vmThread.cpp revision 0:a61af66fc99e
1/* 2 * Copyright 1998-2007 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, 20 * CA 95054 USA or visit www.sun.com if you need additional information or 21 * have any questions. 22 * 23 */ 24 25# include "incls/_precompiled.incl" 26# include "incls/_vmThread.cpp.incl" 27 28// Dummy VM operation to act as first element in our circular double-linked list 29class VM_Dummy: public VM_Operation { 30 VMOp_Type type() const { return VMOp_Dummy; } 31 void doit() {}; 32}; 33 34VMOperationQueue::VMOperationQueue() { 35 // The queue is a circular doubled-linked list, which always contains 36 // one element (i.e., one element means empty). 37 for(int i = 0; i < nof_priorities; i++) { 38 _queue_length[i] = 0; 39 _queue_counter = 0; 40 _queue[i] = new VM_Dummy(); 41 _queue[i]->set_next(_queue[i]); 42 _queue[i]->set_prev(_queue[i]); 43 } 44 _drain_list = NULL; 45} 46 47 48bool VMOperationQueue::queue_empty(int prio) { 49 // It is empty if there is exactly one element 50 bool empty = (_queue[prio] == _queue[prio]->next()); 51 assert( (_queue_length[prio] == 0 && empty) || 52 (_queue_length[prio] > 0 && !empty), "sanity check"); 53 return _queue_length[prio] == 0; 54} 55 56// Inserts an element to the right of the q element 57void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) { 58 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); 59 n->set_prev(q); 60 n->set_next(q->next()); 61 q->next()->set_prev(n); 62 q->set_next(n); 63} 64 65void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) { 66 _queue_length[prio]++; 67 insert(_queue[prio]->next(), op); 68} 69 70void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) { 71 _queue_length[prio]++; 72 insert(_queue[prio]->prev(), op); 73} 74 75 76void VMOperationQueue::unlink(VM_Operation* q) { 77 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check"); 78 q->prev()->set_next(q->next()); 79 q->next()->set_prev(q->prev()); 80} 81 82VM_Operation* VMOperationQueue::queue_remove_front(int prio) { 83 if (queue_empty(prio)) return NULL; 84 assert(_queue_length[prio] >= 0, "sanity check"); 85 _queue_length[prio]--; 86 VM_Operation* r = _queue[prio]->next(); 87 assert(r != _queue[prio], "cannot remove base element"); 88 unlink(r); 89 return r; 90} 91 92VM_Operation* VMOperationQueue::queue_drain(int prio) { 93 if (queue_empty(prio)) return NULL; 94 DEBUG_ONLY(int length = _queue_length[prio];); 95 assert(length >= 0, "sanity check"); 96 _queue_length[prio] = 0; 97 VM_Operation* r = _queue[prio]->next(); 98 assert(r != _queue[prio], "cannot remove base element"); 99 // remove links to base element from head and tail 100 r->set_prev(NULL); 101 _queue[prio]->prev()->set_next(NULL); 102 // restore queue to empty state 103 _queue[prio]->set_next(_queue[prio]); 104 _queue[prio]->set_prev(_queue[prio]); 105 assert(queue_empty(prio), "drain corrupted queue") 106#ifdef DEBUG 107 int len = 0; 108 VM_Operation* cur; 109 for(cur = r; cur != NULL; cur=cur->next()) len++; 110 assert(len == length, "drain lost some ops"); 111#endif 112 return r; 113} 114 115void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) { 116 VM_Operation* cur = _queue[queue]; 117 cur = cur->next(); 118 while (cur != _queue[queue]) { 119 cur->oops_do(f); 120 cur = cur->next(); 121 } 122} 123 124void VMOperationQueue::drain_list_oops_do(OopClosure* f) { 125 VM_Operation* cur = _drain_list; 126 while (cur != NULL) { 127 cur->oops_do(f); 128 cur = cur->next(); 129 } 130} 131 132//----------------------------------------------------------------- 133// High-level interface 134bool VMOperationQueue::add(VM_Operation *op) { 135 // Encapsulates VM queue policy. Currently, that 136 // only involves putting them on the right list 137 if (op->evaluate_at_safepoint()) { 138 queue_add_back(SafepointPriority, op); 139 return true; 140 } 141 142 queue_add_back(MediumPriority, op); 143 return true; 144} 145 146VM_Operation* VMOperationQueue::remove_next() { 147 // Assuming VMOperation queue is two-level priority queue. If there are 148 // more than two priorities, we need a different scheduling algorithm. 