 assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated"); 367 { MutexLockerEx mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag); 368 _should_terminate = true; 369 VMOperationQueue_lock->notify(); 370 } 371 372 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint 373 // because this thread has been removed from the threads list. But anything 374 // that could get blocked by Safepoint should not be used after this point, 375 // otherwise we will hang, since there is no one can end the safepoint. 376 377 // Wait until VM thread is terminated 378 // Note: it should be OK to use Terminator_lock here. But this is called 379 // at a very delicate time (VM shutdown) and we are operating in non- VM 380 // thread at Safepoint. It's safer to not share lock with other threads. 381 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 382 while(!VMThread::is_terminated()) { 383 _terminate_lock->wait(Mutex::_no_safepoint_check_flag); 384 } 385 } 386 } 387 388 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) { 389 assert(event != NULL, "invariant"); 390 assert(event->should_commit(), "invariant"); 391 assert(op != NULL, "invariant"); 392 const bool is_concurrent = op->evaluate_concurrently(); 393 const bool evaluate_at_safepoint = op->evaluate_at_safepoint(); 394 event->set_operation(op->type()); 395 event->set_safepoint(evaluate_at_safepoint); 396 event->set_blocking(!is_concurrent); 397 // Only write caller thread information for non-concurrent vm operations. 398 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown. 399 // This is because the caller thread could have exited already. 400 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread())); 401 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0); 402 event->commit(); 403 } 404 405 void VMThread::evaluate_operation(VM_Operation* op) { 406 ResourceMark rm; 407 408 { 409 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time()); 410 HOTSPOT_VMOPS_BEGIN( 411 (char *) op->name(), strlen(op->name()), 412 op->evaluation_mode()); 413 414 EventExecuteVMOperation event; 415 op->evaluate(); 416 if (event.should_commit()) { 417 post_vm_operation_event(&event, op); 418 } 419 420 HOTSPOT_VMOPS_END( 421 (char *) op->name(), strlen(op->name()), 422 op->evaluation_mode()); 423 } 424 425 // Last access of info in _cur_vm_operation! 426 bool c_heap_allocated = op->is_cheap_allocated(); 427 428 // Mark as completed 429 if (!op->evaluate_concurrently()) { 430 op->calling_thread()->increment_vm_operation_completed_count(); 431 } 432 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call, 433 // since if it is stack allocated the calling thread might have deallocated 434 if (c_heap_allocated) { 435 delete _cur_vm_operation; 436 } 437 } 438 439 bool VMThread::no_op_safepoint_needed(bool check_time) { 440 if (SafepointALot) { 441 _no_op_reason = "SafepointALot"; 442 return true; 443 } 444 if (!SafepointSynchronize::is_cleanup_needed()) { 445 return false; 446 } 447 if (check_time) { 448 long interval = SafepointSynchronize::last_non_safepoint_interval(); 449 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && 450 (interval > GuaranteedSafepointInterval); 451 if (!max_time_exceeded) { 452 return false; 453 } 454 } 455 _no_op_reason = "Cleanup"; 456 return true; 457 } 458 459 void VMThread::loop() { 460 assert(_cur_vm_operation == NULL, "no current one should be executing"); 461 462 while(true) { 463 VM_Operation* safepoint_ops = NULL; 464 // 465 // Wait for VM operation 466 // 467 // use no_safepoint_check to get lock without attempting to "sneak" 468 { MutexLockerEx mu_queue(VMOperationQueue_lock, 469 Mutex::_no_safepoint_check_flag); 470 471 // Look for new operation 472 assert(_cur_vm_operation == NULL, "no current one should be executing"); 473 _cur_vm_operation = _vm_queue->remove_next(); 474 475 // Stall time tracking code 476 if (PrintVMQWaitTime && _cur_vm_operation != NULL && 477 !