1 /* 2 * Copyright (c) 1998, 2023, 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 "classfile/vmSymbols.hpp" 27 #include "gc/shared/suspendibleThreadSet.hpp" 28 #include "jfr/jfrEvents.hpp" 29 #include "logging/log.hpp" 30 #include "logging/logStream.hpp" 31 #include "memory/allocation.inline.hpp" 32 #include "memory/padded.hpp" 33 #include "memory/resourceArea.hpp" 34 #include "memory/universe.hpp" 35 #include "oops/markWord.hpp" 36 #include "oops/oop.inline.hpp" 37 #include "runtime/atomic.hpp" 38 #include "runtime/frame.inline.hpp" 39 #include "runtime/handles.inline.hpp" 40 #include "runtime/handshake.hpp" 41 #include "runtime/interfaceSupport.inline.hpp" 42 #include "runtime/javaThread.hpp" 43 #include "runtime/lockStack.inline.hpp" 44 #include "runtime/mutexLocker.hpp" 45 #include "runtime/objectMonitor.hpp" 46 #include "runtime/objectMonitor.inline.hpp" 47 #include "runtime/os.inline.hpp" 48 #include "runtime/osThread.hpp" 49 #include "runtime/perfData.hpp" 50 #include "runtime/safepointMechanism.inline.hpp" 51 #include "runtime/safepointVerifiers.hpp" 52 #include "runtime/sharedRuntime.hpp" 53 #include "runtime/stubRoutines.hpp" 54 #include "runtime/synchronizer.hpp" 55 #include "runtime/threads.hpp" 56 #include "runtime/timer.hpp" 57 #include "runtime/trimNativeHeap.hpp" 58 #include "runtime/vframe.hpp" 59 #include "runtime/vmThread.hpp" 60 #include "utilities/align.hpp" 61 #include "utilities/dtrace.hpp" 62 #include "utilities/events.hpp" 63 #include "utilities/linkedlist.hpp" 64 #include "utilities/preserveException.hpp" 65 66 class ObjectMonitorsHashtable::PtrList : 67 public LinkedListImpl<ObjectMonitor*, 68 AnyObj::C_HEAP, mtThread, 69 AllocFailStrategy::RETURN_NULL> {}; 70 71 class CleanupObjectMonitorsHashtable: StackObj { 72 public: 73 bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) { 74 list->clear(); // clear the LinkListNodes 75 delete list; // then delete the LinkedList 76 return true; 77 } 78 }; 79 80 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() { 81 CleanupObjectMonitorsHashtable cleanup; 82 _ptrs->unlink(&cleanup); // cleanup the LinkedLists 83 delete _ptrs; // then delete the hash table 84 } 85 86 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) { 87 ObjectMonitorsHashtable::PtrList* list = get_entry(key); 88 if (list == nullptr) { 89 // Create new list and add it to the hash table: 90 list = new (mtThread) ObjectMonitorsHashtable::PtrList; 91 add_entry(key, list); 92 } 93 list->add(om); // Add the ObjectMonitor to the list. 94 _om_count++; 95 } 96 97 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) { 98 ObjectMonitorsHashtable::PtrList* list = get_entry(key); 99 if (list == nullptr || list->find(om) == nullptr) { 100 return false; 101 } 102 return true; 103 } 104 105 void MonitorList::add(ObjectMonitor* m) { 106 ObjectMonitor* head; 107 do { 108 head = Atomic::load(&_head); 109 m->set_next_om(head); 110 } while (Atomic::cmpxchg(&_head, head, m) != head); 111 112 size_t count = Atomic::add(&_count, 1u); 113 if (count > max()) { 114 Atomic::inc(&_max); 115 } 116 } 117 118 size_t MonitorList::count() const { 119 return Atomic::load(&_count); 120 } 121 122 size_t MonitorList::max() const { 123 return Atomic::load(&_max); 124 } 125 126 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated 127 // ObjectMonitors. Returns the number of unlinked ObjectMonitors. 128 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls, 129 elapsedTimer* timer_p, 130 GrowableArray<ObjectMonitor*>* unlinked_list) { 131 size_t unlinked_count = 0; 132 ObjectMonitor* prev = nullptr; 133 ObjectMonitor* head = Atomic::load_acquire(&_head); 134 ObjectMonitor* m = head; 135 // The in-use list head can be null during the final audit. 136 while (m != nullptr) { 137 if (m->is_being_async_deflated()) { 138 // Find next live ObjectMonitor. 139 ObjectMonitor* next = m; 140 do { 141 ObjectMonitor* next_next = next->next_om(); 142 unlinked_count++; 143 unlinked_list->append(next); 144 next = next_next; 145 if (unlinked_count >= (size_t)MonitorDeflationMax) { 146 // Reached the max so bail out on the gathering loop. 147 break; 148 } 149 } while (next != nullptr && next->is_being_async_deflated()); 150 if (prev == nullptr) { 151 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next); 152 if (prev_head != head) { 153 // Find new prev ObjectMonitor that just got inserted. 154 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) { 155 prev = n; 156 } 157 prev->set_next_om(next); 158 } 159 } else { 160 prev->set_next_om(next); 161 } 162 if (unlinked_count >= (size_t)MonitorDeflationMax) { 163 // Reached the max so bail out on the searching loop. 164 break; 165 } 166 m = next; 167 } else { 168 prev = m; 169 m = m->next_om(); 170 } 171 172 if (current->is_Java_thread()) { 173 // A JavaThread must check for a safepoint/handshake and honor it. 174 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking", 175 "unlinked_count", unlinked_count, 176 ls, timer_p); 177 } 178 } 179 Atomic::sub(&_count, unlinked_count); 180 return unlinked_count; 181 } 182 183 MonitorList::Iterator MonitorList::iterator() const { 184 return Iterator(Atomic::load_acquire(&_head)); 185 } 186 187 ObjectMonitor* MonitorList::Iterator::next() { 188 ObjectMonitor* current = _current; 189 _current = current->next_om(); 190 return current; 191 } 192 193 // The "core" versions of monitor enter and exit reside in this file. 194 // The interpreter and compilers contain specialized transliterated 195 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp 196 // fast_lock(...) for instance. If you make changes here, make sure to modify the 197 // interpreter, and both C1 and C2 fast-path inline locking code emission. 198 // 199 // ----------------------------------------------------------------------------- 200 201 #ifdef DTRACE_ENABLED 202 203 // Only bother with this argument setup if dtrace is available 204 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. 205 206 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \ 207 char* bytes = nullptr; \ 208 int len = 0; \ 209 jlong jtid = SharedRuntime::get_java_tid(thread); \ 210 Symbol* klassname = obj->klass()->name(); \ 211 if (klassname != nullptr) { \ 212 bytes = (char*)klassname->bytes(); \ 213 len = klassname->utf8_length(); \ 214 } 215 216 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ 217 { \ 218 if (DTraceMonitorProbes) { \ 219 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 220 HOTSPOT_MONITOR_WAIT(jtid, \ 221 (uintptr_t)(monitor), bytes, len, (millis)); \ 222 } \ 223 } 224 225 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY 226 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL 227 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED 228 229 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ 230 { \ 231 if (DTraceMonitorProbes) { \ 232 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 233 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \ 234 (uintptr_t)(monitor), bytes, len); \ 235 } \ 236 } 237 238 #else // ndef DTRACE_ENABLED 239 240 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;} 241 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;} 242 243 #endif // ndef DTRACE_ENABLED 244 245 // This exists only as a workaround of dtrace bug 6254741 246 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) { 247 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); 248 return 0; 249 } 250 251 static constexpr size_t inflation_lock_count() { 252 return 256; 253 } 254 255 // Static storage for an array of PlatformMutex. 256 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)]; 257 258 static inline PlatformMutex* inflation_lock(size_t index) { 259 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]); 260 } 261 262 void ObjectSynchronizer::initialize() { 263 for (size_t i = 0; i < inflation_lock_count(); i++) { 264 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex(); 265 } 266 // Start the ceiling with the estimate for one thread. 267 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate); 268 269 // Start the timer for deflations, so it does not trigger immediately. 270 _last_async_deflation_time_ns = os::javaTimeNanos(); 271 } 272 273 MonitorList ObjectSynchronizer::_in_use_list; 274 // monitors_used_above_threshold() policy is as follows: 275 // 276 // The ratio of the current _in_use_list count to the ceiling is used 277 // to determine if we are above MonitorUsedDeflationThreshold and need 278 // to do an async monitor deflation cycle. The ceiling is increased by 279 // AvgMonitorsPerThreadEstimate when a thread is added to the system 280 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is 281 // removed from the system. 282 // 283 // Note: If the _in_use_list max exceeds the ceiling, then 284 // monitors_used_above_threshold() will use the in_use_list max instead 285 // of the thread count derived ceiling because we have used more 286 // ObjectMonitors than the estimated average. 287 // 288 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax 289 // no-progress async monitor deflation cycles in a row, then the ceiling 290 // is adjusted upwards by monitors_used_above_threshold(). 291 // 292 // Start the ceiling with the estimate for one thread in initialize() 293 // which is called after cmd line options are processed. 294 static size_t _in_use_list_ceiling = 0; 295 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false; 296 bool volatile ObjectSynchronizer::_is_final_audit = false; 297 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0; 298 static uintx _no_progress_cnt = 0; 299 static bool _no_progress_skip_increment = false; 300 301 #define CHECK_THROW_NOSYNC_IMSE(obj) \ 302 if (EnableValhalla && (obj)->mark().is_inline_type()) { \ 303 JavaThread* THREAD = current; \ 304 ResourceMark rm(THREAD); \ 305 THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \ 306 } 307 308 #define CHECK_THROW_NOSYNC_IMSE_0(obj) \ 309 if (EnableValhalla && (obj)->mark().is_inline_type()) { \ 310 JavaThread* THREAD = current; \ 311 ResourceMark rm(THREAD); \ 312 THROW_MSG_0(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \ 313 } 314 315 // =====================> Quick functions 316 317 // The quick_* forms are special fast-path variants used to improve 318 // performance. In the simplest case, a "quick_*" implementation could 319 // simply return false, in which case the caller will perform the necessary 320 // state transitions and call the slow-path form. 321 // The fast-path is designed to handle frequently arising cases in an efficient 322 // manner and is just a degenerate "optimistic" variant of the slow-path. 323 // returns true -- to indicate the call was satisfied. 