1 /* 2 * Copyright 2007-2011, Ingo Weinhold, ingo_weinhold@gmx.de. 3 * Copyright 2019, Haiku, Inc. All rights reserved. 4 * Distributed under the terms of the MIT License. 5 */ 6 7 #include <condition_variable.h> 8 9 #include <new> 10 #include <stdlib.h> 11 #include <string.h> 12 13 #include <debug.h> 14 #include <kscheduler.h> 15 #include <ksignal.h> 16 #include <int.h> 17 #include <listeners.h> 18 #include <scheduling_analysis.h> 19 #include <thread.h> 20 #include <util/AutoLock.h> 21 #include <util/atomic.h> 22 23 24 #define STATUS_ADDED 1 25 #define STATUS_WAITING 2 26 27 28 static const int kConditionVariableHashSize = 512; 29 30 31 struct ConditionVariableHashDefinition { 32 typedef const void* KeyType; 33 typedef ConditionVariable ValueType; 34 35 size_t HashKey(const void* key) const 36 { return (size_t)key; } 37 size_t Hash(ConditionVariable* variable) const 38 { return (size_t)variable->fObject; } 39 bool Compare(const void* key, ConditionVariable* variable) const 40 { return key == variable->fObject; } 41 ConditionVariable*& GetLink(ConditionVariable* variable) const 42 { return variable->fNext; } 43 }; 44 45 typedef BOpenHashTable<ConditionVariableHashDefinition> ConditionVariableHash; 46 static ConditionVariableHash sConditionVariableHash; 47 static rw_spinlock sConditionVariableHashLock; 48 49 50 static int 51 list_condition_variables(int argc, char** argv) 52 { 53 ConditionVariable::ListAll(); 54 return 0; 55 } 56 57 58 static int 59 dump_condition_variable(int argc, char** argv) 60 { 61 if (argc != 2) { 62 print_debugger_command_usage(argv[0]); 63 return 0; 64 } 65 66 addr_t address = parse_expression(argv[1]); 67 if (address == 0) 68 return 0; 69 70 ConditionVariable* variable = sConditionVariableHash.Lookup((void*)address); 71 72 if (variable == NULL) { 73 // It must be a direct pointer to a condition variable. 74 variable = (ConditionVariable*)address; 75 } 76 77 if (variable != NULL) { 78 variable->Dump(); 79 80 set_debug_variable("_cvar", (addr_t)variable); 81 set_debug_variable("_object", (addr_t)variable->Object()); 82 83 } else 84 kprintf("no condition variable at or with key %p\n", (void*)address); 85 86 return 0; 87 } 88 89 90 // #pragma mark - ConditionVariableEntry 91 92 93 ConditionVariableEntry::ConditionVariableEntry() 94 : fVariable(NULL) 95 { 96 } 97 98 99 ConditionVariableEntry::~ConditionVariableEntry() 100 { 101 // We can use an "unsafe" non-atomic access of fVariable here, since we only 102 // care whether it is non-NULL, not what its specific value is. 103 if (fVariable != NULL) 104 _RemoveFromVariable(); 105 } 106 107 108 bool 109 ConditionVariableEntry::Add(const void* object) 110 { 111 ASSERT(object != NULL); 112 113 InterruptsLocker _; 114 ReadSpinLocker hashLocker(sConditionVariableHashLock); 115 116 ConditionVariable* variable = sConditionVariableHash.Lookup(object); 117 118 if (variable == NULL) { 119 fWaitStatus = B_ENTRY_NOT_FOUND; 120 return false; 121 } 122 123 SpinLocker variableLocker(variable->fLock); 124 hashLocker.Unlock(); 125 126 _AddToLockedVariable(variable); 127 128 return true; 129 } 130 131 132 inline void 133 ConditionVariableEntry::_AddToLockedVariable(ConditionVariable* variable) 134 { 135 ASSERT(fVariable == NULL); 136 137 fThread = thread_get_current_thread(); 138 fVariable = variable; 139 fWaitStatus = STATUS_ADDED; 140 fVariable->fEntries.Add(this); 141 atomic_add(&fVariable->fEntriesCount, 1); 142 } 143 144 145 void 146 ConditionVariableEntry::_RemoveFromVariable() 147 { 148 // This section is critical because it can race with _NotifyLocked on the 149 // variable's thread, so we must not be interrupted during it. 150 InterruptsLocker _; 151 152 ConditionVariable* variable = atomic_pointer_get(&fVariable); 153 if (atomic_pointer_get_and_set(&fThread, (Thread*)NULL) == NULL) { 154 // If fThread was already NULL, that means the variable is already 155 // in the process of clearing us out (or already has finished doing so.) 156 // We thus cannot access fVariable, and must spin until it is cleared. 