1 /* 2 * Copyright (c) 1997, 2025, 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 "code/codeCache.hpp" 26 #include "code/nmethod.hpp" 27 #include "code/pcDesc.hpp" 28 #include "code/scopeDesc.hpp" 29 #include "compiler/compilationPolicy.hpp" 30 #include "gc/shared/collectedHeap.hpp" 31 #include "gc/shared/gcLocker.hpp" 32 #include "gc/shared/oopStorage.hpp" 33 #include "gc/shared/strongRootsScope.hpp" 34 #include "gc/shared/workerThread.hpp" 35 #include "gc/shared/workerUtils.hpp" 36 #include "interpreter/interpreter.hpp" 37 #include "jfr/jfrEvents.hpp" 38 #include "logging/log.hpp" 39 #include "logging/logStream.hpp" 40 #include "memory/resourceArea.hpp" 41 #include "memory/universe.hpp" 42 #include "oops/oop.inline.hpp" 43 #include "oops/symbol.hpp" 44 #include "oops/inlineKlass.hpp" 45 #include "runtime/atomic.hpp" 46 #include "runtime/deoptimization.hpp" 47 #include "runtime/frame.inline.hpp" 48 #include "runtime/globals.hpp" 49 #include "runtime/handles.inline.hpp" 50 #include "runtime/interfaceSupport.inline.hpp" 51 #include "runtime/javaThread.inline.hpp" 52 #include "runtime/mutexLocker.hpp" 53 #include "runtime/orderAccess.hpp" 54 #include "runtime/osThread.hpp" 55 #include "runtime/safepoint.hpp" 56 #include "runtime/safepointMechanism.inline.hpp" 57 #include "runtime/signature.hpp" 58 #include "runtime/stackWatermarkSet.inline.hpp" 59 #include "runtime/stubCodeGenerator.hpp" 60 #include "runtime/stubRoutines.hpp" 61 #include "runtime/synchronizer.hpp" 62 #include "runtime/threads.hpp" 63 #include "runtime/threadSMR.hpp" 64 #include "runtime/threadWXSetters.inline.hpp" 65 #include "runtime/timerTrace.hpp" 66 #include "services/runtimeService.hpp" 67 #include "utilities/events.hpp" 68 #include "utilities/macros.hpp" 69 #include "utilities/systemMemoryBarrier.hpp" 70 71 static void post_safepoint_begin_event(EventSafepointBegin& event, 72 uint64_t safepoint_id, 73 int thread_count, 74 int critical_thread_count) { 75 if (event.should_commit()) { 76 event.set_safepointId(safepoint_id); 77 event.set_totalThreadCount(thread_count); 78 event.set_jniCriticalThreadCount(critical_thread_count); 79 event.commit(); 80 } 81 } 82 83 84 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization& event, 85 uint64_t safepoint_id, 86 int initial_number_of_threads, 87 int threads_waiting_to_block, 88 int iterations) { 89 if (event.should_commit()) { 90 event.set_safepointId(safepoint_id); 91 event.set_initialThreadCount(initial_number_of_threads); 92 event.set_runningThreadCount(threads_waiting_to_block); 93 event.set_iterations(checked_cast<u4>(iterations)); 94 event.commit(); 95 } 96 } 97 98 static void post_safepoint_end_event(EventSafepointEnd& event, uint64_t safepoint_id) { 99 if (event.should_commit()) { 100 event.set_safepointId(safepoint_id); 101 event.commit(); 102 } 103 } 104 105 // SafepointCheck 106 SafepointStateTracker::SafepointStateTracker(uint64_t safepoint_id, bool at_safepoint) 107 : _safepoint_id(safepoint_id), _at_safepoint(at_safepoint) {} 108 109 bool SafepointStateTracker::safepoint_state_changed() { 110 return _safepoint_id != SafepointSynchronize::safepoint_id() || 111 _at_safepoint != SafepointSynchronize::is_at_safepoint(); 112 } 113 114 // -------------------------------------------------------------------------------------------------- 115 // Implementation of Safepoint begin/end 116 117 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized; 118 int SafepointSynchronize::_waiting_to_block = 0; 119 volatile uint64_t SafepointSynchronize::_safepoint_counter = 0; 120 uint64_t SafepointSynchronize::_safepoint_id = 0; 121 const uint64_t SafepointSynchronize::InactiveSafepointCounter = 0; 122 int SafepointSynchronize::_current_jni_active_count = 0; 123 124 WaitBarrier* SafepointSynchronize::_wait_barrier; 125 126 static bool timeout_error_printed = false; 127 128 // Statistic related 129 static jlong _safepoint_begin_time = 0; 130 static volatile int _nof_threads_hit_polling_page = 0; 131 132 void SafepointSynchronize::init(Thread* vmthread) { 133 // WaitBarrier should never be destroyed since we will have 134 // threads waiting on it while exiting. 