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