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 "jfr/jfrEvents.hpp" 28 #include "logging/log.hpp" 29 #include "logging/logStream.hpp" 30 #include "memory/allocation.inline.hpp" 31 #include "memory/padded.hpp" 32 #include "memory/resourceArea.hpp" 33 #include "memory/universe.hpp" 34 #include "oops/markWord.hpp" 35 #include "oops/oop.inline.hpp" 36 #include "runtime/atomic.hpp" 37 #include "runtime/frame.inline.hpp" 38 #include "runtime/handles.inline.hpp" 39 #include "runtime/handshake.hpp" 40 #include "runtime/interfaceSupport.inline.hpp" 41 #include "runtime/javaThread.hpp" 42 #include "runtime/mutexLocker.hpp" 43 #include "runtime/objectMonitor.hpp" 44 #include "runtime/objectMonitor.inline.hpp" 45 #include "runtime/os.inline.hpp" 46 #include "runtime/osThread.hpp" 47 #include "runtime/perfData.hpp" 48 #include "runtime/safepointMechanism.inline.hpp" 49 #include "runtime/safepointVerifiers.hpp" 50 #include "runtime/sharedRuntime.hpp" 51 #include "runtime/stubRoutines.hpp" 52 #include "runtime/synchronizer.hpp" 53 #include "runtime/threads.hpp" 54 #include "runtime/timer.hpp" 55 #include "runtime/vframe.hpp" 56 #include "runtime/vmThread.hpp" 57 #include "utilities/align.hpp" 58 #include "utilities/dtrace.hpp" 59 #include "utilities/events.hpp" 60 #include "utilities/linkedlist.hpp" 61 #include "utilities/preserveException.hpp" 62 63 class ObjectMonitorsHashtable::PtrList : 64 public LinkedListImpl<ObjectMonitor*, 65 AnyObj::C_HEAP, mtThread, 66 AllocFailStrategy::RETURN_NULL> {}; 67 68 class CleanupObjectMonitorsHashtable: StackObj { 69 public: 70 bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) { 71 list->clear(); // clear the LinkListNodes 72 delete list; // then delete the LinkedList 73 return true; 74 } 75 }; 76 77 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() { 78 CleanupObjectMonitorsHashtable cleanup; 79 _ptrs->unlink(&cleanup); // cleanup the LinkedLists 80 delete _ptrs; // then delete the hash table 81 } 82 83 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) { 84 ObjectMonitorsHashtable::PtrList* list = get_entry(key); 85 if (list == nullptr) { 86 // Create new list and add it to the hash table: 87 list = new (mtThread) ObjectMonitorsHashtable::PtrList; 88 add_entry(key, list); 89 } 90 list->add(om); // Add the ObjectMonitor to the list. 91 _om_count++; 92 } 93 94 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) { 95 ObjectMonitorsHashtable::PtrList* list = get_entry(key); 96 if (list == nullptr || list->find(om) == nullptr) { 97 return false; 98 } 99 return true; 100 } 101 102 void MonitorList::add(ObjectMonitor* m) { 103 ObjectMonitor* head; 104 do { 105 head = Atomic::load(&_head); 106 m->set_next_om(head); 107 } while (Atomic::cmpxchg(&_head, head, m) != head); 108 109 size_t count = Atomic::add(&_count, 1u); 110 if (count > max()) { 111 Atomic::inc(&_max); 112 } 113 } 114 115 size_t MonitorList::count() const { 116 return Atomic::load(&_count); 117 } 118 119 size_t MonitorList::max() const { 120 return Atomic::load(&_max); 121 } 122 123 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated 124 // ObjectMonitors. Returns the number of unlinked ObjectMonitors. 125 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls, 126 elapsedTimer* timer_p, 127 GrowableArray<ObjectMonitor*>* unlinked_list) { 128 size_t unlinked_count = 0; 129 ObjectMonitor* prev = nullptr; 130 ObjectMonitor* head = Atomic::load_acquire(&_head); 131 ObjectMonitor* m = head; 132 // The in-use list head can be null during the final audit. 133 while (m != nullptr) { 134 if (m->is_being_async_deflated()) { 135 // Find next live ObjectMonitor. 136 ObjectMonitor* next = m; 137 do { 138 ObjectMonitor* next_next = next->next_om(); 139 unlinked_count++; 140 unlinked_list->append(next); 141 next = next_next; 142 if (unlinked_count >= (size_t)MonitorDeflationMax) { 143 // Reached the max so bail out on the gathering loop. 144 break; 145 } 146 } while (next != nullptr && next->is_being_async_deflated()); 147 if (prev == nullptr) { 148 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next); 149 if (prev_head != head) { 150 // Find new prev ObjectMonitor that just got inserted. 151 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) { 152 prev = n; 153 } 154 prev->set_next_om(next); 155 } 156 } else { 157 prev->set_next_om(next); 158 } 159 if (unlinked_count >= (size_t)MonitorDeflationMax) { 160 // Reached the max so bail out on the searching loop. 161 break; 162 } 163 m = next; 164 } else { 165 prev = m; 166 m = m->next_om(); 167 } 168 169 if (current->is_Java_thread()) { 170 // A JavaThread must check for a safepoint/handshake and honor it. 171 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking", 172 "unlinked_count", unlinked_count, 173 ls, timer_p); 174 } 175 } 176 Atomic::sub(&_count, unlinked_count); 177 return unlinked_count; 178 } 179 180 MonitorList::Iterator MonitorList::iterator() const { 181 return Iterator(Atomic::load_acquire(&_head)); 182 } 183 184 ObjectMonitor* MonitorList::Iterator::next() { 185 ObjectMonitor* current = _current; 186 _current = current->next_om(); 187 return current; 188 } 189 190 // The "core" versions of monitor enter and exit reside in this file. 191 // The interpreter and compilers contain specialized transliterated 192 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp 193 // fast_lock(...) for instance. If you make changes here, make sure to modify the 194 // interpreter, and both C1 and C2 fast-path inline locking code emission. 195 // 196 // ----------------------------------------------------------------------------- 197 198 #ifdef DTRACE_ENABLED 199 200 // Only bother with this argument setup if dtrace is available 201 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. 202 203 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \ 204 char* bytes = nullptr; \ 205 int len = 0; \ 206 jlong jtid = SharedRuntime::get_java_tid(thread); \ 207 Symbol* klassname = obj->klass()->name(); \ 208 if (klassname != nullptr) { \ 209 bytes = (char*)klassname->bytes(); \ 210 len = klassname->utf8_length(); \ 211 } 212 213 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ 214 { \ 215 if (DTraceMonitorProbes) { \ 216 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 217 HOTSPOT_MONITOR_WAIT(jtid, \ 218 (uintptr_t)(monitor), bytes, len, (millis)); \ 219 } \ 220 } 221 222 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY 223 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL 224 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED 225 226 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ 227 { \ 228 if (DTraceMonitorProbes) { \ 229 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 230 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \ 231 (uintptr_t)(monitor), bytes, len); \ 232 } \ 233 } 234 235 #else // ndef DTRACE_ENABLED 236 237 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;} 238 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;} 239 240 #endif // ndef DTRACE_ENABLED 241 242 // This exists only as a workaround of dtrace bug 6254741 243 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) { 244 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); 245 return 0; 246 } 247 248 static const int NINFLATIONLOCKS = 256; 249 static PlatformMutex* gInflationLocks[NINFLATIONLOCKS]; 250 251 void ObjectSynchronizer::initialize() { 252 for (int i = 0; i < NINFLATIONLOCKS; i++) { 253 gInflationLocks[i] = new PlatformMutex(); 254 } 255 // Start the ceiling with the estimate for one thread. 256 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate); 257 } 258 259 MonitorList ObjectSynchronizer::_in_use_list; 260 // monitors_used_above_threshold() policy is as follows: 261 // 262 // The ratio of the current _in_use_list count to the ceiling is used 263 // to determine if we are above MonitorUsedDeflationThreshold and need 264 // to do an async monitor deflation cycle. The ceiling is increased by 265 // AvgMonitorsPerThreadEstimate when a thread is added to the system 266 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is 267 // removed from the system. 268 // 269 // Note: If the _in_use_list max exceeds the ceiling, then 270 // monitors_used_above_threshold() will use the in_use_list max instead 271 // of the thread count derived ceiling because we have used more 272 // ObjectMonitors than the estimated average. 273 // 274 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax 275 // no-progress async monitor deflation cycles in a row, then the ceiling 276 // is adjusted upwards by monitors_used_above_threshold(). 277 // 278 // Start the ceiling with the estimate for one thread in initialize() 279 // which is called after cmd line options are processed. 