1 /* 2 * Copyright (c) 1998, 2022, 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 "gc/shared/suspendibleThreadSet.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/handles.inline.hpp" 39 #include "runtime/handshake.hpp" 40 #include "runtime/interfaceSupport.inline.hpp" 41 #include "runtime/mutexLocker.hpp" 42 #include "runtime/objectMonitor.hpp" 43 #include "runtime/objectMonitor.inline.hpp" 44 #include "runtime/os.inline.hpp" 45 #include "runtime/osThread.hpp" 46 #include "runtime/perfData.hpp" 47 #include "runtime/safepointMechanism.inline.hpp" 48 #include "runtime/safepointVerifiers.hpp" 49 #include "runtime/sharedRuntime.hpp" 50 #include "runtime/stubRoutines.hpp" 51 #include "runtime/synchronizer.hpp" 52 #include "runtime/thread.inline.hpp" 53 #include "runtime/timer.hpp" 54 #include "runtime/vframe.hpp" 55 #include "runtime/vmThread.hpp" 56 #include "utilities/align.hpp" 57 #include "utilities/dtrace.hpp" 58 #include "utilities/events.hpp" 59 #include "utilities/preserveException.hpp" 60 61 class CleanupObjectMonitorsHashtable: StackObj { 62 public: 63 bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) { 64 list->clear(); // clear the LinkListNodes 65 delete list; // then delete the LinkedList 66 return true; 67 } 68 }; 69 70 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() { 71 CleanupObjectMonitorsHashtable cleanup; 72 _ptrs->unlink(&cleanup); // cleanup the LinkedLists 73 delete _ptrs; // then delete the hash table 74 } 75 76 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) { 77 ObjectMonitorsHashtable::PtrList* list = get_entry(key); 78 if (list == nullptr) { 79 // Create new list and add it to the hash table: 80 list = new (ResourceObj::C_HEAP, mtThread) ObjectMonitorsHashtable::PtrList(); 81 add_entry(key, list); 82 } 83 list->add(om); // Add the ObjectMonitor to the list. 84 _om_count++; 85 } 86 87 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) { 88 ObjectMonitorsHashtable::PtrList* list = get_entry(key); 89 if (list == nullptr || list->find(om) == nullptr) { 90 return false; 91 } 92 return true; 93 } 94 95 void MonitorList::add(ObjectMonitor* m) { 96 ObjectMonitor* head; 97 do { 98 head = Atomic::load(&_head); 99 m->set_next_om(head); 100 } while (Atomic::cmpxchg(&_head, head, m) != head); 101 102 size_t count = Atomic::add(&_count, 1u); 103 if (count > max()) { 104 Atomic::inc(&_max); 105 } 106 } 107 108 size_t MonitorList::count() const { 109 return Atomic::load(&_count); 110 } 111 112 size_t MonitorList::max() const { 113 return Atomic::load(&_max); 114 } 115 116 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated 117 // ObjectMonitors. Returns the number of unlinked ObjectMonitors. 118 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls, 119 elapsedTimer* timer_p, 120 GrowableArray<ObjectMonitor*>* unlinked_list) { 121 size_t unlinked_count = 0; 122 ObjectMonitor* prev = NULL; 123 ObjectMonitor* head = Atomic::load_acquire(&_head); 124 ObjectMonitor* m = head; 125 // The in-use list head can be NULL during the final audit. 126 while (m != NULL) { 127 if (m->is_being_async_deflated()) { 128 // Find next live ObjectMonitor. 129 ObjectMonitor* next = m; 130 do { 131 ObjectMonitor* next_next = next->next_om(); 132 unlinked_count++; 133 unlinked_list->append(next); 134 next = next_next; 135 if (unlinked_count >= (size_t)MonitorDeflationMax) { 136 // Reached the max so bail out on the gathering loop. 137 break; 138 } 139 } while (next != NULL && next->is_being_async_deflated()); 140 if (prev == NULL) { 141 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next); 142 if (prev_head != head) { 143 // Find new prev ObjectMonitor that just got inserted. 144 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) { 145 prev = n; 146 } 147 prev->set_next_om(next); 148 } 149 } else { 150 prev->set_next_om(next); 151 } 152 if (unlinked_count >= (size_t)MonitorDeflationMax) { 153 // Reached the max so bail out on the searching loop. 154 break; 155 } 156 m = next; 157 } else { 158 prev = m; 159 m = m->next_om(); 160 } 161 162 if (current->is_Java_thread()) { 163 // A JavaThread must check for a safepoint/handshake and honor it. 164 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking", 165 "unlinked_count", unlinked_count, 166 ls, timer_p); 167 } 168 } 169 Atomic::sub(&_count, unlinked_count); 170 return unlinked_count; 171 } 172 173 MonitorList::Iterator MonitorList::iterator() const { 174 return Iterator(Atomic::load_acquire(&_head)); 175 } 176 177 ObjectMonitor* MonitorList::Iterator::next() { 178 ObjectMonitor* current = _current; 179 _current = current->next_om(); 180 return current; 181 } 182 183 // The "core" versions of monitor enter and exit reside in this file. 184 // The interpreter and compilers contain specialized transliterated 185 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp 186 // fast_lock(...) for instance. If you make changes here, make sure to modify the 187 // interpreter, and both C1 and C2 fast-path inline locking code emission. 188 // 189 // ----------------------------------------------------------------------------- 190 191 #ifdef DTRACE_ENABLED 192 193 // Only bother with this argument setup if dtrace is available 194 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly. 195 196 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \ 197 char* bytes = NULL; \ 198 int len = 0; \ 199 jlong jtid = SharedRuntime::get_java_tid(thread); \ 200 Symbol* klassname = obj->klass()->name(); \ 201 if (klassname != NULL) { \ 202 bytes = (char*)klassname->bytes(); \ 203 len = klassname->utf8_length(); \ 204 } 205 206 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \ 207 { \ 208 if (DTraceMonitorProbes) { \ 209 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 210 HOTSPOT_MONITOR_WAIT(jtid, \ 211 (uintptr_t)(monitor), bytes, len, (millis)); \ 212 } \ 213 } 214 215 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY 216 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL 217 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED 218 219 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \ 220 { \ 221 if (DTraceMonitorProbes) { \ 222 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \ 223 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \ 224 (uintptr_t)(monitor), bytes, len); \ 225 } \ 226 } 227 228 #else // ndef DTRACE_ENABLED 229 230 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;} 231 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;} 232 233 #endif // ndef DTRACE_ENABLED 234 235 // This exists only as a workaround of dtrace bug 6254741 236 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) { 237 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr); 238 return 0; 239 } 240 241 static const int NINFLATIONLOCKS = 256; 242 static os::PlatformMutex* gInflationLocks[NINFLATIONLOCKS]; 243 244 void ObjectSynchronizer::initialize() { 245 for (int i = 0; i < NINFLATIONLOCKS; i++) { 246 gInflationLocks[i] = new os::PlatformMutex(); 247 } 248 // Start the ceiling with the estimate for one thread. 249 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate); 250 } 251 252 MonitorList ObjectSynchronizer::_in_use_list; 253 // monitors_used_above_threshold() policy is as follows: 254 // 255 // The ratio of the current _in_use_list count to the ceiling is used 256 // to determine if we are above MonitorUsedDeflationThreshold and need 257 // to do an async monitor deflation cycle. The ceiling is increased by 258 // AvgMonitorsPerThreadEstimate when a thread is added to the system 259 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is 260 // removed from the system. 261 // 262 // Note: If the _in_use_list max exceeds the ceiling, then 263 // monitors_used_above_threshold() will use the in_use_list max instead 264 // of the thread count derived ceiling because we have used more 265 // ObjectMonitors than the estimated average. 266 // 267 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax 268 // no-progress async monitor deflation cycles in a row, then the ceiling 269 // is adjusted upwards by monitors_used_above_threshold(). 270 // 271 // Start the ceiling with the estimate for one thread in initialize() 272 // which is called after cmd line options are processed. 273 static size_t _in_use_list_ceiling = 0; 274 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false; 275 bool volatile ObjectSynchronizer::_is_final_audit = false; 276 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0; 277 static uintx _no_progress_cnt = 0; 278 279 // =====================> Quick functions 280 281 // The quick_* forms are special fast-path variants used to improve 282 // performance. In the simplest case, a "quick_*" implementation could 283 // simply return false, in which case the caller will perform the necessary 284 // state transitions and call the slow-path form. 285 // The fast-path is designed to handle frequently arising cases in an efficient 286 // manner and is just a degenerate "optimistic" variant of the slow-path. 287 // returns true -- to indicate the call was satisfied. 