157 int32 tries = 0; 158 while (atomic_pointer_get(&fVariable) != NULL) { 159 tries++; 160 if ((tries % 10000) == 0) 161 panic("variable pointer was not unset for a long time!"); 162 cpu_pause(); 163 } 164 165 return; 166 } 167 168 while (true) { 169 if (atomic_pointer_get(&fVariable) == NULL) { 170 // The variable must have cleared us out. Acknowledge this and return. 171 atomic_add(&variable->fEntriesCount, -1); 172 return; 173 } 174 175 // There is of course a small race between checking the pointer and then 176 // the try_acquire in which the variable might clear out our fVariable. 177 // However, in the case where we were the ones to clear fThread, the 178 // variable will notice that and then wait for us to acknowledge the 179 // removal by decrementing fEntriesCount, as we do above; and until 180 // we do that, we may validly use our cached pointer to the variable. 181 if (try_acquire_spinlock(&variable->fLock)) 182 break; 183 } 184 185 // We now hold the variable's lock. Remove ourselves. 186 if (fVariable->fEntries.Contains(this)) 187 fVariable->fEntries.Remove(this); 188 189 atomic_pointer_set(&fVariable, (ConditionVariable*)NULL); 190 atomic_add(&variable->fEntriesCount, -1); 191 release_spinlock(&variable->fLock); 192 } 193 194 195 status_t 196 ConditionVariableEntry::Wait(uint32 flags, bigtime_t timeout) 197 { 198 #if KDEBUG 199 if (!are_interrupts_enabled()) { 200 panic("ConditionVariableEntry::Wait() called with interrupts " 201 "disabled, entry: %p, variable: %p", this, fVariable); 202 return B_ERROR; 203 } 204 #endif 205 206 // The race in-between get_and_set and (re)set is irrelevant, because 207 // if the status really is <= 0, we have already been or are about to 208 // be removed from the variable, and nothing else is going to set the status. 209 status_t waitStatus = atomic_get_and_set(&fWaitStatus, STATUS_WAITING); 210 if (waitStatus <= 0) { 211 fWaitStatus = waitStatus; 212 return waitStatus; 213 } 214 215 InterruptsLocker _; 216 217 thread_prepare_to_block(thread_get_current_thread(), flags, 218 THREAD_BLOCK_TYPE_CONDITION_VARIABLE, atomic_pointer_get(&fVariable)); 219 220 waitStatus = atomic_get(&fWaitStatus); 221 if (waitStatus <= 0) { 222 // We were just woken up! Unblock ourselves immediately. 223 thread_unblock(thread_get_current_thread(), waitStatus); 224 } 225 226 status_t error; 227 if ((flags & (B_RELATIVE_TIMEOUT | B_ABSOLUTE_TIMEOUT)) != 0) 228 error = thread_block_with_timeout(flags, timeout); 229 else 230 error = thread_block(); 231 232 _RemoveFromVariable(); 233 return error; 234 } 235 236 237 status_t 238 ConditionVariableEntry::Wait(const void* object, uint32 flags, 239 bigtime_t timeout) 240 { 241 if (Add(object)) 242 return Wait(flags, timeout); 243 return B_ENTRY_NOT_FOUND; 244 } 245 246 247 // #pragma mark - ConditionVariable 248 249 250 /*! Initialization method for anonymous (unpublished) condition variables. 251 */ 252 void 253 ConditionVariable::Init(const void* object, const char* objectType) 254 { 255 fObject = object; 256 fObjectType = objectType; 257 new(&fEntries) EntryList; 258 fEntriesCount = 0; 259 B_INITIALIZE_SPINLOCK(&fLock); 260 261 T_SCHEDULING_ANALYSIS(InitConditionVariable(this, object, objectType)); 262 NotifyWaitObjectListeners(&WaitObjectListener::ConditionVariableInitialized, 263 this); 264 } 265 266 267 void 268 ConditionVariable::Publish(const void* object, const char* objectType) 269 { 270 ASSERT(object != NULL); 271 272 fObject = object; 273 fObjectType = objectType; 274 new(&fEntries) EntryList; 275 fEntriesCount = 0; 276 B_INITIALIZE_SPINLOCK(&fLock); 277 278 T_SCHEDULING_ANALYSIS(InitConditionVariable(this, object, objectType)); 279 NotifyWaitObjectListeners(&WaitObjectListener::ConditionVariableInitialized, 280 this); 281 282 InterruptsWriteSpinLocker _(sConditionVariableHashLock); 283 284 ASSERT_PRINT(sConditionVariableHash.Lookup(object) == NULL, 285 "condition variable: %p\n", sConditionVariableHash.Lookup(object)); 286 287 sConditionVariableHash.InsertUnchecked(this); 288 } 289 290 291 void 292 ConditionVariable::Unpublish() 293 { 294 ASSERT(fObject != NULL); 295 296 InterruptsLocker _; 297 WriteSpinLocker hashLocker(sConditionVariableHashLock); 298 SpinLocker selfLocker(fLock); 299 300 #if KDEBUG 301 ConditionVariable* variable = sConditionVariableHash.Lookup(fObject); 