280 static size_t _in_use_list_ceiling = 0; 281 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false; 282 bool volatile ObjectSynchronizer::_is_final_audit = false; 283 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0; 284 static uintx _no_progress_cnt = 0; 285 286 // =====================> Quick functions 287 288 // The quick_* forms are special fast-path variants used to improve 289 // performance. In the simplest case, a "quick_*" implementation could 290 // simply return false, in which case the caller will perform the necessary 291 // state transitions and call the slow-path form. 292 // The fast-path is designed to handle frequently arising cases in an efficient 293 // manner and is just a degenerate "optimistic" variant of the slow-path. 294 // returns true -- to indicate the call was satisfied. 295 // returns false -- to indicate the call needs the services of the slow-path. 296 // A no-loitering ordinance is in effect for code in the quick_* family 297 // operators: safepoints or indefinite blocking (blocking that might span a 298 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon 299 // entry. 300 // 301 // Consider: An interesting optimization is to have the JIT recognize the 302 // following common idiom: 303 // synchronized (someobj) { .... ; notify(); } 304 // That is, we find a notify() or notifyAll() call that immediately precedes 305 // the monitorexit operation. In that case the JIT could fuse the operations 306 // into a single notifyAndExit() runtime primitive. 307 308 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) { 309 assert(current->thread_state() == _thread_in_Java, "invariant"); 310 NoSafepointVerifier nsv; 311 if (obj == nullptr) return false; // slow-path for invalid obj 312 const markWord mark = obj->mark(); 313 314 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 315 // Degenerate notify 316 // stack-locked by caller so by definition the implied waitset is empty. 317 return true; 318 } 319 320 if (mark.has_monitor()) { 321 ObjectMonitor* const mon = mark.monitor(); 322 assert(mon->object() == oop(obj), "invariant"); 323 if (mon->owner() != current) return false; // slow-path for IMS exception 324 325 if (mon->first_waiter() != nullptr) { 326 // We have one or more waiters. Since this is an inflated monitor 327 // that we own, we can transfer one or more threads from the waitset 328 // to the entrylist here and now, avoiding the slow-path. 329 if (all) { 330 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current); 331 } else { 332 DTRACE_MONITOR_PROBE(notify, mon, obj, current); 333 } 334 int free_count = 0; 335 do { 336 mon->INotify(current); 337 ++free_count; 338 } while (mon->first_waiter() != nullptr && all); 339 OM_PERFDATA_OP(Notifications, inc(free_count)); 340 } 341 return true; 342 } 343 344 // other IMS exception states take the slow-path 345 return false; 346 } 347 348 349 // The LockNode emitted directly at the synchronization site would have 350 // been too big if it were to have included support for the cases of inflated 351 // recursive enter and exit, so they go here instead. 352 // Note that we can't safely call AsyncPrintJavaStack() from within 353 // quick_enter() as our thread state remains _in_Java. 354 355 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current, 356 BasicLock * lock) { 357 assert(current->thread_state() == _thread_in_Java, "invariant"); 358 NoSafepointVerifier nsv; 359 if (obj == nullptr) return false; // Need to throw NPE 360 361 if (obj->klass()->is_value_based()) { 362 return false; 363 } 364 365 const markWord mark = obj->mark(); 366 367 if (mark.has_monitor()) { 368 ObjectMonitor* const m = mark.monitor(); 369 // An async deflation or GC can race us before we manage to make 370 // the ObjectMonitor busy by setting the owner below. If we detect 371 // that race we just bail out to the slow-path here. 372 if (m->object_peek() == nullptr) { 373 return false; 374 } 375 JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw()); 376 377 // Lock contention and Transactional Lock Elision (TLE) diagnostics 378 // and observability 379 // Case: light contention possibly amenable to TLE 380 // Case: TLE inimical operations such as nested/recursive synchronization 381 382 if (owner == current) { 383 m->_recursions++; 384 current->inc_held_monitor_count(); 385 return true; 386 } 387 388 // This Java Monitor is inflated so obj's header will never be 389 // displaced to this thread's BasicLock. Make the displaced header 390 // non-null so this BasicLock is not seen as recursive nor as 391 // being locked. We do this unconditionally so that this thread's 392 // BasicLock cannot be mis-interpreted by any stack walkers. For 393 // performance reasons, stack walkers generally first check for 394 // stack-locking in the object's header, the second check is for 395 // recursive stack-locking in the displaced header in the BasicLock, 396 // and last are the inflated Java Monitor (ObjectMonitor) checks. 397 lock->set_displaced_header(markWord::unused_mark()); 398 399 if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) { 400 assert(m->_recursions == 0, "invariant"); 401 current->inc_held_monitor_count(); 402 return true; 403 } 404 } 405 406 // Note that we could inflate in quick_enter. 407 // This is likely a useful optimization 408 // Critically, in quick_enter() we must not: 409 // -- block indefinitely, or 410 // -- reach a safepoint 411 412 return false; // revert to slow-path 413 } 414 415 // Handle notifications when synchronizing on value based classes 416 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) { 417 frame last_frame = current->last_frame(); 418 bool bcp_was_adjusted = false; 419 // Don't decrement bcp if it points to the frame's first instruction. This happens when 420 // handle_sync_on_value_based_class() is called because of a synchronized method. There 421 // is no actual monitorenter instruction in the byte code in this case. 422 if (last_frame.is_interpreted_frame() && 423 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) { 424 // adjust bcp to point back to monitorenter so that we print the correct line numbers 425 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1); 426 bcp_was_adjusted = true; 427 } 428 429 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) { 430 ResourceMark rm(current); 431 stringStream ss; 432 current->print_active_stack_on(&ss); 433 char* base = (char*)strstr(ss.base(), "at"); 434 char* newline = (char*)strchr(ss.base(), '\n'); 435 if (newline != nullptr) { 436 *newline = '\0'; 437 } 438 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base); 439 } else { 440 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses"); 441 ResourceMark rm(current); 442 Log(valuebasedclasses) vblog; 443 444 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name()); 445 if (current->has_last_Java_frame()) { 446 LogStream info_stream(vblog.info()); 447 current->print_active_stack_on(&info_stream); 448 } else { 449 vblog.info("Cannot find the last Java frame"); 450 } 451 452 EventSyncOnValueBasedClass event; 453 if (event.should_commit()) { 454 event.set_valueBasedClass(obj->klass()); 455 event.commit(); 456 } 457 } 458 459 if (bcp_was_adjusted) { 460 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1); 461 } 462 } 463 464 static bool useHeavyMonitors() { 465 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) 466 return UseHeavyMonitors; 467 #else 468 return false; 469 #endif 470 } 471 472 // ----------------------------------------------------------------------------- 473 // Monitor Enter/Exit 474 // The interpreter and compiler assembly code tries to lock using the fast path 475 // of this algorithm. Make sure to update that code if the following function is 476 // changed. The implementation is extremely sensitive to race condition. Be careful. 477 478 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) { 479 if (obj->klass()->is_value_based()) { 480 handle_sync_on_value_based_class(obj, current); 481 } 482 483 current->inc_held_monitor_count(); 484 485 if (!useHeavyMonitors()) { 486 markWord mark = obj->mark(); 487 if (mark.is_neutral()) { 488 // Anticipate successful CAS -- the ST of the displaced mark must 489 // be visible <= the ST performed by the CAS. 490 lock->set_displaced_header(mark); 491 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) { 492 return; 493 } 494 // Fall through to inflate() ... 