135 _wait_barrier = new WaitBarrier(vmthread); 136 SafepointTracing::init(); 137 } 138 139 void SafepointSynchronize::increment_jni_active_count() { 140 assert(Thread::current()->is_VM_thread(), "Only VM thread may increment"); 141 ++_current_jni_active_count; 142 } 143 144 void SafepointSynchronize::decrement_waiting_to_block() { 145 assert(_waiting_to_block > 0, "sanity check"); 146 assert(Thread::current()->is_VM_thread(), "Only VM thread may decrement"); 147 --_waiting_to_block; 148 } 149 150 bool SafepointSynchronize::thread_not_running(ThreadSafepointState *cur_state) { 151 if (!cur_state->is_running()) { 152 // Robustness: asserted in the caller, but handle/tolerate it for release bits. 153 LogTarget(Error, safepoint) lt; 154 if (lt.is_enabled()) { 155 ResourceMark rm; 156 LogStream ls(lt); 157 ls.print("Illegal initial state detected: "); 158 cur_state->print_on(&ls); 159 } 160 return true; 161 } 162 cur_state->examine_state_of_thread(SafepointSynchronize::safepoint_counter()); 163 if (!cur_state->is_running()) { 164 return true; 165 } 166 LogTarget(Trace, safepoint) lt; 167 if (lt.is_enabled()) { 168 ResourceMark rm; 169 LogStream ls(lt); 170 cur_state->print_on(&ls); 171 } 172 return false; 173 } 174 175 #ifdef ASSERT 176 static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) { 177 int a = 0; 178 const ThreadSafepointState *tmp_tss = tss_head; 179 while (tmp_tss != nullptr) { 180 ++a; 181 assert(tmp_tss->is_running(), "Illegal initial state"); 182 tmp_tss = tmp_tss->get_next(); 183 } 184 assert(a == still_running, "Must be the same"); 185 } 186 #endif // ASSERT 187 188 static void back_off(int64_t start_time) { 189 // We start with fine-grained nanosleeping until a millisecond has 190 // passed, at which point we resort to plain naked_short_sleep. 191 if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) { 192 os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS)); 193 } else { 194 os::naked_short_sleep(1); 195 } 196 } 197 198 int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running) 199 { 200 JavaThreadIteratorWithHandle jtiwh; 201 202 #ifdef ASSERT 203 for (; JavaThread *cur = jtiwh.next(); ) { 204 assert(cur->safepoint_state()->is_running(), "Illegal initial state"); 205 } 206 jtiwh.rewind(); 207 #endif // ASSERT 208 209 // Iterate through all threads until it has been determined how to stop them all at a safepoint. 210 int still_running = nof_threads; 211 ThreadSafepointState *tss_head = nullptr; 212 ThreadSafepointState **p_prev = &tss_head; 213 for (; JavaThread *cur = jtiwh.next(); ) { 214 ThreadSafepointState *cur_tss = cur->safepoint_state(); 215 assert(cur_tss->get_next() == nullptr, "Must be null"); 216 if (thread_not_running(cur_tss)) { 217 --still_running; 218 } else { 219 *p_prev = cur_tss; 220 p_prev = cur_tss->next_ptr(); 221 } 222 } 223 *p_prev = nullptr; 224 225 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);) 226 227 *initial_running = still_running; 228 229 // If there is no thread still running, we are already done. 230 if (still_running <= 0) { 231 assert(tss_head == nullptr, "Must be empty"); 232 return 1; 233 } 234 235 int iterations = 1; // The first iteration is above. 236 int64_t start_time = os::javaTimeNanos(); 237 238 do { 239 // Check if this has taken too long: 240 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) { 241 print_safepoint_timeout(); 242 } 243 244 p_prev = &tss_head; 245 ThreadSafepointState *cur_tss = tss_head; 246 while (cur_tss != nullptr) { 247 assert(cur_tss->is_running(), "Illegal initial state"); 248 if (thread_not_running(cur_tss)) { 249 --still_running; 250 *p_prev = nullptr; 251 ThreadSafepointState *tmp = cur_tss; 252 cur_tss = cur_tss->get_next(); 253 tmp->set_next(nullptr); 254 } else { 255 *p_prev = cur_tss; 256 p_prev = cur_tss->next_ptr(); 257 cur_tss = cur_tss->get_next(); 258 } 259 } 260 261 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);) 262 263 if (still_running > 0) { 264 back_off(start_time); 265 } 266 267 iterations++; 268 } while (still_running > 0); 269 270 assert(tss_head == nullptr, "Must be empty"); 271 272 return iterations; 273 } 274 275 void SafepointSynchronize::arm_safepoint() { 276 // Begin the process of bringing the system to a safepoint. 277 // Java threads can be in several different states and are 278 // stopped by different mechanisms: 279 // 280 // 1. Running interpreted 281 // When executing branching/returning byte codes interpreter 282 // checks if the poll is armed, if so blocks in SS::block(). 283 // 2. Running in native code 284 // When returning from the native code, a Java thread must check 285 // the safepoint _state to see if we must block. If the 286 // VM thread sees a Java thread in native, it does 287 // not wait for this thread to block. The order of the memory 288 // writes and reads of both the safepoint state and the Java 289 // threads state is critical. In order to guarantee that the 290 // memory writes are serialized with respect to each other, 291 // the VM thread issues a memory barrier instruction. 292 // 3. Running compiled Code 293 // Compiled code reads the local polling page that 294 // is set to fault if we are trying to get to a safepoint. 