1 /* 2 * Copyright (c) 1998, 2019, 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 "runtime/interfaceSupport.inline.hpp" 28 #include "runtime/mutex.hpp" 29 #include "runtime/osThread.hpp" 30 #include "runtime/safepointMechanism.inline.hpp" 31 #include "runtime/thread.inline.hpp" 32 #include "utilities/events.inline.hpp" 33 #include "utilities/macros.hpp" 34 35 #ifdef ASSERT 36 void Mutex::check_block_state(Thread* thread) { 37 if (!_allow_vm_block && thread->is_VM_thread()) { 38 // JavaThreads are checked to make sure that they do not hold _allow_vm_block locks during operations 39 // that could safepoint. Make sure the vm thread never uses locks with _allow_vm_block == false. 40 fatal("VM thread could block on lock that may be held by a JavaThread during safepoint: %s", name()); 41 } 42 43 assert(!os::ThreadCrashProtection::is_crash_protected(thread), 44 "locking not allowed when crash protection is set"); 45 } 46 47 void Mutex::check_safepoint_state(Thread* thread) { 48 check_block_state(thread); 49 50 // If the JavaThread checks for safepoint, verify that the lock wasn't created with safepoint_check_never. 51 if (thread->is_active_Java_thread()) { 52 assert(_safepoint_check_required != _safepoint_check_never, 53 "This lock should %s have a safepoint check for Java threads: %s", 54 _safepoint_check_required ? "always" : "never", name()); 55 56 // Also check NoSafepointVerifier, and thread state is _thread_in_vm 57 thread->check_for_valid_safepoint_state(); 58 } else { 59 // If initialized with safepoint_check_never, a NonJavaThread should never ask to safepoint check either. 60 assert(_safepoint_check_required != _safepoint_check_never, 61 "NonJavaThread should not check for safepoint"); 62 } 63 } 64 65 void Mutex::check_no_safepoint_state(Thread* thread) { 66 check_block_state(thread); 67 assert(!thread->is_active_Java_thread() || _safepoint_check_required != _safepoint_check_always, 68 "This lock should %s have a safepoint check for Java threads: %s", 69 _safepoint_check_required ? "always" : "never", name()); 70 } 71 #endif // ASSERT 72 73 void Mutex::lock_slow(Thread* self) { 74 Mutex* in_flight_mutex = NULL; 75 DEBUG_ONLY(int retry_cnt = 0;) 76 bool is_active_Java_thread = self->is_active_Java_thread(); 77 do { 78 // The lock is contended 79 80 #ifdef ASSERT 81 if (retry_cnt++ > 3) { 82 log_trace(vmmutex)("JavaThread " INTPTR_FORMAT " on %d attempt trying to acquire vmmutex %s", p2i(self), retry_cnt, _name); 83 } 84 #endif // ASSERT 85 86 // Is it a JavaThread participating in the safepoint protocol. 87 if (is_active_Java_thread) { 88 assert(rank() > Mutex::special, "Potential deadlock with special or lesser rank mutex"); 89 { ThreadBlockInVMWithDeadlockCheck tbivmdc((JavaThread *) self, &in_flight_mutex); 90 in_flight_mutex = this; // save for ~ThreadBlockInVMWithDeadlockCheck 91 _lock.lock(); 92 } 93 if (in_flight_mutex != NULL) { 94 // Not unlocked by ~ThreadBlockInVMWithDeadlockCheck 95 break; 96 } 97 } else { 98 _lock.lock(); 99 break; 100 } 101 } while(!_lock.try_lock()); 102 103 assert_owner(NULL); 104 set_owner(self); 105 } 106 107 108 void Monitor::notify() { 109 assert_owner(Thread::current()); 110 _lock.notify(); 111 } 112 113 void Monitor::notify_all() { 114 assert_owner(Thread::current()); 115 _lock.notify_all(); 116 } 117 118 #ifdef ASSERT 119 void Monitor::assert_wait_lock_state(Thread* self) { 120 Mutex* least = get_least_ranked_lock_besides_this(self->owned_locks()); 121 assert(least != this, "Specification of get_least_... call above"); 122 if (least != NULL && least->rank() <= special) { 123 ::tty->print("Attempting to wait on