495 } else if (mark.has_locker() && 496 current->is_lock_owned((address)mark.locker())) { 497 assert(lock != mark.locker(), "must not re-lock the same lock"); 498 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock"); 499 lock->set_displaced_header(markWord::from_pointer(nullptr)); 500 return; 501 } 502 503 // The object header will never be displaced to this lock, 504 // so it does not matter what the value is, except that it 505 // must be non-zero to avoid looking like a re-entrant lock, 506 // and must not look locked either. 507 lock->set_displaced_header(markWord::unused_mark()); 508 } else if (VerifyHeavyMonitors) { 509 guarantee(!obj->mark().has_locker(), "must not be stack-locked"); 510 } 511 512 // An async deflation can race after the inflate() call and before 513 // enter() can make the ObjectMonitor busy. enter() returns false if 514 // we have lost the race to async deflation and we simply try again. 515 while (true) { 516 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter); 517 if (monitor->enter(current)) { 518 return; 519 } 520 } 521 } 522 523 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) { 524 current->dec_held_monitor_count(); 525 526 if (!useHeavyMonitors()) { 527 markWord mark = object->mark(); 528 529 markWord dhw = lock->displaced_header(); 530 if (dhw.value() == 0) { 531 // If the displaced header is null, then this exit matches up with 532 // a recursive enter. No real work to do here except for diagnostics. 533 #ifndef PRODUCT 534 if (mark != markWord::INFLATING()) { 535 // Only do diagnostics if we are not racing an inflation. Simply 536 // exiting a recursive enter of a Java Monitor that is being 537 // inflated is safe; see the has_monitor() comment below. 538 assert(!mark.is_neutral(), "invariant"); 539 assert(!mark.has_locker() || 540 current->is_lock_owned((address)mark.locker()), "invariant"); 541 if (mark.has_monitor()) { 542 // The BasicLock's displaced_header is marked as a recursive 543 // enter and we have an inflated Java Monitor (ObjectMonitor). 544 // This is a special case where the Java Monitor was inflated 545 // after this thread entered the stack-lock recursively. When a 546 // Java Monitor is inflated, we cannot safely walk the Java 547 // Monitor owner's stack and update the BasicLocks because a 548 // Java Monitor can be asynchronously inflated by a thread that 549 // does not own the Java Monitor. 550 ObjectMonitor* m = mark.monitor(); 551 assert(m->object()->mark() == mark, "invariant"); 552 assert(m->is_entered(current), "invariant"); 553 } 554 } 555 #endif 556 return; 557 } 558 559 if (mark == markWord::from_pointer(lock)) { 560 // If the object is stack-locked by the current thread, try to 561 // swing the displaced header from the BasicLock back to the mark. 562 assert(dhw.is_neutral(), "invariant"); 563 if (object->cas_set_mark(dhw, mark) == mark) { 564 return; 565 } 566 } 567 } else if (VerifyHeavyMonitors) { 568 guarantee(!object->mark().has_locker(), "must not be stack-locked"); 569 } 570 571 // We have to take the slow-path of possible inflation and then exit. 572 // The ObjectMonitor* can't be async deflated until ownership is 573 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 574 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal); 575 monitor->exit(current); 576 } 577 578 // ----------------------------------------------------------------------------- 579 // Class Loader support to workaround deadlocks on the class loader lock objects 580 // Also used by GC 581 // complete_exit()/reenter() are used to wait on a nested lock 582 // i.e. to give up an outer lock completely and then re-enter 583 // Used when holding nested locks - lock acquisition order: lock1 then lock2 584 // 1) complete_exit lock1 - saving recursion count 585 // 2) wait on lock2 586 // 3) when notified on lock2, unlock lock2 587 // 4) reenter lock1 with original recursion count 588 // 5) lock lock2 589 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 590 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) { 591 // The ObjectMonitor* can't be async deflated until ownership is 592 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 593 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal); 594 intx recur_count = monitor->complete_exit(current); 595 current->dec_held_monitor_count(recur_count + 1); 596 return recur_count; 597 } 598 599 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 600 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) { 601 // An async deflation can race after the inflate() call and before 602 // reenter() -> enter() can make the ObjectMonitor busy. reenter() -> 603 // enter() returns false if we have lost the race to async deflation 604 // and we simply try again. 605 while (true) { 606 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal); 607 if (monitor->reenter(recursions, current)) { 608 current->inc_held_monitor_count(recursions + 1); 609 return; 610 } 611 } 612 } 613 614 // ----------------------------------------------------------------------------- 615 // JNI locks on java objects 616 // NOTE: must use heavy weight monitor to handle jni monitor enter 617 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) { 618 if (obj->klass()->is_value_based()) { 619 handle_sync_on_value_based_class(obj, current); 620 } 621 622 // the current locking is from JNI instead of Java code 623 current->set_current_pending_monitor_is_from_java(false); 624 // An async deflation can race after the inflate() call and before 625 // enter() can make the ObjectMonitor busy. enter() returns false if 626 // we have lost the race to async deflation and we simply try again. 627 while (true) { 628 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter); 629 if (monitor->enter(current)) { 630 current->inc_held_monitor_count(1, true); 631 break; 632 } 633 } 634 current->set_current_pending_monitor_is_from_java(true); 635 } 636 637 // NOTE: must use heavy weight monitor to handle jni monitor exit 638 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) { 639 JavaThread* current = THREAD; 640 641 // The ObjectMonitor* can't be async deflated until ownership is 642 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 643 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit); 644 // If this thread has locked the object, exit the monitor. We 645 // intentionally do not use CHECK on check_owner because we must exit the 646 // monitor even if an exception was already pending. 647 if (monitor->check_owner(THREAD)) { 648 monitor->exit(current); 649 current->dec_held_monitor_count(1, true); 650 } 651 } 652 653 // ----------------------------------------------------------------------------- 654 // Internal VM locks on java objects 655 // standard constructor, allows locking failures 656 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) { 657 _thread = thread; 658 _thread->check_for_valid_safepoint_state(); 659 _obj = obj; 660 661 if (_obj() != nullptr) { 662 ObjectSynchronizer::enter(_obj, &_lock, _thread); 663 } 664 } 665 666 ObjectLocker::~ObjectLocker() { 667 if (_obj() != nullptr) { 668 ObjectSynchronizer::exit(_obj(), &_lock, _thread); 669 } 670 } 671 672 673 // ----------------------------------------------------------------------------- 674 // Wait/Notify/NotifyAll 675 // NOTE: must use heavy weight monitor to handle wait() 676 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { 677 JavaThread* current = THREAD; 678 if (millis < 0) { 679 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 680 } 681 // The ObjectMonitor* can't be async deflated because the _waiters 682 // field is incremented before ownership is dropped and decremented 683 // after ownership is regained. 684 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait); 685 686 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis); 687 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code 688 689 // This dummy call is in place to get around dtrace bug 6254741. Once 690 // that's fixed we can uncomment the following line, remove the call 691 // and change this function back into a "void" func. 692 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); 693 int ret_code = dtrace_waited_probe(monitor, obj, THREAD); 694 return ret_code; 695 } 696 697 void ObjectSynchronizer::notify(Handle obj, TRAPS) { 698 JavaThread* current = THREAD; 699 700 markWord mark = obj->mark(); 701 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 702 // Not inflated so there can't be any waiters to notify. 703 return; 704 } 705 // The ObjectMonitor* can't be async deflated until ownership is 706 // dropped by the calling thread. 707 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify); 708 monitor->notify(CHECK); 709 } 710 711 // NOTE: see comment of notify() 712 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { 713 JavaThread* current = THREAD; 714 715 markWord mark = obj->mark(); 716 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 717 // Not inflated so there can't be any waiters to notify. 