288 // returns false -- to indicate the call needs the services of the slow-path. 289 // A no-loitering ordinance is in effect for code in the quick_* family 290 // operators: safepoints or indefinite blocking (blocking that might span a 291 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon 292 // entry. 293 // 294 // Consider: An interesting optimization is to have the JIT recognize the 295 // following common idiom: 296 // synchronized (someobj) { .... ; notify(); } 297 // That is, we find a notify() or notifyAll() call that immediately precedes 298 // the monitorexit operation. In that case the JIT could fuse the operations 299 // into a single notifyAndExit() runtime primitive. 300 301 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) { 302 assert(current->thread_state() == _thread_in_Java, "invariant"); 303 NoSafepointVerifier nsv; 304 if (obj == NULL) return false; // slow-path for invalid obj 305 const markWord mark = obj->mark(); 306 307 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 308 // Degenerate notify 309 // stack-locked by caller so by definition the implied waitset is empty. 310 return true; 311 } 312 313 if (mark.has_monitor()) { 314 ObjectMonitor* const mon = mark.monitor(); 315 assert(mon->object() == oop(obj), "invariant"); 316 if (mon->owner() != current) return false; // slow-path for IMS exception 317 318 if (mon->first_waiter() != NULL) { 319 // We have one or more waiters. Since this is an inflated monitor 320 // that we own, we can transfer one or more threads from the waitset 321 // to the entrylist here and now, avoiding the slow-path. 322 if (all) { 323 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current); 324 } else { 325 DTRACE_MONITOR_PROBE(notify, mon, obj, current); 326 } 327 int free_count = 0; 328 do { 329 mon->INotify(current); 330 ++free_count; 331 } while (mon->first_waiter() != NULL && all); 332 OM_PERFDATA_OP(Notifications, inc(free_count)); 333 } 334 return true; 335 } 336 337 // other IMS exception states take the slow-path 338 return false; 339 } 340 341 342 // The LockNode emitted directly at the synchronization site would have 343 // been too big if it were to have included support for the cases of inflated 344 // recursive enter and exit, so they go here instead. 345 // Note that we can't safely call AsyncPrintJavaStack() from within 346 // quick_enter() as our thread state remains _in_Java. 347 348 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current, 349 BasicLock * lock) { 350 assert(current->thread_state() == _thread_in_Java, "invariant"); 351 NoSafepointVerifier nsv; 352 if (obj == NULL) return false; // Need to throw NPE 353 354 if (obj->klass()->is_value_based()) { 355 return false; 356 } 357 358 const markWord mark = obj->mark(); 359 360 if (mark.has_monitor()) { 361 ObjectMonitor* const m = mark.monitor(); 362 // An async deflation or GC can race us before we manage to make 363 // the ObjectMonitor busy by setting the owner below. If we detect 364 // that race we just bail out to the slow-path here. 365 if (m->object_peek() == NULL) { 366 return false; 367 } 368 JavaThread* const owner = (JavaThread*) m->owner_raw(); 369 370 // Lock contention and Transactional Lock Elision (TLE) diagnostics 371 // and observability 372 // Case: light contention possibly amenable to TLE 373 // Case: TLE inimical operations such as nested/recursive synchronization 374 375 if (owner == current) { 376 m->_recursions++; 377 return true; 378 } 379 380 // This Java Monitor is inflated so obj's header will never be 381 // displaced to this thread's BasicLock. Make the displaced header 382 // non-NULL so this BasicLock is not seen as recursive nor as 383 // being locked. We do this unconditionally so that this thread's 384 // BasicLock cannot be mis-interpreted by any stack walkers. For 385 // performance reasons, stack walkers generally first check for 386 // stack-locking in the object's header, the second check is for 387 // recursive stack-locking in the displaced header in the BasicLock, 388 // and last are the inflated Java Monitor (ObjectMonitor) checks. 389 lock->set_displaced_header(markWord::unused_mark()); 390 391 if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) { 392 assert(m->_recursions == 0, "invariant"); 393 return true; 394 } 395 } 396 397 // Note that we could inflate in quick_enter. 398 // This is likely a useful optimization 399 // Critically, in quick_enter() we must not: 400 // -- block indefinitely, or 401 // -- reach a safepoint 402 403 return false; // revert to slow-path 404 } 405 406 // Handle notifications when synchronizing on value based classes 407 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) { 408 frame last_frame = current->last_frame(); 409 bool bcp_was_adjusted = false; 410 // Don't decrement bcp if it points to the frame's first instruction. This happens when 411 // handle_sync_on_value_based_class() is called because of a synchronized method. There 412 // is no actual monitorenter instruction in the byte code in this case. 413 if (last_frame.is_interpreted_frame() && 414 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) { 415 // adjust bcp to point back to monitorenter so that we print the correct line numbers 416 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1); 417 bcp_was_adjusted = true; 418 } 419 420 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) { 421 ResourceMark rm(current); 422 stringStream ss; 423 current->print_stack_on(&ss); 424 char* base = (char*)strstr(ss.base(), "at"); 425 char* newline = (char*)strchr(ss.base(), '\n'); 426 if (newline != NULL) { 427 *newline = '\0'; 428 } 429 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base); 430 } else { 431 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses"); 432 ResourceMark rm(current); 433 Log(valuebasedclasses) vblog; 434 435 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name()); 436 if (current->has_last_Java_frame()) { 437 LogStream info_stream(vblog.info()); 438 current->print_stack_on(&info_stream); 439 } else { 440 vblog.info("Cannot find the last Java frame"); 441 } 442 443 EventSyncOnValueBasedClass event; 444 if (event.should_commit()) { 445 event.set_valueBasedClass(obj->klass()); 446 event.commit(); 447 } 448 } 449 450 if (bcp_was_adjusted) { 451 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1); 452 } 453 } 454 455 static bool useHeavyMonitors() { 456 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) 457 return UseHeavyMonitors; 458 #else 459 return false; 460 #endif 461 } 462 463 // ----------------------------------------------------------------------------- 464 // Monitor Enter/Exit 465 // The interpreter and compiler assembly code tries to lock using the fast path 466 // of this algorithm. Make sure to update that code if the following function is 467 // changed. The implementation is extremely sensitive to race condition. Be careful. 468 469 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) { 470 if (obj->klass()->is_value_based()) { 471 handle_sync_on_value_based_class(obj, current); 472 } 473 474 if (!useHeavyMonitors()) { 475 markWord mark = obj->mark(); 476 if (mark.is_neutral()) { 477 // Anticipate successful CAS -- the ST of the displaced mark must 478 // be visible <= the ST performed by the CAS. 479 lock->set_displaced_header(mark); 480 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) { 481 return; 482 } 483 // Fall through to inflate() ... 484 } else if (mark.has_locker() && 485 current->is_lock_owned((address)mark.locker())) { 486 assert(lock != mark.locker(), "must not re-lock the same lock"); 487 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock"); 488 lock->set_displaced_header(markWord::from_pointer(NULL)); 489 return; 490 } 491 492 // The object header will never be displaced to this lock, 493 // so it does not matter what the value is, except that it 494 // must be non-zero to avoid looking like a re-entrant lock, 495 // and must not look locked either. 496 lock->set_displaced_header(markWord::unused_mark()); 497 } else if (VerifyHeavyMonitors) { 498 guarantee(!obj->mark().has_locker(), "must not be stack-locked"); 499 } 500 501 // An async deflation can race after the inflate() call and before 502 // enter() can make the ObjectMonitor busy. enter() returns false if 503 // we have lost the race to async deflation and we simply try again. 504 while (true) { 505 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter); 506 if (monitor->enter(current)) { 507 return; 508 } 509 } 510 } 511 512 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) { 513 if (!useHeavyMonitors()) { 514 markWord mark = object->mark(); 515 516 markWord dhw = lock->displaced_header(); 517 if (dhw.value() == 0) { 518 // If the displaced header is NULL, then this exit matches up with 519 // a recursive enter. No real work to do here except for diagnostics. 520 #ifndef PRODUCT 521 if (mark != markWord::INFLATING()) { 522 // Only do diagnostics if we are not racing an inflation. Simply 523 // exiting a recursive enter of a Java Monitor that is being 524 // inflated is safe; see the has_monitor() comment below. 