1 /*
2 * Copyright (c) 1998, 2025, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "logging/log.hpp"
26 #include "memory/resourceArea.hpp"
27 #include "runtime/interfaceSupport.inline.hpp"
28 #include "runtime/javaThread.inline.hpp"
29 #include "runtime/mutex.hpp"
30 #include "runtime/os.inline.hpp"
31 #include "runtime/osThread.hpp"
32 #include "runtime/safepointMechanism.inline.hpp"
33 #include "runtime/semaphore.inline.hpp"
34 #include "runtime/threadCrashProtection.hpp"
35 #include "utilities/events.hpp"
36 #include "utilities/macros.hpp"
37
38 class InFlightMutexRelease {
39 private:
40 Mutex* _in_flight_mutex;
41 public:
42 InFlightMutexRelease(Mutex* in_flight_mutex) : _in_flight_mutex(in_flight_mutex) {
43 assert(in_flight_mutex != nullptr, "must be");
44 }
45 void operator()(JavaThread* current) {
46 _in_flight_mutex->release_for_safepoint();
47 _in_flight_mutex = nullptr;
48 }
49 bool not_released() { return _in_flight_mutex != nullptr; }
50 };
51
52 #ifdef ASSERT
53 void Mutex::check_block_state(Thread* thread) {
54 if (!_allow_vm_block && thread->is_VM_thread()) {
55 // JavaThreads are checked to make sure that they do not hold _allow_vm_block locks during operations
56 // that could safepoint. Make sure the vm thread never uses locks with _allow_vm_block == false.
57 fatal("VM thread could block on lock that may be held by a JavaThread during safepoint: %s", name());
58 }
59
60 assert(!ThreadCrashProtection::is_crash_protected(thread),
61 "locking not allowed when crash protection is set");
62 }
63
64 void Mutex::check_safepoint_state(Thread* thread) {
65 check_block_state(thread);
66
67 // If the lock acquisition checks for safepoint, verify that the lock was created with rank that
68 // has safepoint checks. Technically this doesn't affect NonJavaThreads since they won't actually
69 // check for safepoint, but let's make the rule unconditional unless there's a good reason not to.
70 assert(_rank > nosafepoint,
71 "This lock should not be taken with a safepoint check: %s", name());
72
73 if (thread->is_active_Java_thread()) {
74 // Also check NoSafepointVerifier, and thread state is _thread_in_vm
75 JavaThread::cast(thread)->check_for_valid_safepoint_state();
76 }
77 }
78
79 void Mutex::check_no_safepoint_state(Thread* thread) {
80 check_block_state(thread);
81 assert(!thread->is_active_Java_thread() || _rank <= nosafepoint,
82 "This lock should always have a safepoint check for Java threads: %s",
83 name());
84 }
85 #endif // ASSERT
86
87 void Mutex::lock_contended(Thread* self) {
88 DEBUG_ONLY(int retry_cnt = 0;)
89 bool is_active_Java_thread = self->is_active_Java_thread();
90 do {
91 #ifdef ASSERT
92 if (retry_cnt++ > 3) {
93 log_trace(vmmutex)("JavaThread " INTPTR_FORMAT " on %d attempt trying to acquire vmmutex %s", p2i(self), retry_cnt, _name);
94 }
95 #endif // ASSERT
96
97 // Is it a JavaThread participating in the safepoint protocol.
98 if (is_active_Java_thread) {
99 InFlightMutexRelease ifmr(this);
100 assert(rank() > Mutex::nosafepoint, "Potential deadlock with nosafepoint or lesser rank mutex");
101 {
102 ThreadBlockInVMPreprocess<InFlightMutexRelease> tbivmdc(JavaThread::cast(self), ifmr);
103 _lock.lock();
104 }
105 if (ifmr.not_released()) {
106 // Not unlocked by ~ThreadBlockInVMPreprocess
107 break;
108 }
109 } else {
110 _lock.lock();
111 break;
112 }
113 } while (!_lock.try_lock());
114 }
115
116 void Mutex::lock(Thread* self) {
117 assert(owner() != self, "invariant");
118
119 check_safepoint_state(self);
120 check_rank(self);
121
122 if (!_lock.try_lock()) {
123 // The lock is contended, use contended slow-path function to lock
124 lock_contended(self);
125 }
126
127 assert_owner(nullptr);
128 set_owner(self);
129 }
130
131 void Mutex::lock() {
132 lock(Thread::current());
133 }
134
135 // Lock without safepoint check - a degenerate variant of lock() for use by
136 // JavaThreads when it is known to be safe to not check for a safepoint when
137 // acquiring this lock. If the thread blocks acquiring the lock it is not
138 // safepoint-safe and so will prevent a safepoint from being reached. If used
139 // in the wrong way this can lead to a deadlock with the safepoint code.