718 return; 719 } 720 // The ObjectMonitor* can't be async deflated until ownership is 721 // dropped by the calling thread. 722 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify); 723 monitor->notifyAll(CHECK); 724 } 725 726 // ----------------------------------------------------------------------------- 727 // Hash Code handling 728 729 struct SharedGlobals { 730 char _pad_prefix[OM_CACHE_LINE_SIZE]; 731 // This is a highly shared mostly-read variable. 732 // To avoid false-sharing it needs to be the sole occupant of a cache line. 733 volatile int stw_random; 734 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int)); 735 // Hot RW variable -- Sequester to avoid false-sharing 736 volatile int hc_sequence; 737 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int)); 738 }; 739 740 static SharedGlobals GVars; 741 742 static markWord read_stable_mark(oop obj) { 743 markWord mark = obj->mark_acquire(); 744 if (!mark.is_being_inflated()) { 745 return mark; // normal fast-path return 746 } 747 748 int its = 0; 749 for (;;) { 750 markWord mark = obj->mark_acquire(); 751 if (!mark.is_being_inflated()) { 752 return mark; // normal fast-path return 753 } 754 755 // The object is being inflated by some other thread. 756 // The caller of read_stable_mark() must wait for inflation to complete. 757 // Avoid live-lock. 758 759 ++its; 760 if (its > 10000 || !os::is_MP()) { 761 if (its & 1) { 762 os::naked_yield(); 763 } else { 764 // Note that the following code attenuates the livelock problem but is not 765 // a complete remedy. A more complete solution would require that the inflating 766 // thread hold the associated inflation lock. The following code simply restricts 767 // the number of spinners to at most one. We'll have N-2 threads blocked 768 // on the inflationlock, 1 thread holding the inflation lock and using 769 // a yield/park strategy, and 1 thread in the midst of inflation. 770 // A more refined approach would be to change the encoding of INFLATING 771 // to allow encapsulation of a native thread pointer. Threads waiting for 772 // inflation to complete would use CAS to push themselves onto a singly linked 773 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag 774 // and calling park(). When inflation was complete the thread that accomplished inflation 775 // would detach the list and set the markword to inflated with a single CAS and 776 // then for each thread on the list, set the flag and unpark() the thread. 777 778 // Index into the lock array based on the current object address. 779 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be"); 780 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1); 781 int YieldThenBlock = 0; 782 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant"); 783 gInflationLocks[ix]->lock(); 784 while (obj->mark_acquire() == markWord::INFLATING()) { 785 // Beware: naked_yield() is advisory and has almost no effect on some platforms 786 // so we periodically call current->_ParkEvent->park(1). 787 // We use a mixed spin/yield/block mechanism. 788 if ((YieldThenBlock++) >= 16) { 789 Thread::current()->_ParkEvent->park(1); 790 } else { 791 os::naked_yield(); 792 } 793 } 794 gInflationLocks[ix]->unlock(); 795 } 796 } else { 797 SpinPause(); // SMP-polite spinning 798 } 799 } 800 } 801 802 // hashCode() generation : 803 // 804 // Possibilities: 805 // * MD5Digest of {obj,stw_random} 806 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function. 807 // * A DES- or AES-style SBox[] mechanism 808 // * One of the Phi-based schemes, such as: 809 // 2654435761 = 2^32 * Phi (golden ratio) 810 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ; 811 // * A variation of Marsaglia's shift-xor RNG scheme. 812 // * (obj ^ stw_random) is appealing, but can result 813 // in undesirable regularity in the hashCode values of adjacent objects 814 // (objects allocated back-to-back, in particular). This could potentially 815 // result in hashtable collisions and reduced hashtable efficiency. 816 // There are simple ways to "diffuse" the middle address bits over the 817 // generated hashCode values: 818 819 static inline intptr_t get_next_hash(Thread* current, oop obj) { 820 intptr_t value = 0; 821 if (hashCode == 0) { 822 // This form uses global Park-Miller RNG. 823 // On MP system we'll have lots of RW access to a global, so the 824 // mechanism induces lots of coherency traffic. 825 value = os::random(); 826 } else if (hashCode == 1) { 827 // This variation has the property of being stable (idempotent) 828 // between STW operations. This can be useful in some of the 1-0 829 // synchronization schemes. 830 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3; 831 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random; 832 } else if (hashCode == 2) { 833 value = 1; // for sensitivity testing 834 } else if (hashCode == 3) { 835 value = ++GVars.hc_sequence; 836 } else if (hashCode == 4) { 837 value = cast_from_oop<intptr_t>(obj); 838 } else { 839 // Marsaglia's xor-shift scheme with thread-specific state 840 // This is probably the best overall implementation -- we'll 841 // likely make this the default in future releases. 842 unsigned t = current->_hashStateX; 843 t ^= (t << 11); 844 current->_hashStateX = current->_hashStateY; 845 current->_hashStateY = current->_hashStateZ; 846 current->_hashStateZ = current->_hashStateW; 847 unsigned v = current->_hashStateW; 848 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)); 849 current->_hashStateW = v; 850 value = v; 851 } 852 853 value &= markWord::hash_mask; 854 if (value == 0) value = 0xBAD; 855 assert(value != markWord::no_hash, "invariant"); 856 return value; 857 } 858 859 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) { 860 861 while (true) { 862 ObjectMonitor* monitor = nullptr; 863 markWord temp, test; 864 intptr_t hash; 865 markWord mark = read_stable_mark(obj); 866 if (VerifyHeavyMonitors) { 867 assert(UseHeavyMonitors, "+VerifyHeavyMonitors requires +UseHeavyMonitors"); 868 guarantee(!mark.has_locker(), "must not be stack locked"); 869 } 870 if (mark.is_neutral()) { // if this is a normal header 871 hash = mark.hash(); 872 if (hash != 0) { // if it has a hash, just return it 873 return hash; 874 } 875 hash = get_next_hash(current, obj); // get a new hash 876 temp = mark.copy_set_hash(hash); // merge the hash into header 877 // try to install the hash 878 test = obj->cas_set_mark(temp, mark); 879 if (test == mark) { // if the hash was installed, return it 880 return hash; 881 } 882 // Failed to install the hash. It could be that another thread 883 // installed the hash just before our attempt or inflation has 884 // occurred or... so we fall thru to inflate the monitor for 885 // stability and then install the hash. 886 } else if (mark.has_monitor()) { 887 monitor = mark.monitor(); 888 temp = monitor->header(); 889 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 890 hash = temp.hash(); 891 if (hash != 0) { 892 // It has a hash. 893 894 // Separate load of dmw/header above from the loads in 895 // is_being_async_deflated(). 896 897 // dmw/header and _contentions may get written by different threads. 898 // Make sure to observe them in the same order when having several observers. 899 OrderAccess::loadload_for_IRIW(); 900 901 if (monitor->is_being_async_deflated()) { 902 // But we can't safely use the hash if we detect that async 903 // deflation has occurred. So we attempt to restore the 904 // header/dmw to the object's header so that we only retry 905 // once if the deflater thread happens to be slow. 906 monitor->install_displaced_markword_in_object(obj); 907 continue; 908 } 909 return hash; 910 } 911 // Fall thru so we only have one place that installs the hash in 912 // the ObjectMonitor. 913 } else if (current->is_lock_owned((address)mark.locker())) { 914 // This is a stack lock owned by the calling thread so fetch the 915 // displaced markWord from the BasicLock on the stack. 916 temp = mark.displaced_mark_helper(); 917 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 918 hash = temp.hash(); 919 if (hash != 0) { // if it has a hash, just return it 920 return hash; 921 } 922 // WARNING: 923 // The displaced header in the BasicLock on a thread's stack 924 // is strictly immutable. It CANNOT be changed in ANY cases. 925 // So we have to inflate the stack lock into an ObjectMonitor 926 // even if the current thread owns the lock. The BasicLock on 927 // a thread's stack can be asynchronously read by other threads 928 // during an inflate() call so any change to that stack memory 929 // may not propagate to other threads correctly. 