295 // 4. Blocked 296 // A thread which is blocked will not be allowed to return from the 297 // block condition until the safepoint operation is complete. 298 // 5. In VM or Transitioning between states 299 // If a Java thread is currently running in the VM or transitioning 300 // between states, the safepointing code will poll the thread state 301 // until the thread blocks itself when it attempts transitions to a 302 // new state or locking a safepoint checked monitor. 303 304 // We must never miss a thread with correct safepoint id, so we must make sure we arm 305 // the wait barrier for the next safepoint id/counter. 306 // Arming must be done after resetting _current_jni_active_count, _waiting_to_block. 307 _wait_barrier->arm(static_cast<int>(_safepoint_counter + 1)); 308 309 assert((_safepoint_counter & 0x1) == 0, "must be even"); 310 // The store to _safepoint_counter must happen after any stores in arming. 311 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1); 312 313 // We are synchronizing 314 OrderAccess::storestore(); // Ordered with _safepoint_counter 315 _state = _synchronizing; 316 317 // Arming the per thread poll while having _state != _not_synchronized means safepointing 318 log_trace(safepoint)("Setting thread local yield flag for threads"); 319 OrderAccess::storestore(); // storestore, global state -> local state 320 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { 321 // Make sure the threads start polling, it is time to yield. 322 SafepointMechanism::arm_local_poll(cur); 323 } 324 if (UseSystemMemoryBarrier) { 325 SystemMemoryBarrier::emit(); // storestore|storeload, global state -> local state 326 } else { 327 OrderAccess::fence(); // storestore|storeload, global state -> local state 328 } 329 } 330 331 // Roll all threads forward to a safepoint and suspend them all 332 void SafepointSynchronize::begin() { 333 assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint"); 334 335 EventSafepointBegin begin_event; 336 SafepointTracing::begin(VMThread::vm_op_type()); 337 338 Universe::heap()->safepoint_synchronize_begin(); 339 340 // By getting the Threads_lock, we assure that no threads are about to start or 341 // exit. It is released again in SafepointSynchronize::end(). 342 Threads_lock->lock(); 343 344 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state"); 345 346 int nof_threads = Threads::number_of_threads(); 347 348 _nof_threads_hit_polling_page = 0; 349 350 log_debug(safepoint)("Safepoint synchronization initiated using %s wait barrier. (%d threads)", _wait_barrier->description(), nof_threads); 351 352 // Reset the count of active JNI critical threads 353 _current_jni_active_count = 0; 354 355 // Set number of threads to wait for 356 _waiting_to_block = nof_threads; 357 358 jlong safepoint_limit_time = 0; 359 if (SafepointTimeout) { 360 // Set the limit time, so that it can be compared to see if this has taken 361 // too long to complete. 362 safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)(SafepointTimeoutDelay * NANOSECS_PER_MILLISEC); 363 timeout_error_printed = false; 364 } 365 366 EventSafepointStateSynchronization sync_event; 367 int initial_running = 0; 368 369 // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before. 370 arm_safepoint(); 371 372 // Will spin until all threads are safe. 373 int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running); 374 assert(_waiting_to_block == 0, "No thread should be running"); 375 376 #ifndef PRODUCT 377 // Mark all threads 378 if (VerifyCrossModifyFence) { 379 JavaThreadIteratorWithHandle jtiwh; 380 for (; JavaThread *cur = jtiwh.next(); ) { 381 cur->set_requires_cross_modify_fence(true); 382 } 383 } 384 385 if (safepoint_limit_time != 0) { 386 jlong current_time = os::javaTimeNanos(); 387 if (safepoint_limit_time < current_time) { 388 log_warning(safepoint)("# SafepointSynchronize: Finished after " 389 INT64_FORMAT_W(6) " ms", 390 (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS)); 391 } 392 } 393 #endif 394 395 assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); 396 397 // Record state 398 _state = _synchronized; 399 400 OrderAccess::fence(); 401 402 // Set the new id 403 ++_safepoint_id; 404 405 #ifdef ASSERT 406 // Make sure all the threads were visited. 