1 /*
2 * Copyright (c) 1998, 2024, 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 "logging/log.hpp"
27 #include "memory/resourceArea.hpp"
28 #include "runtime/interfaceSupport.inline.hpp"
29 #include "runtime/javaThread.inline.hpp"
30 #include "runtime/mutex.hpp"
31 #include "runtime/os.inline.hpp"
32 #include "runtime/osThread.hpp"
33 #include "runtime/safepointMechanism.inline.hpp"
34 #include "runtime/semaphore.inline.hpp"
35 #include "runtime/threadCrashProtection.hpp"
36 #include "utilities/events.hpp"
37 #include "utilities/macros.hpp"
38
39 class InFlightMutexRelease {
40 private:
41 Mutex* _in_flight_mutex;
42 public:
43 InFlightMutexRelease(Mutex* in_flight_mutex) : _in_flight_mutex(in_flight_mutex) {
44 assert(in_flight_mutex != nullptr, "must be");
45 }
46 void operator()(JavaThread* current) {
47 _in_flight_mutex->release_for_safepoint();
48 _in_flight_mutex = nullptr;
49 }
50 bool not_released() { return _in_flight_mutex != nullptr; }
51 };
52
53 #ifdef ASSERT
54 void Mutex::check_block_state(Thread* thread) {
55 if (!_allow_vm_block && thread->is_VM_thread()) {
56 // JavaThreads are checked to make sure that they do not hold _allow_vm_block locks during operations
57 // that could safepoint. Make sure the vm thread never uses locks with _allow_vm_block == false.
58 fatal("VM thread could block on lock that may be held by a JavaThread during safepoint: %s", name());
59 }
60
61 assert(!ThreadCrashProtection::is_crash_protected(thread),
62 "locking not allowed when crash protection is set");
63 }
64
65 void Mutex::check_safepoint_state(Thread* thread) {
66 check_block_state(thread);
67
68 // If the lock acquisition checks for safepoint, verify that the lock was created with rank that
69 // has safepoint checks. Technically this doesn't affect NonJavaThreads since they won't actually
70 // check for safepoint, but let's make the rule unconditional unless there's a good reason not to.
71 assert(_rank > nosafepoint,
72 "This lock should not be taken with a safepoint check: %s", name());
73
74 if (thread->is_active_Java_thread()) {
75 // Also check NoSafepointVerifier, and thread state is _thread_in_vm
76 JavaThread::cast(thread)->check_for_valid_safepoint_state();
77 }
78 }
79
80 void Mutex::check_no_safepoint_state(Thread* thread) {
81 check_block_state(thread);
82 assert(!thread->is_active_Java_thread() || _rank <= nosafepoint,
83 "This lock should always have a safepoint check for Java threads: %s",
84 name());
85 }
86 #endif // ASSERT
87
88 void Mutex::lock_contended(Thread* self) {
89 DEBUG_ONLY(int retry_cnt = 0;)
90 bool is_active_Java_thread = self->is_active_Java_thread();
91 do {
92 #ifdef ASSERT
93 if (retry_cnt++ > 3) {
94 log_trace(vmmutex)("JavaThread " INTPTR_FORMAT " on %d attempt trying to acquire vmmutex %s", p2i(self), retry_cnt, _name);
95 }
96 #endif // ASSERT
97
98 // Is it a JavaThread participating in the safepoint protocol.