930 } 931 932 // Inflate the monitor to set the hash. 933 934 // An async deflation can race after the inflate() call and before we 935 // can update the ObjectMonitor's header with the hash value below. 936 monitor = inflate(current, obj, inflate_cause_hash_code); 937 // Load ObjectMonitor's header/dmw field and see if it has a hash. 938 mark = monitor->header(); 939 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 940 hash = mark.hash(); 941 if (hash == 0) { // if it does not have a hash 942 hash = get_next_hash(current, obj); // get a new hash 943 temp = mark.copy_set_hash(hash) ; // merge the hash into header 944 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 945 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value()); 946 test = markWord(v); 947 if (test != mark) { 948 // The attempt to update the ObjectMonitor's header/dmw field 949 // did not work. This can happen if another thread managed to 950 // merge in the hash just before our cmpxchg(). 951 // If we add any new usages of the header/dmw field, this code 952 // will need to be updated. 953 hash = test.hash(); 954 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value()); 955 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash"); 956 } 957 if (monitor->is_being_async_deflated()) { 958 // If we detect that async deflation has occurred, then we 959 // attempt to restore the header/dmw to the object's header 960 // so that we only retry once if the deflater thread happens 961 // to be slow. 962 monitor->install_displaced_markword_in_object(obj); 963 continue; 964 } 965 } 966 // We finally get the hash. 967 return hash; 968 } 969 } 970 971 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current, 972 Handle h_obj) { 973 assert(current == JavaThread::current(), "Can only be called on current thread"); 974 oop obj = h_obj(); 975 976 markWord mark = read_stable_mark(obj); 977 978 // Uncontended case, header points to stack 979 if (mark.has_locker()) { 980 return current->is_lock_owned((address)mark.locker()); 981 } 982 // Contended case, header points to ObjectMonitor (tagged pointer) 983 if (mark.has_monitor()) { 984 // The first stage of async deflation does not affect any field 985 // used by this comparison so the ObjectMonitor* is usable here. 986 ObjectMonitor* monitor = mark.monitor(); 987 return monitor->is_entered(current) != 0; 988 } 989 // Unlocked case, header in place 990 assert(mark.is_neutral(), "sanity check"); 991 return false; 992 } 993 994 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) { 995 oop obj = h_obj(); 996 address owner = nullptr; 997 998 markWord mark = read_stable_mark(obj); 999 1000 // Uncontended case, header points to stack 1001 if (mark.has_locker()) { 1002 owner = (address) mark.locker(); 1003 } 1004 1005 // Contended case, header points to ObjectMonitor (tagged pointer) 1006 else if (mark.has_monitor()) { 1007 // The first stage of async deflation does not affect any field 1008 // used by this comparison so the ObjectMonitor* is usable here. 1009 ObjectMonitor* monitor = mark.monitor(); 1010 assert(monitor != nullptr, "monitor should be non-null"); 1011 owner = (address) monitor->owner(); 1012 } 1013 1014 if (owner != nullptr) { 1015 // owning_thread_from_monitor_owner() may also return null here 1016 return Threads::owning_thread_from_monitor_owner(t_list, owner); 1017 } 1018 1019 // Unlocked case, header in place 1020 // Cannot have assertion since this object may have been 1021 // locked by another thread when reaching here. 1022 // assert(mark.is_neutral(), "sanity check"); 1023 1024 return nullptr; 1025 } 1026 1027 // Visitors ... 1028 1029 // Iterate ObjectMonitors where the owner == thread; this does NOT include 1030 // ObjectMonitors where owner is set to a stack lock address in thread. 1031 // 1032 // This version of monitors_iterate() works with the in-use monitor list. 1033 // 1034 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) { 1035 MonitorList::Iterator iter = _in_use_list.iterator(); 1036 while (iter.has_next()) { 1037 ObjectMonitor* mid = iter.next(); 1038 if (mid->owner() != thread) { 1039 // Not owned by the target thread and intentionally skips when owner 1040 // is set to a stack lock address in the target thread. 1041 continue; 1042 } 1043 if (!mid->is_being_async_deflated() && mid->object_peek() != nullptr) { 1044 // Only process with closure if the object is set. 1045 1046 // monitors_iterate() is only called at a safepoint or when the 1047 // target thread is suspended or when the target thread is 1048 // operating on itself. The current closures in use today are 1049 // only interested in an owned ObjectMonitor and ownership 1050 // cannot be dropped under the calling contexts so the 1051 // ObjectMonitor cannot be async deflated. 1052 closure->do_monitor(mid); 1053 } 1054 } 1055 } 1056 1057 // This version of monitors_iterate() works with the specified linked list. 1058 // 1059 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, 1060 ObjectMonitorsHashtable::PtrList* list, 1061 JavaThread* thread) { 1062 typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator; 1063 ObjectMonitorIterator iter(list->head()); 1064 while (!iter.is_empty()) { 1065 ObjectMonitor* mid = *iter.next(); 1066 // Owner set to a stack lock address in thread should never be seen here: 1067 assert(mid->owner() == thread, "must be"); 1068 if (!mid->is_being_async_deflated() && mid->object_peek() != nullptr) { 1069 // Only process with closure if the object is set. 1070 1071 // monitors_iterate() is only called at a safepoint or when the 1072 // target thread is suspended or when the target thread is 1073 // operating on itself. The current closures in use today are 1074 // only interested in an owned ObjectMonitor and ownership 1075 // cannot be dropped under the calling contexts so the 1076 // ObjectMonitor cannot be async deflated. 1077 closure->do_monitor(mid); 1078 } 1079 } 1080 } 1081 1082 static bool monitors_used_above_threshold(MonitorList* list) { 1083 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy 1084 return false; 1085 } 1086 // Start with ceiling based on a per-thread estimate: 1087 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling(); 1088 size_t old_ceiling = ceiling; 1089 if (ceiling < list->max()) { 1090 // The max used by the system has exceeded the ceiling so use that: 1091 ceiling = list->max(); 1092 } 1093 size_t monitors_used = list->count(); 1094 if (monitors_used == 0) { // empty list is easy 1095 return false; 1096 } 1097 if (NoAsyncDeflationProgressMax != 0 && 1098 _no_progress_cnt >= NoAsyncDeflationProgressMax) { 1099 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0; 1100 size_t new_ceiling = ceiling + (ceiling * remainder) + 1; 1101 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling); 1102 log_info(monitorinflation)("Too many deflations without progress; " 1103 "bumping in_use_list_ceiling from " SIZE_FORMAT 1104 " to " SIZE_FORMAT, old_ceiling, new_ceiling); 1105 _no_progress_cnt = 0; 1106 ceiling = new_ceiling; 1107 } 1108 1109 // Check if our monitor usage is above the threshold: 1110 size_t monitor_usage = (monitors_used * 100LL) / ceiling; 1111 return int(monitor_usage) > MonitorUsedDeflationThreshold; 1112 } 1113 1114 size_t ObjectSynchronizer::in_use_list_ceiling() { 1115 return _in_use_list_ceiling; 1116 } 1117 1118 void ObjectSynchronizer::dec_in_use_list_ceiling() { 1119 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate); 1120 } 1121 1122 void ObjectSynchronizer::inc_in_use_list_ceiling() { 1123 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate); 1124 } 1125 1126 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) { 1127 _in_use_list_ceiling = new_value; 1128 } 1129 1130 bool ObjectSynchronizer::is_async_deflation_needed() { 1131 if (is_async_deflation_requested()) { 1132 // Async deflation request. 1133 return true; 1134 } 1135 if (AsyncDeflationInterval > 0 && 1136 time_since_last_async_deflation_ms() > AsyncDeflationInterval && 1137 monitors_used_above_threshold(&_in_use_list)) { 1138 // It's been longer than our specified deflate interval and there 1139 // are too many monitors in use. We don't deflate more frequently 1140 // than AsyncDeflationInterval (unless is_async_deflation_requested) 1141 // in order to not swamp the MonitorDeflationThread. 1142 return true; 1143 } 1144 return false; 1145 } 1146 1147 bool ObjectSynchronizer::request_deflate_idle_monitors() { 1148 JavaThread* current = JavaThread::current(); 1149 bool ret_code = false; 1150 1151 jlong last_time = last_async_deflation_time_ns(); 1152 set_is_async_deflation_requested(true); 1153 { 1154 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag); 1155 ml.notify_all(); 1156 } 1157 const int N_CHECKS = 5; 1158 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds 1159 if (last_async_deflation_time_ns() > last_time) { 1160 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i); 1161 ret_code = true; 1162 break; 1163 } 1164 { 1165 // JavaThread has to honor the blocking protocol. 