525 assert(!mark.is_neutral(), "invariant"); 526 assert(!mark.has_locker() || 527 current->is_lock_owned((address)mark.locker()), "invariant"); 528 if (mark.has_monitor()) { 529 // The BasicLock's displaced_header is marked as a recursive 530 // enter and we have an inflated Java Monitor (ObjectMonitor). 531 // This is a special case where the Java Monitor was inflated 532 // after this thread entered the stack-lock recursively. When a 533 // Java Monitor is inflated, we cannot safely walk the Java 534 // Monitor owner's stack and update the BasicLocks because a 535 // Java Monitor can be asynchronously inflated by a thread that 536 // does not own the Java Monitor. 537 ObjectMonitor* m = mark.monitor(); 538 assert(m->object()->mark() == mark, "invariant"); 539 assert(m->is_entered(current), "invariant"); 540 } 541 } 542 #endif 543 return; 544 } 545 546 if (mark == markWord::from_pointer(lock)) { 547 // If the object is stack-locked by the current thread, try to 548 // swing the displaced header from the BasicLock back to the mark. 549 assert(dhw.is_neutral(), "invariant"); 550 if (object->cas_set_mark(dhw, mark) == mark) { 551 return; 552 } 553 } 554 } else if (VerifyHeavyMonitors) { 555 guarantee(!object->mark().has_locker(), "must not be stack-locked"); 556 } 557 558 // We have to take the slow-path of possible inflation and then exit. 559 // The ObjectMonitor* can't be async deflated until ownership is 560 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 561 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal); 562 monitor->exit(current); 563 } 564 565 // ----------------------------------------------------------------------------- 566 // Class Loader support to workaround deadlocks on the class loader lock objects 567 // Also used by GC 568 // complete_exit()/reenter() are used to wait on a nested lock 569 // i.e. to give up an outer lock completely and then re-enter 570 // Used when holding nested locks - lock acquisition order: lock1 then lock2 571 // 1) complete_exit lock1 - saving recursion count 572 // 2) wait on lock2 573 // 3) when notified on lock2, unlock lock2 574 // 4) reenter lock1 with original recursion count 575 // 5) lock lock2 576 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 577 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) { 578 // The ObjectMonitor* can't be async deflated until ownership is 579 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 580 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal); 581 intptr_t ret_code = monitor->complete_exit(current); 582 return ret_code; 583 } 584 585 // NOTE: must use heavy weight monitor to handle complete_exit/reenter() 586 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) { 587 // An async deflation can race after the inflate() call and before 588 // reenter() -> enter() can make the ObjectMonitor busy. reenter() -> 589 // enter() returns false if we have lost the race to async deflation 590 // and we simply try again. 591 while (true) { 592 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal); 593 if (monitor->reenter(recursions, current)) { 594 return; 595 } 596 } 597 } 598 599 // ----------------------------------------------------------------------------- 600 // JNI locks on java objects 601 // NOTE: must use heavy weight monitor to handle jni monitor enter 602 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) { 603 if (obj->klass()->is_value_based()) { 604 handle_sync_on_value_based_class(obj, current); 605 } 606 607 // the current locking is from JNI instead of Java code 608 current->set_current_pending_monitor_is_from_java(false); 609 // An async deflation can race after the inflate() call and before 610 // enter() can make the ObjectMonitor busy. enter() returns false if 611 // we have lost the race to async deflation and we simply try again. 612 while (true) { 613 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter); 614 if (monitor->enter(current)) { 615 break; 616 } 617 } 618 current->set_current_pending_monitor_is_from_java(true); 619 } 620 621 // NOTE: must use heavy weight monitor to handle jni monitor exit 622 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) { 623 JavaThread* current = THREAD; 624 625 // The ObjectMonitor* can't be async deflated until ownership is 626 // dropped inside exit() and the ObjectMonitor* must be !is_busy(). 627 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit); 628 // If this thread has locked the object, exit the monitor. We 629 // intentionally do not use CHECK on check_owner because we must exit the 630 // monitor even if an exception was already pending. 631 if (monitor->check_owner(THREAD)) { 632 monitor->exit(current); 633 } 634 } 635 636 // ----------------------------------------------------------------------------- 637 // Internal VM locks on java objects 638 // standard constructor, allows locking failures 639 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) { 640 _thread = thread; 641 _thread->check_for_valid_safepoint_state(); 642 _obj = obj; 643 644 if (_obj() != NULL) { 645 ObjectSynchronizer::enter(_obj, &_lock, _thread); 646 } 647 } 648 649 ObjectLocker::~ObjectLocker() { 650 if (_obj() != NULL) { 651 ObjectSynchronizer::exit(_obj(), &_lock, _thread); 652 } 653 } 654 655 656 // ----------------------------------------------------------------------------- 657 // Wait/Notify/NotifyAll 658 // NOTE: must use heavy weight monitor to handle wait() 659 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) { 660 JavaThread* current = THREAD; 661 if (millis < 0) { 662 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative"); 663 } 664 // The ObjectMonitor* can't be async deflated because the _waiters 665 // field is incremented before ownership is dropped and decremented 666 // after ownership is regained. 667 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait); 668 669 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis); 670 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code 671 672 // This dummy call is in place to get around dtrace bug 6254741. Once 673 // that's fixed we can uncomment the following line, remove the call 674 // and change this function back into a "void" func. 675 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD); 676 int ret_code = dtrace_waited_probe(monitor, obj, THREAD); 677 return ret_code; 678 } 679 680 // No exception are possible in this case as we only use this internally when locking is 681 // correct and we have to wait until notified - so no interrupts or timeouts. 682 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, JavaThread* current) { 683 // The ObjectMonitor* can't be async deflated because the _waiters 684 // field is incremented before ownership is dropped and decremented 685 // after ownership is regained. 686 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait); 687 monitor->wait(0 /* wait-forever */, false /* not interruptible */, current); 688 } 689 690 void ObjectSynchronizer::notify(Handle obj, TRAPS) { 691 JavaThread* current = THREAD; 692 693 markWord mark = obj->mark(); 694 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 695 // Not inflated so there can't be any waiters to notify. 696 return; 697 } 698 // The ObjectMonitor* can't be async deflated until ownership is 699 // dropped by the calling thread. 700 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify); 701 monitor->notify(CHECK); 702 } 703 704 // NOTE: see comment of notify() 705 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) { 706 JavaThread* current = THREAD; 707 708 markWord mark = obj->mark(); 709 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) { 710 // Not inflated so there can't be any waiters to notify. 711 return; 712 } 713 // The ObjectMonitor* can't be async deflated until ownership is 714 // dropped by the calling thread. 715 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify); 716 monitor->notifyAll(CHECK); 717 } 718 719 // ----------------------------------------------------------------------------- 720 // Hash Code handling 721 722 struct SharedGlobals { 723 char _pad_prefix[OM_CACHE_LINE_SIZE]; 724 // This is a highly shared mostly-read variable. 725 // To avoid false-sharing it needs to be the sole occupant of a cache line. 726 volatile int stw_random; 727 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int)); 728 // Hot RW variable -- Sequester to avoid false-sharing 729 volatile int hc_sequence; 730 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int)); 731 }; 732 733 static SharedGlobals GVars; 734 735 markWord ObjectSynchronizer::read_stable_mark(oop obj) { 736 markWord mark = obj->mark_acquire(); 737 if (!mark.is_being_inflated()) { 738 return mark; // normal fast-path return 739 } 740 741 int its = 0; 742 for (;;) { 743 markWord mark = obj->mark_acquire(); 744 if (!mark.is_being_inflated()) { 745 return mark; // normal fast-path return 746 } 747 748 // The object is being inflated by some other thread. 749 // The caller of read_stable_mark() must wait for inflation to complete. 