149 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2, 150 "current algorithm does not work"); 151 152 // simple counter based scheduling to prevent starvation of lower priority 153 // queue. -- see 4390175 154 int high_prio, low_prio; 155 if (_queue_counter++ < 10) { 156 high_prio = SafepointPriority; 157 low_prio = MediumPriority; 158 } else { 159 _queue_counter = 0; 160 high_prio = MediumPriority; 161 low_prio = SafepointPriority; 162 } 163 164 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio); 165} 166 167void VMOperationQueue::oops_do(OopClosure* f) { 168 for(int i = 0; i < nof_priorities; i++) { 169 queue_oops_do(i, f); 170 } 171 drain_list_oops_do(f); 172} 173 174 175//------------------------------------------------------------------------------------------------------------------ 176// Implementation of VMThread stuff 177 178bool VMThread::_should_terminate = false; 179bool VMThread::_terminated = false; 180Monitor* VMThread::_terminate_lock = NULL; 181VMThread* VMThread::_vm_thread = NULL; 182VM_Operation* VMThread::_cur_vm_operation = NULL; 183VMOperationQueue* VMThread::_vm_queue = NULL; 184PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL; 185 186 187void VMThread::create() { 188 assert(vm_thread() == NULL, "we can only allocate one VMThread"); 189 _vm_thread = new VMThread(); 190 191 // Create VM operation queue 192 _vm_queue = new VMOperationQueue(); 193 guarantee(_vm_queue != NULL, "just checking"); 194 195 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true); 196 197 if (UsePerfData) { 198 // jvmstat performance counters 199 Thread* THREAD = Thread::current(); 200 _perf_accumulated_vm_operation_time = 201 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime", 202 PerfData::U_Ticks, CHECK); 203 } 204} 205 206 207VMThread::VMThread() : Thread() { 208 // nothing to do 209} 210 211void VMThread::destroy() { 212 if (_vm_thread != NULL) { 213 delete _vm_thread; 214 _vm_thread = NULL; // VM thread is gone 215 } 216} 217 218void VMThread::run() { 219 assert(this == vm_thread(), "check"); 220 221 this->initialize_thread_local_storage(); 222 this->record_stack_base_and_size(); 223 // Notify_lock wait checks on active_handles() to rewait in 224 // case of spurious wakeup, it should wait on the last 225 // value set prior to the notify 226 this->set_active_handles(JNIHandleBlock::allocate_block()); 227 228 { 229 MutexLocker ml(Notify_lock); 230 Notify_lock->notify(); 231 } 232 // Notify_lock is destroyed by Threads::create_vm() 233 234 int prio = (VMThreadPriority == -1) 235 ? os::java_to_os_priority[NearMaxPriority] 236 : VMThreadPriority; 237 // Note that I cannot call os::set_priority because it expects Java 238 // priorities and I am *explicitly* using OS priorities so that it's 239 // possible to set the VM thread priority higher than any Java thread. 240 os::set_native_priority( this, prio ); 241 242 // Wait for VM_Operations until termination 243 this->loop(); 244 245 // Note the intention to exit before safepointing. 246 // 6295565 This has the effect of waiting for any large tty 247 // outputs to finish. 248 if (xtty != NULL) { 249 ttyLocker ttyl; 250 xtty->begin_elem("destroy_vm"); 251 xtty->stamp(); 252 xtty->end_elem(); 253 assert(should_terminate(), "termination flag must be set"); 254 } 255 256 // 4526887 let VM thread exit at Safepoint 257 SafepointSynchronize::begin(); 258 259 if (VerifyBeforeExit) { 260 HandleMark hm(VMThread::vm_thread()); 261 // Among other things, this ensures that Eden top is correct. 262 Universe::heap()->prepare_for_verify(); 263 os::check_heap(); 264 Universe::verify(true, true); // Silent verification to not polute normal output 265 } 266 267 CompileBroker::set_should_block(); 268 269 // wait for threads (compiler threads or daemon threads) in the 270 // _thread_in_native state to block. 271 VM_Exit::wait_for_threads_in_native_to_block(); 272 273 // signal other threads that VM process is gone 274 { 275 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows 276 // VM thread to enter any lock at Safepoint as long as its _owner is NULL. 277 // If that happens after _terminate_lock->wait() has unset _owner 278 // but before it actually drops the lock and waits, the notification below 279 // may get lost and we will have a hang. To avoid this, we need to use 280 // Mutex::lock_without_safepoint_check(). 