324 // returns false -- to indicate the call needs the services of the slow-path. 325 // A no-loitering ordinance is in effect for code in the quick_* family 326 // operators: safepoints or indefinite blocking (blocking that might span a 327 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon 328 // entry. 329 // 330 // Consider: An interesting optimization is to have the JIT recognize the 331 // following common idiom: 332 // synchronized (someobj) { .... ; notify(); } 333 // That is, we find a notify() or notifyAll() call that immediately precedes 334 // the monitorexit operation. In that case the JIT could fuse the operations 335 // into a single notifyAndExit() runtime primitive. 336 337 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) { 338 assert(current->thread_state() == _thread_in_Java, "invariant"); 339 NoSafepointVerifier nsv; 340 if (obj == nullptr) return false; // slow-path for invalid obj 341 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type"); 342 const markWord mark = obj->mark(); 343 344 if (LockingMode == LM_LIGHTWEIGHT) { 345 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) { 346 // Degenerate notify 347 // fast-locked by caller so by definition the implied waitset is empty. 348 return true; 349 } 350 } else if (LockingMode == LM_LEGACY) { 351 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 352 // Degenerate notify 353 // stack-locked by caller so by definition the implied waitset is empty. 354 return true; 355 } 356 } 357 358 if (mark.has_monitor()) { 359 ObjectMonitor* const mon = mark.monitor(); 360 assert(mon->object() == oop(obj), "invariant"); 361 if (mon->owner() != current) return false; // slow-path for IMS exception 362 363 if (mon->first_waiter() != nullptr) { 364 // We have one or more waiters. Since this is an inflated monitor 365 // that we own, we can transfer one or more threads from the waitset 366 // to the entrylist here and now, avoiding the slow-path. 367 if (all) { 368 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current); 369 } else { 370 DTRACE_MONITOR_PROBE(notify, mon, obj, current); 371 } 372 int free_count = 0; 373 do { 374 mon->INotify(current); 375 ++free_count; 376 } while (mon->first_waiter() != nullptr && all); 377 OM_PERFDATA_OP(Notifications, inc(free_count)); 378 } 379 return true; 380 } 381 382 // other IMS exception states take the slow-path 383 return false; 384 } 385 386 387 // The LockNode emitted directly at the synchronization site would have 388 // been too big if it were to have included support for the cases of inflated 389 // recursive enter and exit, so they go here instead. 390 // Note that we can't safely call AsyncPrintJavaStack() from within 391 // quick_enter() as our thread state remains _in_Java. 392 393 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current, 394 BasicLock * lock) { 395 assert(current->thread_state() == _thread_in_Java, "invariant"); 396 NoSafepointVerifier nsv; 397 if (obj == nullptr) return false; // Need to throw NPE 398 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type"); 399 400 if (obj->klass()->is_value_based()) { 401 return false; 402 } 403 404 const markWord mark = obj->mark(); 405 406 if (mark.has_monitor()) { 407 ObjectMonitor* const m = mark.monitor(); 408 // An async deflation or GC can race us before we manage to make 409 // the ObjectMonitor busy by setting the owner below. If we detect 410 // that race we just bail out to the slow-path here. 411 if (m->object_peek() == nullptr) { 412 return false; 413 } 414 JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw()); 415 416 // Lock contention and Transactional Lock Elision (TLE) diagnostics 417 // and observability 418 // Case: light contention possibly amenable to TLE 419 // Case: TLE inimical operations such as nested/recursive synchronization 420 421 if (owner == current) { 422 m->_recursions++; 423 current->inc_held_monitor_count(); 424 return true; 425 } 426 427 if (LockingMode != LM_LIGHTWEIGHT) { 428 // This Java Monitor is inflated so obj's header will never be 429 // displaced to this thread's BasicLock. Make the displaced header 430 // non-null so this BasicLock is not seen as recursive nor as 431 // being locked. We do this unconditionally so that this thread's 432 // BasicLock cannot be mis-interpreted by any stack walkers. For 433 // performance reasons, stack walkers generally first check for 434 // stack-locking in the object's header, the second check is for 435 // recursive stack-locking in the displaced header in the BasicLock, 436 // and last are the inflated Java Monitor (ObjectMonitor) checks. 437 lock->set_displaced_header(markWord::unused_mark()); 438 } 439 440 if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) { 441 assert(m->_recursions == 0, "invariant"); 442 current->inc_held_monitor_count(); 443 return true; 444 } 445 } 446 447 // Note that we could inflate in quick_enter. 448 // This is likely a useful optimization 449 // Critically, in quick_enter() we must not: 450 // -- block indefinitely, or 451 // -- reach a safepoint 452 453 return false; // revert to slow-path 454 } 455 456 // Handle notifications when synchronizing on value based classes 457 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) { 458 frame last_frame = current->last_frame(); 459 bool bcp_was_adjusted = false; 460 // Don't decrement bcp if it points to the frame's first instruction. This happens when 461 // handle_sync_on_value_based_class() is called because of a synchronized method. There 462 // is no actual monitorenter instruction in the byte code in this case. 463 if (last_frame.is_interpreted_frame() && 464 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) { 465 // adjust bcp to point back to monitorenter so that we print the correct line numbers 466 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1); 467 bcp_was_adjusted = true; 468 } 469 470 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) { 471 ResourceMark rm(current); 472 stringStream ss; 473 current->print_active_stack_on(&ss); 474 char* base = (char*)strstr(ss.base(), "at"); 475 char* newline = (char*)strchr(ss.base(), '\n'); 476 if (newline != nullptr) { 477 *newline = '\0'; 478 } 479 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base); 480 } else { 481 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses"); 482 ResourceMark rm(current); 483 Log(valuebasedclasses) vblog; 484 485 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name()); 486 if (current->has_last_Java_frame()) { 487 LogStream info_stream(vblog.info()); 488 current->print_active_stack_on(&info_stream); 489 } else { 490 vblog.info("Cannot find the last Java frame"); 491 } 492 493 EventSyncOnValueBasedClass event; 494 if (event.should_commit()) { 495 event.set_valueBasedClass(obj->klass()); 496 event.commit(); 497 } 498 } 499 500 if (bcp_was_adjusted) { 501 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1); 502 } 503 } 504 505 static bool useHeavyMonitors() { 506 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390) 507 return LockingMode == LM_MONITOR; 508 #else 509 return false; 510 #endif 511 } 512 513 // ----------------------------------------------------------------------------- 514 // Monitor Enter/Exit 515 // The interpreter and compiler assembly code tries to lock using the fast path 516 // of this algorithm. Make sure to update that code if the following function is 517 // changed. The implementation is extremely sensitive to race condition. Be careful. 518 519 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) { 520 CHECK_THROW_NOSYNC_IMSE(obj); 521 if (obj->klass()->is_value_based()) { 522 handle_sync_on_value_based_class(obj, current); 523 } 524 525 current->inc_held_monitor_count(); 526 527 if (!useHeavyMonitors()) { 528 if (LockingMode == LM_LIGHTWEIGHT) { 529 // Fast-locking does not use the 'lock' argument. 530 LockStack& lock_stack = current->lock_stack(); 531 if (lock_stack.can_push()) { 532 markWord mark = obj()->mark_acquire(); 533 if (mark.is_neutral()) { 534 assert(!lock_stack.contains(obj()), "thread must not already hold the lock"); 535 // Try to swing into 'fast-locked' state. 536 markWord locked_mark = mark.set_fast_locked(); 537 markWord old_mark = obj()->cas_set_mark(locked_mark, mark); 538 if (old_mark == mark) { 539 // Successfully fast-locked, push object to lock-stack and return. 540 lock_stack.push(obj()); 541 return; 542 } 543 } 544 } 545 // All other paths fall-through to inflate-enter. 546 } else if (LockingMode == LM_LEGACY) { 547 markWord mark = obj->mark(); 548 if (mark.is_neutral()) { 549 // Anticipate successful CAS -- the ST of the displaced mark must 550 // be visible <= the ST performed by the CAS. 551 lock->set_displaced_header(mark); 552 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) { 553 return; 554 } 555 // Fall through to inflate() ... 556 } else if (mark.has_locker() && 557 current->is_lock_owned((address) mark.locker())) { 558 assert(lock != mark.locker(), "must not re-lock the same lock"); 559 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock"); 560 lock->set_displaced_header(markWord::from_pointer(nullptr)); 561 return; 562 } 563 564 // The object header will never be displaced to this lock, 565 // so it does not matter what the value is, except that it 566 // must be non-zero to avoid looking like a re-entrant lock, 567 // and must not look locked either. 