750 // Avoid live-lock. 751 752 ++its; 753 if (its > 10000 || !os::is_MP()) { 754 if (its & 1) { 755 os::naked_yield(); 756 } else { 757 // Note that the following code attenuates the livelock problem but is not 758 // a complete remedy. A more complete solution would require that the inflating 759 // thread hold the associated inflation lock. The following code simply restricts 760 // the number of spinners to at most one. We'll have N-2 threads blocked 761 // on the inflationlock, 1 thread holding the inflation lock and using 762 // a yield/park strategy, and 1 thread in the midst of inflation. 763 // A more refined approach would be to change the encoding of INFLATING 764 // to allow encapsulation of a native thread pointer. Threads waiting for 765 // inflation to complete would use CAS to push themselves onto a singly linked 766 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag 767 // and calling park(). When inflation was complete the thread that accomplished inflation 768 // would detach the list and set the markword to inflated with a single CAS and 769 // then for each thread on the list, set the flag and unpark() the thread. 770 771 // Index into the lock array based on the current object address. 772 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be"); 773 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1); 774 int YieldThenBlock = 0; 775 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant"); 776 gInflationLocks[ix]->lock(); 777 while (obj->mark_acquire() == markWord::INFLATING()) { 778 // Beware: naked_yield() is advisory and has almost no effect on some platforms 779 // so we periodically call current->_ParkEvent->park(1). 780 // We use a mixed spin/yield/block mechanism. 781 if ((YieldThenBlock++) >= 16) { 782 Thread::current()->_ParkEvent->park(1); 783 } else { 784 os::naked_yield(); 785 } 786 } 787 gInflationLocks[ix]->unlock(); 788 } 789 } else { 790 SpinPause(); // SMP-polite spinning 791 } 792 } 793 } 794 795 // Safely load a mark word from an object, even with racing stack-locking or monitor inflation. 796 // The protocol is a partial inflation-protocol: it installs INFLATING into the object's mark 797 // word in order to prevent an stack-locks or inflations from interferring (or detect such 798 // interference and retry), but then, instead of creating and installing a monitor, simply 799 // read and return the real mark word. 800 markWord ObjectSynchronizer::stable_mark(oop object) { 801 for (;;) { 802 const markWord mark = read_stable_mark(object); 803 assert(!mark.is_being_inflated(), "read_stable_mark must prevent inflating mark"); 804 805 // The mark can be in one of the following states: 806 // * Inflated - just return mark from inflated monitor 807 // * Stack-locked - coerce it to inflating, and then return displaced mark 808 // * Neutral - return mark 809 // * Marked - return mark 810 811 // CASE: inflated 812 if (mark.has_monitor()) { 813 ObjectMonitor* inf = mark.monitor(); 814 markWord dmw = inf->header(); 815 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 816 return dmw; 817 } 818 819 // CASE: stack-locked 820 // Could be stack-locked either by this thread or by some other thread. 821 if (mark.has_locker()) { 822 BasicLock* lock = mark.locker(); 823 if (Thread::current()->is_lock_owned((address)lock)) { 824 // If locked by this thread, it is safe to access the displaced header. 825 markWord dmw = lock->displaced_header(); 826 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 827 return dmw; 828 } 829 830 // Otherwise, attempt to temporarily install INFLATING into the mark-word, 831 // to prevent inflation or unlocking by competing thread. 832 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark); 833 if (cmp != mark) { 834 continue; // Interference -- just retry 835 } 836 837 // fetch the displaced mark from the owner's stack. 838 // The owner can't die or unwind past the lock while our INFLATING 839 // object is in the mark. Furthermore the owner can't complete 840 // an unlock on the object, either. 841 markWord dmw = mark.displaced_mark_helper(); 842 // Catch if the object's header is not neutral (not locked and 843 // not marked is what we care about here). 844 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 845 846 // Must preserve store ordering. The monitor state must 847 // be stable at the time of publishing the monitor address. 848 assert(object->mark() == markWord::INFLATING(), "invariant"); 849 // Release semantics so that above set_object() is seen first. 850 object->release_set_mark(mark); 851 852 return dmw; 853 } 854 855 // CASE: neutral or marked (for GC) 856 // Catch if the object's header is not neutral or marked (it must not be locked). 857 assert(mark.is_neutral() || mark.is_marked(), "invariant: header=" INTPTR_FORMAT, mark.value()); 858 return mark; 859 } 860 } 861 862 // hashCode() generation : 863 // 864 // Possibilities: 865 // * MD5Digest of {obj,stw_random} 866 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function. 867 // * A DES- or AES-style SBox[] mechanism 868 // * One of the Phi-based schemes, such as: 869 // 2654435761 = 2^32 * Phi (golden ratio) 870 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ; 871 // * A variation of Marsaglia's shift-xor RNG scheme. 872 // * (obj ^ stw_random) is appealing, but can result 873 // in undesirable regularity in the hashCode values of adjacent objects 874 // (objects allocated back-to-back, in particular). This could potentially 875 // result in hashtable collisions and reduced hashtable efficiency. 876 // There are simple ways to "diffuse" the middle address bits over the 877 // generated hashCode values: 878 879 static inline intptr_t get_next_hash(Thread* current, oop obj) { 880 intptr_t value = 0; 881 if (hashCode == 0) { 882 // This form uses global Park-Miller RNG. 883 // On MP system we'll have lots of RW access to a global, so the 884 // mechanism induces lots of coherency traffic. 885 value = os::random(); 886 } else if (hashCode == 1) { 887 // This variation has the property of being stable (idempotent) 888 // between STW operations. This can be useful in some of the 1-0 889 // synchronization schemes. 890 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3; 891 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random; 892 } else if (hashCode == 2) { 893 value = 1; // for sensitivity testing 894 } else if (hashCode == 3) { 895 value = ++GVars.hc_sequence; 896 } else if (hashCode == 4) { 897 value = cast_from_oop<intptr_t>(obj); 898 } else { 899 // Marsaglia's xor-shift scheme with thread-specific state 900 // This is probably the best overall implementation -- we'll 901 // likely make this the default in future releases. 902 unsigned t = current->_hashStateX; 903 t ^= (t << 11); 904 current->_hashStateX = current->_hashStateY; 905 current->_hashStateY = current->_hashStateZ; 906 current->_hashStateZ = current->_hashStateW; 907 unsigned v = current->_hashStateW; 908 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)); 909 current->_hashStateW = v; 910 value = v; 911 } 912 913 value &= markWord::hash_mask; 914 if (value == 0) value = 0xBAD; 915 assert(value != markWord::no_hash, "invariant"); 916 return value; 917 } 918 919 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) { 920 921 while (true) { 922 ObjectMonitor* monitor = NULL; 923 markWord temp, test; 924 intptr_t hash; 925 markWord mark = read_stable_mark(obj); 926 if (VerifyHeavyMonitors) { 927 assert(UseHeavyMonitors, "+VerifyHeavyMonitors requires +UseHeavyMonitors"); 928 guarantee(!mark.has_locker(), "must not be stack locked"); 929 } 930 if (mark.is_neutral()) { // if this is a normal header 931 hash = mark.hash(); 932 if (hash != 0) { // if it has a hash, just return it 933 return hash; 934 } 935 hash = get_next_hash(current, obj); // get a new hash 936 temp = mark.copy_set_hash(hash); // merge the hash into header 937 // try to install the hash 938 test = obj->cas_set_mark(temp, mark); 939 if (test == mark) { // if the hash was installed, return it 940 return hash; 941 } 942 // Failed to install the hash. It could be that another thread 943 // installed the hash just before our attempt or inflation has 944 // occurred or... so we fall thru to inflate the monitor for 945 // stability and then install the hash. 946 } else if (mark.has_monitor()) { 947 monitor = mark.monitor(); 948 temp = monitor->header(); 949 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 950 hash = temp.hash(); 951 if (hash != 0) { 952 // It has a hash. 953 954 // Separate load of dmw/header above from the loads in 955 // is_being_async_deflated(). 956 957 // dmw/header and _contentions may get written by different threads. 958 // Make sure to observe them in the same order when having several observers. 959 OrderAccess::loadload_for_IRIW(); 960 961 if (monitor->is_being_async_deflated()) { 962 // But we can't safely use the hash if we detect that async 963 // deflation has occurred. So we attempt to restore the 964 // header/dmw to the object's header so that we only retry 965 // once if the deflater thread happens to be slow. 966 monitor->install_displaced_markword_in_object(obj); 967 continue; 968 } 969 return hash; 970 } 971 // Fall thru so we only have one place that installs the hash in 972 // the ObjectMonitor. 