281 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 282 _terminated = true; 283 _terminate_lock->notify(); 284 } 285 286 // Deletion must be done synchronously by the JNI DestroyJavaVM thread 287 // so that the VMThread deletion completes before the main thread frees 288 // up the CodeHeap. 289 290} 291 292 293// Notify the VMThread that the last non-daemon JavaThread has terminated, 294// and wait until operation is performed. 295void VMThread::wait_for_vm_thread_exit() { 296 { MutexLocker mu(VMOperationQueue_lock); 297 _should_terminate = true; 298 VMOperationQueue_lock->notify(); 299 } 300 301 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint 302 // because this thread has been removed from the threads list. But anything 303 // that could get blocked by Safepoint should not be used after this point, 304 // otherwise we will hang, since there is no one can end the safepoint. 305 306 // Wait until VM thread is terminated 307 // Note: it should be OK to use Terminator_lock here. But this is called 308 // at a very delicate time (VM shutdown) and we are operating in non- VM 309 // thread at Safepoint. It's safer to not share lock with other threads. 310 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag); 311 while(!VMThread::is_terminated()) { 312 _terminate_lock->wait(Mutex::_no_safepoint_check_flag); 313 } 314 } 315} 316 317void VMThread::print_on(outputStream* st) const { 318 st->print("\"%s\" ", name()); 319 Thread::print_on(st); 320 st->cr(); 321} 322 323void VMThread::evaluate_operation(VM_Operation* op) { 324 ResourceMark rm; 325 326 { 327 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time()); 328 op->evaluate(); 329 } 330 331 // Last access of info in _cur_vm_operation! 332 bool c_heap_allocated = op->is_cheap_allocated(); 333 334 // Mark as completed 335 if (!op->evaluate_concurrently()) { 336 op->calling_thread()->increment_vm_operation_completed_count(); 337 } 338 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call, 339 // since if it is stack allocated the calling thread might have deallocated 340 if (c_heap_allocated) { 341 delete _cur_vm_operation; 342 } 343} 344 345 346void VMThread::loop() { 347 assert(_cur_vm_operation == NULL, "no current one should be executing"); 348 349 while(true) { 350 VM_Operation* safepoint_ops = NULL; 351 // 352 // Wait for VM operation 353 // 354 // use no_safepoint_check to get lock without attempting to "sneak" 355 { MutexLockerEx mu_queue(VMOperationQueue_lock, 356 Mutex::_no_safepoint_check_flag); 357 358 // Look for new operation 359 assert(_cur_vm_operation == NULL, "no current one should be executing"); 360 _cur_vm_operation = _vm_queue->remove_next(); 361 362 // Stall time tracking code 363 if (PrintVMQWaitTime && _cur_vm_operation != NULL && 364 !_cur_vm_operation->evaluate_concurrently()) { 365 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp(); 366 if (stall > 0) 367 tty->print_cr("%s stall: %Ld", _cur_vm_operation->name(), stall); 368 } 369 370 while (!should_terminate() && _cur_vm_operation == NULL) { 371 // wait with a timeout to guarantee safepoints at regular intervals 372 bool timedout = 373 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag, 374 GuaranteedSafepointInterval); 375 376 // Support for self destruction 377 if ((SelfDestructTimer != 0) && !is_error_reported() && 378 (os::elapsedTime() > SelfDestructTimer * 60)) { 379 tty->print_cr("VM self-destructed"); 380 exit(-1); 381 } 382 383 if (timedout && (SafepointALot || 384 SafepointSynchronize::is_cleanup_needed())) { 385 MutexUnlockerEx mul(VMOperationQueue_lock, 386 Mutex::_no_safepoint_check_flag); 387 // Force a safepoint since we have not had one for at least 388 // 'GuaranteedSafepointInterval' milliseconds. This will run all 389 // the clean-up processing that needs to be done regularly at a 390 // safepoint 391 SafepointSynchronize::begin(); 392 #ifdef ASSERT 393 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot(); 394 #endif 395 SafepointSynchronize::end(); 396 } 397 _cur_vm_operation = _vm_queue->remove_next(); 398 399 // If we are at a safepoint we will evaluate all the operations that 400 // follow that also