568 lock->set_displaced_header(markWord::unused_mark()); 569 } 570 } else if (VerifyHeavyMonitors) { 571 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked"); 572 } 573 574 // An async deflation can race after the inflate() call and before 575 // enter() can make the ObjectMonitor busy. enter() returns false if 576 // we have lost the race to async deflation and we simply try again. 577 while (true) { 578 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter); 579 if (monitor->enter(current)) { 580 return; 581 } 582 } 583 } 584 585 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) { 586 current->dec_held_monitor_count(); 587 588 if (!useHeavyMonitors()) { 589 markWord mark = object->mark(); 590 if (EnableValhalla && mark.is_inline_type()) { 591 return; 592 } 593 if (LockingMode == LM_LIGHTWEIGHT) { 594 // Fast-locking does not use the 'lock' argument. 595 if (mark.is_fast_locked()) { 596 markWord unlocked_mark = mark.set_unlocked(); 597 markWord old_mark = object->cas_set_mark(unlocked_mark, mark); 598 if (old_mark != mark) { 599 // Another thread won the CAS, it must have inflated the monitor. 600 // It can only have installed an anonymously locked monitor at this point. 601 // Fetch that monitor, set owner correctly to this thread, and 602 // exit it (allowing waiting threads to enter). 603 assert(old_mark.has_monitor(), "must have monitor"); 604 ObjectMonitor* monitor = old_mark.monitor(); 605 assert(monitor->is_owner_anonymous(), "must be anonymous owner"); 606 monitor->set_owner_from_anonymous(current); 607 monitor->exit(current); 608 } 609 LockStack& lock_stack = current->lock_stack(); 610 lock_stack.remove(object); 611 return; 612 } 613 } else if (LockingMode == LM_LEGACY) { 614 markWord dhw = lock->displaced_header(); 615 if (dhw.value() == 0) { 616 // If the displaced header is null, then this exit matches up with 617 // a recursive enter. No real work to do here except for diagnostics. 618 #ifndef PRODUCT 619 if (mark != markWord::INFLATING()) { 620 // Only do diagnostics if we are not racing an inflation. Simply 621 // exiting a recursive enter of a Java Monitor that is being 622 // inflated is safe; see the has_monitor() comment below. 623 assert(!mark.is_neutral(), "invariant"); 624 assert(!mark.has_locker() || 625 current->is_lock_owned((address)mark.locker()), "invariant"); 626 if (mark.has_monitor()) { 627 // The BasicLock's displaced_header is marked as a recursive 628 // enter and we have an inflated Java Monitor (ObjectMonitor). 629 // This is a special case where the Java Monitor was inflated 630 // after this thread entered the stack-lock recursively. When a 631 // Java Monitor is inflated, we cannot safely walk the Java 632 // Monitor owner's stack and update the BasicLocks because a 633 // Java Monitor can be asynchronously inflated by a thread that 634 // does not own the Java Monitor. 635 ObjectMonitor* m = mark.monitor(); 636 assert(m->object()->mark() == mark, "invariant"); 637 assert(m->is_entered(current), "invariant"); 638 } 639 } 640 #endif 641 return; 642 } 643 644 if (mark == markWord::from_pointer(lock)) { 645 // If the object is stack-locked by the current thread, try to 646 // swing the displaced header from the BasicLock back to the mark. 647 assert(dhw.is_neutral(), "invariant"); 648 if (object->cas_set_mark(dhw, mark) == mark) { 649 return; 650 } 651 } 652 } 653 } else if (VerifyHeavyMonitors) { 654 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked"); 655 } 656 657 // We have to take the slow-path of possible inflation and then exit. 658 // The ObjectMonitor* can't be async deflated until ownership is 659 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 660 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal); 661 if (LockingMode == LM_LIGHTWEIGHT && monitor->is_owner_anonymous()) { 662 // It must be owned by us. Pop lock object from lock stack. 663 LockStack& lock_stack = current->lock_stack(); 664 oop popped = lock_stack.pop(); 665 assert(popped == object, "must be owned by this thread"); 666 monitor->set_owner_from_anonymous(current); 667 } 668 monitor->exit(current); 669 } 670 671 // ----------------------------------------------------------------------------- 672 // JNI locks on java objects 673 // NOTE: must use heavy weight monitor to handle jni monitor enter 674 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) { 675 if (obj->klass()->is_value_based()) { 676 handle_sync_on_value_based_class(obj, current); 677 } 678 CHECK_THROW_NOSYNC_IMSE(obj); 679 680 // the current locking is from JNI instead of Java code 681 current->set_current_pending_monitor_is_from_java(false); 682 // An async deflation can race after the inflate() call and before 683 // enter() can make the ObjectMonitor busy. enter() returns false if 684 // we have lost the race to async deflation and we simply try again. 685 while (true) { 686 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter); 687 if (monitor->enter(current)) { 688 current->inc_held_monitor_count(1, true); 689 break; 690 } 691 } 692 current->set_current_pending_monitor_is_from_java(true); 693 } 694 695 // NOTE: must use heavy weight monitor to handle jni monitor exit 696 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) { 697 JavaThread* current = THREAD; 698 CHECK_THROW_NOSYNC_IMSE(obj); 699 700 // The ObjectMonitor* can't be async deflated until ownership is 701 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 702 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit); 703 // If this thread has locked the object, exit the monitor. We 704 // intentionally do not use CHECK on check_owner because we must exit the 705 // monitor even if an exception was already pending. 706 if (monitor->check_owner(THREAD)) { 707 monitor->exit(current); 708 current->dec_held_monitor_count(1, true); 709 } 710 } 711 712 // ----------------------------------------------------------------------------- 713 // Internal VM locks on java objects 714 // standard constructor, allows locking failures 715 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) { 716 _thread = thread; 717 _thread->check_for_valid_safepoint_state(); 718 _obj = obj; 719 720 if (_obj() != nullptr) { 721 ObjectSynchronizer::enter(_obj, &_lock, _thread); 722 } 723 } 724 725 ObjectLocker::~ObjectLocker() { 726 if (_obj() != nullptr) { 727 ObjectSynchronizer::exit(_obj(), &_lock, _thread); 728 } 729 } 730 731 732 // ----------------------------------------------------------------------------- 733 // Wait/Notify/NotifyAll 734 // NOTE: must use heavy weight monitor to handle wait() 735 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { 736 JavaThread* current = THREAD; 737 CHECK_THROW_NOSYNC_IMSE_0(obj); 738 if (millis < 0) { 739 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 740 } 741 // The ObjectMonitor* can't be async deflated because the _waiters 742 // field is incremented before ownership is dropped and decremented 743 // after ownership is regained. 744 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait); 745 746 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis); 747 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code 748 749 // This dummy call is in place to get around dtrace bug 6254741. Once 750 // that's fixed we can uncomment the following line, remove the call 751 // and change this function back into a "void" func. 752 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); 753 int ret_code = dtrace_waited_probe(monitor, obj, THREAD); 754 return ret_code; 755 } 756 757 void ObjectSynchronizer::notify(Handle obj, TRAPS) { 758 JavaThread* current = THREAD; 759 CHECK_THROW_NOSYNC_IMSE(obj); 760 761 markWord mark = obj->mark(); 762 if (LockingMode == LM_LIGHTWEIGHT) { 763 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) { 764 // Not inflated so there can't be any waiters to notify. 765 return; 766 } 767 } else if (LockingMode == LM_LEGACY) { 768 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 769 // Not inflated so there can't be any waiters to notify. 770 return; 771 } 772 } 773 // The ObjectMonitor* can't be async deflated until ownership is 774 // dropped by the calling thread. 775 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify); 776 monitor->notify(CHECK); 777 } 778 779 // NOTE: see comment of notify() 780 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { 781 JavaThread* current = THREAD; 782 CHECK_THROW_NOSYNC_IMSE(obj); 783 784 markWord mark = obj->mark(); 785 if (LockingMode == LM_LIGHTWEIGHT) { 786 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) { 787 // Not inflated so there can't be any waiters to notify. 788 return; 789 } 790 } else if (LockingMode == LM_LEGACY) { 791 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 792 // Not inflated so there can't be any waiters to notify. 793 return; 794 } 795 } 796 // The ObjectMonitor* can't be async deflated until ownership is 797 // dropped by the calling thread. 798 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify); 799 monitor->notifyAll(CHECK); 800 } 801 802 // ----------------------------------------------------------------------------- 803 // Hash Code handling 804 805 struct SharedGlobals { 806 char _pad_prefix[OM_CACHE_LINE_SIZE]; 807 // This is a highly shared mostly-read variable. 808 // To avoid false-sharing it needs to be the sole occupant of a cache line. 809 volatile int stw_random; 810 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int)); 811 // Hot RW variable -- Sequester to avoid false-sharing 812 volatile int hc_sequence; 813 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int)); 814 }; 815 816 static SharedGlobals GVars; 817 818 static markWord read_stable_mark(oop obj) { 819 markWord mark = obj->mark_acquire(); 820 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) { 821 // New lightweight locking does not use the markWord::INFLATING() protocol. 822 return mark; // normal fast-path return 823 } 824 825 int its = 0; 826 for (;;) { 827 markWord mark = obj->mark_acquire(); 828 if (!mark.is_being_inflated()) { 829 return mark; // normal fast-path return 830 } 831 832 // The object is being inflated by some other thread. 833 // The caller of read_stable_mark() must wait for inflation to complete. 