99 if (is_active_Java_thread) {
100 InFlightMutexRelease ifmr(this);
101 assert(rank() > Mutex::nosafepoint, "Potential deadlock with nosafepoint or lesser rank mutex");
102 {
103 ThreadBlockInVMPreprocess<InFlightMutexRelease> tbivmdc(JavaThread::cast(self), ifmr);
104 _lock.lock();
105 }
106 if (ifmr.not_released()) {
107 // Not unlocked by ~ThreadBlockInVMPreprocess
108 break;
109 }
110 } else {
111 _lock.lock();
112 break;
113 }
114 } while (!_lock.try_lock());
115 }
116
117 void Mutex::lock(Thread* self) {
118 assert(owner() != self, "invariant");
119
120 check_safepoint_state(self);
121 check_rank(self);
122
123 if (!_lock.try_lock()) {
124 // The lock is contended, use contended slow-path function to lock
125 lock_contended(self);
126 }
127
128 assert_owner(nullptr);
129 set_owner(self);
130 }
131
132 void Mutex::lock() {
133 lock(Thread::current());
134 }
135
136 // Lock without safepoint check - a degenerate variant of lock() for use by
137 // JavaThreads when it is known to be safe to not check for a safepoint when
138 // acquiring this lock. If the thread blocks acquiring the lock it is not
139 // safepoint-safe and so will prevent a safepoint from being reached. If used
140 // in the wrong way this can lead to a deadlock with the safepoint code.
141
142 void Mutex::lock_without_safepoint_check(Thread * self) {
143 assert(owner() != self, "invariant");
144
145 check_no_safepoint_state(self);
146 check_rank(self);
147
148 _lock.lock();
149 assert_owner(nullptr);
150 set_owner(self);
151 }
152
153 void Mutex::lock_without_safepoint_check() {
154 lock_without_safepoint_check(Thread::current());
155 }
156
157
158 // Returns true if thread succeeds in grabbing the lock, otherwise false.
159 bool Mutex::try_lock_inner(bool do_rank_checks) {
160 Thread * const self = Thread::current();
161 // Checking the owner hides the potential difference in recursive locking behaviour
162 // on some platforms.
163 if (owner() == self) {
164 return false;
165 }
166
167 if (do_rank_checks) {
168 check_rank(self);
169 }
170 // Some safepoint checking locks use try_lock, so cannot check
171 // safepoint state, but can check blocking state.
172 check_block_state(self);
173
174 if (_lock.try_lock()) {
175 assert_owner(nullptr);
176 set_owner(self);
177 return true;
178 }
179 return false;
180 }
181
182 bool Mutex::try_lock() {
183 return try_lock_inner(true /* do_rank_checks */);
184 }
185
186 bool Mutex::try_lock_without_rank_check() {
187 bool res = try_lock_inner(false /* do_rank_checks */);
188 DEBUG_ONLY(if (res) _skip_rank_check = true;)
189 return res;
190 }
191
192 void Mutex::release_for_safepoint() {
193 assert_owner(nullptr);
194 _lock.unlock();
195 }
196
197 void Mutex::unlock() {
198 DEBUG_ONLY(assert_owner(Thread::current()));
199 set_owner(nullptr);
200 _lock.unlock();
201 }
202
203 void Monitor::notify() {
204 DEBUG_ONLY(assert_owner(Thread::current()));
205 _lock.notify();
206 }
207
208 void Monitor::notify_all() {
209 DEBUG_ONLY(assert_owner(Thread::current()));
210 _lock.notify_all();
211 }
212
213 // timeout is in milliseconds - with zero meaning never timeout
214 bool Monitor::wait_without_safepoint_check(uint64_t timeout) {
215 Thread* const self = Thread::current();
216
217 assert_owner(self);
218 check_rank(self);
219
220 // conceptually set the owner to null in anticipation of
221 // abdicating the lock in wait
222 set_owner(nullptr);
223
224 // Check safepoint state after resetting owner and possible NSV.
225 check_no_safepoint_state(self);
226
227 int wait_status = _lock.wait(timeout);
228 set_owner(self);
229 return wait_status != 0; // return true IFF timeout
230 }
231
232 // timeout is in milliseconds - with zero meaning never timeout
233 bool Monitor::wait(uint64_t timeout) {
234 JavaThread* const self = JavaThread::current();
235 // Safepoint checking logically implies an active JavaThread.
236 assert(self->is_active_Java_thread(), "invariant");
237
238 assert_owner(self);
239 check_rank(self);
240
241 // conceptually set the owner to null in anticipation of
242 // abdicating the lock in wait
243 set_owner(nullptr);
244
245 // Check safepoint state after resetting owner and possible NSV.