407 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) { 408 assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread"); 409 } 410 #endif // ASSERT 411 412 post_safepoint_synchronize_event(sync_event, 413 _safepoint_id, 414 initial_running, 415 _waiting_to_block, iterations); 416 417 SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page); 418 419 post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count); 420 } 421 422 void SafepointSynchronize::disarm_safepoint() { 423 uint64_t active_safepoint_counter = _safepoint_counter; 424 { 425 JavaThreadIteratorWithHandle jtiwh; 426 #ifdef ASSERT 427 // A pending_exception cannot be installed during a safepoint. The threads 428 // may install an async exception after they come back from a safepoint into 429 // pending_exception after they unblock. But that should happen later. 430 for (; JavaThread *cur = jtiwh.next(); ) { 431 assert (!(cur->has_pending_exception() && 432 cur->safepoint_state()->is_at_poll_safepoint()), 433 "safepoint installed a pending exception"); 434 } 435 #endif // ASSERT 436 437 OrderAccess::fence(); // keep read and write of _state from floating up 438 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization"); 439 440 // Change state first to _not_synchronized. 441 // No threads should see _synchronized when running. 442 _state = _not_synchronized; 443 444 // Set the next dormant (even) safepoint id. 445 assert((_safepoint_counter & 0x1) == 1, "must be odd"); 446 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1); 447 448 OrderAccess::fence(); // Keep the local state from floating up. 449 450 jtiwh.rewind(); 451 for (; JavaThread *current = jtiwh.next(); ) { 452 // Clear the visited flag to ensure that the critical counts are collected properly. 453 DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);) 454 ThreadSafepointState* cur_state = current->safepoint_state(); 455 assert(!cur_state->is_running(), "Thread not suspended at safepoint"); 456 cur_state->restart(); // TSS _running 457 assert(cur_state->is_running(), "safepoint state has not been reset"); 458 } 459 } // ~JavaThreadIteratorWithHandle 460 461 // Release threads lock, so threads can be created/destroyed again. 462 Threads_lock->unlock(); 463 464 // Wake threads after local state is correctly set. 465 _wait_barrier->disarm(); 466 } 467 468 // Wake up all threads, so they are ready to resume execution after the safepoint 469 // operation has been carried out 470 void SafepointSynchronize::end() { 471 assert(Threads_lock->owned_by_self(), "must hold Threads_lock"); 472 SafepointTracing::leave(); 473 474 EventSafepointEnd event; 475 assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint"); 476 477 disarm_safepoint(); 478 479 Universe::heap()->safepoint_synchronize_end(); 480 481 SafepointTracing::end(); 482 483 post_safepoint_end_event(event, safepoint_id()); 484 } 485 486 // Methods for determining if a JavaThread is safepoint safe. 487 488 // False means unsafe with undetermined state. 489 // True means a determined state, but it may be an unsafe state. 490 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter. 491 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) { 492 assert((safepoint_count != InactiveSafepointCounter && 493 Thread::current() == (Thread*)VMThread::vm_thread() && 494 SafepointSynchronize::_state != _not_synchronized) 495 || safepoint_count == InactiveSafepointCounter, "Invalid check"); 496 497 // To handle the thread_blocked state on the backedge of the WaitBarrier from 498 // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we 499 // re-read state after we read thread safepoint id. The JavaThread changes its 500 // thread state from thread_blocked before resetting safepoint id to 0. 501 // This guarantees the second read will be from an updated thread state. It can 502 // either be different state making this an unsafe state or it can see blocked 503 // again. When we see blocked twice with a 0 safepoint id, either: 504 // - It is normally blocked, e.g. on Mutex, TBIVM. 505 // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier. 506 // - It was in SS:block() but now on a Mutex. 507 // All of these cases are safe. 508 509 *state = thread->thread_state(); 510 OrderAccess::loadload(); 511 uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire 512 if (sid != InactiveSafepointCounter && sid != safepoint_count) { 513 // In an old safepoint, state not relevant. 514 return false; 515 } 516 return *state == thread->thread_state(); 517 } 518 519 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) { 520 switch(state) { 521 case _thread_in_native: 522 // native threads are safe if they have no java stack or have walkable stack 523 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable(); 524 525 case _thread_blocked: 526 // On wait_barrier or blocked. 527 // Blocked threads should already have walkable stack. 