834 // Avoid live-lock. 835 836 ++its; 837 if (its > 10000 || !os::is_MP()) { 838 if (its & 1) { 839 os::naked_yield(); 840 } else { 841 // Note that the following code attenuates the livelock problem but is not 842 // a complete remedy. A more complete solution would require that the inflating 843 // thread hold the associated inflation lock. The following code simply restricts 844 // the number of spinners to at most one. We'll have N-2 threads blocked 845 // on the inflationlock, 1 thread holding the inflation lock and using 846 // a yield/park strategy, and 1 thread in the midst of inflation. 847 // A more refined approach would be to change the encoding of INFLATING 848 // to allow encapsulation of a native thread pointer. Threads waiting for 849 // inflation to complete would use CAS to push themselves onto a singly linked 850 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag 851 // and calling park(). When inflation was complete the thread that accomplished inflation 852 // would detach the list and set the markword to inflated with a single CAS and 853 // then for each thread on the list, set the flag and unpark() the thread. 854 855 // Index into the lock array based on the current object address. 856 static_assert(is_power_of_2(inflation_lock_count()), "must be"); 857 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1); 858 int YieldThenBlock = 0; 859 assert(ix < inflation_lock_count(), "invariant"); 860 inflation_lock(ix)->lock(); 861 while (obj->mark_acquire() == markWord::INFLATING()) { 862 // Beware: naked_yield() is advisory and has almost no effect on some platforms 863 // so we periodically call current->_ParkEvent->park(1). 864 // We use a mixed spin/yield/block mechanism. 865 if ((YieldThenBlock++) >= 16) { 866 Thread::current()->_ParkEvent->park(1); 867 } else { 868 os::naked_yield(); 869 } 870 } 871 inflation_lock(ix)->unlock(); 872 } 873 } else { 874 SpinPause(); // SMP-polite spinning 875 } 876 } 877 } 878 879 // hashCode() generation : 880 // 881 // Possibilities: 882 // * MD5Digest of {obj,stw_random} 883 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function. 884 // * A DES- or AES-style SBox[] mechanism 885 // * One of the Phi-based schemes, such as: 886 // 2654435761 = 2^32 * Phi (golden ratio) 887 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ; 888 // * A variation of Marsaglia's shift-xor RNG scheme. 889 // * (obj ^ stw_random) is appealing, but can result 890 // in undesirable regularity in the hashCode values of adjacent objects 891 // (objects allocated back-to-back, in particular). This could potentially 892 // result in hashtable collisions and reduced hashtable efficiency. 893 // There are simple ways to "diffuse" the middle address bits over the 894 // generated hashCode values: 895 896 static inline intptr_t get_next_hash(Thread* current, oop obj) { 897 intptr_t value = 0; 898 if (hashCode == 0) { 899 // This form uses global Park-Miller RNG. 900 // On MP system we'll have lots of RW access to a global, so the 901 // mechanism induces lots of coherency traffic. 902 value = os::random(); 903 } else if (hashCode == 1) { 904 // This variation has the property of being stable (idempotent) 905 // between STW operations. This can be useful in some of the 1-0 906 // synchronization schemes. 907 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3; 908 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random; 909 } else if (hashCode == 2) { 910 value = 1; // for sensitivity testing 911 } else if (hashCode == 3) { 912 value = ++GVars.hc_sequence; 913 } else if (hashCode == 4) { 914 value = cast_from_oop<intptr_t>(obj); 915 } else { 916 // Marsaglia's xor-shift scheme with thread-specific state 917 // This is probably the best overall implementation -- we'll 918 // likely make this the default in future releases. 919 unsigned t = current->_hashStateX; 920 t ^= (t << 11); 921 current->_hashStateX = current->_hashStateY; 922 current->_hashStateY = current->_hashStateZ; 923 current->_hashStateZ = current->_hashStateW; 924 unsigned v = current->_hashStateW; 925 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)); 926 current->_hashStateW = v; 927 value = v; 928 } 929 930 value &= markWord::hash_mask; 931 if (value == 0) value = 0xBAD; 932 assert(value != markWord::no_hash, "invariant"); 933 return value; 934 } 935 936 // Can be called from non JavaThreads (e.g., VMThread) for FastHashCode 937 // calculations as part of JVM/TI tagging. 938 static bool is_lock_owned(Thread* thread, oop obj) { 939 assert(LockingMode == LM_LIGHTWEIGHT, "only call this with new lightweight locking enabled"); 940 return thread->is_Java_thread() ? JavaThread::cast(thread)->lock_stack().contains(obj) : false; 941 } 942 943 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) { 944 if (EnableValhalla && obj->klass()->is_inline_klass()) { 945 // VM should be calling bootstrap method 946 ShouldNotReachHere(); 947 } 948 949 while (true) { 950 ObjectMonitor* monitor = nullptr; 951 markWord temp, test; 952 intptr_t hash; 953 markWord mark = read_stable_mark(obj); 954 if (VerifyHeavyMonitors) { 955 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)"); 956 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked"); 957 } 958 if (mark.is_neutral()) { // if this is a normal header 959 hash = mark.hash(); 960 if (hash != 0) { // if it has a hash, just return it 961 return hash; 962 } 963 hash = get_next_hash(current, obj); // get a new hash 964 temp = mark.copy_set_hash(hash); // merge the hash into header 965 // try to install the hash 966 test = obj->cas_set_mark(temp, mark); 967 if (test == mark) { // if the hash was installed, return it 968 return hash; 969 } 970 // Failed to install the hash. It could be that another thread 971 // installed the hash just before our attempt or inflation has 972 // occurred or... so we fall thru to inflate the monitor for 973 // stability and then install the hash. 974 } else if (mark.has_monitor()) { 975 monitor = mark.monitor(); 976 temp = monitor->header(); 977 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 978 hash = temp.hash(); 979 if (hash != 0) { 980 // It has a hash. 981 982 // Separate load of dmw/header above from the loads in 983 // is_being_async_deflated(). 984 985 // dmw/header and _contentions may get written by different threads. 986 // Make sure to observe them in the same order when having several observers. 987 OrderAccess::loadload_for_IRIW(); 988 989 if (monitor->is_being_async_deflated()) { 990 // But we can't safely use the hash if we detect that async 991 // deflation has occurred. So we attempt to restore the 992 // header/dmw to the object's header so that we only retry 993 // once if the deflater thread happens to be slow. 994 monitor->install_displaced_markword_in_object(obj); 995 continue; 996 } 997 return hash; 998 } 999 // Fall thru so we only have one place that installs the hash in 1000 // the ObjectMonitor. 1001 } else if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked() && is_lock_owned(current, obj)) { 1002 // This is a fast-lock owned by the calling thread so use the 1003 // markWord from the object. 1004 hash = mark.hash(); 1005 if (hash != 0) { // if it has a hash, just return it 1006 return hash; 1007 } 1008 } else if (LockingMode == LM_LEGACY && mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 1009 // This is a stack-lock owned by the calling thread so fetch the 1010 // displaced markWord from the BasicLock on the stack. 1011 temp = mark.displaced_mark_helper(); 1012 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 1013 hash = temp.hash(); 1014 if (hash != 0) { // if it has a hash, just return it 1015 return hash; 1016 } 1017 // WARNING: 1018 // The displaced header in the BasicLock on a thread's stack 1019 // is strictly immutable. It CANNOT be changed in ANY cases. 1020 // So we have to inflate the stack-lock into an ObjectMonitor 1021 // even if the current thread owns the lock. The BasicLock on 1022 // a thread's stack can be asynchronously read by other threads 1023 // during an inflate() call so any change to that stack memory 1024 // may not propagate to other threads correctly. 1025 } 1026 1027 // Inflate the monitor to set the hash. 1028 1029 // An async deflation can race after the inflate() call and before we 1030 // can update the ObjectMonitor's header with the hash value below. 1031 monitor = inflate(current, obj, inflate_cause_hash_code); 1032 // Load ObjectMonitor's header/dmw field and see if it has a hash. 1033 mark = monitor->header(); 1034 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 1035 hash = mark.hash(); 1036 if (hash == 0) { // if it does not have a hash 1037 hash = get_next_hash(current, obj); // get a new hash 1038 temp = mark.copy_set_hash(hash) ; // merge the hash into header 1039 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 1040 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value()); 1041 test = markWord(v); 1042 if (test != mark) { 1043 // The attempt to update the ObjectMonitor's header/dmw field 1044 // did not work. This can happen if another thread managed to 1045 // merge in the hash just before our cmpxchg(). 1046 // If we add any new usages of the header/dmw field, this code 1047 // will need to be updated. 1048 hash = test.hash(); 1049 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value()); 1050 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash"); 1051 } 1052 if (monitor->is_being_async_deflated()) { 1053 // If we detect that async deflation has occurred, then we 1054 // attempt to restore the header/dmw to the object's header 1055 // so that we only retry once if the deflater thread happens 1056 // to be slow. 1057 monitor->install_displaced_markword_in_object(obj); 1058 continue; 1059 } 1060 } 1061 // We finally get the hash. 1062 return hash; 1063 } 1064 } 1065 1066 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current, 1067 Handle h_obj) { 1068 if (EnableValhalla && h_obj->mark().is_inline_type()) { 1069 return false; 1070 } 1071 assert(current == JavaThread::current(), "Can only be called on current thread"); 1072 oop obj = h_obj(); 1073 1074 markWord mark = read_stable_mark(obj); 1075 1076 if (LockingMode == LM_LEGACY && mark.has_locker()) { 1077 // stack-locked case, header points into owner's stack 1078 return current->is_lock_owned((address)mark.locker()); 1079 } 1080 1081 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) { 1082 // fast-locking case, see if lock is in current's lock stack 1083 return current->lock_stack().contains(h_obj()); 1084 } 1085 1086 if (mark.has_monitor()) { 1087 // Inflated monitor so header points to ObjectMonitor (tagged pointer). 