140
141 void Mutex::lock_without_safepoint_check(Thread * self) {
142 assert(owner() != self, "invariant");
143
144 check_no_safepoint_state(self);
145 check_rank(self);
146
147 _lock.lock();
148 assert_owner(nullptr);
149 set_owner(self);
150 }
151
152 void Mutex::lock_without_safepoint_check() {
153 lock_without_safepoint_check(Thread::current());
154 }
155
156
157 // Returns true if thread succeeds in grabbing the lock, otherwise false.
158 bool Mutex::try_lock_inner(bool do_rank_checks) {
159 Thread * const self = Thread::current();
160 // Checking the owner hides the potential difference in recursive locking behaviour
161 // on some platforms.
162 if (owner() == self) {
163 return false;
164 }
165
166 if (do_rank_checks) {
167 check_rank(self);
168 }
169 // Some safepoint checking locks use try_lock, so cannot check
170 // safepoint state, but can check blocking state.
171 check_block_state(self);
172
173 if (_lock.try_lock()) {
174 assert_owner(nullptr);
175 set_owner(self);
176 return true;
177 }
178 return false;
179 }
180
181 bool Mutex::try_lock() {
182 return try_lock_inner(true /* do_rank_checks */);
183 }
184
185 bool Mutex::try_lock_without_rank_check() {
186 bool res = try_lock_inner(false /* do_rank_checks */);
187 DEBUG_ONLY(if (res) _skip_rank_check = true;)
188 return res;
189 }
190
191 void Mutex::release_for_safepoint() {
192 assert_owner(nullptr);
193 _lock.unlock();
194 }
195
196 void Mutex::unlock() {
197 DEBUG_ONLY(assert_owner(Thread::current()));
198 set_owner(nullptr);
199 _lock.unlock();
200 }
201
202 void Monitor::notify() {
203 DEBUG_ONLY(assert_owner(Thread::current()));
204 _lock.notify();
205 }
206
207 void Monitor::notify_all() {
208 DEBUG_ONLY(assert_owner(Thread::current()));
209 _lock.notify_all();
210 }
211
212 // timeout is in milliseconds - with zero meaning never timeout
213 bool Monitor::wait_without_safepoint_check(uint64_t timeout) {
214 Thread* const self = Thread::current();
215
216 assert_owner(self);
217 check_rank(self);
218
219 // conceptually set the owner to null in anticipation of
220 // abdicating the lock in wait
221 set_owner(nullptr);
222
223 // Check safepoint state after resetting owner and possible NSV.
224 check_no_safepoint_state(self);
225
226 int wait_status = _lock.wait(timeout);
227 set_owner(self);
228 return wait_status != 0; // return true IFF timeout
229 }
230
231 // timeout is in milliseconds - with zero meaning never timeout
232 bool Monitor::wait(uint64_t timeout) {
233 JavaThread* const self = JavaThread::current();
234 // Safepoint checking logically implies an active JavaThread.
235 assert(self->is_active_Java_thread(), "invariant");
236
237 assert_owner(self);
238 check_rank(self);
239
240 // conceptually set the owner to null in anticipation of
241 // abdicating the lock in wait
242 set_owner(nullptr);
243
244 // Check safepoint state after resetting owner and possible NSV.
245 check_safepoint_state(self);
246
247 int wait_status;
248 InFlightMutexRelease ifmr(this);
249
250 {
251 ThreadBlockInVMPreprocess<InFlightMutexRelease> tbivmdc(self, ifmr);
252 OSThreadWaitState osts(self->osthread(), false /* not Object.wait() */);
253
254 wait_status = _lock.wait(timeout);
255 }
256
257 if (ifmr.not_released()) {
258 // Not unlocked by ~ThreadBlockInVMPreprocess
259 assert_owner(nullptr);
260 // Conceptually reestablish ownership of the lock.