_cur_vm_operation->evaluate_concurrently()) { 478 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp(); 479 if (stall > 0) 480 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall); 481 } 482 483 while (!should_terminate() && _cur_vm_operation == NULL) { 484 // wait with a timeout to guarantee safepoints at regular intervals 485 bool timedout = 486 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag, 487 GuaranteedSafepointInterval); 488 489 // Support for self destruction 490 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() && 491 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) { 492 tty->print_cr("VM self-destructed"); 493 exit(-1); 494 } 495 496 if (timedout && VMThread::no_op_safepoint_needed(false)) { 497 MutexUnlockerEx mul(VMOperationQueue_lock, 498 Mutex::_no_safepoint_check_flag); 499 // Force a safepoint since we have not had one for at least 500 // 'GuaranteedSafepointInterval' milliseconds. This will run all 501 // the clean-up processing that needs to be done regularly at a 502 // safepoint 503 SafepointSynchronize::begin(); 504 #ifdef ASSERT 505 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot(); 506 #endif 507 SafepointSynchronize::end(); 508 } 509 _cur_vm_operation = _vm_queue->remove_next(); 510 511 // If we are at a safepoint we will evaluate all the operations that 512 // follow that also require a safepoint 513 if (_cur_vm_operation != NULL && 514 _cur_vm_operation->evaluate_at_safepoint()) { 515 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 516 } 517 } 518 519 if (should_terminate()) break; 520 } // Release mu_queue_lock 521 522 // 523 // Execute VM operation 524 // 525 { HandleMark hm(VMThread::vm_thread()); 526 527 EventMark em("Executing VM operation: %s", vm_operation()->name()); 528 assert(_cur_vm_operation != NULL, "we should have found an operation to execute"); 529 530 // If we are at a safepoint we will evaluate all the operations that 531 // follow that also require a safepoint 532 if (_cur_vm_operation->evaluate_at_safepoint()) { 533 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name()); 534 535 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned 536 537 SafepointSynchronize::begin(); 538 539 if (_timeout_task != NULL) { 540 _timeout_task->arm(); 541 } 542 543 evaluate_operation(_cur_vm_operation); 544 // now process all queued safepoint ops, iteratively draining 545 // the queue until there are none left 546 do { 547 _cur_vm_operation = safepoint_ops; 548 if (_cur_vm_operation != NULL) { 549 do { 550 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name()); 551 // evaluate_operation deletes the op object so we have 552 // to grab the next op now 553 VM_Operation* next = _cur_vm_operation->next(); 554 _vm_queue->set_drain_list(next); 555 evaluate_operation(_cur_vm_operation); 556 _cur_vm_operation = next; 557 if (log_is_enabled(Debug, safepoint, stats)) { 558 SafepointSynchronize::inc_vmop_coalesced_count(); 559 } 560 } while (_cur_vm_operation != NULL); 561 } 562 // There is a chance that a thread enqueued a safepoint op 563 // since we released the op-queue lock and initiated the safepoint. 564 // So we drain the queue again if there is anything there, as an 565 // optimization to try and reduce the number of safepoints. 566 // As the safepoint synchronizes us with JavaThreads we will see 567 // any enqueue made by a JavaThread, but the peek will not 568 // necessarily detect a concurrent enqueue by a GC thread, but 569 // that simply means the op will wait for the next major cycle of the 570 // VMThread - just as it would if the GC thread lost the race for 571 // the lock. 572 if (_vm_queue->peek_at_safepoint_priority()) { 573 // must hold lock while draining queue 574 MutexLockerEx mu_queue(VMOperationQueue_lock, 575 Mutex::_no_safepoint_check_flag); 576 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 577 } else { 578 safepoint_ops = NULL; 579 } 580 } while(safepoint_ops != NULL); 581 582 _vm_queue->set_drain_list(NULL); 583 584 if (_timeout_task != NULL) { 585 _timeout_task->disarm(); 586 } 587 588 // Complete safepoint synchronization 589 SafepointSynchronize::end(); 590 591 } else { // not a safepoint operation 592 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name()); 593 if (TraceLongCompiles) { 594 elapsedTimer t; 595 t.start(); 596 evaluate_operation(_cur_vm_operation); 597 t.stop(); 598 double secs = t.seconds(); 599 if (secs * 1e3 > LongCompileThreshold) { 600 // XXX - _cur_vm_operation should not be accessed after 601 // the completed count has been incremented; the waiting 602 // thread may have already freed this memory. 