require a safepoint 401 if (_cur_vm_operation != NULL && 402 _cur_vm_operation->evaluate_at_safepoint()) { 403 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 404 } 405 } 406 407 if (should_terminate()) break; 408 } // Release mu_queue_lock 409 410 // 411 // Execute VM operation 412 // 413 { HandleMark hm(VMThread::vm_thread()); 414 415 EventMark em("Executing VM operation: %s", vm_operation()->name()); 416 assert(_cur_vm_operation != NULL, "we should have found an operation to execute"); 417 418 // Give the VM thread an extra quantum. Jobs tend to be bursty and this 419 // helps the VM thread to finish up the job. 420 // FIXME: When this is enabled and there are many threads, this can degrade 421 // performance significantly. 422 if( VMThreadHintNoPreempt ) 423 os::hint_no_preempt(); 424 425 // If we are at a safepoint we will evaluate all the operations that 426 // follow that also require a safepoint 427 if (_cur_vm_operation->evaluate_at_safepoint()) { 428 429 if (PrintGCApplicationConcurrentTime) { 430 gclog_or_tty->print_cr("Application time: %3.7f seconds", 431 RuntimeService::last_application_time_sec()); 432 } 433 434 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned 435 436 SafepointSynchronize::begin(); 437 evaluate_operation(_cur_vm_operation); 438 // now process all queued safepoint ops, iteratively draining 439 // the queue until there are none left 440 do { 441 _cur_vm_operation = safepoint_ops; 442 if (_cur_vm_operation != NULL) { 443 do { 444 // evaluate_operation deletes the op object so we have 445 // to grab the next op now 446 VM_Operation* next = _cur_vm_operation->next(); 447 _vm_queue->set_drain_list(next); 448 evaluate_operation(_cur_vm_operation); 449 _cur_vm_operation = next; 450 if (PrintSafepointStatistics) { 451 SafepointSynchronize::inc_vmop_coalesced_count(); 452 } 453 } while (_cur_vm_operation != NULL); 454 } 455 // There is a chance that a thread enqueued a safepoint op 456 // since we released the op-queue lock and initiated the safepoint. 457 // So we drain the queue again if there is anything there, as an 458 // optimization to try and reduce the number of safepoints. 459 // As the safepoint synchronizes us with JavaThreads we will see 460 // any enqueue made by a JavaThread, but the peek will not 461 // necessarily detect a concurrent enqueue by a GC thread, but 462 // that simply means the op will wait for the next major cycle of the 463 // VMThread - just as it would if the GC thread lost the race for 464 // the lock. 465 if (_vm_queue->peek_at_safepoint_priority()) { 466 // must hold lock while draining queue 467 MutexLockerEx mu_queue(VMOperationQueue_lock, 468 Mutex::_no_safepoint_check_flag); 469 safepoint_ops = _vm_queue->drain_at_safepoint_priority(); 470 } else { 471 safepoint_ops = NULL; 472 } 473 } while(safepoint_ops != NULL); 474 475 _vm_queue->set_drain_list(NULL); 476 477 // Complete safepoint synchronization 478 SafepointSynchronize::end(); 479 480 if (PrintGCApplicationStoppedTime) { 481 gclog_or_tty->print_cr("Total time for which application threads " 482 "were stopped: %3.7f seconds", 483 RuntimeService::last_safepoint_time_sec()); 484 } 485 486 } else { // not a safepoint operation 487 if (TraceLongCompiles) { 488 elapsedTimer t; 489 t.start(); 490 evaluate_operation(_cur_vm_operation); 491 t.stop(); 492 double secs = t.seconds(); 493 if (secs * 1e3 > LongCompileThreshold) { 494 // XXX - _cur_vm_operation should not be accessed after 495 // the completed count has been incremented; the waiting 496 // thread may have already freed this memory. 497 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs); 498 } 499 } else { 500 evaluate_operation(_cur_vm_operation); 501 } 502 503 _cur_vm_operation = NULL; 504 } 505 } 506 507 // 508 // Notify (potential) waiting Java thread(s) - lock without safepoint 509 // check so that sneaking is not possible 510 { MutexLockerEx mu(VMOperationRequest_lock, 511 Mutex::_no_safepoint_check_flag); 512 VMOperationRequest_lock->notify_all(); 513 } 514 515 // 516 // We want to make sure that we get to a safepoint regularly. 