261 set_owner(self);
262 } else {
263 lock(self);
264 }
265
266 return wait_status != 0; // return true IFF timeout
267 }
268
269 static const int MAX_NUM_MUTEX = 1204;
270 static Mutex* _internal_mutex_arr[MAX_NUM_MUTEX];
271 Mutex** Mutex::_mutex_array = _internal_mutex_arr;
272 int Mutex::_num_mutex = 0;
273
274 void Mutex::add_mutex(Mutex* var) {
275 assert(Mutex::_num_mutex < MAX_NUM_MUTEX, "increase MAX_NUM_MUTEX");
276 Mutex::_mutex_array[_num_mutex++] = var;
277 }
278
279 Mutex::~Mutex() {
280 assert_owner(nullptr);
281 os::free(const_cast<char*>(_name));
282 }
283
284 Mutex::Mutex(Rank rank, const char * name, bool allow_vm_block) : _owner(nullptr) {
285 assert(os::mutex_init_done(), "Too early!");
286 assert(name != nullptr, "Mutex requires a name");
287 _name = os::strdup(name, mtInternal);
288 #ifdef ASSERT
289 _allow_vm_block = allow_vm_block;
290 _rank = rank;
291 _skip_rank_check = false;
292
293 assert(_rank >= static_cast<Rank>(0) && _rank <= safepoint, "Bad lock rank %s: %s", rank_name(), name);
294
295 // The allow_vm_block also includes allowing other non-Java threads to block or
296 // allowing Java threads to block in native.
297 assert(_rank > nosafepoint || _allow_vm_block,
298 "Locks that don't check for safepoint should always allow the vm to block: %s", name);
299 #endif
300 }
301
302 bool Mutex::owned_by_self() const {
303 return owner() == Thread::current();
304 }
305
306 void Mutex::print_on_error(outputStream* st) const {
307 st->print("[" PTR_FORMAT, p2i(this));
308 st->print("] %s", _name);
309 st->print(" - owner thread: " PTR_FORMAT, p2i(owner()));
310 }
311
312 // ----------------------------------------------------------------------------------
313 // Non-product code
314 //
315 #ifdef ASSERT
316 static Mutex::Rank _ranks[] = { Mutex::event, Mutex::service, Mutex::stackwatermark, Mutex::tty, Mutex::oopstorage,
317 Mutex::nosafepoint, Mutex::safepoint };
318
319 static const char* _rank_names[] = { "event", "service", "stackwatermark", "tty", "oopstorage",
320 "nosafepoint", "safepoint" };
321
322 static const int _num_ranks = 7;
323
324 static const char* rank_name_internal(Mutex::Rank r) {
325 // Find closest rank and print out the name
326 stringStream st;
327 for (int i = 0; i < _num_ranks; i++) {
328 if (r == _ranks[i]) {
329 return _rank_names[i];
330 } else if (r > _ranks[i] && (i < _num_ranks-1 && r < _ranks[i+1])) {
331 int delta = static_cast<int>(_ranks[i+1]) - static_cast<int>(r);
332 st.print("%s-%d", _rank_names[i+1], delta);
333 return st.as_string();
334 }
335 }
336 return "fail";
337 }
338
339 const char* Mutex::rank_name() const {
340 return rank_name_internal(_rank);
341 }
342
343
344 void Mutex::assert_no_overlap(Rank orig, Rank adjusted, int adjust) {
345 int i = 0;
346 while (_ranks[i] < orig) i++;
347 // underflow is caught in constructor
348 if (i != 0 && adjusted > event && adjusted <= _ranks[i-1]) {
349 ResourceMark rm;
350 assert(adjusted > _ranks[i-1],
351 "Rank %s-%d overlaps with %s",
352 rank_name_internal(orig), adjust, rank_name_internal(adjusted));
353 }
354 }
355 #endif // ASSERT
356
357 #ifndef PRODUCT
358 void Mutex::print_on(outputStream* st) const {
359 st->print("Mutex: [" PTR_FORMAT "] %s - owner: " PTR_FORMAT,
360 p2i(this), _name, p2i(owner()));
361 if (_allow_vm_block) {
362 st->print("%s", " allow_vm_block");
363 }
364 DEBUG_ONLY(st->print(" %s", rank_name()));
365 st->cr();
366 }
367
368 void Mutex::print() const {
369 print_on(::tty);
370 }
371 #endif // PRODUCT
372
373 #ifdef ASSERT
374 void Mutex::assert_owner(Thread * expected) {
375 const char* msg = "invalid owner";
376 if (expected == nullptr) {
377 msg = "should be un-owned";
378 }
379 else if (expected == Thread::current()) {
380 msg = "should be owned by current thread";
381 }
382 assert(owner() == expected,
383 "%s: owner=" INTPTR_FORMAT ", should be=" INTPTR_FORMAT,
384 msg, p2i(owner()), p2i(expected));
385 }
386
387 Mutex* Mutex::get_least_ranked_lock(Mutex* locks) {
388 Mutex *res, *tmp;
389 for (res = tmp = locks; tmp != nullptr; tmp = tmp->next()) {
390 if (tmp->rank() < res->rank()) {
391 res = tmp;
392 }
393 }
394 return res;
395 }
396
397 Mutex* Mutex::get_least_ranked_lock_besides_this(Mutex* locks) {
398 Mutex *res, *tmp;
399 for (res = nullptr, tmp = locks; tmp != nullptr; tmp = tmp->next()) {
400 if (tmp != this && (res == nullptr || tmp->rank() < res->rank())) {
401 res = tmp;
402 }
403 }
404 assert(res != this, "invariant");
405 return res;
406 }
407
408 // Tests for rank violations that might indicate exposure to deadlock.