603 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs); 604 } 605 } else { 606 evaluate_operation(_cur_vm_operation); 607 } 608 609 _cur_vm_operation = NULL; 610 } 611 } 612 613 // 614 // Notify (potential) waiting Java thread(s) - lock without safepoint 615 // check so that sneaking is not possible 616 { MutexLockerEx mu(VMOperationRequest_lock, 617 Mutex::_no_safepoint_check_flag); 618 VMOperationRequest_lock->notify_all(); 619 } 620 621 // 622 // We want to make sure that we get to a safepoint regularly. 623 // 624 if (VMThread::no_op_safepoint_needed(true)) { 625 HandleMark hm(VMThread::vm_thread()); 626 SafepointSynchronize::begin(); 627 SafepointSynchronize::end(); 628 } 629 } 630 } 631 632 // A SkipGCALot object is used to elide the usual effect of gc-a-lot 633 // over a section of execution by a thread. Currently, it's used only to 634 // prevent re-entrant calls to GC. 635 class SkipGCALot : public StackObj { 636 private: 637 bool _saved; 638 Thread* _t; 639 640 public: 641 #ifdef ASSERT 642 SkipGCALot(Thread* t) : _t(t) { 643 _saved = _t->skip_gcalot(); 644 _t->set_skip_gcalot(true); 645 } 646 647 ~SkipGCALot() { 648 assert(_t->skip_gcalot(), "Save-restore protocol invariant"); 649 _t->set_skip_gcalot(_saved); 650 } 651 #else 652 SkipGCALot(Thread* t) { } 653 ~SkipGCALot() { } 654 #endif 655 }; 656 657 void VMThread::execute(VM_Operation* op) { 658 Thread* t = Thread::current(); 659 660 if (!t->is_VM_thread()) { 661 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot 662 // JavaThread or WatcherThread 663 bool concurrent = op->evaluate_concurrently(); 664 // only blocking VM operations need to verify the caller's safepoint state: 665 if (!concurrent) { 666 t->check_for_valid_safepoint_state(true); 667 } 668 669 // New request from Java thread, evaluate prologue 670 if (!op->doit_prologue()) { 671 return; // op was cancelled 672 } 673 674 // Setup VM_operations for execution 675 op->set_calling_thread(t, Thread::get_priority(t)); 676 677 // It does not make sense to execute the epilogue, if the VM operation object is getting 678 // deallocated by the VM thread. 679 bool execute_epilog = !op->is_cheap_allocated(); 680 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated"); 681 682 // Get ticket number for non-concurrent VM operations 683 int ticket = 0; 684 if (!concurrent) { 685 ticket = t->vm_operation_ticket(); 686 } 687 688 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the 689 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests 690 // to be queued up during a safepoint synchronization. 691 { 692 VMOperationQueue_lock->lock_without_safepoint_check(); 693 log_debug(vmthread)("Adding VM operation: %s", op->name()); 694 bool ok = _vm_queue->add(op); 695 op->set_timestamp(os::javaTimeMillis()); 696 VMOperationQueue_lock->notify(); 697 VMOperationQueue_lock->unlock(); 698 // VM_Operation got skipped 699 if (!ok) { 700 assert(concurrent, "can only skip concurrent tasks"); 701 if (op->is_cheap_allocated()) delete op; 702 return; 703 } 704 } 705 706 if (!concurrent) { 707 // Wait for completion of request (non-concurrent) 708 // Note: only a JavaThread triggers the safepoint check when locking 709 MutexLocker mu(VMOperationRequest_lock); 710 while(t->vm_operation_completed_count() < ticket) { 711 VMOperationRequest_lock->wait(!t->is_Java_thread()); 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(), prev_vm_operation->priority()); 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 }