monitor %s/%d while holding" 124 " lock %s/%d -- possible deadlock", 125 name(), rank(), least->name(), least->rank()); 126 assert(false, "Shouldn't block(wait) while holding a lock of rank special"); 127 } 128 } 129 #endif // ASSERT 130 131 bool Monitor::wait_without_safepoint_check(long timeout) { 132 Thread* const self = Thread::current(); 133 134 // timeout is in milliseconds - with zero meaning never timeout 135 assert(timeout >= 0, "negative timeout"); 136 137 assert_owner(self); 138 assert_wait_lock_state(self); 139 140 // conceptually set the owner to NULL in anticipation of 141 // abdicating the lock in wait 142 set_owner(NULL); 143 // Check safepoint state after resetting owner and possible NSV. 144 check_no_safepoint_state(self); 145 146 int wait_status = _lock.wait(timeout); 147 set_owner(self); 148 return wait_status != 0; // return true IFF timeout 149 } 150 151 bool Monitor::wait(long timeout, bool as_suspend_equivalent) { 152 Thread* const self = Thread::current(); 153 154 // timeout is in milliseconds - with zero meaning never timeout 155 assert(timeout >= 0, "negative timeout"); 156 157 assert_owner(self); 158 159 // Safepoint checking logically implies an active JavaThread. 160 guarantee(self->is_active_Java_thread(), "invariant"); 161 assert_wait_lock_state(self); 162 163 int wait_status; 164 // conceptually set the owner to NULL in anticipation of 165 // abdicating the lock in wait 166 set_owner(NULL); 167 // Check safepoint state after resetting owner and possible NSV. 168 check_safepoint_state(self); 169 JavaThread *jt = (JavaThread *)self; 170 Mutex* in_flight_mutex = NULL; 171 172 { 173 ThreadBlockInVMWithDeadlockCheck tbivmdc(jt, &in_flight_mutex); 174 OSThreadWaitState osts(self->osthread(), false /* not Object.wait() */); 175 if (as_suspend_equivalent) { 176 jt->set_suspend_equivalent(); 177 // cleared by handle_special_suspend_equivalent_condition() or 178 // java_suspend_self() 179 } 180 181 wait_status = _lock.wait(timeout); 182 in_flight_mutex = this; // save for ~ThreadBlockInVMWithDeadlockCheck 183 184 // were we externally suspended while we were waiting? 185 if (as_suspend_equivalent && jt->handle_special_suspend_equivalent_condition()) { 186 // Our event wait has finished and we own the lock, but 187 // while we were waiting another thread suspended us. We don't 188 // want to hold the lock while suspended because that 189 // would surprise the thread that suspended us. 190 _lock.unlock(); 191 jt->java_suspend_self(); 192 _lock.lock(); 193 } 194 } 195 196 if (in_flight_mutex != NULL) { 197 // Not unlocked by ~ThreadBlockInVMWithDeadlockCheck 198 assert_owner(NULL); 199 // Conceptually reestablish ownership of the lock. 200 set_owner(self); 201 } else { 202 lock(self); 203 } 204 205 return wait_status != 0; // return true IFF timeout 206 } 207 208 Mutex::~Mutex() { 209 assert_owner(NULL); 210 } 211 212 // Only Threads_lock, Heap_lock and SR_lock may be safepoint_check_sometimes. 213 bool is_sometimes_ok(const char* name) { 214 return (strcmp(name, "Threads_lock") == 0 || strcmp(name, "Heap_lock") == 0 || strcmp(name, "SR_lock") == 0); 215 } 216 217 Mutex::Mutex(int Rank, const char * name, bool allow_vm_block, 218 SafepointCheckRequired safepoint_check_required) : _owner(NULL) { 219 assert(os::mutex_init_done(), "Too early!"); 220 if (name == NULL) { 221 strcpy(_name, "UNKNOWN"); 222 } else { 223 strncpy(_name, name, MUTEX_NAME_LEN - 1); 224 _name[MUTEX_NAME_LEN - 1] = '\0'; 225 } 226 #ifdef ASSERT 227 _allow_vm_block = allow_vm_block; 228 _rank = Rank; 229 _safepoint_check_required = safepoint_check_required; 230 231 