409 void Mutex::check_rank(Thread* thread) {
410 Mutex* locks_owned = thread->owned_locks();
411
412 // We expect the locks already acquired to be in increasing rank order,
413 // modulo locks acquired in try_lock_without_rank_check()
414 for (Mutex* tmp = locks_owned; tmp != nullptr; tmp = tmp->next()) {
415 if (tmp->next() != nullptr) {
416 assert(tmp->rank() < tmp->next()->rank()
417 || tmp->skip_rank_check(), "mutex rank anomaly?");
418 }
419 }
420
421 if (owned_by_self()) {
422 // wait() case
423 Mutex* least = get_least_ranked_lock_besides_this(locks_owned);
424 // For JavaThreads, we enforce not holding locks of rank nosafepoint or lower while waiting
425 // because the held lock has a NoSafepointVerifier so waiting on a lower ranked lock will not be
426 // able to check for safepoints first with a TBIVM.
427 // For all threads, we enforce not holding the tty lock or below, since this could block progress also.
428 // Also "this" should be the monitor with lowest rank owned by this thread.
429 if (least != nullptr && ((least->rank() <= Mutex::nosafepoint && thread->is_Java_thread()) ||
430 least->rank() <= Mutex::tty ||
431 least->rank() <= this->rank())) {
432 ResourceMark rm(thread);
433 assert(false, "Attempting to wait on monitor %s/%s while holding lock %s/%s -- "
434 "possible deadlock. %s", name(), rank_name(), least->name(), least->rank_name(),
435 least->rank() <= this->rank() ?
436 "Should wait on the least ranked monitor from all owned locks." :
437 thread->is_Java_thread() ?
438 "Should not block(wait) while holding a lock of rank nosafepoint or below." :
439 "Should not block(wait) while holding a lock of rank tty or below.");
440 }
441 } else {
442 // lock()/lock_without_safepoint_check()/try_lock() case
443 Mutex* least = get_least_ranked_lock(locks_owned);
444 // Deadlock prevention rules require us to acquire Mutexes only in
445 // a global total order. For example, if m1 is the lowest ranked mutex
446 // that the thread holds and m2 is the mutex the thread is trying
447 // to acquire, then deadlock prevention rules require that the rank
448 // of m2 be less than the rank of m1. This prevents circular waits.
449 if (least != nullptr && least->rank() <= this->rank()) {
450 ResourceMark rm(thread);
451 if (least->rank() > Mutex::tty) {
452 // Printing owned locks acquires tty lock. If the least rank was below or equal
453 // tty, then deadlock detection code would circle back here, until we run
454 // out of stack and crash hard. Print locks only when it is safe.
455 thread->print_owned_locks();
456 }
457 assert(false, "Attempting to acquire lock %s/%s out of order with lock %s/%s -- "
458 "possible deadlock", this->name(), this->rank_name(), least->name(), least->rank_name());
459 }
460 }
461 }
462
463 // Called immediately after lock acquisition or release as a diagnostic
464 // to track the lock-set of the thread.
465 // Rather like an EventListener for _owner (:>).
466
467 void Mutex::set_owner_implementation(Thread *new_owner) {
468 // This function is solely responsible for maintaining
469 // and checking the invariant that threads and locks
470 // are in a 1/N relation, with some some locks unowned.
471 // It uses the Mutex::_owner, Mutex::_next, and
472 // Thread::_owned_locks fields, and no other function
473 // changes those fields.
474 // It is illegal to set the mutex from one non-null
475 // owner to another--it must be owned by null as an
476 // intermediate state.
477
478 if (new_owner != nullptr) {
479 // the thread is acquiring this lock
480
481 assert(new_owner == Thread::current(), "Should I be doing this?");
482 assert(owner() == nullptr, "setting the owner thread of an already owned mutex");
483 raw_set_owner(new_owner); // set the owner
484
485 // link "this" into the owned locks list
486 this->_next = new_owner->_owned_locks;
487 new_owner->_owned_locks = this;
488
489 // NSV implied with locking allow_vm_block flag.