528 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable"); 529 return true; 530 531 default: 532 return false; 533 } 534 } 535 536 bool SafepointSynchronize::handshake_safe(JavaThread *thread) { 537 if (thread->is_terminated()) { 538 return true; 539 } 540 JavaThreadState stable_state; 541 if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) { 542 return safepoint_safe_with(thread, stable_state); 543 } 544 return false; 545 } 546 547 548 // ------------------------------------------------------------------------------------------------------- 549 // Implementation of Safepoint blocking point 550 551 void SafepointSynchronize::block(JavaThread *thread) { 552 assert(thread != nullptr, "thread must be set"); 553 554 // Threads shouldn't block if they are in the middle of printing, but... 555 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id()); 556 557 // Only bail from the block() call if the thread is gone from the 558 // thread list; starting to exit should still block. 559 if (thread->is_terminated()) { 560 // block current thread if we come here from native code when VM is gone 561 thread->block_if_vm_exited(); 562 563 // otherwise do nothing 564 return; 565 } 566 567 JavaThreadState state = thread->thread_state(); 568 thread->frame_anchor()->make_walkable(); 569 570 uint64_t safepoint_id = SafepointSynchronize::safepoint_counter(); 571 572 // We have no idea where the VMThread is, it might even be at next safepoint. 573 // So we can miss this poll, but stop at next. 574 575 // Load dependent store, it must not pass loading of safepoint_id. 576 thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store 577 578 // This part we can skip if we notice we miss or are in a future safepoint. 579 OrderAccess::storestore(); 580 // Load in wait barrier should not float up 581 thread->set_thread_state_fence(_thread_blocked); 582 583 _wait_barrier->wait(static_cast<int>(safepoint_id)); 584 assert(_state != _synchronized, "Can't be"); 585 586 // If barrier is disarmed stop store from floating above loads in barrier. 587 OrderAccess::loadstore(); 588 thread->set_thread_state(state); 589 590 // Then we reset the safepoint id to inactive. 591 thread->safepoint_state()->reset_safepoint_id(); // Release store 592 593 OrderAccess::fence(); 594 595 guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter, 596 "The safepoint id should be set only in block path"); 597 598 // cross_modify_fence is done by SafepointMechanism::process_if_requested 599 // which is the only caller here. 600 } 601 602 // ------------------------------------------------------------------------------------------------------ 603 // Exception handlers 604 605 606 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) { 607 assert(thread->thread_state() == _thread_in_Java, "should come from Java code"); 608 thread->set_thread_state(_thread_in_vm); 609 610 // Enable WXWrite: the function is called implicitly from java code. 611 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread)); 612 613 if (log_is_enabled(Info, safepoint, stats)) { 614 Atomic::inc(&_nof_threads_hit_polling_page); 615 } 616 617 ThreadSafepointState* state = thread->safepoint_state(); 618 619 state->handle_polling_page_exception(); 620 621 thread->set_thread_state(_thread_in_Java); 622 } 623 624 625 void SafepointSynchronize::print_safepoint_timeout() { 626 if (!timeout_error_printed) { 627 timeout_error_printed = true; 628 // Print out the thread info which didn't reach the safepoint for debugging 629 // purposes (useful when there are lots of threads in the debugger). 630 LogTarget(Warning, safepoint) lt; 631 if (lt.is_enabled()) { 632 ResourceMark rm; 633 LogStream ls(lt); 634 635 ls.cr(); 636 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:"); 637 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint."); 638 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:"); 639 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) { 640 if (cur_thread->safepoint_state()->is_running()) { 641 ls.print("# "); 642 cur_thread->print_on(&ls); 643 ls.cr(); 644 } 645 } 646 ls.print_cr("# SafepointSynchronize::begin: (End of list)"); 647 } 648 } 649 650 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout & 651 // ShowMessageBoxOnError. 652 if (AbortVMOnSafepointTimeout && (os::elapsedTime() * MILLIUNITS > AbortVMOnSafepointTimeoutDelay)) { 653 // Send the blocking thread a signal to terminate and write an error file. 654 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) { 655 if (cur_thread->safepoint_state()->is_running()) { 656 if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) { 657 break; // Could not send signal. Report fatal error. 