1088 // The first stage of async deflation does not affect any field 1089 // used by this comparison so the ObjectMonitor* is usable here. 1090 ObjectMonitor* monitor = mark.monitor(); 1091 return monitor->is_entered(current) != 0; 1092 } 1093 // Unlocked case, header in place 1094 assert(mark.is_neutral(), "sanity check"); 1095 return false; 1096 } 1097 1098 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) { 1099 oop obj = h_obj(); 1100 markWord mark = read_stable_mark(obj); 1101 1102 if (LockingMode == LM_LEGACY && mark.has_locker()) { 1103 // stack-locked so header points into owner's stack. 1104 // owning_thread_from_monitor_owner() may also return null here: 1105 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker()); 1106 } 1107 1108 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) { 1109 // fast-locked so get owner from the object. 1110 // owning_thread_from_object() may also return null here: 1111 return Threads::owning_thread_from_object(t_list, h_obj()); 1112 } 1113 1114 if (mark.has_monitor()) { 1115 // Inflated monitor so header points to ObjectMonitor (tagged pointer). 1116 // The first stage of async deflation does not affect any field 1117 // used by this comparison so the ObjectMonitor* is usable here. 1118 ObjectMonitor* monitor = mark.monitor(); 1119 assert(monitor != nullptr, "monitor should be non-null"); 1120 // owning_thread_from_monitor() may also return null here: 1121 return Threads::owning_thread_from_monitor(t_list, monitor); 1122 } 1123 1124 // Unlocked case, header in place 1125 // Cannot have assertion since this object may have been 1126 // locked by another thread when reaching here. 1127 // assert(mark.is_neutral(), "sanity check"); 1128 1129 return nullptr; 1130 } 1131 1132 // Visitors ... 1133 1134 // Iterate ObjectMonitors where the owner == thread; this does NOT include 1135 // ObjectMonitors where owner is set to a stack-lock address in thread. 1136 // 1137 // This version of monitors_iterate() works with the in-use monitor list. 1138 // 1139 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) { 1140 MonitorList::Iterator iter = _in_use_list.iterator(); 1141 while (iter.has_next()) { 1142 ObjectMonitor* mid = iter.next(); 1143 if (mid->owner() != thread) { 1144 // Not owned by the target thread and intentionally skips when owner 1145 // is set to a stack-lock address in the target thread. 1146 continue; 1147 } 1148 if (!mid->is_being_async_deflated() && mid->object_peek() != nullptr) { 1149 // Only process with closure if the object is set. 1150 1151 // monitors_iterate() is only called at a safepoint or when the 1152 // target thread is suspended or when the target thread is 1153 // operating on itself. The current closures in use today are 1154 // only interested in an owned ObjectMonitor and ownership 1155 // cannot be dropped under the calling contexts so the 1156 // ObjectMonitor cannot be async deflated. 1157 closure->do_monitor(mid); 1158 } 1159 } 1160 } 1161 1162 // This version of monitors_iterate() works with the specified linked list. 1163 // 1164 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, 1165 ObjectMonitorsHashtable::PtrList* list, 1166 JavaThread* thread) { 1167 typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator; 1168 ObjectMonitorIterator iter(list->head()); 1169 while (!iter.is_empty()) { 1170 ObjectMonitor* mid = *iter.next(); 1171 // Owner set to a stack-lock address in thread should never be seen here: 1172 assert(mid->owner() == thread, "must be"); 1173 if (!mid->is_being_async_deflated() && mid->object_peek() != nullptr) { 1174 // Only process with closure if the object is set. 1175 1176 // monitors_iterate() is only called at a safepoint or when the 1177 // target thread is suspended or when the target thread is 1178 // operating on itself. The current closures in use today are 1179 // only interested in an owned ObjectMonitor and ownership 1180 // cannot be dropped under the calling contexts so the 1181 // ObjectMonitor cannot be async deflated. 1182 closure->do_monitor(mid); 1183 } 1184 } 1185 } 1186 1187 static bool monitors_used_above_threshold(MonitorList* list) { 1188 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy 1189 return false; 1190 } 1191 // Start with ceiling based on a per-thread estimate: 1192 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling(); 1193 size_t old_ceiling = ceiling; 1194 if (ceiling < list->max()) { 1195 // The max used by the system has exceeded the ceiling so use that: 1196 ceiling = list->max(); 1197 } 1198 size_t monitors_used = list->count(); 1199 if (monitors_used == 0) { // empty list is easy 1200 return false; 1201 } 1202 if (NoAsyncDeflationProgressMax != 0 && 1203 _no_progress_cnt >= NoAsyncDeflationProgressMax) { 1204 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0; 1205 size_t new_ceiling = ceiling + (ceiling * remainder) + 1; 1206 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling); 1207 log_info(monitorinflation)("Too many deflations without progress; " 1208 "bumping in_use_list_ceiling from " SIZE_FORMAT 1209 " to " SIZE_FORMAT, old_ceiling, new_ceiling); 1210 _no_progress_cnt = 0; 1211 ceiling = new_ceiling; 1212 } 1213 1214 // Check if our monitor usage is above the threshold: 1215 size_t monitor_usage = (monitors_used * 100LL) / ceiling; 1216 if (int(monitor_usage) > MonitorUsedDeflationThreshold) { 1217 log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT 1218 ", monitor_usage=" SIZE_FORMAT ", threshold=" INTX_FORMAT, 1219 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold); 1220 return true; 1221 } 1222 1223 return false; 1224 } 1225 1226 size_t ObjectSynchronizer::in_use_list_ceiling() { 1227 return _in_use_list_ceiling; 1228 } 1229 1230 void ObjectSynchronizer::dec_in_use_list_ceiling() { 1231 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate); 1232 } 1233 1234 void ObjectSynchronizer::inc_in_use_list_ceiling() { 1235 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate); 1236 } 1237 1238 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) { 1239 _in_use_list_ceiling = new_value; 1240 } 1241 1242 bool ObjectSynchronizer::is_async_deflation_needed() { 1243 if (is_async_deflation_requested()) { 1244 // Async deflation request. 1245 log_info(monitorinflation)("Async deflation needed: explicit request"); 1246 return true; 1247 } 1248 1249 jlong time_since_last = time_since_last_async_deflation_ms(); 1250 1251 if (AsyncDeflationInterval > 0 && 1252 time_since_last > AsyncDeflationInterval && 1253 monitors_used_above_threshold(&_in_use_list)) { 1254 // It's been longer than our specified deflate interval and there 1255 // are too many monitors in use. We don't deflate more frequently 1256 // than AsyncDeflationInterval (unless is_async_deflation_requested) 1257 // in order to not swamp the MonitorDeflationThread. 1258 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold"); 1259 return true; 1260 } 1261 1262 if (GuaranteedAsyncDeflationInterval > 0 && 1263 time_since_last > GuaranteedAsyncDeflationInterval) { 1264 // It's been longer than our specified guaranteed deflate interval. 1265 // We need to clean up the used monitors even if the threshold is 1266 // not reached, to keep the memory utilization at bay when many threads 1267 // touched many monitors. 1268 log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) " 1269 "is greater than time since last deflation (" JLONG_FORMAT " ms)", 1270 GuaranteedAsyncDeflationInterval, time_since_last); 1271 1272 // If this deflation has no progress, then it should not affect the no-progress 1273 // tracking, otherwise threshold heuristics would think it was triggered, experienced 1274 // no progress, and needs to backoff more aggressively. In this "no progress" case, 1275 // the generic code would bump the no-progress counter, and we compensate for that 1276 // by telling it to skip the update. 1277 // 1278 // If this deflation has progress, then it should let non-progress tracking 1279 // know about this, otherwise the threshold heuristics would kick in, potentially 1280 // experience no-progress due to aggressive cleanup by this deflation, and think 1281 // it is still in no-progress stride. In this "progress" case, the generic code would 1282 // zero the counter, and we allow it to happen. 1283 _no_progress_skip_increment = true; 1284 1285 return true; 1286 } 1287 1288 return false; 1289 } 1290 1291 bool ObjectSynchronizer::request_deflate_idle_monitors() { 1292 JavaThread* current = JavaThread::current(); 1293 bool ret_code = false; 1294 1295 jlong last_time = last_async_deflation_time_ns(); 1296 set_is_async_deflation_requested(true); 1297 { 1298 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag); 1299 ml.notify_all(); 1300 } 1301 const int N_CHECKS = 5; 1302 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds 1303 if (last_async_deflation_time_ns() > last_time) { 1304 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i); 1305 ret_code = true; 1306 break; 1307 } 1308 { 1309 // JavaThread has to honor the blocking protocol. 