assert(_safepoint_check_required != _safepoint_check_sometimes || is_sometimes_ok(name), 232 "Lock has _safepoint_check_sometimes %s", name); 233 234 assert(_rank > special || _allow_vm_block, 235 "Special locks or below should allow the vm to block"); 236 assert(_rank > special || _safepoint_check_required == _safepoint_check_never, 237 "Special locks or below should never safepoint"); 238 #endif 239 } 240 241 Monitor::Monitor(int Rank, const char * name, bool allow_vm_block, 242 SafepointCheckRequired safepoint_check_required) : 243 Mutex(Rank, name, allow_vm_block, safepoint_check_required) {} 244 245 bool Mutex::owned_by_self() const { 246 return _owner == Thread::current(); 247 } 248 249 void Mutex::print_on_error(outputStream* st) const { 250 st->print("[" PTR_FORMAT, p2i(this)); 251 st->print("] %s", _name); 252 st->print(" - owner thread: " PTR_FORMAT, p2i(_owner)); 253 } 254 255 // ---------------------------------------------------------------------------------- 256 // Non-product code 257 258 #ifndef PRODUCT 259 const char* print_safepoint_check(Mutex::SafepointCheckRequired safepoint_check) { 260 switch (safepoint_check) { 261 case Mutex::_safepoint_check_never: return "safepoint_check_never"; 262 case Mutex::_safepoint_check_sometimes: return "safepoint_check_sometimes"; 263 case Mutex::_safepoint_check_always: return "safepoint_check_always"; 264 default: return ""; 265 } 266 } 267 268 void Mutex::print_on(outputStream* st) const { 269 st->print("Mutex: [" PTR_FORMAT "] %s - owner: " PTR_FORMAT, 270 p2i(this), _name, p2i(_owner)); 271 if (_allow_vm_block) { 272 st->print("%s", " allow_vm_block"); 273 } 274 st->print(" %s", print_safepoint_check(_safepoint_check_required)); 275 st->cr(); 276 } 277 #endif 278 279 #ifdef ASSERT 280 void Mutex::assert_owner(Thread * expected) { 281 const char* msg = "invalid owner"; 282 if (expected == NULL) { 283 msg = "should be un-owned"; 284 } 285 else if (expected == Thread::current()) { 286 msg = "should be owned by current thread"; 287 } 288 assert(_owner == expected, 289 "%s: owner=" INTPTR_FORMAT ", should be=" INTPTR_FORMAT, 290 msg, p2i(_owner), p2i(expected)); 291 } 292 293 Mutex* Mutex::get_least_ranked_lock(Mutex* locks) { 294 Mutex *res, *tmp; 295 for (res = tmp = locks; tmp != NULL; tmp = tmp->next()) { 296 if (tmp->rank() < res->rank()) { 297 res = tmp; 298 } 299 } 300 if (!SafepointSynchronize::is_at_safepoint()) { 301 // In this case, we expect the held locks to be 302 // in increasing rank order (modulo any native ranks) 303 for (tmp = locks; tmp != NULL; tmp = tmp->next()) { 304 if (tmp->next() != NULL) { 305 assert(tmp->rank() == Mutex::native || 306 tmp->rank() <= tmp->next()->rank(), "mutex rank anomaly?"); 307 } 308 } 309 } 310 return res; 311 } 312 313 Mutex* Mutex::get_least_ranked_lock_besides_this(Mutex* locks) { 314 Mutex *res, *tmp; 315 for (res = NULL, tmp = locks; tmp != NULL; tmp = tmp->next()) { 316 if (tmp != this && (res == NULL || tmp->rank() < res->rank())) { 317 res = tmp; 318 } 319 } 320 if (!SafepointSynchronize::is_at_safepoint()) { 321 // In this case, we expect the held locks to be 322 // in increasing rank order (modulo any native ranks) 323 for (tmp = locks; tmp != NULL; tmp = tmp->next()) { 324 if (tmp->next() != NULL) { 325 assert(tmp->rank() == Mutex::native || 326 tmp->rank() <= tmp->next()->rank(), "mutex rank anomaly?"); 327 } 328 } 329 } 330 return res; 331 } 332 333 bool Mutex::contains(Mutex* locks, Mutex* lock) { 334 for (; locks != NULL; locks = locks->next()) { 335 if (locks == lock) { 336 return true; 337 } 338 } 339 return false; 340 } 341 342 // NSV implied with locking allow_vm_block or !safepoint_check locks. 