490 // The tty_lock is special because it is released for the safepoint by
491 // the safepoint mechanism.
492 if (new_owner->is_Java_thread() && _allow_vm_block && this != tty_lock) {
493 JavaThread::cast(new_owner)->inc_no_safepoint_count();
494 }
495
496 } else {
497 // the thread is releasing this lock
498
499 Thread* old_owner = owner();
500 _last_owner = old_owner;
501 _skip_rank_check = false;
502
503 assert(old_owner != nullptr, "removing the owner thread of an unowned mutex");
504 assert(old_owner == Thread::current(), "removing the owner thread of an unowned mutex");
505
506 raw_set_owner(nullptr); // set the owner
507
508 Mutex* locks = old_owner->owned_locks();
509
510 // remove "this" from the owned locks list
511
512 Mutex* prev = nullptr;
513 bool found = false;
514 for (; locks != nullptr; prev = locks, locks = locks->next()) {
515 if (locks == this) {
516 found = true;
517 break;
518 }
519 }
520 assert(found, "Removing a lock not owned");
521 if (prev == nullptr) {
522 old_owner->_owned_locks = _next;
523 } else {
524 prev->_next = _next;
525 }
526 _next = nullptr;
527
528 // ~NSV implied with locking allow_vm_block flag.
529 if (old_owner->is_Java_thread() && _allow_vm_block && this != tty_lock) {
530 JavaThread::cast(old_owner)->dec_no_safepoint_count();
531 }
532 }
533 }
534 #endif // ASSERT
535
536 // Print all mutexes/monitors that are currently owned by a thread; called
537 // by fatal error handler.
538 void Mutex::print_owned_locks_on_error(outputStream* st) {
539 st->print("VM Mutex/Monitor currently owned by a thread: ");
540 bool none = true;
541 for (int i = 0; i < _num_mutex; i++) {
542 // see if it has an owner
543 if (_mutex_array[i]->owner() != nullptr) {
544 if (none) {
545 // print format used by Mutex::print_on_error()
546 st->print_cr(" ([mutex/lock_event])");
547 none = false;
548 }
549 _mutex_array[i]->print_on_error(st);
550 st->cr();
551 }
552 }
553 if (none) st->print_cr("None");
554 }
555
556 void Mutex::print_lock_ranks(outputStream* st) {
557 st->print_cr("VM Mutex/Monitor ranks: ");
558
559 #ifdef ASSERT
560 // Be extra defensive and figure out the bounds on
561 // ranks right here. This also saves a bit of time
562 // in the #ranks*#mutexes loop below.
563 int min_rank = INT_MAX;
564 int max_rank = INT_MIN;
565 for (int i = 0; i < _num_mutex; i++) {
566 Mutex* m = _mutex_array[i];
567 int r = (int) m->rank();
568 if (min_rank > r) min_rank = r;
569 if (max_rank < r) max_rank = r;
570 }
571
572 // Print the listings rank by rank
573 for (int r = min_rank; r <= max_rank; r++) {
574 bool first = true;
575 for (int i = 0; i < _num_mutex; i++) {
576 Mutex* m = _mutex_array[i];
577 if (r != (int) m->rank()) continue;
578
579 if (first) {
580 st->cr();
581 st->print_cr("Rank \"%s\":", m->rank_name());
582 first = false;
583 }
584 st->print_cr(" %s", m->name());
585 }
586 }
587 #else
588 st->print_cr(" Only known in debug builds.");
589 #endif // ASSERT
590 }
591
592 RecursiveMutex::RecursiveMutex() : _sem(1), _owner(nullptr), _recursions(0) {}
593
594 void RecursiveMutex::lock(Thread* current) {
595 assert(current == Thread::current(), "must be current thread");
596 if (current == _owner) {
597 _recursions++;
598 } else {
599 // can be called by jvmti by VMThread.
600 if (current->is_Java_thread()) {
601 _sem.wait_with_safepoint_check(JavaThread::cast(current));
602 } else {
603 _sem.wait();
604 }
605 _recursions++;
606 assert(_recursions == 1, "should be");
607 _owner = current;
608 }
609 }
610
611 void RecursiveMutex::unlock(Thread* current) {
612 assert(current == Thread::current(), "must be current thread");
613 assert(current == _owner, "must be owner");
614 _recursions--;
615 if (_recursions == 0) {
616 _owner = nullptr;
617 _sem.signal();
618 }
619 }