658 } 659 // Give cur_thread a chance to report the error and terminate the VM. 660 os::naked_sleep(3000); 661 } 662 } 663 fatal("Safepoint sync time longer than %.6f ms detected when executing %s.", 664 SafepointTimeoutDelay, VMThread::vm_operation()->name()); 665 } 666 } 667 668 // ------------------------------------------------------------------------------------------------------- 669 // Implementation of ThreadSafepointState 670 671 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) 672 : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false), 673 _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(nullptr) { 674 } 675 676 void ThreadSafepointState::create(JavaThread *thread) { 677 ThreadSafepointState *state = new ThreadSafepointState(thread); 678 thread->set_safepoint_state(state); 679 } 680 681 void ThreadSafepointState::destroy(JavaThread *thread) { 682 if (thread->safepoint_state()) { 683 delete(thread->safepoint_state()); 684 thread->set_safepoint_state(nullptr); 685 } 686 } 687 688 uint64_t ThreadSafepointState::get_safepoint_id() const { 689 return Atomic::load_acquire(&_safepoint_id); 690 } 691 692 void ThreadSafepointState::reset_safepoint_id() { 693 Atomic::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter); 694 } 695 696 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) { 697 Atomic::release_store(&_safepoint_id, safepoint_id); 698 } 699 700 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) { 701 assert(is_running(), "better be running or just have hit safepoint poll"); 702 703 JavaThreadState stable_state; 704 if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) { 705 // We could not get stable state of the JavaThread. 706 // Consider it running and just return. 707 return; 708 } 709 710 if (safepoint_safe_with(_thread, stable_state)) { 711 account_safe_thread(); 712 return; 713 } 714 715 // All other thread states will continue to run until they 716 // transition and self-block in state _blocked 717 // Safepoint polling in compiled code causes the Java threads to do the same. 718 // Note: new threads may require a malloc so they must be allowed to finish 719 720 assert(is_running(), "examine_state_of_thread on non-running thread"); 721 return; 722 } 723 724 void ThreadSafepointState::account_safe_thread() { 725 SafepointSynchronize::decrement_waiting_to_block(); 726 if (_thread->in_critical()) { 727 // Notice that this thread is in a critical section 728 SafepointSynchronize::increment_jni_active_count(); 729 } 730 DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());) 731 assert(!_safepoint_safe, "Must be unsafe before safe"); 732 _safepoint_safe = true; 733 734 // The oops in the monitor cache are cleared to prevent stale cache entries 735 // from keeping dead objects alive. Because these oops are always cleared 736 // before safepoint operations they are not visited in JavaThread::oops_do. 737 _thread->om_clear_monitor_cache(); 738 } 739 740 void ThreadSafepointState::restart() { 741 assert(_safepoint_safe, "Must be safe before unsafe"); 742 _safepoint_safe = false; 743 } 744 745 void ThreadSafepointState::print_on(outputStream *st) const { 746 const char *s = _safepoint_safe ? "_at_safepoint" : "_running"; 747 748 st->print_cr("Thread: " INTPTR_FORMAT 749 " [0x%2x] State: %s _at_poll_safepoint %d", 750 p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint); 751 752 _thread->print_thread_state_on(st); 753 } 754 755 // --------------------------------------------------------------------------------------------------------------------- 756 757 // Process pending operation. 758 void ThreadSafepointState::handle_polling_page_exception() { 759 JavaThread* self = thread(); 760 assert(self == JavaThread::current(), "must be self"); 761 762 // Step 1: Find the nmethod from the return address 763 address real_return_addr = self->saved_exception_pc(); 764 765 CodeBlob *cb = CodeCache::find_blob(real_return_addr); 766 assert(cb != nullptr && cb->is_nmethod(), "return address should be in nmethod"); 767 nmethod* nm = cb->as_nmethod(); 768 769 // Find frame of caller 770 frame stub_fr = self->last_frame(); 771 CodeBlob* stub_cb = stub_fr.cb(); 772 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub"); 773 RegisterMap map(self, 774 RegisterMap::UpdateMap::include, 775 RegisterMap::ProcessFrames::skip, 776 RegisterMap::WalkContinuation::skip); 777 frame caller_fr = stub_fr.sender(&map); 778 779 // Should only be poll_return or poll 780 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" ); 781 782 // This is a poll immediately before a return. The exception handling code 783 // has already had the effect of causing the return to occur, so the execution 784 // will continue immediately after the call. In addition, the oopmap at the 785 // return point does not mark the return value as an oop (if it is), so 786 // it needs a handle here to be updated. 