1310 ThreadBlockInVM tbivm(current); 1311 os::naked_short_sleep(999); // sleep for almost 1 second 1312 } 1313 } 1314 if (!ret_code) { 1315 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS); 1316 } 1317 1318 return ret_code; 1319 } 1320 1321 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() { 1322 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS); 1323 } 1324 1325 static void post_monitor_inflate_event(EventJavaMonitorInflate* event, 1326 const oop obj, 1327 ObjectSynchronizer::InflateCause cause) { 1328 assert(event != nullptr, "invariant"); 1329 event->set_monitorClass(obj->klass()); 1330 event->set_address((uintptr_t)(void*)obj); 1331 event->set_cause((u1)cause); 1332 event->commit(); 1333 } 1334 1335 // Fast path code shared by multiple functions 1336 void ObjectSynchronizer::inflate_helper(oop obj) { 1337 markWord mark = obj->mark_acquire(); 1338 if (mark.has_monitor()) { 1339 ObjectMonitor* monitor = mark.monitor(); 1340 markWord dmw = monitor->header(); 1341 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value()); 1342 return; 1343 } 1344 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal); 1345 } 1346 1347 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object, 1348 const InflateCause cause) { 1349 if (EnableValhalla) { 1350 guarantee(!object->klass()->is_inline_klass(), "Attempt to inflate inline type"); 1351 } 1352 1353 EventJavaMonitorInflate event; 1354 1355 for (;;) { 1356 const markWord mark = object->mark_acquire(); 1357 1358 // The mark can be in one of the following states: 1359 // * inflated - Just return if using stack-locking. 1360 // If using fast-locking and the ObjectMonitor owner 1361 // is anonymous and the current thread owns the 1362 // object lock, then we make the current thread the 1363 // ObjectMonitor owner and remove the lock from the 1364 // current thread's lock stack. 1365 // * fast-locked - Coerce it to inflated from fast-locked. 1366 // * stack-locked - Coerce it to inflated from stack-locked. 1367 // * INFLATING - Busy wait for conversion from stack-locked to 1368 // inflated. 1369 // * neutral - Aggressively inflate the object. 1370 1371 // CASE: inflated 1372 if (mark.has_monitor()) { 1373 ObjectMonitor* inf = mark.monitor(); 1374 markWord dmw = inf->header(); 1375 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1376 if (LockingMode == LM_LIGHTWEIGHT && inf->is_owner_anonymous() && is_lock_owned(current, object)) { 1377 inf->set_owner_from_anonymous(current); 1378 JavaThread::cast(current)->lock_stack().remove(object); 1379 } 1380 return inf; 1381 } 1382 1383 if (LockingMode != LM_LIGHTWEIGHT) { 1384 // New lightweight locking does not use INFLATING. 1385 // CASE: inflation in progress - inflating over a stack-lock. 1386 // Some other thread is converting from stack-locked to inflated. 1387 // Only that thread can complete inflation -- other threads must wait. 1388 // The INFLATING value is transient. 1389 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. 1390 // We could always eliminate polling by parking the thread on some auxiliary list. 1391 if (mark == markWord::INFLATING()) { 1392 read_stable_mark(object); 1393 continue; 1394 } 1395 } 1396 1397 // CASE: fast-locked 1398 // Could be fast-locked either by current or by some other thread. 1399 // 1400 // Note that we allocate the ObjectMonitor speculatively, _before_ 1401 // attempting to set the object's mark to the new ObjectMonitor. If 1402 // this thread owns the monitor, then we set the ObjectMonitor's 1403 // owner to this thread. Otherwise, we set the ObjectMonitor's owner 1404 // to anonymous. If we lose the race to set the object's mark to the 1405 // new ObjectMonitor, then we just delete it and loop around again. 1406 // 1407 LogStreamHandle(Trace, monitorinflation) lsh; 1408 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) { 1409 ObjectMonitor* monitor = new ObjectMonitor(object); 1410 monitor->set_header(mark.set_unlocked()); 1411 bool own = is_lock_owned(current, object); 1412 if (own) { 1413 // Owned by us. 1414 monitor->set_owner_from(nullptr, current); 1415 } else { 1416 // Owned by somebody else. 1417 monitor->set_owner_anonymous(); 1418 } 1419 markWord monitor_mark = markWord::encode(monitor); 1420 markWord old_mark = object->cas_set_mark(monitor_mark, mark); 1421 if (old_mark == mark) { 1422 // Success! Return inflated monitor. 1423 if (own) { 1424 JavaThread::cast(current)->lock_stack().remove(object); 1425 } 1426 // Once the ObjectMonitor is configured and object is associated 1427 // with the ObjectMonitor, it is safe to allow async deflation: 1428 _in_use_list.add(monitor); 1429 1430 // Hopefully the performance counters are allocated on distinct 1431 // cache lines to avoid false sharing on MP systems ... 1432 OM_PERFDATA_OP(Inflations, inc()); 1433 if (log_is_enabled(Trace, monitorinflation)) { 1434 ResourceMark rm(current); 1435 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark=" 1436 INTPTR_FORMAT ", type='%s'", p2i(object), 1437 object->mark().value(), object->klass()->external_name()); 1438 } 1439 if (event.should_commit()) { 1440 post_monitor_inflate_event(&event, object, cause); 1441 } 1442 return monitor; 1443 } else { 1444 delete monitor; 1445 continue; // Interference -- just retry 1446 } 1447 } 1448 1449 // CASE: stack-locked 1450 // Could be stack-locked either by current or by some other thread. 1451 // 1452 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting 1453 // to install INFLATING into the mark word. We originally installed INFLATING, 1454 // allocated the ObjectMonitor, and then finally STed the address of the 1455 // ObjectMonitor into the mark. This was correct, but artificially lengthened 1456 // the interval in which INFLATING appeared in the mark, thus increasing 1457 // the odds of inflation contention. If we lose the race to set INFLATING, 1458 // then we just delete the ObjectMonitor and loop around again. 1459 // 1460 if (LockingMode == LM_LEGACY && mark.has_locker()) { 1461 assert(LockingMode != LM_LIGHTWEIGHT, "cannot happen with new lightweight locking"); 1462 ObjectMonitor* m = new ObjectMonitor(object); 1463 // Optimistically prepare the ObjectMonitor - anticipate successful CAS 1464 // We do this before the CAS in order to minimize the length of time 1465 // in which INFLATING appears in the mark. 1466 1467 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark); 1468 if (cmp != mark) { 1469 delete m; 1470 continue; // Interference -- just retry 1471 } 1472 1473 // We've successfully installed INFLATING (0) into the mark-word. 1474 // This is the only case where 0 will appear in a mark-word. 1475 // Only the singular thread that successfully swings the mark-word 1476 // to 0 can perform (or more precisely, complete) inflation. 1477 // 1478 // Why do we CAS a 0 into the mark-word instead of just CASing the 1479 // mark-word from the stack-locked value directly to the new inflated state? 1480 // Consider what happens when a thread unlocks a stack-locked object. 1481 // It attempts to use CAS to swing the displaced header value from the 1482 // on-stack BasicLock back into the object header. Recall also that the 1483 // header value (hash code, etc) can reside in (a) the object header, or 1484 // (b) a displaced header associated with the stack-lock, or (c) a displaced 1485 // header in an ObjectMonitor. The inflate() routine must copy the header 1486 // value from the BasicLock on the owner's stack to the ObjectMonitor, all 1487 // the while preserving the hashCode stability invariants. If the owner 1488 // decides to release the lock while the value is 0, the unlock will fail 1489 // and control will eventually pass from slow_exit() to inflate. The owner 1490 // will then spin, waiting for the 0 value to disappear. Put another way, 1491 // the 0 causes the owner to stall if the owner happens to try to 1492 // drop the lock (restoring the header from the BasicLock to the object) 1493 // while inflation is in-progress. This protocol avoids races that might 1494 // would otherwise permit hashCode values to change or "flicker" for an object. 1495 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable. 1496 // 0 serves as a "BUSY" inflate-in-progress indicator. 1497 1498 1499 // fetch the displaced mark from the owner's stack. 1500 // The owner can't die or unwind past the lock while our INFLATING 1501 // object is in the mark. Furthermore the owner can't complete 1502 // an unlock on the object, either. 1503 markWord dmw = mark.displaced_mark_helper(); 1504 // Catch if the object's header is not neutral (not locked and 1505 // not marked is what we care about here). 1506 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1507 1508 // Setup monitor fields to proper values -- prepare the monitor 1509 m->set_header(dmw); 1510 1511 // Optimization: if the mark.locker stack address is associated 1512 // with this thread we could simply set m->_owner = current. 1513 // Note that a thread can inflate an object 1514 // that it has stack-locked -- as might happen in wait() -- directly 1515 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom. 1516 m->set_owner_from(nullptr, mark.locker()); 1517 // TODO-FIXME: assert BasicLock->dhw != 0. 1518 1519 // Must preserve store ordering. The monitor state must 1520 // be stable at the time of publishing the monitor address. 1521 guarantee(object->mark() == markWord::INFLATING(), "invariant"); 1522 // Release semantics so that above set_object() is seen first. 1523 object->release_set_mark(markWord::encode(m)); 1524 1525 // Once ObjectMonitor is configured and the object is associated 1526 // with the ObjectMonitor, it is safe to allow async deflation: 1527 _in_use_list.add(m); 1528 1529 // Hopefully the performance counters are allocated on distinct cache lines 1530 // to avoid false sharing on MP systems ... 1531 OM_PERFDATA_OP(Inflations, inc()); 1532 if (log_is_enabled(Trace, monitorinflation)) { 1533 ResourceMark rm(current); 1534 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark=" 1535 INTPTR_FORMAT ", type='%s'", p2i(object), 1536 object->mark().value(), object->klass()->external_name()); 1537 } 1538 if (event.should_commit()) { 1539 post_monitor_inflate_event(&event, object, cause); 1540 } 1541 return m; 1542 } 1543 1544 // CASE: neutral 1545 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. 1546 // If we know we're inflating for entry it's better to inflate by swinging a 1547 // pre-locked ObjectMonitor pointer into the object header. A successful 1548 // CAS inflates the object *and* confers ownership to the inflating thread. 