1166 ThreadBlockInVM tbivm(current); 1167 os::naked_short_sleep(999); // sleep for almost 1 second 1168 } 1169 } 1170 if (!ret_code) { 1171 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS); 1172 } 1173 1174 return ret_code; 1175 } 1176 1177 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() { 1178 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS); 1179 } 1180 1181 static void post_monitor_inflate_event(EventJavaMonitorInflate* event, 1182 const oop obj, 1183 ObjectSynchronizer::InflateCause cause) { 1184 assert(event != nullptr, "invariant"); 1185 event->set_monitorClass(obj->klass()); 1186 event->set_address((uintptr_t)(void*)obj); 1187 event->set_cause((u1)cause); 1188 event->commit(); 1189 } 1190 1191 // Fast path code shared by multiple functions 1192 void ObjectSynchronizer::inflate_helper(oop obj) { 1193 markWord mark = obj->mark_acquire(); 1194 if (mark.has_monitor()) { 1195 ObjectMonitor* monitor = mark.monitor(); 1196 markWord dmw = monitor->header(); 1197 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value()); 1198 return; 1199 } 1200 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal); 1201 } 1202 1203 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object, 1204 const InflateCause cause) { 1205 EventJavaMonitorInflate event; 1206 1207 for (;;) { 1208 const markWord mark = object->mark_acquire(); 1209 1210 // The mark can be in one of the following states: 1211 // * Inflated - just return 1212 // * Stack-locked - coerce it to inflated 1213 // * INFLATING - busy wait for conversion to complete 1214 // * Neutral - aggressively inflate the object. 1215 1216 // CASE: inflated 1217 if (mark.has_monitor()) { 1218 ObjectMonitor* inf = mark.monitor(); 1219 markWord dmw = inf->header(); 1220 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1221 return inf; 1222 } 1223 1224 // CASE: inflation in progress - inflating over a stack-lock. 1225 // Some other thread is converting from stack-locked to inflated. 1226 // Only that thread can complete inflation -- other threads must wait. 1227 // The INFLATING value is transient. 1228 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. 1229 // We could always eliminate polling by parking the thread on some auxiliary list. 1230 if (mark == markWord::INFLATING()) { 1231 read_stable_mark(object); 1232 continue; 1233 } 1234 1235 // CASE: stack-locked 1236 // Could be stack-locked either by this thread or by some other thread. 1237 // 1238 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting 1239 // to install INFLATING into the mark word. We originally installed INFLATING, 1240 // allocated the ObjectMonitor, and then finally STed the address of the 1241 // ObjectMonitor into the mark. This was correct, but artificially lengthened 1242 // the interval in which INFLATING appeared in the mark, thus increasing 1243 // the odds of inflation contention. 1244 1245 LogStreamHandle(Trace, monitorinflation) lsh; 1246 1247 if (mark.has_locker()) { 1248 ObjectMonitor* m = new ObjectMonitor(object); 1249 // Optimistically prepare the ObjectMonitor - anticipate successful CAS 1250 // We do this before the CAS in order to minimize the length of time 1251 // in which INFLATING appears in the mark. 1252 1253 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark); 1254 if (cmp != mark) { 1255 delete m; 1256 continue; // Interference -- just retry 1257 } 1258 1259 // We've successfully installed INFLATING (0) into the mark-word. 1260 // This is the only case where 0 will appear in a mark-word. 1261 // Only the singular thread that successfully swings the mark-word 1262 // to 0 can perform (or more precisely, complete) inflation. 1263 // 1264 // Why do we CAS a 0 into the mark-word instead of just CASing the 1265 // mark-word from the stack-locked value directly to the new inflated state? 1266 // Consider what happens when a thread unlocks a stack-locked object. 1267 // It attempts to use CAS to swing the displaced header value from the 1268 // on-stack BasicLock back into the object header. Recall also that the 1269 // header value (hash code, etc) can reside in (a) the object header, or 1270 // (b) a displaced header associated with the stack-lock, or (c) a displaced 1271 // header in an ObjectMonitor. The inflate() routine must copy the header 1272 // value from the BasicLock on the owner's stack to the ObjectMonitor, all 1273 // the while preserving the hashCode stability invariants. If the owner 1274 // decides to release the lock while the value is 0, the unlock will fail 1275 // and control will eventually pass from slow_exit() to inflate. The owner 1276 // will then spin, waiting for the 0 value to disappear. Put another way, 1277 // the 0 causes the owner to stall if the owner happens to try to 1278 // drop the lock (restoring the header from the BasicLock to the object) 1279 // while inflation is in-progress. This protocol avoids races that might 1280 // would otherwise permit hashCode values to change or "flicker" for an object. 1281 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable. 1282 // 0 serves as a "BUSY" inflate-in-progress indicator. 1283 1284 1285 // fetch the displaced mark from the owner's stack. 1286 // The owner can't die or unwind past the lock while our INFLATING 1287 // object is in the mark. Furthermore the owner can't complete 1288 // an unlock on the object, either. 1289 markWord dmw = mark.displaced_mark_helper(); 1290 // Catch if the object's header is not neutral (not locked and 1291 // not marked is what we care about here). 1292 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1293 1294 // Setup monitor fields to proper values -- prepare the monitor 1295 m->set_header(dmw); 1296 1297 // Optimization: if the mark.locker stack address is associated 1298 // with this thread we could simply set m->_owner = current. 1299 // Note that a thread can inflate an object 1300 // that it has stack-locked -- as might happen in wait() -- directly 1301 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom. 1302 m->set_owner_from(nullptr, mark.locker()); 1303 // TODO-FIXME: assert BasicLock->dhw != 0. 1304 1305 // Must preserve store ordering. The monitor state must 1306 // be stable at the time of publishing the monitor address. 1307 guarantee(object->mark() == markWord::INFLATING(), "invariant"); 1308 // Release semantics so that above set_object() is seen first. 1309 object->release_set_mark(markWord::encode(m)); 1310 1311 // Once ObjectMonitor is configured and the object is associated 1312 // with the ObjectMonitor, it is safe to allow async deflation: 1313 _in_use_list.add(m); 1314 1315 // Hopefully the performance counters are allocated on distinct cache lines 1316 // to avoid false sharing on MP systems ... 1317 OM_PERFDATA_OP(Inflations, inc()); 1318 if (log_is_enabled(Trace, monitorinflation)) { 1319 ResourceMark rm(current); 1320 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark=" 1321 INTPTR_FORMAT ", type='%s'", p2i(object), 1322 object->mark().value(), object->klass()->external_name()); 1323 } 1324 if (event.should_commit()) { 1325 post_monitor_inflate_event(&event, object, cause); 1326 } 1327 return m; 1328 } 1329 1330 // CASE: neutral 1331 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. 1332 // If we know we're inflating for entry it's better to inflate by swinging a 1333 // pre-locked ObjectMonitor pointer into the object header. A successful 1334 // CAS inflates the object *and* confers ownership to the inflating thread. 1335 // In the current implementation we use a 2-step mechanism where we CAS() 1336 // to inflate and then CAS() again to try to swing _owner from null to current. 1337 // An inflateTry() method that we could call from enter() would be useful. 1338 1339 // Catch if the object's header is not neutral (not locked and 1340 // not marked is what we care about here). 1341 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 1342 ObjectMonitor* m = new ObjectMonitor(object); 1343 // prepare m for installation - set monitor to initial state 1344 m->set_header(mark); 1345 1346 if (object->cas_set_mark(markWord::encode(m), mark) != mark) { 1347 delete m; 1348 m = nullptr; 1349 continue; 1350 // interference - the markword changed - just retry. 1351 // The state-transitions are one-way, so there's no chance of 1352 // live-lock -- "Inflated" is an absorbing state. 