246 check_safepoint_state(self);
247
248 int wait_status;
249 InFlightMutexRelease ifmr(this);
250
251 {
252 ThreadBlockInVMPreprocess<InFlightMutexRelease> tbivmdc(self, ifmr);
253 OSThreadWaitState osts(self->osthread(), false /* not Object.wait() */);
254
255 wait_status = _lock.wait(timeout);
256 }
257
258 if (ifmr.not_released()) {
259 // Not unlocked by ~ThreadBlockInVMPreprocess
260 assert_owner(nullptr);
261 // Conceptually reestablish ownership of the lock.
262 set_owner(self);
263 } else {
264 lock(self);
265 }
266
267 return wait_status != 0; // return true IFF timeout
268 }
269
270 Mutex::~Mutex() {
271 assert_owner(nullptr);
272 os::free(const_cast<char*>(_name));
273 }
274
275 Mutex::Mutex(Rank rank, const char * name, bool allow_vm_block) : _owner(nullptr) {
276 assert(os::mutex_init_done(), "Too early!");
277 assert(name != nullptr, "Mutex requires a name");
278 _name = os::strdup(name, mtInternal);
279 #ifdef ASSERT
280 _allow_vm_block = allow_vm_block;
281 _rank = rank;
282 _skip_rank_check = false;
283
284 assert(_rank >= static_cast<Rank>(0) && _rank <= safepoint, "Bad lock rank %s: %s", rank_name(), name);
285
286 // The allow_vm_block also includes allowing other non-Java threads to block or
287 // allowing Java threads to block in native.
288 assert(_rank > nosafepoint || _allow_vm_block,
289 "Locks that don't check for safepoint should always allow the vm to block: %s", name);
290 #endif
291 }
292
293 bool Mutex::owned_by_self() const {
294 return owner() == Thread::current();
295 }
296
297 void Mutex::print_on_error(outputStream* st) const {
298 st->print("[" PTR_FORMAT, p2i(this));
299 st->print("] %s", _name);
300 st->print(" - owner thread: " PTR_FORMAT, p2i(owner()));
301 }
302
303 // ----------------------------------------------------------------------------------
304 // Non-product code
305 //
306 #ifdef ASSERT
307 static Mutex::Rank _ranks[] = { Mutex::event, Mutex::service, Mutex::stackwatermark, Mutex::tty, Mutex::oopstorage,
308 Mutex::nosafepoint, Mutex::safepoint };
309
310 static const char* _rank_names[] = { "event", "service", "stackwatermark", "tty", "oopstorage",
311 "nosafepoint", "safepoint" };
312
313 static const int _num_ranks = 7;
314
315 static const char* rank_name_internal(Mutex::Rank r) {
316 // Find closest rank and print out the name
317 stringStream st;
318 for (int i = 0; i < _num_ranks; i++) {
319 if (r == _ranks[i]) {
320 return _rank_names[i];
321 } else if (r > _ranks[i] && (i < _num_ranks-1 && r < _ranks[i+1])) {
322 int delta = static_cast<int>(_ranks[i+1]) - static_cast<int>(r);
323 st.print("%s-%d", _rank_names[i+1], delta);
324 return st.as_string();
325 }
326 }
327 return "fail";
328 }
329
330 const char* Mutex::rank_name() const {
331 return rank_name_internal(_rank);
332 }
333
334
335 void Mutex::assert_no_overlap(Rank orig, Rank adjusted, int adjust) {
336 int i = 0;
337 while (_ranks[i] < orig) i++;
338 // underflow is caught in constructor
339 if (i != 0 && adjusted > event && adjusted <= _ranks[i-1]) {
340 ResourceMark rm;
341 assert(adjusted > _ranks[i-1],
342 "Rank %s-%d overlaps with %s",
343 rank_name_internal(orig), adjust, rank_name_internal(adjusted));
344 }
345 }
346 #endif // ASSERT
347
348 #ifndef PRODUCT
349 void Mutex::print_on(outputStream* st) const {
350 st->print("Mutex: [" PTR_FORMAT "] %s - owner: " PTR_FORMAT,
351 p2i(this), _name, p2i(owner()));
352 if (_allow_vm_block) {