1549 // In the current implementation we use a 2-step mechanism where we CAS() 1550 // to inflate and then CAS() again to try to swing _owner from null to current. 1551 // An inflateTry() method that we could call from enter() would be useful. 1552 1553 // Catch if the object's header is not neutral (not locked and 1554 // not marked is what we care about here). 1555 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 1556 ObjectMonitor* m = new ObjectMonitor(object); 1557 // prepare m for installation - set monitor to initial state 1558 m->set_header(mark); 1559 1560 if (object->cas_set_mark(markWord::encode(m), mark) != mark) { 1561 delete m; 1562 m = nullptr; 1563 continue; 1564 // interference - the markword changed - just retry. 1565 // The state-transitions are one-way, so there's no chance of 1566 // live-lock -- "Inflated" is an absorbing state. 1567 } 1568 1569 // Once the ObjectMonitor is configured and object is associated 1570 // with the ObjectMonitor, it is safe to allow async deflation: 1571 _in_use_list.add(m); 1572 1573 // Hopefully the performance counters are allocated on distinct 1574 // cache lines to avoid false sharing on MP systems ... 1575 OM_PERFDATA_OP(Inflations, inc()); 1576 if (log_is_enabled(Trace, monitorinflation)) { 1577 ResourceMark rm(current); 1578 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark=" 1579 INTPTR_FORMAT ", type='%s'", p2i(object), 1580 object->mark().value(), object->klass()->external_name()); 1581 } 1582 if (event.should_commit()) { 1583 post_monitor_inflate_event(&event, object, cause); 1584 } 1585 return m; 1586 } 1587 } 1588 1589 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name, 1590 const char* cnt_name, size_t cnt, 1591 LogStream* ls, elapsedTimer* timer_p) { 1592 if (!SafepointMechanism::should_process(current)) { 1593 return; 1594 } 1595 1596 // A safepoint/handshake has started. 1597 if (ls != nullptr) { 1598 timer_p->stop(); 1599 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling=" 1600 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1601 op_name, cnt_name, cnt, in_use_list_ceiling(), 1602 _in_use_list.count(), _in_use_list.max()); 1603 } 1604 1605 { 1606 // Honor block request. 1607 ThreadBlockInVM tbivm(current); 1608 } 1609 1610 if (ls != nullptr) { 1611 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT 1612 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name, 1613 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1614 timer_p->start(); 1615 } 1616 } 1617 1618 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle 1619 // ObjectMonitors. Returns the number of deflated ObjectMonitors. 1620 // 1621 // If table != nullptr, we gather owned ObjectMonitors indexed by the 1622 // owner in the table. Please note that ObjectMonitors where the owner 1623 // is set to a stack-lock address are NOT associated with the JavaThread 1624 // that holds that stack-lock. All of the current consumers of 1625 // ObjectMonitorsHashtable info only care about JNI locked monitors and 1626 // those do not have the owner set to a stack-lock address. 1627 // 1628 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls, 1629 elapsedTimer* timer_p, 1630 ObjectMonitorsHashtable* table) { 1631 MonitorList::Iterator iter = _in_use_list.iterator(); 1632 size_t deflated_count = 0; 1633 1634 while (iter.has_next()) { 1635 if (deflated_count >= (size_t)MonitorDeflationMax) { 1636 break; 1637 } 1638 ObjectMonitor* mid = iter.next(); 1639 if (mid->deflate_monitor()) { 1640 deflated_count++; 1641 } else if (table != nullptr) { 1642 // The caller is interested in the owned ObjectMonitors. This does 1643 // not include when owner is set to a stack-lock address in thread. 1644 // This also does not capture unowned ObjectMonitors that cannot be 1645 // deflated because of a waiter. 1646 void* key = mid->owner(); 1647 // Since deflate_idle_monitors() and deflate_monitor_list() can be 1648 // called more than once, we have to make sure the entry has not 1649 // already been added. 1650 if (key != nullptr && !table->has_entry(key, mid)) { 1651 table->add_entry(key, mid); 1652 } 1653 } 1654 1655 if (current->is_Java_thread()) { 1656 // A JavaThread must check for a safepoint/handshake and honor it. 1657 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count", 1658 deflated_count, ls, timer_p); 1659 } 1660 } 1661 1662 return deflated_count; 1663 } 1664 1665 class HandshakeForDeflation : public HandshakeClosure { 1666 public: 1667 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {} 1668 1669 void do_thread(Thread* thread) { 1670 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread=" 1671 INTPTR_FORMAT, p2i(thread)); 1672 } 1673 }; 1674 1675 class VM_RendezvousGCThreads : public VM_Operation { 1676 public: 1677 bool evaluate_at_safepoint() const override { return false; } 1678 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; } 1679 void doit() override { 1680 SuspendibleThreadSet::synchronize(); 1681 SuspendibleThreadSet::desynchronize(); 1682 }; 1683 }; 1684 1685 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list) { 1686 NativeHeapTrimmer::SuspendMark sm("monitor deletion"); 1687 size_t count = 0; 1688 for (ObjectMonitor* monitor: *delete_list) { 1689 delete monitor; 1690 count++; 1691 } 1692 return count; 1693 } 1694 1695 // This function is called by the MonitorDeflationThread to deflate 1696 // ObjectMonitors. It is also called via do_final_audit_and_print_stats() 1697 // and VM_ThreadDump::doit() by the VMThread. 1698 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) { 1699 Thread* current = Thread::current(); 1700 if (current->is_Java_thread()) { 1701 // The async deflation request has been processed. 1702 _last_async_deflation_time_ns = os::javaTimeNanos(); 1703 set_is_async_deflation_requested(false); 1704 } 1705 1706 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1707 LogStreamHandle(Info, monitorinflation) lsh_info; 1708 LogStream* ls = nullptr; 1709 if (log_is_enabled(Debug, monitorinflation)) { 1710 ls = &lsh_debug; 1711 } else if (log_is_enabled(Info, monitorinflation)) { 1712 ls = &lsh_info; 1713 } 1714 1715 elapsedTimer timer; 1716 if (ls != nullptr) { 1717 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1718 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1719 timer.start(); 1720 } 1721 1722 // Deflate some idle ObjectMonitors. 1723 size_t deflated_count = deflate_monitor_list(current, ls, &timer, table); 1724 size_t unlinked_count = 0; 1725 size_t deleted_count = 0; 1726 if (deflated_count > 0 || is_final_audit()) { 1727 // There are ObjectMonitors that have been deflated or this is the 1728 // final audit and all the remaining ObjectMonitors have been 1729 // deflated, BUT the MonitorDeflationThread blocked for the final 1730 // safepoint during unlinking. 1731 1732 // Unlink deflated ObjectMonitors from the in-use list. 1733 ResourceMark rm; 1734 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count); 1735 unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, &delete_list); 1736 if (current->is_monitor_deflation_thread()) { 1737 if (ls != nullptr) { 1738 timer.stop(); 1739 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT 1740 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count=" 1741 SIZE_FORMAT ", max=" SIZE_FORMAT, 1742 unlinked_count, in_use_list_ceiling(), 1743 _in_use_list.count(), _in_use_list.max()); 1744 } 1745 1746 // A JavaThread needs to handshake in order to safely free the 1747 // ObjectMonitors that were deflated in this cycle. 1748 HandshakeForDeflation hfd_hc; 1749 Handshake::execute(&hfd_hc); 1750 // Also, we sync and desync GC threads around the handshake, so that they can 1751 // safely read the mark-word and look-through to the object-monitor, without 1752 // being afraid that the object-monitor is going away. 1753 VM_RendezvousGCThreads sync_gc; 1754 VMThread::execute(&sync_gc); 1755 1756 if (ls != nullptr) { 1757 ls->print_cr("after handshaking: in_use_list stats: ceiling=" 1758 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1759 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1760 timer.start(); 1761 } 1762 } else { 1763 // This is not a monitor deflation thread. 1764 // No handshake or rendezvous is needed when we are already at safepoint. 1765 assert_at_safepoint(); 1766 } 1767 1768 // After the handshake, safely free the ObjectMonitors that were 1769 // deflated and unlinked in this cycle. 1770 if (current->is_Java_thread()) { 1771 if (ls != nullptr) { 1772 timer.stop(); 1773 ls->print_cr("before setting blocked: unlinked_count=" SIZE_FORMAT 1774 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count=" 1775 SIZE_FORMAT ", max=" SIZE_FORMAT, 1776 unlinked_count, in_use_list_ceiling(), 1777 _in_use_list.count(), _in_use_list.max()); 1778 } 1779 // Mark the calling JavaThread blocked (safepoint safe) while we free 1780 // the ObjectMonitors so we don't delay safepoints whilst doing that. 1781 ThreadBlockInVM tbivm(JavaThread::cast(current)); 1782 if (ls != nullptr) { 1783 ls->print_cr("after setting blocked: in_use_list stats: ceiling=" 1784 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1785 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1786 timer.start(); 1787 } 1788 deleted_count = delete_monitors(&delete_list); 1789 // ThreadBlockInVM is destroyed here 1790 } else { 1791 // A non-JavaThread can just free the ObjectMonitors: 1792 deleted_count = delete_monitors(&delete_list); 1793 } 1794 assert(unlinked_count == deleted_count, "must be"); 1795 } 1796 1797 if (ls != nullptr) { 1798 timer.stop(); 1799 if (deflated_count != 0 || unlinked_count != 0 || log_is_enabled(Debug, monitorinflation)) { 1800 ls->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs", 1801 deflated_count, unlinked_count, timer.seconds()); 1802 } 1803 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1804 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1805 if (table != nullptr) { 1806 ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT, 1807 table->key_count(), table->om_count()); 1808 } 1809 } 1810 1811 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count())); 1812 OM_PERFDATA_OP(Deflations, inc(deflated_count)); 1813 1814 GVars.stw_random = os::random(); 1815 1816 if (deflated_count != 0) { 1817 _no_progress_cnt = 0; 1818 } else if (_no_progress_skip_increment) { 1819 _no_progress_skip_increment = false; 1820 } else { 1821 _no_progress_cnt++; 1822 } 1823 1824 return deflated_count; 1825 } 1826 1827 // Monitor cleanup on JavaThread::exit 1828 1829 // Iterate through monitor cache and attempt to release thread's monitors 1830 class ReleaseJavaMonitorsClosure: public MonitorClosure { 1831 private: 1832 JavaThread* _thread; 1833 1834 public: 1835 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {} 1836 void do_monitor(ObjectMonitor* mid) { 1837 intx rec = mid->complete_exit(_thread); 1838 _thread->dec_held_monitor_count(rec + 1); 1839 } 1840 }; 1841 1842 // Release all inflated monitors owned by current thread. Lightweight monitors are 1843 // ignored. This is meant to be called during JNI thread detach which assumes 1844 // all remaining monitors are heavyweight. All exceptions are swallowed. 