973 } else if (current->is_lock_owned((address)mark.locker())) { 974 // This is a stack lock owned by the calling thread so fetch the 975 // displaced markWord from the BasicLock on the stack. 976 temp = mark.displaced_mark_helper(); 977 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 978 hash = temp.hash(); 979 if (hash != 0) { // if it has a hash, just return it 980 return hash; 981 } 982 // WARNING: 983 // The displaced header in the BasicLock on a thread's stack 984 // is strictly immutable. It CANNOT be changed in ANY cases. 985 // So we have to inflate the stack lock into an ObjectMonitor 986 // even if the current thread owns the lock. The BasicLock on 987 // a thread's stack can be asynchronously read by other threads 988 // during an inflate() call so any change to that stack memory 989 // may not propagate to other threads correctly. 990 } 991 992 // Inflate the monitor to set the hash. 993 994 // An async deflation can race after the inflate() call and before we 995 // can update the ObjectMonitor's header with the hash value below. 996 monitor = inflate(current, obj, inflate_cause_hash_code); 997 // Load ObjectMonitor's header/dmw field and see if it has a hash. 998 mark = monitor->header(); 999 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 1000 hash = mark.hash(); 1001 if (hash == 0) { // if it does not have a hash 1002 hash = get_next_hash(current, obj); // get a new hash 1003 temp = mark.copy_set_hash(hash) ; // merge the hash into header 1004 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value()); 1005 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value()); 1006 test = markWord(v); 1007 if (test != mark) { 1008 // The attempt to update the ObjectMonitor's header/dmw field 1009 // did not work. This can happen if another thread managed to 1010 // merge in the hash just before our cmpxchg(). 1011 // If we add any new usages of the header/dmw field, this code 1012 // will need to be updated. 1013 hash = test.hash(); 1014 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value()); 1015 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash"); 1016 } 1017 if (monitor->is_being_async_deflated()) { 1018 // If we detect that async deflation has occurred, then we 1019 // attempt to restore the header/dmw to the object's header 1020 // so that we only retry once if the deflater thread happens 1021 // to be slow. 1022 monitor->install_displaced_markword_in_object(obj); 1023 continue; 1024 } 1025 } 1026 // We finally get the hash. 1027 return hash; 1028 } 1029 } 1030 1031 // Deprecated -- use FastHashCode() instead. 1032 1033 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) { 1034 return FastHashCode(Thread::current(), obj()); 1035 } 1036 1037 1038 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current, 1039 Handle h_obj) { 1040 assert(current == JavaThread::current(), "Can only be called on current thread"); 1041 oop obj = h_obj(); 1042 1043 markWord mark = read_stable_mark(obj); 1044 1045 // Uncontended case, header points to stack 1046 if (mark.has_locker()) { 1047 return current->is_lock_owned((address)mark.locker()); 1048 } 1049 // Contended case, header points to ObjectMonitor (tagged pointer) 1050 if (mark.has_monitor()) { 1051 // The first stage of async deflation does not affect any field 1052 // used by this comparison so the ObjectMonitor* is usable here. 1053 ObjectMonitor* monitor = mark.monitor(); 1054 return monitor->is_entered(current) != 0; 1055 } 1056 // Unlocked case, header in place 1057 assert(mark.is_neutral(), "sanity check"); 1058 return false; 1059 } 1060 1061 // FIXME: jvmti should call this 1062 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) { 1063 oop obj = h_obj(); 1064 address owner = NULL; 1065 1066 markWord mark = read_stable_mark(obj); 1067 1068 // Uncontended case, header points to stack 1069 if (mark.has_locker()) { 1070 owner = (address) mark.locker(); 1071 } 1072 1073 // Contended case, header points to ObjectMonitor (tagged pointer) 1074 else if (mark.has_monitor()) { 1075 // The first stage of async deflation does not affect any field 1076 // used by this comparison so the ObjectMonitor* is usable here. 1077 ObjectMonitor* monitor = mark.monitor(); 1078 assert(monitor != NULL, "monitor should be non-null"); 1079 owner = (address) monitor->owner(); 1080 } 1081 1082 if (owner != NULL) { 1083 // owning_thread_from_monitor_owner() may also return NULL here 1084 return Threads::owning_thread_from_monitor_owner(t_list, owner); 1085 } 1086 1087 // Unlocked case, header in place 1088 // Cannot have assertion since this object may have been 1089 // locked by another thread when reaching here. 1090 // assert(mark.is_neutral(), "sanity check"); 1091 1092 return NULL; 1093 } 1094 1095 // Visitors ... 1096 1097 // Iterate ObjectMonitors where the owner == thread; this does NOT include 1098 // ObjectMonitors where owner is set to a stack lock address in thread. 1099 // 1100 // This version of monitors_iterate() works with the in-use monitor list. 1101 // 1102 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) { 1103 MonitorList::Iterator iter = _in_use_list.iterator(); 1104 while (iter.has_next()) { 1105 ObjectMonitor* mid = iter.next(); 1106 if (mid->owner() != thread) { 1107 // Not owned by the target thread and intentionally skips when owner 1108 // is set to a stack lock address in the target thread. 1109 continue; 1110 } 1111 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) { 1112 // Only process with closure if the object is set. 1113 1114 // monitors_iterate() is only called at a safepoint or when the 1115 // target thread is suspended or when the target thread is 1116 // operating on itself. The current closures in use today are 1117 // only interested in an owned ObjectMonitor and ownership 1118 // cannot be dropped under the calling contexts so the 1119 // ObjectMonitor cannot be async deflated. 1120 closure->do_monitor(mid); 1121 } 1122 } 1123 } 1124 1125 // This version of monitors_iterate() works with the specified linked list. 1126 // 1127 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, 1128 ObjectMonitorsHashtable::PtrList* list, 1129 JavaThread* thread) { 1130 typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator; 1131 ObjectMonitorIterator iter(list->head()); 1132 while (!iter.is_empty()) { 1133 ObjectMonitor* mid = *iter.next(); 1134 // Owner set to a stack lock address in thread should never be seen here: 1135 assert(mid->owner() == thread, "must be"); 1136 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) { 1137 // Only process with closure if the object is set. 1138 1139 // monitors_iterate() is only called at a safepoint or when the 1140 // target thread is suspended or when the target thread is 1141 // operating on itself. The current closures in use today are 1142 // only interested in an owned ObjectMonitor and ownership 1143 // cannot be dropped under the calling contexts so the 1144 // ObjectMonitor cannot be async deflated. 1145 closure->do_monitor(mid); 1146 } 1147 } 1148 } 1149 1150 static bool monitors_used_above_threshold(MonitorList* list) { 1151 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy 1152 return false; 1153 } 1154 // Start with ceiling based on a per-thread estimate: 1155 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling(); 1156 size_t old_ceiling = ceiling; 1157 if (ceiling < list->max()) { 1158 // The max used by the system has exceeded the ceiling so use that: 1159 ceiling = list->max(); 1160 } 1161 size_t monitors_used = list->count(); 1162 if (monitors_used == 0) { // empty list is easy 1163 return false; 1164 } 1165 if (NoAsyncDeflationProgressMax != 0 && 1166 _no_progress_cnt >= NoAsyncDeflationProgressMax) { 1167 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0; 1168 size_t new_ceiling = ceiling + (ceiling * remainder) + 1; 1169 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling); 1170 log_info(monitorinflation)("Too many deflations without progress; " 1171 "bumping in_use_list_ceiling from " SIZE_FORMAT 1172 " to " SIZE_FORMAT, old_ceiling, new_ceiling); 1173 _no_progress_cnt = 0; 1174 ceiling = new_ceiling; 1175 } 1176 1177 // Check if our monitor usage is above the threshold: 1178 size_t monitor_usage = (monitors_used * 100LL) / ceiling; 1179 return int(monitor_usage) > MonitorUsedDeflationThreshold; 1180 } 1181 1182 size_t ObjectSynchronizer::in_use_list_ceiling() { 1183 return _in_use_list_ceiling; 1184 } 1185 1186 void ObjectSynchronizer::dec_in_use_list_ceiling() { 1187 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate); 1188 } 1189 1190 void ObjectSynchronizer::inc_in_use_list_ceiling() { 1191 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate); 1192 } 1193 1194 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) { 1195 _in_use_list_ceiling = new_value; 1196 } 1197 1198 bool ObjectSynchronizer::is_async_deflation_needed() { 1199 if (is_async_deflation_requested()) { 1200 // Async deflation request. 