787 if( nm->is_at_poll_return(real_return_addr) ) { 788 ResourceMark rm; 789 // See if return type is an oop. 790 Method* method = nm->method(); 791 bool return_oop = method->is_returning_oop(); 792 HandleMark hm(self); 793 GrowableArray<Handle> return_values; 794 InlineKlass* vk = nullptr; 795 if (return_oop && InlineTypeReturnedAsFields && 796 (method->result_type() == T_OBJECT)) { 797 // Check if an inline type is returned as fields 798 vk = InlineKlass::returned_inline_klass(map); 799 if (vk != nullptr) { 800 // We're at a safepoint at the return of a method that returns 801 // multiple values. We must make sure we preserve the oop values 802 // across the safepoint. 803 assert(vk == method->returns_inline_type(thread()), "bad inline klass"); 804 vk->save_oop_fields(map, return_values); 805 return_oop = false; 806 } 807 } 808 809 if (return_oop) { 810 // The oop result has been saved on the stack together with all 811 // the other registers. In order to preserve it over GCs we need 812 // to keep it in a handle. 813 oop result = caller_fr.saved_oop_result(&map); 814 assert(oopDesc::is_oop_or_null(result), "must be oop"); 815 return_values.push(Handle(self, result)); 816 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer"); 817 } 818 819 // We get here if compiled return polls found a reason to call into the VM. 820 // One condition for that is that the top frame is not yet safe to use. 821 // The following stack watermark barrier poll will catch such situations. 822 StackWatermarkSet::after_unwind(self); 823 824 // Process pending operation 825 SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */); 826 827 // restore oop result, if any 828 if (return_oop) { 829 assert(return_values.length() == 1, "only one return value"); 830 caller_fr.set_saved_oop_result(&map, return_values.pop()()); 831 } else if (vk != nullptr) { 832 vk->restore_oop_results(map, return_values); 833 } 834 } 835 836 // This is a safepoint poll. Verify the return address and block. 837 else { 838 839 // verify the blob built the "return address" correctly 840 assert(real_return_addr == caller_fr.pc(), "must match"); 841 842 set_at_poll_safepoint(true); 843 // Process pending operation 844 // We never deliver an async exception at a polling point as the 845 // compiler may not have an exception handler for it (polling at 846 // a return point is ok though). We will check for a pending async 847 // exception below and deoptimize if needed. We also cannot deoptimize 848 // and still install the exception here because live registers needed 849 // during deoptimization are clobbered by the exception path. The 850 // exception will just be delivered once we get into the interpreter. 851 SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */); 852 set_at_poll_safepoint(false); 853 854 if (self->has_async_exception_condition()) { 855 Deoptimization::deoptimize_frame(self, caller_fr.id()); 856 log_info(exceptions)("deferred async exception at compiled safepoint"); 857 } 858 859 // If an exception has been installed we must verify that the top frame wasn't deoptimized. 860 if (self->has_pending_exception() ) { 861 RegisterMap map(self, 862 RegisterMap::UpdateMap::include, 863 RegisterMap::ProcessFrames::skip, 864 RegisterMap::WalkContinuation::skip); 865 frame caller_fr = stub_fr.sender(&map); 866 if (caller_fr.is_deoptimized_frame()) { 867 // The exception path will destroy registers that are still 868 // live and will be needed during deoptimization, so if we 869 // have an exception now things are messed up. We only check 870 // at this scope because for a poll return it is ok to deoptimize 871 // while having a pending exception since the call we are returning 872 // from already collides with exception handling registers and 873 // so there is no issue (the exception handling path kills call 874 // result registers but this is ok since the exception kills 875 // the result anyway). 876 fatal("Exception installed and deoptimization is pending"); 877 } 878 } 879 } 880 } 881 882 883 // ------------------------------------------------------------------------------------------------------- 884 // Implementation of SafepointTracing 885 886 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0; 887 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0; 888 jlong SafepointTracing::_last_safepoint_leave_time_ns = 0; 889 jlong SafepointTracing::_last_safepoint_end_time_ns = 0; 890 jlong SafepointTracing::_last_app_time_ns = 0; 891 int SafepointTracing::_nof_threads = 0; 892 int SafepointTracing::_nof_running = 0; 893 int SafepointTracing::_page_trap = 0; 894 VM_Operation::VMOp_Type SafepointTracing::_current_type; 895 jlong SafepointTracing::_max_sync_time = 0; 896 jlong SafepointTracing::_max_vmop_time = 0; 897 uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0}; 898 899 void SafepointTracing::init() { 900 // Application start 901 _last_safepoint_end_time_ns = os::javaTimeNanos(); 902 } 903 904 // Helper method to print the header. 