343 void Mutex::no_safepoint_verifier(Thread* thread, bool enable) { 344 // The tty_lock is special because it is released for the safepoint by 345 // the safepoint mechanism. 346 if (this == tty_lock) { 347 return; 348 } 349 350 if (_allow_vm_block) { 351 if (enable) { 352 thread->_no_safepoint_count++; 353 } else { 354 thread->_no_safepoint_count--; 355 } 356 } 357 } 358 359 // Called immediately after lock acquisition or release as a diagnostic 360 // to track the lock-set of the thread and test for rank violations that 361 // might indicate exposure to deadlock. 362 // Rather like an EventListener for _owner (:>). 363 364 void Mutex::set_owner_implementation(Thread *new_owner) { 365 // This function is solely responsible for maintaining 366 // and checking the invariant that threads and locks 367 // are in a 1/N relation, with some some locks unowned. 368 // It uses the Mutex::_owner, Mutex::_next, and 369 // Thread::_owned_locks fields, and no other function 370 // changes those fields. 371 // It is illegal to set the mutex from one non-NULL 372 // owner to another--it must be owned by NULL as an 373 // intermediate state. 374 375 if (new_owner != NULL) { 376 // the thread is acquiring this lock 377 378 assert(new_owner == Thread::current(), "Should I be doing this?"); 379 assert(_owner == NULL, "setting the owner thread of an already owned mutex"); 380 _owner = new_owner; // set the owner 381 382 // link "this" into the owned locks list 383 384 Mutex* locks = get_least_ranked_lock(new_owner->owned_locks()); 385 // Mutex::set_owner_implementation is a friend of Thread 386 387 assert(this->rank() >= 0, "bad lock rank"); 388 389 // Deadlock avoidance rules require us to acquire Mutexes only in 390 // a global total order. For example m1 is the lowest ranked mutex 391 // that the thread holds and m2 is the mutex the thread is trying 392 // to acquire, then deadlock avoidance rules require that the rank 393 // of m2 be less than the rank of m1. 394 // The rank Mutex::native is an exception in that it is not subject 395 // to the verification rules. 396 if (this->rank() != Mutex::native && 397 this->rank() != Mutex::suspend_resume && 398 locks != NULL && locks->rank() <= this->rank() && 399 !SafepointSynchronize::is_at_safepoint()) { 400 new_owner->print_owned_locks(); 401 fatal("acquiring lock %s/%d out of order with lock %s/%d -- " 402 "possible deadlock", this->name(), this->rank(), 403 locks->name(), locks->rank()); 404 } 405 406 this->_next = new_owner->_owned_locks; 407 new_owner->_owned_locks = this; 408 409 // NSV implied with locking allow_vm_block flag. 410 no_safepoint_verifier(new_owner, true); 411 412 } else { 413 // the thread is releasing this lock 414 415 Thread* old_owner = _owner; 416 _last_owner = old_owner; 417 418 assert(old_owner != NULL, "removing the owner thread of an unowned mutex"); 419 assert(old_owner == Thread::current(), "removing the owner thread of an unowned mutex"); 420 421 _owner = NULL; // set the owner 422 423 Mutex* locks = old_owner->owned_locks(); 424 425 // remove "this" from the owned locks list 426 427 Mutex* prev = NULL; 428 bool found = false; 429 for (; locks != NULL; prev = locks, locks = locks->next()) { 430 if (locks == this) { 431 found = true; 432 break; 433 } 434 } 435 assert(found, "Removing a lock not owned"); 436 if (prev == NULL) { 437 old_owner->_owned_locks = _next; 438 } else { 439 prev->_next = _next; 440 } 441 _next = NULL; 442 443 // ~NSV implied with locking allow_vm_block flag. 444 no_safepoint_verifier(old_owner, false); 445 } 446 } 447 #endif // ASSERT