353 st->print("%s", " allow_vm_block");
354 }
355 DEBUG_ONLY(st->print(" %s", rank_name()));
356 st->cr();
357 }
358
359 void Mutex::print() const {
360 print_on(::tty);
361 }
362 #endif // PRODUCT
363
364 #ifdef ASSERT
365 void Mutex::assert_owner(Thread * expected) {
366 const char* msg = "invalid owner";
367 if (expected == nullptr) {
368 msg = "should be un-owned";
369 }
370 else if (expected == Thread::current()) {
371 msg = "should be owned by current thread";
372 }
373 assert(owner() == expected,
374 "%s: owner=" INTPTR_FORMAT ", should be=" INTPTR_FORMAT,
375 msg, p2i(owner()), p2i(expected));
376 }
377
378 Mutex* Mutex::get_least_ranked_lock(Mutex* locks) {
379 Mutex *res, *tmp;
380 for (res = tmp = locks; tmp != nullptr; tmp = tmp->next()) {
381 if (tmp->rank() < res->rank()) {
382 res = tmp;
383 }
384 }
385 return res;
386 }
387
388 Mutex* Mutex::get_least_ranked_lock_besides_this(Mutex* locks) {
389 Mutex *res, *tmp;
390 for (res = nullptr, tmp = locks; tmp != nullptr; tmp = tmp->next()) {
391 if (tmp != this && (res == nullptr || tmp->rank() < res->rank())) {
392 res = tmp;
393 }
394 }
395 assert(res != this, "invariant");
396 return res;
397 }
398
399 // Tests for rank violations that might indicate exposure to deadlock.
400 void Mutex::check_rank(Thread* thread) {
401 Mutex* locks_owned = thread->owned_locks();
402
403 // We expect the locks already acquired to be in increasing rank order,
404 // modulo locks acquired in try_lock_without_rank_check()
405 for (Mutex* tmp = locks_owned; tmp != nullptr; tmp = tmp->next()) {
406 if (tmp->next() != nullptr) {
407 assert(tmp->rank() < tmp->next()->rank()
408 || tmp->skip_rank_check(), "mutex rank anomaly?");
409 }
410 }
411
412 if (owned_by_self()) {
413 // wait() case
414 Mutex* least = get_least_ranked_lock_besides_this(locks_owned);
415 // For JavaThreads, we enforce not holding locks of rank nosafepoint or lower while waiting
416 // because the held lock has a NoSafepointVerifier so waiting on a lower ranked lock will not be
417 // able to check for safepoints first with a TBIVM.
418 // For all threads, we enforce not holding the tty lock or below, since this could block progress also.
419 // Also "this" should be the monitor with lowest rank owned by this thread.
420 if (least != nullptr && ((least->rank() <= Mutex::nosafepoint && thread->is_Java_thread()) ||
421 least->rank() <= Mutex::tty ||
422 least->rank() <= this->rank())) {
423 ResourceMark rm(thread);
424 assert(false, "Attempting to wait on monitor %s/%s while holding lock %s/%s -- "
425 "possible deadlock. %s", name(), rank_name(), least->name(), least->rank_name(),
426 least->rank() <= this->rank() ?
427 "Should wait on the least ranked monitor from all owned locks." :
428 thread->is_Java_thread() ?
429 "Should not block(wait) while holding a lock of rank nosafepoint or below." :
430 "Should not block(wait) while holding a lock of rank tty or below.");
431 }
432 } else {
433 // lock()/lock_without_safepoint_check()/try_lock() case
434 Mutex* least = get_least_ranked_lock(locks_owned);
435 // Deadlock prevention rules require us to acquire Mutexes only in
436 // a global total order. For example, if m1 is the lowest ranked mutex
437 // that the thread holds and m2 is the mutex the thread is trying
438 // to acquire, then deadlock prevention rules require that the rank
439 // of m2 be less than the rank of m1. This prevents circular waits.