905 static void print_header(outputStream* st) { 906 // The number of spaces is significant here, and should match the format 907 // specifiers in print_statistics(). 908 909 st->print("VM Operation " 910 "[ threads: total initial_running ]" 911 "[ time: sync vmop total ]"); 912 913 st->print_cr(" page_trap_count"); 914 } 915 916 // This prints a nice table. To get the statistics to not shift due to the logging uptime 917 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none 918 void SafepointTracing::statistics_log() { 919 LogTarget(Info, safepoint, stats) lt; 920 assert (lt.is_enabled(), "should only be called when printing statistics is enabled"); 921 LogStream ls(lt); 922 923 static int _cur_stat_index = 0; 924 925 // Print header every 30 entries 926 if ((_cur_stat_index % 30) == 0) { 927 print_header(&ls); 928 _cur_stat_index = 1; // wrap 929 } else { 930 _cur_stat_index++; 931 } 932 933 ls.print("%-28s [ " 934 INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " " 935 "]", 936 VM_Operation::name(_current_type), 937 _nof_threads, 938 _nof_running); 939 ls.print("[ " 940 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]", 941 (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns), 942 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns), 943 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns)); 944 945 ls.print_cr(INT32_FORMAT_W(16), _page_trap); 946 } 947 948 // This method will be called when VM exits. This tries to summarize the sampling. 949 // Current thread may already be deleted, so don't use ResourceMark. 950 void SafepointTracing::statistics_exit_log() { 951 if (!log_is_enabled(Info, safepoint, stats)) { 952 return; 953 } 954 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) { 955 if (_op_count[index] != 0) { 956 log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index), 957 _op_count[index]); 958 } 959 } 960 961 log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns", 962 (int64_t)(_max_sync_time)); 963 log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) " 964 INT64_FORMAT " ns", 965 (int64_t)(_max_vmop_time)); 966 } 967 968 void SafepointTracing::begin(VM_Operation::VMOp_Type type) { 969 _op_count[type]++; 970 _current_type = type; 971 972 // update the time stamp to begin recording safepoint time 973 _last_safepoint_begin_time_ns = os::javaTimeNanos(); 974 _last_safepoint_sync_time_ns = 0; 975 976 _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns; 977 _last_safepoint_end_time_ns = 0; 978 979 RuntimeService::record_safepoint_begin(_last_app_time_ns); 980 } 981 982 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) { 983 _last_safepoint_sync_time_ns = os::javaTimeNanos(); 984 _nof_threads = nof_threads; 985 _nof_running = nof_running; 986 _page_trap = traps; 987 RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns); 988 } 989 990 void SafepointTracing::leave() { 991 _last_safepoint_leave_time_ns = os::javaTimeNanos(); 992 } 993 994 void SafepointTracing::end() { 995 _last_safepoint_end_time_ns = os::javaTimeNanos(); 996 997 if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) { 998 _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns; 999 } 1000 if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) { 1001 _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns; 1002 } 1003 if (log_is_enabled(Info, safepoint, stats)) { 1004 statistics_log(); 1005 } 1006 1007 log_info(safepoint)( 1008 "Safepoint \"%s\", " 1009 "Time since last: " JLONG_FORMAT " ns, " 1010 "Reaching safepoint: " JLONG_FORMAT " ns, " 1011 "At safepoint: " JLONG_FORMAT " ns, " 1012 "Leaving safepoint: " JLONG_FORMAT " ns, " 1013 "Total: " JLONG_FORMAT " ns, " 1014 "Threads: %d runnable, %d total", 1015 VM_Operation::name(_current_type), 1016 _last_app_time_ns, 1017 _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns, 1018 _last_safepoint_leave_time_ns - _last_safepoint_sync_time_ns, 1019 _last_safepoint_end_time_ns - _last_safepoint_leave_time_ns, 1020 _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns, 1021 _nof_running, 1022 _nof_threads 1023 ); 1024 1025 RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns); 1026 }