517 // 518 if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) { 519 long interval = SafepointSynchronize::last_non_safepoint_interval(); 520 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval); 521 if (SafepointALot || max_time_exceeded) { 522 HandleMark hm(VMThread::vm_thread()); 523 SafepointSynchronize::begin(); 524 SafepointSynchronize::end(); 525 } 526 } 527 } 528} 529 530void VMThread::execute(VM_Operation* op) { 531 Thread* t = Thread::current(); 532 533 if (!t->is_VM_thread()) { 534 // JavaThread or WatcherThread 535 t->check_for_valid_safepoint_state(true); 536 537 // New request from Java thread, evaluate prologue 538 if (!op->doit_prologue()) { 539 return; // op was cancelled 540 } 541 542 // Setup VM_operations for execution 543 op->set_calling_thread(t, Thread::get_priority(t)); 544 545 // It does not make sense to execute the epilogue, if the VM operation object is getting 546 // deallocated by the VM thread. 547 bool concurrent = op->evaluate_concurrently(); 548 bool execute_epilog = !op->is_cheap_allocated(); 549 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated"); 550 551 // Get ticket number for non-concurrent VM operations 552 int ticket = 0; 553 if (!concurrent) { 554 ticket = t->vm_operation_ticket(); 555 } 556 557 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the 558 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests 559 // to be queued up during a safepoint synchronization. 560 { 561 VMOperationQueue_lock->lock_without_safepoint_check(); 562 bool ok = _vm_queue->add(op); 563 op->set_timestamp(os::javaTimeMillis()); 564 VMOperationQueue_lock->notify(); 565 VMOperationQueue_lock->unlock(); 566 // VM_Operation got skipped 567 if (!ok) { 568 assert(concurrent, "can only skip concurrent tasks"); 569 if (op->is_cheap_allocated()) delete op; 570 return; 571 } 572 } 573 574 if (!concurrent) { 575 // Wait for completion of request (non-concurrent) 576 // Note: only a JavaThread triggers the safepoint check when locking 577 MutexLocker mu(VMOperationRequest_lock); 578 while(t->vm_operation_completed_count() < ticket) { 579 VMOperationRequest_lock->wait(!t->is_Java_thread()); 580 } 581 } 582 583 if (execute_epilog) { 584 op->doit_epilogue(); 585 } 586 } else { 587 // invoked by VM thread; usually nested VM operation 588 assert(t->is_VM_thread(), "must be a VM thread"); 589 VM_Operation* prev_vm_operation = vm_operation(); 590 if (prev_vm_operation != NULL) { 591 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler 592 // does not allow nested scavenges or compiles. 593 if (!prev_vm_operation->allow_nested_vm_operations()) { 594 fatal2("Nested VM operation %s requested by operation %s", op->name(), vm_operation()->name()); 595 } 596 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority()); 597 } 598 599 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name()); 600 601 // Release all internal handles after operation is evaluated 602 HandleMark hm(t); 603 _cur_vm_operation = op; 604 605 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) { 606 SafepointSynchronize::begin(); 607 op->evaluate(); 608 SafepointSynchronize::end(); 609 } else { 610 op->evaluate(); 611 } 612 613 // Free memory if needed 614 if (op->is_cheap_allocated()) delete op; 615 616 _cur_vm_operation = prev_vm_operation; 617 } 618} 619 620 621void VMThread::oops_do(OopClosure* f) { 622 Thread::oops_do(f); 623 _vm_queue->oops_do(f); 624} 625 626//------------------------------------------------------------------------------------------------------------------ 627#ifndef PRODUCT 628 629void VMOperationQueue::verify_queue(int prio) { 630 // Check that list is correctly linked 631 int length = _queue_length[prio]; 632 VM_Operation *cur = _queue[prio]; 633 int i; 634 635 // Check forward links 636 for(i = 0; i < length; i++) { 637 cur = cur->next(); 638 assert(cur != _queue[prio], "list to short (forward)"); 639 } 640 assert(cur->next() == _queue[prio], "list to long (forward)"); 641 642 // Check backwards links 643 cur = _queue[prio]; 644 for(i = 0; i < length; i++) { 645 cur = cur->prev(); 646 assert(cur != _queue[prio], "list to short (backwards)"); 647 } 648 assert(cur->prev() == _queue[prio], "list to long (backwards)"); 649} 650 651#endif 652 653void VMThread::verify() { 654 oops_do(&VerifyOopClosure::verify_oop); 655} 656