1353 } 1354 1355 // Once the ObjectMonitor is configured and object is associated 1356 // with the ObjectMonitor, it is safe to allow async deflation: 1357 _in_use_list.add(m); 1358 1359 // Hopefully the performance counters are allocated on distinct 1360 // cache lines to avoid false sharing on MP systems ... 1361 OM_PERFDATA_OP(Inflations, inc()); 1362 if (log_is_enabled(Trace, monitorinflation)) { 1363 ResourceMark rm(current); 1364 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark=" 1365 INTPTR_FORMAT ", type='%s'", p2i(object), 1366 object->mark().value(), object->klass()->external_name()); 1367 } 1368 if (event.should_commit()) { 1369 post_monitor_inflate_event(&event, object, cause); 1370 } 1371 return m; 1372 } 1373 } 1374 1375 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name, 1376 const char* cnt_name, size_t cnt, 1377 LogStream* ls, elapsedTimer* timer_p) { 1378 if (!SafepointMechanism::should_process(current)) { 1379 return; 1380 } 1381 1382 // A safepoint/handshake has started. 1383 if (ls != nullptr) { 1384 timer_p->stop(); 1385 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling=" 1386 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1387 op_name, cnt_name, cnt, in_use_list_ceiling(), 1388 _in_use_list.count(), _in_use_list.max()); 1389 } 1390 1391 { 1392 // Honor block request. 1393 ThreadBlockInVM tbivm(current); 1394 } 1395 1396 if (ls != nullptr) { 1397 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT 1398 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name, 1399 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1400 timer_p->start(); 1401 } 1402 } 1403 1404 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle 1405 // ObjectMonitors. Returns the number of deflated ObjectMonitors. 1406 // 1407 // If table != nullptr, we gather owned ObjectMonitors indexed by the 1408 // owner in the table. Please note that ObjectMonitors where the owner 1409 // is set to a stack lock address are NOT associated with the JavaThread 1410 // that holds that stack lock. All of the current consumers of 1411 // ObjectMonitorsHashtable info only care about JNI locked monitors and 1412 // those do not have the owner set to a stack lock address. 1413 // 1414 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls, 1415 elapsedTimer* timer_p, 1416 ObjectMonitorsHashtable* table) { 1417 MonitorList::Iterator iter = _in_use_list.iterator(); 1418 size_t deflated_count = 0; 1419 1420 while (iter.has_next()) { 1421 if (deflated_count >= (size_t)MonitorDeflationMax) { 1422 break; 1423 } 1424 ObjectMonitor* mid = iter.next(); 1425 if (mid->deflate_monitor()) { 1426 deflated_count++; 1427 } else if (table != nullptr) { 1428 // The caller is interested in the owned ObjectMonitors. This does 1429 // not include when owner is set to a stack lock address in thread. 1430 // This also does not capture unowned ObjectMonitors that cannot be 1431 // deflated because of a waiter. 1432 void* key = mid->owner(); 1433 // Since deflate_idle_monitors() and deflate_monitor_list() can be 1434 // called more than once, we have to make sure the entry has not 1435 // already been added. 1436 if (key != nullptr && !table->has_entry(key, mid)) { 1437 table->add_entry(key, mid); 1438 } 1439 } 1440 1441 if (current->is_Java_thread()) { 1442 // A JavaThread must check for a safepoint/handshake and honor it. 1443 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count", 1444 deflated_count, ls, timer_p); 1445 } 1446 } 1447 1448 return deflated_count; 1449 } 1450 1451 class HandshakeForDeflation : public HandshakeClosure { 1452 public: 1453 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {} 1454 1455 void do_thread(Thread* thread) { 1456 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread=" 1457 INTPTR_FORMAT, p2i(thread)); 1458 } 1459 }; 1460 1461 // This function is called by the MonitorDeflationThread to deflate 1462 // ObjectMonitors. It is also called via do_final_audit_and_print_stats() 1463 // and VM_ThreadDump::doit() by the VMThread. 1464 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) { 1465 Thread* current = Thread::current(); 1466 if (current->is_Java_thread()) { 1467 // The async deflation request has been processed. 1468 _last_async_deflation_time_ns = os::javaTimeNanos(); 1469 set_is_async_deflation_requested(false); 1470 } 1471 1472 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1473 LogStreamHandle(Info, monitorinflation) lsh_info; 1474 LogStream* ls = nullptr; 1475 if (log_is_enabled(Debug, monitorinflation)) { 1476 ls = &lsh_debug; 1477 } else if (log_is_enabled(Info, monitorinflation)) { 1478 ls = &lsh_info; 1479 } 1480 1481 elapsedTimer timer; 1482 if (ls != nullptr) { 1483 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1484 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1485 timer.start(); 1486 } 1487 1488 // Deflate some idle ObjectMonitors. 1489 size_t deflated_count = deflate_monitor_list(current, ls, &timer, table); 1490 size_t unlinked_count = 0; 1491 size_t deleted_count = 0; 1492 if (deflated_count > 0 || is_final_audit()) { 1493 // There are ObjectMonitors that have been deflated or this is the 1494 // final audit and all the remaining ObjectMonitors have been 1495 // deflated, BUT the MonitorDeflationThread blocked for the final 1496 // safepoint during unlinking. 1497 1498 // Unlink deflated ObjectMonitors from the in-use list. 1499 ResourceMark rm; 1500 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count); 1501 unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, &delete_list); 1502 if (current->is_Java_thread()) { 1503 if (ls != nullptr) { 1504 timer.stop(); 1505 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT 1506 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count=" 1507 SIZE_FORMAT ", max=" SIZE_FORMAT, 1508 unlinked_count, in_use_list_ceiling(), 1509 _in_use_list.count(), _in_use_list.max()); 1510 } 1511 1512 // A JavaThread needs to handshake in order to safely free the 1513 // ObjectMonitors that were deflated in this cycle. 1514 HandshakeForDeflation hfd_hc; 1515 Handshake::execute(&hfd_hc); 1516 1517 if (ls != nullptr) { 1518 ls->print_cr("after handshaking: in_use_list stats: ceiling=" 1519 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1520 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1521 timer.start(); 1522 } 1523 } 1524 1525 // After the handshake, safely free the ObjectMonitors that were 1526 // deflated in this cycle. 1527 for (ObjectMonitor* monitor: delete_list) { 1528 delete monitor; 1529 deleted_count++; 1530 1531 if (current->is_Java_thread()) { 1532 // A JavaThread must check for a safepoint/handshake and honor it. 1533 chk_for_block_req(JavaThread::cast(current), "deletion", "deleted_count", 1534 deleted_count, ls, &timer); 1535 } 1536 } 1537 assert(unlinked_count == deleted_count, "must be"); 1538 } 1539 1540 if (ls != nullptr) { 1541 timer.stop(); 1542 if (deflated_count != 0 || unlinked_count != 0 || log_is_enabled(Debug, monitorinflation)) { 1543 ls->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs", 1544 deflated_count, unlinked_count, timer.seconds()); 1545 } 1546 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1547 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1548 if (table != nullptr) { 1549 ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT, 1550 table->key_count(), table->om_count()); 1551 } 1552 } 1553 1554 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count())); 1555 OM_PERFDATA_OP(Deflations, inc(deflated_count)); 1556 1557 GVars.stw_random = os::random(); 1558 1559 if (deflated_count != 0) { 1560 _no_progress_cnt = 0; 1561 } else { 1562 _no_progress_cnt++; 1563 } 1564 1565 return deflated_count; 1566 } 1567 1568 // Monitor cleanup on JavaThread::exit 1569 1570 // Iterate through monitor cache and attempt to release thread's monitors 1571 class ReleaseJavaMonitorsClosure: public MonitorClosure { 1572 private: 1573 JavaThread* _thread; 1574 1575 public: 1576 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {} 1577 void do_monitor(ObjectMonitor* mid) { 1578 intx rec = mid->complete_exit(_thread); 1579 _thread->dec_held_monitor_count(rec + 1); 1580 } 1581 }; 1582 1583 // Release all inflated monitors owned by current thread. Lightweight monitors are 1584 // ignored. This is meant to be called during JNI thread detach which assumes 1585 // all remaining monitors are heavyweight. All exceptions are swallowed. 1586 // Scanning the extant monitor list can be time consuming. 1587 // A simple optimization is to add a per-thread flag that indicates a thread 1588 // called jni_monitorenter() during its lifetime. 