1845 // Scanning the extant monitor list can be time consuming. 1846 // A simple optimization is to add a per-thread flag that indicates a thread 1847 // called jni_monitorenter() during its lifetime. 1848 // 1849 // Instead of NoSafepointVerifier it might be cheaper to 1850 // use an idiom of the form: 1851 // auto int tmp = SafepointSynchronize::_safepoint_counter ; 1852 // <code that must not run at safepoint> 1853 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; 1854 // Since the tests are extremely cheap we could leave them enabled 1855 // for normal product builds. 1856 1857 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) { 1858 assert(current == JavaThread::current(), "must be current Java thread"); 1859 NoSafepointVerifier nsv; 1860 ReleaseJavaMonitorsClosure rjmc(current); 1861 ObjectSynchronizer::monitors_iterate(&rjmc, current); 1862 assert(!current->has_pending_exception(), "Should not be possible"); 1863 current->clear_pending_exception(); 1864 assert(current->held_monitor_count() == 0, "Should not be possible"); 1865 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count. 1866 current->clear_jni_monitor_count(); 1867 } 1868 1869 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) { 1870 switch (cause) { 1871 case inflate_cause_vm_internal: return "VM Internal"; 1872 case inflate_cause_monitor_enter: return "Monitor Enter"; 1873 case inflate_cause_wait: return "Monitor Wait"; 1874 case inflate_cause_notify: return "Monitor Notify"; 1875 case inflate_cause_hash_code: return "Monitor Hash Code"; 1876 case inflate_cause_jni_enter: return "JNI Monitor Enter"; 1877 case inflate_cause_jni_exit: return "JNI Monitor Exit"; 1878 default: 1879 ShouldNotReachHere(); 1880 } 1881 return "Unknown"; 1882 } 1883 1884 //------------------------------------------------------------------------------ 1885 // Debugging code 1886 1887 u_char* ObjectSynchronizer::get_gvars_addr() { 1888 return (u_char*)&GVars; 1889 } 1890 1891 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() { 1892 return (u_char*)&GVars.hc_sequence; 1893 } 1894 1895 size_t ObjectSynchronizer::get_gvars_size() { 1896 return sizeof(SharedGlobals); 1897 } 1898 1899 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() { 1900 return (u_char*)&GVars.stw_random; 1901 } 1902 1903 // Do the final audit and print of ObjectMonitor stats; must be done 1904 // by the VMThread at VM exit time. 1905 void ObjectSynchronizer::do_final_audit_and_print_stats() { 1906 assert(Thread::current()->is_VM_thread(), "sanity check"); 1907 1908 if (is_final_audit()) { // Only do the audit once. 1909 return; 1910 } 1911 set_is_final_audit(); 1912 log_info(monitorinflation)("Starting the final audit."); 1913 1914 if (log_is_enabled(Info, monitorinflation)) { 1915 // Do deflations in order to reduce the in-use monitor population 1916 // that is reported by ObjectSynchronizer::log_in_use_monitor_details() 1917 // which is called by ObjectSynchronizer::audit_and_print_stats(). 1918 while (deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) > 0) { 1919 ; // empty 1920 } 1921 // The other audit_and_print_stats() call is done at the Debug 1922 // level at a safepoint in SafepointSynchronize::do_cleanup_tasks. 1923 audit_and_print_stats(true /* on_exit */); 1924 } 1925 } 1926 1927 // This function can be called at a safepoint or it can be called when 1928 // we are trying to exit the VM. When we are trying to exit the VM, the 1929 // list walker functions can run in parallel with the other list 1930 // operations so spin-locking is used for safety. 1931 // 1932 // Calls to this function can be added in various places as a debugging 1933 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor 1934 // details logged at the Info level and 'false' for the 'on_exit' 1935 // parameter to have in-use monitor details logged at the Trace level. 1936 // 1937 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) { 1938 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant"); 1939 1940 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1941 LogStreamHandle(Info, monitorinflation) lsh_info; 1942 LogStreamHandle(Trace, monitorinflation) lsh_trace; 1943 LogStream* ls = nullptr; 1944 if (log_is_enabled(Trace, monitorinflation)) { 1945 ls = &lsh_trace; 1946 } else if (log_is_enabled(Debug, monitorinflation)) { 1947 ls = &lsh_debug; 1948 } else if (log_is_enabled(Info, monitorinflation)) { 1949 ls = &lsh_info; 1950 } 1951 assert(ls != nullptr, "sanity check"); 1952 1953 int error_cnt = 0; 1954 1955 ls->print_cr("Checking in_use_list:"); 1956 chk_in_use_list(ls, &error_cnt); 1957 1958 if (error_cnt == 0) { 1959 ls->print_cr("No errors found in in_use_list checks."); 1960 } else { 1961 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt); 1962 } 1963 1964 if ((on_exit && log_is_enabled(Info, monitorinflation)) || 1965 (!on_exit && log_is_enabled(Trace, monitorinflation))) { 1966 // When exiting this log output is at the Info level. When called 1967 // at a safepoint, this log output is at the Trace level since 1968 // there can be a lot of it. 1969 log_in_use_monitor_details(ls); 1970 } 1971 1972 ls->flush(); 1973 1974 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt); 1975 } 1976 1977 // Check the in_use_list; log the results of the checks. 1978 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) { 1979 size_t l_in_use_count = _in_use_list.count(); 1980 size_t l_in_use_max = _in_use_list.max(); 1981 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count, 1982 l_in_use_max); 1983 1984 size_t ck_in_use_count = 0; 1985 MonitorList::Iterator iter = _in_use_list.iterator(); 1986 while (iter.has_next()) { 1987 ObjectMonitor* mid = iter.next(); 1988 chk_in_use_entry(mid, out, error_cnt_p); 1989 ck_in_use_count++; 1990 } 1991 1992 if (l_in_use_count == ck_in_use_count) { 1993 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count=" 1994 SIZE_FORMAT, l_in_use_count, ck_in_use_count); 1995 } else { 1996 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to " 1997 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count, 1998 ck_in_use_count); 1999 } 2000 2001 size_t ck_in_use_max = _in_use_list.max(); 2002 if (l_in_use_max == ck_in_use_max) { 2003 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max=" 2004 SIZE_FORMAT, l_in_use_max, ck_in_use_max); 2005 } else { 2006 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to " 2007 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max); 2008 } 2009 } 2010 2011 // Check an in-use monitor entry; log any errors. 2012 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out, 2013 int* error_cnt_p) { 2014 if (n->owner_is_DEFLATER_MARKER()) { 2015 // This should not happen, but if it does, it is not fatal. 2016 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is " 2017 "deflated.", p2i(n)); 2018 return; 2019 } 2020 if (n->header().value() == 0) { 2021 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must " 2022 "have non-null _header field.", p2i(n)); 2023 *error_cnt_p = *error_cnt_p + 1; 2024 } 2025 const oop obj = n->object_peek(); 2026 if (obj != nullptr) { 2027 const markWord mark = obj->mark(); 2028 if (!mark.has_monitor()) { 2029 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's " 2030 "object does not think it has a monitor: obj=" 2031 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n), 2032 p2i(obj), mark.value()); 2033 *error_cnt_p = *error_cnt_p + 1; 2034 } 2035 ObjectMonitor* const obj_mon = mark.monitor(); 2036 if (n != obj_mon) { 2037 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's " 2038 "object does not refer to the same monitor: obj=" 2039 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon=" 2040 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon)); 2041 *error_cnt_p = *error_cnt_p + 1; 2042 } 2043 } 2044 } 2045 2046 // Log details about ObjectMonitors on the in_use_list. The 'BHL' 2047 // flags indicate why the entry is in-use, 'object' and 'object type' 2048 // indicate the associated object and its type. 2049 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) { 2050 stringStream ss; 2051 if (_in_use_list.count() > 0) { 2052 out->print_cr("In-use monitor info:"); 2053 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)"); 2054 out->print_cr("%18s %s %18s %18s", 2055 "monitor", "BHL", "object", "object type"); 2056 out->print_cr("================== === ================== =================="); 2057 MonitorList::Iterator iter = _in_use_list.iterator(); 2058 while (iter.has_next()) { 2059 ObjectMonitor* mid = iter.next(); 2060 const oop obj = mid->object_peek(); 2061 const markWord mark = mid->header(); 2062 ResourceMark rm; 2063 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid), 2064 mid->is_busy(), mark.hash() != 0, mid->owner() != nullptr, 2065 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name()); 2066 if (mid->is_busy()) { 2067 out->print(" (%s)", mid->is_busy_to_string(&ss)); 2068 ss.reset(); 2069 } 2070 out->cr(); 2071 } 2072 } 2073 2074 out->flush(); 2075 }