1201 return true; 1202 } 1203 if (AsyncDeflationInterval > 0 && 1204 time_since_last_async_deflation_ms() > AsyncDeflationInterval && 1205 monitors_used_above_threshold(&_in_use_list)) { 1206 // It's been longer than our specified deflate interval and there 1207 // are too many monitors in use. We don't deflate more frequently 1208 // than AsyncDeflationInterval (unless is_async_deflation_requested) 1209 // in order to not swamp the MonitorDeflationThread. 1210 return true; 1211 } 1212 return false; 1213 } 1214 1215 bool ObjectSynchronizer::request_deflate_idle_monitors() { 1216 JavaThread* current = JavaThread::current(); 1217 bool ret_code = false; 1218 1219 jlong last_time = last_async_deflation_time_ns(); 1220 set_is_async_deflation_requested(true); 1221 { 1222 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag); 1223 ml.notify_all(); 1224 } 1225 const int N_CHECKS = 5; 1226 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds 1227 if (last_async_deflation_time_ns() > last_time) { 1228 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i); 1229 ret_code = true; 1230 break; 1231 } 1232 { 1233 // JavaThread has to honor the blocking protocol. 1234 ThreadBlockInVM tbivm(current); 1235 os::naked_short_sleep(999); // sleep for almost 1 second 1236 } 1237 } 1238 if (!ret_code) { 1239 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS); 1240 } 1241 1242 return ret_code; 1243 } 1244 1245 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() { 1246 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS); 1247 } 1248 1249 static void post_monitor_inflate_event(EventJavaMonitorInflate* event, 1250 const oop obj, 1251 ObjectSynchronizer::InflateCause cause) { 1252 assert(event != NULL, "invariant"); 1253 assert(event->should_commit(), "invariant"); 1254 event->set_monitorClass(obj->klass()); 1255 event->set_address((uintptr_t)(void*)obj); 1256 event->set_cause((u1)cause); 1257 event->commit(); 1258 } 1259 1260 // Fast path code shared by multiple functions 1261 void ObjectSynchronizer::inflate_helper(oop obj) { 1262 markWord mark = obj->mark_acquire(); 1263 if (mark.has_monitor()) { 1264 ObjectMonitor* monitor = mark.monitor(); 1265 markWord dmw = monitor->header(); 1266 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value()); 1267 return; 1268 } 1269 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal); 1270 } 1271 1272 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object, 1273 const InflateCause cause) { 1274 EventJavaMonitorInflate event; 1275 1276 for (;;) { 1277 const markWord mark = object->mark_acquire(); 1278 1279 // The mark can be in one of the following states: 1280 // * Inflated - just return 1281 // * Stack-locked - coerce it to inflated 1282 // * INFLATING - busy wait for conversion to complete 1283 // * Neutral - aggressively inflate the object. 1284 1285 // CASE: inflated 1286 if (mark.has_monitor()) { 1287 ObjectMonitor* inf = mark.monitor(); 1288 markWord dmw = inf->header(); 1289 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1290 return inf; 1291 } 1292 1293 // CASE: inflation in progress - inflating over a stack-lock. 1294 // Some other thread is converting from stack-locked to inflated. 1295 // Only that thread can complete inflation -- other threads must wait. 1296 // The INFLATING value is transient. 1297 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish. 1298 // We could always eliminate polling by parking the thread on some auxiliary list. 1299 if (mark == markWord::INFLATING()) { 1300 read_stable_mark(object); 1301 continue; 1302 } 1303 1304 // CASE: stack-locked 1305 // Could be stack-locked either by this thread or by some other thread. 1306 // 1307 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting 1308 // to install INFLATING into the mark word. We originally installed INFLATING, 1309 // allocated the ObjectMonitor, and then finally STed the address of the 1310 // ObjectMonitor into the mark. This was correct, but artificially lengthened 1311 // the interval in which INFLATING appeared in the mark, thus increasing 1312 // the odds of inflation contention. 1313 1314 LogStreamHandle(Trace, monitorinflation) lsh; 1315 1316 if (mark.has_locker()) { 1317 ObjectMonitor* m = new ObjectMonitor(object); 1318 // Optimistically prepare the ObjectMonitor - anticipate successful CAS 1319 // We do this before the CAS in order to minimize the length of time 1320 // in which INFLATING appears in the mark. 1321 1322 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark); 1323 if (cmp != mark) { 1324 delete m; 1325 continue; // Interference -- just retry 1326 } 1327 1328 // We've successfully installed INFLATING (0) into the mark-word. 1329 // This is the only case where 0 will appear in a mark-word. 1330 // Only the singular thread that successfully swings the mark-word 1331 // to 0 can perform (or more precisely, complete) inflation. 1332 // 1333 // Why do we CAS a 0 into the mark-word instead of just CASing the 1334 // mark-word from the stack-locked value directly to the new inflated state? 1335 // Consider what happens when a thread unlocks a stack-locked object. 1336 // It attempts to use CAS to swing the displaced header value from the 1337 // on-stack BasicLock back into the object header. Recall also that the 1338 // header value (hash code, etc) can reside in (a) the object header, or 1339 // (b) a displaced header associated with the stack-lock, or (c) a displaced 1340 // header in an ObjectMonitor. The inflate() routine must copy the header 1341 // value from the BasicLock on the owner's stack to the ObjectMonitor, all 1342 // the while preserving the hashCode stability invariants. If the owner 1343 // decides to release the lock while the value is 0, the unlock will fail 1344 // and control will eventually pass from slow_exit() to inflate. The owner 1345 // will then spin, waiting for the 0 value to disappear. Put another way, 1346 // the 0 causes the owner to stall if the owner happens to try to 1347 // drop the lock (restoring the header from the BasicLock to the object) 1348 // while inflation is in-progress. This protocol avoids races that might 1349 // would otherwise permit hashCode values to change or "flicker" for an object. 1350 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable. 1351 // 0 serves as a "BUSY" inflate-in-progress indicator. 1352 1353 1354 // fetch the displaced mark from the owner's stack. 1355 // The owner can't die or unwind past the lock while our INFLATING 1356 // object is in the mark. Furthermore the owner can't complete 1357 // an unlock on the object, either. 1358 markWord dmw = mark.displaced_mark_helper(); 1359 // Catch if the object's header is not neutral (not locked and 1360 // not marked is what we care about here). 1361 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value()); 1362 1363 // Setup monitor fields to proper values -- prepare the monitor 1364 m->set_header(dmw); 1365 1366 // Optimization: if the mark.locker stack address is associated 1367 // with this thread we could simply set m->_owner = current. 1368 // Note that a thread can inflate an object 1369 // that it has stack-locked -- as might happen in wait() -- directly 1370 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom. 1371 m->set_owner_from(NULL, mark.locker()); 1372 // TODO-FIXME: assert BasicLock->dhw != 0. 1373 1374 // Must preserve store ordering. The monitor state must 1375 // be stable at the time of publishing the monitor address. 1376 guarantee(object->mark() == markWord::INFLATING(), "invariant"); 1377 // Release semantics so that above set_object() is seen first. 1378 object->release_set_mark(markWord::encode(m)); 1379 1380 // Once ObjectMonitor is configured and the object is associated 1381 // with the ObjectMonitor, it is safe to allow async deflation: 1382 _in_use_list.add(m); 1383 1384 // Hopefully the performance counters are allocated on distinct cache lines 1385 // to avoid false sharing on MP systems ... 1386 OM_PERFDATA_OP(Inflations, inc()); 1387 if (log_is_enabled(Trace, monitorinflation)) { 1388 ResourceMark rm(current); 1389 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark=" 1390 INTPTR_FORMAT ", type='%s'", p2i(object), 1391 object->mark().value(), object->klass()->external_name()); 1392 } 1393 if (event.should_commit()) { 1394 post_monitor_inflate_event(&event, object, cause); 1395 } 1396 return m; 1397 } 1398 1399 // CASE: neutral 1400 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner. 1401 // If we know we're inflating for entry it's better to inflate by swinging a 1402 // pre-locked ObjectMonitor pointer into the object header. A successful 1403 // CAS inflates the object *and* confers ownership to the inflating thread. 1404 // In the current implementation we use a 2-step mechanism where we CAS() 1405 // to inflate and then CAS() again to try to swing _owner from NULL to current. 1406 // An inflateTry() method that we could call from enter() would be useful. 1407 1408 // Catch if the object's header is not neutral (not locked and 1409 // not marked is what we care about here). 