1589 // 1590 // Instead of NoSafepointVerifier it might be cheaper to 1591 // use an idiom of the form: 1592 // auto int tmp = SafepointSynchronize::_safepoint_counter ; 1593 // <code that must not run at safepoint> 1594 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; 1595 // Since the tests are extremely cheap we could leave them enabled 1596 // for normal product builds. 1597 1598 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) { 1599 assert(current == JavaThread::current(), "must be current Java thread"); 1600 NoSafepointVerifier nsv; 1601 ReleaseJavaMonitorsClosure rjmc(current); 1602 ObjectSynchronizer::monitors_iterate(&rjmc, current); 1603 assert(!current->has_pending_exception(), "Should not be possible"); 1604 current->clear_pending_exception(); 1605 assert(current->held_monitor_count() == 0, "Should not be possible"); 1606 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count. 1607 current->clear_jni_monitor_count(); 1608 } 1609 1610 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) { 1611 switch (cause) { 1612 case inflate_cause_vm_internal: return "VM Internal"; 1613 case inflate_cause_monitor_enter: return "Monitor Enter"; 1614 case inflate_cause_wait: return "Monitor Wait"; 1615 case inflate_cause_notify: return "Monitor Notify"; 1616 case inflate_cause_hash_code: return "Monitor Hash Code"; 1617 case inflate_cause_jni_enter: return "JNI Monitor Enter"; 1618 case inflate_cause_jni_exit: return "JNI Monitor Exit"; 1619 default: 1620 ShouldNotReachHere(); 1621 } 1622 return "Unknown"; 1623 } 1624 1625 //------------------------------------------------------------------------------ 1626 // Debugging code 1627 1628 u_char* ObjectSynchronizer::get_gvars_addr() { 1629 return (u_char*)&GVars; 1630 } 1631 1632 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() { 1633 return (u_char*)&GVars.hc_sequence; 1634 } 1635 1636 size_t ObjectSynchronizer::get_gvars_size() { 1637 return sizeof(SharedGlobals); 1638 } 1639 1640 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() { 1641 return (u_char*)&GVars.stw_random; 1642 } 1643 1644 // Do the final audit and print of ObjectMonitor stats; must be done 1645 // by the VMThread at VM exit time. 1646 void ObjectSynchronizer::do_final_audit_and_print_stats() { 1647 assert(Thread::current()->is_VM_thread(), "sanity check"); 1648 1649 if (is_final_audit()) { // Only do the audit once. 1650 return; 1651 } 1652 set_is_final_audit(); 1653 log_info(monitorinflation)("Starting the final audit."); 1654 1655 if (log_is_enabled(Info, monitorinflation)) { 1656 // Do deflations in order to reduce the in-use monitor population 1657 // that is reported by ObjectSynchronizer::log_in_use_monitor_details() 1658 // which is called by ObjectSynchronizer::audit_and_print_stats(). 1659 while (deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) > 0) { 1660 ; // empty 1661 } 1662 // The other audit_and_print_stats() call is done at the Debug 1663 // level at a safepoint in SafepointSynchronize::do_cleanup_tasks. 1664 audit_and_print_stats(true /* on_exit */); 1665 } 1666 } 1667 1668 // This function can be called at a safepoint or it can be called when 1669 // we are trying to exit the VM. When we are trying to exit the VM, the 1670 // list walker functions can run in parallel with the other list 1671 // operations so spin-locking is used for safety. 1672 // 1673 // Calls to this function can be added in various places as a debugging 1674 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor 1675 // details logged at the Info level and 'false' for the 'on_exit' 1676 // parameter to have in-use monitor details logged at the Trace level. 1677 // 1678 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) { 1679 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant"); 1680 1681 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1682 LogStreamHandle(Info, monitorinflation) lsh_info; 1683 LogStreamHandle(Trace, monitorinflation) lsh_trace; 1684 LogStream* ls = nullptr; 1685 if (log_is_enabled(Trace, monitorinflation)) { 1686 ls = &lsh_trace; 1687 } else if (log_is_enabled(Debug, monitorinflation)) { 1688 ls = &lsh_debug; 1689 } else if (log_is_enabled(Info, monitorinflation)) { 1690 ls = &lsh_info; 1691 } 1692 assert(ls != nullptr, "sanity check"); 1693 1694 int error_cnt = 0; 1695 1696 ls->print_cr("Checking in_use_list:"); 1697 chk_in_use_list(ls, &error_cnt); 1698 1699 if (error_cnt == 0) { 1700 ls->print_cr("No errors found in in_use_list checks."); 1701 } else { 1702 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt); 1703 } 1704 1705 if ((on_exit && log_is_enabled(Info, monitorinflation)) || 1706 (!on_exit && log_is_enabled(Trace, monitorinflation))) { 1707 // When exiting this log output is at the Info level. When called 1708 // at a safepoint, this log output is at the Trace level since 1709 // there can be a lot of it. 1710 log_in_use_monitor_details(ls); 1711 } 1712 1713 ls->flush(); 1714 1715 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt); 1716 } 1717 1718 // Check the in_use_list; log the results of the checks. 1719 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) { 1720 size_t l_in_use_count = _in_use_list.count(); 1721 size_t l_in_use_max = _in_use_list.max(); 1722 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count, 1723 l_in_use_max); 1724 1725 size_t ck_in_use_count = 0; 1726 MonitorList::Iterator iter = _in_use_list.iterator(); 1727 while (iter.has_next()) { 1728 ObjectMonitor* mid = iter.next(); 1729 chk_in_use_entry(mid, out, error_cnt_p); 1730 ck_in_use_count++; 1731 } 1732 1733 if (l_in_use_count == ck_in_use_count) { 1734 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count=" 1735 SIZE_FORMAT, l_in_use_count, ck_in_use_count); 1736 } else { 1737 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to " 1738 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count, 1739 ck_in_use_count); 1740 } 1741 1742 size_t ck_in_use_max = _in_use_list.max(); 1743 if (l_in_use_max == ck_in_use_max) { 1744 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max=" 1745 SIZE_FORMAT, l_in_use_max, ck_in_use_max); 1746 } else { 1747 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to " 1748 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max); 1749 } 1750 } 1751 1752 // Check an in-use monitor entry; log any errors. 1753 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out, 1754 int* error_cnt_p) { 1755 if (n->owner_is_DEFLATER_MARKER()) { 1756 // This should not happen, but if it does, it is not fatal. 1757 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is " 1758 "deflated.", p2i(n)); 1759 return; 1760 } 1761 if (n->header().value() == 0) { 1762 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must " 1763 "have non-null _header field.", p2i(n)); 1764 *error_cnt_p = *error_cnt_p + 1; 1765 } 1766 const oop obj = n->object_peek(); 1767 if (obj != nullptr) { 1768 const markWord mark = obj->mark(); 1769 if (!mark.has_monitor()) { 1770 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's " 1771 "object does not think it has a monitor: obj=" 1772 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n), 1773 p2i(obj), mark.value()); 1774 *error_cnt_p = *error_cnt_p + 1; 1775 } 1776 ObjectMonitor* const obj_mon = mark.monitor(); 1777 if (n != obj_mon) { 1778 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's " 1779 "object does not refer to the same monitor: obj=" 1780 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon=" 1781 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon)); 1782 *error_cnt_p = *error_cnt_p + 1; 1783 } 1784 } 1785 } 1786 1787 // Log details about ObjectMonitors on the in_use_list. The 'BHL' 1788 // flags indicate why the entry is in-use, 'object' and 'object type' 1789 // indicate the associated object and its type. 1790 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) { 1791 stringStream ss; 1792 if (_in_use_list.count() > 0) { 1793 out->print_cr("In-use monitor info:"); 1794 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)"); 1795 out->print_cr("%18s %s %18s %18s", 1796 "monitor", "BHL", "object", "object type"); 1797 out->print_cr("================== === ================== =================="); 1798 MonitorList::Iterator iter = _in_use_list.iterator(); 1799 while (iter.has_next()) { 1800 ObjectMonitor* mid = iter.next(); 1801 const oop obj = mid->object_peek(); 1802 const markWord mark = mid->header(); 1803 ResourceMark rm; 1804 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid), 1805 mid->is_busy(), mark.hash() != 0, mid->owner() != nullptr, 1806 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name()); 1807 if (mid->is_busy()) { 1808 out->print(" (%s)", mid->is_busy_to_string(&ss)); 1809 ss.reset(); 1810 } 1811 out->cr(); 1812 } 1813 } 1814 1815 out->flush(); 1816 }