440 if (least != nullptr && least->rank() <= this->rank()) {
441 ResourceMark rm(thread);
442 if (least->rank() > Mutex::tty) {
443 // Printing owned locks acquires tty lock. If the least rank was below or equal
444 // tty, then deadlock detection code would circle back here, until we run
445 // out of stack and crash hard. Print locks only when it is safe.
446 thread->print_owned_locks();
447 }
448 assert(false, "Attempting to acquire lock %s/%s out of order with lock %s/%s -- "
449 "possible deadlock", this->name(), this->rank_name(), least->name(), least->rank_name());
450 }
451 }
452 }
453
454 // Called immediately after lock acquisition or release as a diagnostic
455 // to track the lock-set of the thread.
456 // Rather like an EventListener for _owner (:>).
457
458 void Mutex::set_owner_implementation(Thread *new_owner) {
459 // This function is solely responsible for maintaining
460 // and checking the invariant that threads and locks
461 // are in a 1/N relation, with some some locks unowned.
462 // It uses the Mutex::_owner, Mutex::_next, and
463 // Thread::_owned_locks fields, and no other function
464 // changes those fields.
465 // It is illegal to set the mutex from one non-null
466 // owner to another--it must be owned by null as an
467 // intermediate state.
468
469 if (new_owner != nullptr) {
470 // the thread is acquiring this lock
471
472 assert(new_owner == Thread::current(), "Should I be doing this?");
473 assert(owner() == nullptr, "setting the owner thread of an already owned mutex");
474 raw_set_owner(new_owner); // set the owner
475
476 // link "this" into the owned locks list
477 this->_next = new_owner->_owned_locks;
478 new_owner->_owned_locks = this;
479
480 // NSV implied with locking allow_vm_block flag.
481 // The tty_lock is special because it is released for the safepoint by
482 // the safepoint mechanism.
483 if (new_owner->is_Java_thread() && _allow_vm_block && this != tty_lock) {
484 JavaThread::cast(new_owner)->inc_no_safepoint_count();
485 }
486
487 } else {
488 // the thread is releasing this lock
489
490 Thread* old_owner = owner();
491 _last_owner = old_owner;
492 _skip_rank_check = false;
493
494 assert(old_owner != nullptr, "removing the owner thread of an unowned mutex");
495 assert(old_owner == Thread::current(), "removing the owner thread of an unowned mutex");
496
497 raw_set_owner(nullptr); // set the owner
498
499 Mutex* locks = old_owner->owned_locks();
500
501 // remove "this" from the owned locks list
502
503 Mutex* prev = nullptr;
504 bool found = false;
505 for (; locks != nullptr; prev = locks, locks = locks->next()) {
506 if (locks == this) {
507 found = true;
508 break;
509 }
510 }
511 assert(found, "Removing a lock not owned");
512 if (prev == nullptr) {
513 old_owner->_owned_locks = _next;
514 } else {
515 prev->_next = _next;
516 }
517 _next = nullptr;
518
519 // ~NSV implied with locking allow_vm_block flag.
520 if (old_owner->is_Java_thread() && _allow_vm_block && this != tty_lock) {
521 JavaThread::cast(old_owner)->dec_no_safepoint_count();
522 }
523 }
524 }
525 #endif // ASSERT
526
527
528 RecursiveMutex::RecursiveMutex() : _sem(1), _owner(nullptr), _recursions(0) {}
529
530 void RecursiveMutex::lock(Thread* current) {
531 assert(current == Thread::current(), "must be current thread");
532 if (current == _owner) {
533 _recursions++;
534 } else {
535 // can be called by jvmti by VMThread.
536 if (current->is_Java_thread()) {
537 _sem.wait_with_safepoint_check(JavaThread::cast(current));
538 } else {
539 _sem.wait();
540 }
541 _recursions++;
542 assert(_recursions == 1, "should be");
543 _owner = current;
544 }
545 }
546
547 void RecursiveMutex::unlock(Thread* current) {
548 assert(current == Thread::current(), "must be current thread");
549 assert(current == _owner, "must be owner");
550 _recursions--;
551 if (_recursions == 0) {
552 _owner = nullptr;
553 _sem.signal();
554 }
555 }