1410 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value()); 1411 ObjectMonitor* m = new ObjectMonitor(object); 1412 // prepare m for installation - set monitor to initial state 1413 m->set_header(mark); 1414 1415 if (object->cas_set_mark(markWord::encode(m), mark) != mark) { 1416 delete m; 1417 m = NULL; 1418 continue; 1419 // interference - the markword changed - just retry. 1420 // The state-transitions are one-way, so there's no chance of 1421 // live-lock -- "Inflated" is an absorbing state. 1422 } 1423 1424 // Once the ObjectMonitor is configured and object is associated 1425 // with the ObjectMonitor, it is safe to allow async deflation: 1426 _in_use_list.add(m); 1427 1428 // Hopefully the performance counters are allocated on distinct 1429 // cache lines to avoid false sharing on MP systems ... 1430 OM_PERFDATA_OP(Inflations, inc()); 1431 if (log_is_enabled(Trace, monitorinflation)) { 1432 ResourceMark rm(current); 1433 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark=" 1434 INTPTR_FORMAT ", type='%s'", p2i(object), 1435 object->mark().value(), object->klass()->external_name()); 1436 } 1437 if (event.should_commit()) { 1438 post_monitor_inflate_event(&event, object, cause); 1439 } 1440 return m; 1441 } 1442 } 1443 1444 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name, 1445 const char* cnt_name, size_t cnt, 1446 LogStream* ls, elapsedTimer* timer_p) { 1447 if (!SafepointMechanism::should_process(current)) { 1448 return; 1449 } 1450 1451 // A safepoint/handshake has started. 1452 if (ls != NULL) { 1453 timer_p->stop(); 1454 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling=" 1455 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1456 op_name, cnt_name, cnt, in_use_list_ceiling(), 1457 _in_use_list.count(), _in_use_list.max()); 1458 } 1459 1460 { 1461 // Honor block request. 1462 ThreadBlockInVM tbivm(current); 1463 } 1464 1465 if (ls != NULL) { 1466 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT 1467 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name, 1468 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1469 timer_p->start(); 1470 } 1471 } 1472 1473 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle 1474 // ObjectMonitors. Returns the number of deflated ObjectMonitors. 1475 // 1476 // If table != nullptr, we gather owned ObjectMonitors indexed by the 1477 // owner in the table. Please note that ObjectMonitors where the owner 1478 // is set to a stack lock address are NOT associated with the JavaThread 1479 // that holds that stack lock. All of the current consumers of 1480 // ObjectMonitorsHashtable info only care about JNI locked monitors and 1481 // those do not have the owner set to a stack lock address. 1482 // 1483 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls, 1484 elapsedTimer* timer_p, 1485 ObjectMonitorsHashtable* table) { 1486 MonitorList::Iterator iter = _in_use_list.iterator(); 1487 size_t deflated_count = 0; 1488 1489 while (iter.has_next()) { 1490 if (deflated_count >= (size_t)MonitorDeflationMax) { 1491 break; 1492 } 1493 ObjectMonitor* mid = iter.next(); 1494 if (mid->deflate_monitor()) { 1495 deflated_count++; 1496 } else if (table != nullptr) { 1497 // The caller is interested in the owned ObjectMonitors. This does 1498 // not include when owner is set to a stack lock address in thread. 1499 // This also does not capture unowned ObjectMonitors that cannot be 1500 // deflated because of a waiter. 1501 void* key = mid->owner(); 1502 // Since deflate_idle_monitors() and deflate_monitor_list() can be 1503 // called more than once, we have to make sure the entry has not 1504 // already been added. 1505 if (key != nullptr && !table->has_entry(key, mid)) { 1506 table->add_entry(key, mid); 1507 } 1508 } 1509 1510 if (current->is_Java_thread()) { 1511 // A JavaThread must check for a safepoint/handshake and honor it. 1512 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count", 1513 deflated_count, ls, timer_p); 1514 } 1515 } 1516 1517 return deflated_count; 1518 } 1519 1520 class HandshakeForDeflation : public HandshakeClosure { 1521 public: 1522 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {} 1523 1524 void do_thread(Thread* thread) { 1525 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread=" 1526 INTPTR_FORMAT, p2i(thread)); 1527 } 1528 }; 1529 1530 class VM_RendezvousGCThreads : public VM_Operation { 1531 public: 1532 bool evaluate_at_safepoint() const override { return false; } 1533 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; } 1534 void doit() override { 1535 SuspendibleThreadSet::synchronize(); 1536 SuspendibleThreadSet::desynchronize(); 1537 }; 1538 }; 1539 1540 // This function is called by the MonitorDeflationThread to deflate 1541 // ObjectMonitors. It is also called via do_final_audit_and_print_stats() 1542 // and VM_ThreadDump::doit() by the VMThread. 1543 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) { 1544 Thread* current = Thread::current(); 1545 if (current->is_Java_thread()) { 1546 // The async deflation request has been processed. 1547 _last_async_deflation_time_ns = os::javaTimeNanos(); 1548 set_is_async_deflation_requested(false); 1549 } 1550 1551 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1552 LogStreamHandle(Info, monitorinflation) lsh_info; 1553 LogStream* ls = NULL; 1554 if (log_is_enabled(Debug, monitorinflation)) { 1555 ls = &lsh_debug; 1556 } else if (log_is_enabled(Info, monitorinflation)) { 1557 ls = &lsh_info; 1558 } 1559 1560 elapsedTimer timer; 1561 if (ls != NULL) { 1562 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1563 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1564 timer.start(); 1565 } 1566 1567 // Deflate some idle ObjectMonitors. 1568 size_t deflated_count = deflate_monitor_list(current, ls, &timer, table); 1569 if (deflated_count > 0 || is_final_audit()) { 1570 // There are ObjectMonitors that have been deflated or this is the 1571 // final audit and all the remaining ObjectMonitors have been 1572 // deflated, BUT the MonitorDeflationThread blocked for the final 1573 // safepoint during unlinking. 1574 1575 // Unlink deflated ObjectMonitors from the in-use list. 1576 ResourceMark rm; 1577 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count); 1578 size_t unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, 1579 &delete_list); 1580 if (current->is_Java_thread()) { 1581 if (ls != NULL) { 1582 timer.stop(); 1583 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT 1584 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count=" 1585 SIZE_FORMAT ", max=" SIZE_FORMAT, 1586 unlinked_count, in_use_list_ceiling(), 1587 _in_use_list.count(), _in_use_list.max()); 1588 } 1589 1590 // A JavaThread needs to handshake in order to safely free the 1591 // ObjectMonitors that were deflated in this cycle. 1592 // Also, we sync and desync GC threads around the handshake, so that they can 1593 // safely read the mark-word and look-through to the object-monitor, without 1594 // being afraid that the object-monitor is going away. 1595 HandshakeForDeflation hfd_hc; 1596 Handshake::execute(&hfd_hc); 1597 VM_RendezvousGCThreads sync_gc; 1598 VMThread::execute(&sync_gc); 1599 1600 if (ls != NULL) { 1601 ls->print_cr("after handshaking: in_use_list stats: ceiling=" 1602 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1603 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1604 timer.start(); 1605 } 1606 } 1607 1608 // After the handshake, safely free the ObjectMonitors that were 1609 // deflated in this cycle. 1610 size_t deleted_count = 0; 1611 for (ObjectMonitor* monitor: delete_list) { 1612 delete monitor; 1613 deleted_count++; 1614 1615 if (current->is_Java_thread()) { 1616 // A JavaThread must check for a safepoint/handshake and honor it. 1617 chk_for_block_req(JavaThread::cast(current), "deletion", "deleted_count", 1618 deleted_count, ls, &timer); 1619 } 1620 } 1621 } 1622 1623 if (ls != NULL) { 1624 timer.stop(); 1625 if (deflated_count != 0 || log_is_enabled(Debug, monitorinflation)) { 1626 ls->print_cr("deflated " SIZE_FORMAT " monitors in %3.7f secs", 1627 deflated_count, timer.seconds()); 1628 } 1629 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, 1630 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max()); 1631 if (table != nullptr) { 1632 ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT, 1633 table->key_count(), table->om_count()); 1634 } 1635 } 1636 1637 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count())); 1638 OM_PERFDATA_OP(Deflations, inc(deflated_count)); 1639 1640 GVars.stw_random = os::random(); 1641 1642 if (deflated_count != 0) { 1643 _no_progress_cnt = 0; 1644 } else { 1645 _no_progress_cnt++; 1646 } 1647 1648 return deflated_count; 1649 } 1650 1651 // Monitor cleanup on JavaThread::exit 1652 1653 // Iterate through monitor cache and attempt to release thread's monitors 1654 class ReleaseJavaMonitorsClosure: public MonitorClosure { 1655 private: 1656 JavaThread* _thread; 1657 1658 public: 1659 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {} 1660 void do_monitor(ObjectMonitor* mid) { 1661 (void)mid->complete_exit(_thread); 1662 } 1663 }; 1664 1665 // Release all inflated monitors owned by current thread. Lightweight monitors are 1666 // ignored. This is meant to be called during JNI thread detach which assumes 1667 // all remaining monitors are heavyweight. All exceptions are swallowed. 1668 // Scanning the extant monitor list can be time consuming. 1669 // A simple optimization is to add a per-thread flag that indicates a thread 1670 // called jni_monitorenter() during its lifetime. 1671 // 1672 // Instead of NoSafepointVerifier it might be cheaper to 1673 // use an idiom of the form: 1674 // auto int tmp = SafepointSynchronize::_safepoint_counter ; 1675 // <code that must not run at safepoint> 1676 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ; 1677 // Since the tests are extremely cheap we could leave them enabled 1678 // for normal product builds. 1679 1680 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) { 1681 assert(current == JavaThread::current(), "must be current Java thread"); 1682 NoSafepointVerifier nsv; 1683 ReleaseJavaMonitorsClosure rjmc(current); 1684 ObjectSynchronizer::monitors_iterate(&rjmc, current); 1685 assert(!current->has_pending_exception(), "Should not be possible"); 1686 current->clear_pending_exception(); 1687 } 1688 1689 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) { 1690 switch (cause) { 1691 case inflate_cause_vm_internal: return "VM Internal"; 1692 case inflate_cause_monitor_enter: return "Monitor Enter"; 1693 case inflate_cause_wait: return "Monitor Wait"; 1694 case inflate_cause_notify: return "Monitor Notify"; 1695 case inflate_cause_hash_code: return "Monitor Hash Code"; 1696 case inflate_cause_jni_enter: return "JNI Monitor Enter"; 1697 case inflate_cause_jni_exit: return "JNI Monitor Exit"; 1698 default: 1699 ShouldNotReachHere(); 1700 } 1701 return "Unknown"; 1702 } 1703 1704 //------------------------------------------------------------------------------ 1705 // Debugging code 1706 1707 u_char* ObjectSynchronizer::get_gvars_addr() { 1708 return (u_char*)&GVars; 1709 } 1710 1711 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() { 1712 return (u_char*)&GVars.hc_sequence; 1713 } 1714 1715 size_t ObjectSynchronizer::get_gvars_size() { 1716 return sizeof(SharedGlobals); 1717 } 1718 1719 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() { 1720 return (u_char*)&GVars.stw_random; 1721 } 1722 1723 // Do the final audit and print of ObjectMonitor stats; must be done 1724 // by the VMThread at VM exit time. 1725 void ObjectSynchronizer::do_final_audit_and_print_stats() { 1726 assert(Thread::current()->is_VM_thread(), "sanity check"); 1727 1728 if (is_final_audit()) { // Only do the audit once. 1729 return; 1730 } 1731 set_is_final_audit(); 1732 1733 if (log_is_enabled(Info, monitorinflation)) { 1734 // Do a deflation in order to reduce the in-use monitor population 1735 // that is reported by ObjectSynchronizer::log_in_use_monitor_details() 1736 // which is called by ObjectSynchronizer::audit_and_print_stats(). 1737 while (ObjectSynchronizer::deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) >= (size_t)MonitorDeflationMax) { 1738 ; // empty 1739 } 1740 // The other audit_and_print_stats() call is done at the Debug 1741 // level at a safepoint in ObjectSynchronizer::do_safepoint_work(). 1742 ObjectSynchronizer::audit_and_print_stats(true /* on_exit */); 1743 } 1744 } 1745 1746 // This function can be called at a safepoint or it can be called when 1747 // we are trying to exit the VM. When we are trying to exit the VM, the 1748 // list walker functions can run in parallel with the other list 1749 // operations so spin-locking is used for safety. 1750 // 1751 // Calls to this function can be added in various places as a debugging 1752 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor 1753 // details logged at the Info level and 'false' for the 'on_exit' 1754 // parameter to have in-use monitor details logged at the Trace level. 1755 // 1756 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) { 1757 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant"); 1758 1759 LogStreamHandle(Debug, monitorinflation) lsh_debug; 1760 LogStreamHandle(Info, monitorinflation) lsh_info; 1761 LogStreamHandle(Trace, monitorinflation) lsh_trace; 1762 LogStream* ls = NULL; 1763 if (log_is_enabled(Trace, monitorinflation)) { 1764 ls = &lsh_trace; 1765 } else if (log_is_enabled(Debug, monitorinflation)) { 1766 ls = &lsh_debug; 1767 } else if (log_is_enabled(Info, monitorinflation)) { 1768 ls = &lsh_info; 1769 } 1770 assert(ls != NULL, "sanity check"); 1771 1772 int error_cnt = 0; 1773 1774 ls->print_cr("Checking in_use_list:"); 1775 chk_in_use_list(ls, &error_cnt); 1776 1777 if (error_cnt == 0) { 1778 ls->print_cr("No errors found in in_use_list checks."); 1779 } else { 1780 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt); 1781 } 1782 1783 if ((on_exit && log_is_enabled(Info, monitorinflation)) || 1784 (!on_exit && log_is_enabled(Trace, monitorinflation))) { 1785 // When exiting this log output is at the Info level. When called 1786 // at a safepoint, this log output is at the Trace level since 1787 // there can be a lot of it. 1788 log_in_use_monitor_details(ls); 1789 } 1790 1791 ls->flush(); 1792 1793 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt); 1794 } 1795 1796 // Check the in_use_list; log the results of the checks. 1797 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) { 1798 size_t l_in_use_count = _in_use_list.count(); 1799 size_t l_in_use_max = _in_use_list.max(); 1800 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count, 1801 l_in_use_max); 1802 1803 size_t ck_in_use_count = 0; 1804 MonitorList::Iterator iter = _in_use_list.iterator(); 1805 while (iter.has_next()) { 1806 ObjectMonitor* mid = iter.next(); 1807 chk_in_use_entry(mid, out, error_cnt_p); 1808 ck_in_use_count++; 1809 } 1810 1811 if (l_in_use_count == ck_in_use_count) { 1812 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count=" 1813 SIZE_FORMAT, l_in_use_count, ck_in_use_count); 1814 } else { 1815 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to " 1816 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count, 1817 ck_in_use_count); 1818 } 1819 1820 size_t ck_in_use_max = _in_use_list.max(); 1821 if (l_in_use_max == ck_in_use_max) { 1822 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max=" 1823 SIZE_FORMAT, l_in_use_max, ck_in_use_max); 1824 } else { 1825 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to " 1826 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max); 1827 } 1828 } 1829 1830 // Check an in-use monitor entry; log any errors. 1831 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out, 1832 int* error_cnt_p) { 1833 if (n->owner_is_DEFLATER_MARKER()) { 1834 // This should not happen, but if it does, it is not fatal. 1835 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is " 1836 "deflated.", p2i(n)); 1837 return; 1838 } 1839 if (n->header().value() == 0) { 1840 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must " 1841 "have non-NULL _header field.", p2i(n)); 1842 *error_cnt_p = *error_cnt_p + 1; 1843 } 1844 const oop obj = n->object_peek(); 1845 if (obj != NULL) { 1846 const markWord mark = obj->mark(); 1847 if (!mark.has_monitor()) { 1848 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's " 1849 "object does not think it has a monitor: obj=" 1850 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n), 1851 p2i(obj), mark.value()); 1852 *error_cnt_p = *error_cnt_p + 1; 1853 } 1854 ObjectMonitor* const obj_mon = mark.monitor(); 1855 if (n != obj_mon) { 1856 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's " 1857 "object does not refer to the same monitor: obj=" 1858 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon=" 1859 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon)); 1860 *error_cnt_p = *error_cnt_p + 1; 1861 } 1862 } 1863 } 1864 1865 // Log details about ObjectMonitors on the in_use_list. The 'BHL' 1866 // flags indicate why the entry is in-use, 'object' and 'object type' 1867 // indicate the associated object and its type. 1868 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) { 1869 stringStream ss; 1870 if (_in_use_list.count() > 0) { 1871 out->print_cr("In-use monitor info:"); 1872 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)"); 1873 out->print_cr("%18s %s %18s %18s", 1874 "monitor", "BHL", "object", "object type"); 1875 out->print_cr("================== === ================== =================="); 1876 MonitorList::Iterator iter = _in_use_list.iterator(); 1877 while (iter.has_next()) { 1878 ObjectMonitor* mid = iter.next(); 1879 const oop obj = mid->object_peek(); 1880 const markWord mark = mid->header(); 1881 ResourceMark rm; 1882 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid), 1883 mid->is_busy(), mark.hash() != 0, mid->owner() != NULL, 1884 p2i(obj), obj == NULL ? "" : obj->klass()->external_name()); 1885 if (mid->is_busy()) { 1886 out->print(" (%s)", mid->is_busy_to_string(&ss)); 1887 ss.reset(); 1888 } 1889 out->cr(); 1890 } 1891 } 1892 1893 out->flush(); 1894 }