302 if (variable != this) { 303 panic("Condition variable %p not published, found: %p", this, variable); 304 return; 305 } 306 #endif 307 308 sConditionVariableHash.RemoveUnchecked(this); 309 fObject = NULL; 310 fObjectType = NULL; 311 312 hashLocker.Unlock(); 313 314 if (!fEntries.IsEmpty()) 315 _NotifyLocked(true, B_ENTRY_NOT_FOUND); 316 } 317 318 319 void 320 ConditionVariable::Add(ConditionVariableEntry* entry) 321 { 322 InterruptsSpinLocker _(fLock); 323 entry->_AddToLockedVariable(this); 324 } 325 326 327 status_t 328 ConditionVariable::Wait(uint32 flags, bigtime_t timeout) 329 { 330 ConditionVariableEntry entry; 331 Add(&entry); 332 return entry.Wait(flags, timeout); 333 } 334 335 336 /*static*/ void 337 ConditionVariable::NotifyOne(const void* object, status_t result) 338 { 339 InterruptsReadSpinLocker locker(sConditionVariableHashLock); 340 ConditionVariable* variable = sConditionVariableHash.Lookup(object); 341 locker.Unlock(); 342 if (variable == NULL) 343 return; 344 345 variable->NotifyOne(result); 346 } 347 348 349 /*static*/ void 350 ConditionVariable::NotifyAll(const void* object, status_t result) 351 { 352 InterruptsReadSpinLocker locker(sConditionVariableHashLock); 353 ConditionVariable* variable = sConditionVariableHash.Lookup(object); 354 locker.Unlock(); 355 if (variable == NULL) 356 return; 357 358 variable->NotifyAll(result); 359 } 360 361 362 void 363 ConditionVariable::_Notify(bool all, status_t result) 364 { 365 InterruptsSpinLocker _(fLock); 366 367 if (!fEntries.IsEmpty()) { 368 if (result > B_OK) { 369 panic("tried to notify with invalid result %" B_PRId32 "\n", result); 370 result = B_ERROR; 371 } 372 373 _NotifyLocked(all, result); 374 } 375 } 376 377 378 /*! Called with interrupts disabled and the condition variable's spinlock held. 379 */ 380 void 381 ConditionVariable::_NotifyLocked(bool all, status_t result) 382 { 383 // Dequeue and wake up the blocked threads. 384 while (ConditionVariableEntry* entry = fEntries.RemoveHead()) { 385 Thread* thread = atomic_pointer_get_and_set(&entry->fThread, (Thread*)NULL); 386 if (thread == NULL) { 387 // The entry must be in the process of trying to remove itself from us. 388 // Clear its variable and wait for it to acknowledge this in fEntriesCount, 389 // as it is the one responsible for decrementing that. 390 const int32 oldCount = atomic_get(&fEntriesCount); 391 atomic_pointer_set(&entry->fVariable, (ConditionVariable*)NULL); 392 393 // As fEntriesCount is only modified while our lock is held, nothing else 394 // will modify it while we are spinning, since we hold it at present. 395 int32 tries = 0; 396 while (atomic_get(&fEntriesCount) == oldCount) { 397 tries++; 398 if ((tries % 10000) == 0) 399 panic("entries count was not decremented for a long time!"); 400 cpu_pause(); 401 } 402 } else { 403 status_t waitStatus = atomic_get_and_set(&entry->fWaitStatus, result); 404 405 SpinLocker threadLocker(thread->scheduler_lock); 406 if (waitStatus == STATUS_WAITING && thread->state != B_THREAD_WAITING) { 407 // The thread is not in B_THREAD_WAITING state, so we must unblock it early, 408 // in case it tries to re-block itself immediately after we unset fVariable. 409 thread_unblock_locked(thread, result); 410 waitStatus = result; 411 } 412 413 // No matter what the thread is doing, as we were the ones to clear its 414 // fThread, so we are the ones responsible for decrementing fEntriesCount. 415 // (We may not validly access the entry once we unset its fVariable.) 416 atomic_pointer_set(&entry->fVariable, (ConditionVariable*)NULL); 417 atomic_add(&fEntriesCount, -1); 418 419 // If the thread was in B_THREAD_WAITING state, we unblock it after unsetting 420 // fVariable, because otherwise it will wake up before thread_unblock returns 421 // and spin while waiting for us to do so. 422 if (waitStatus == STATUS_WAITING) 423 thread_unblock_locked(thread, result); 424 } 425 426 if (!all) 427 break; 428 } 429 } 430 431 432 /*static*/ void 433 ConditionVariable::ListAll() 434 { 435 kprintf(" variable object (type) waiting threads\n"); 436 kprintf("------------------------------------------------------------\n"); 437 ConditionVariableHash::Iterator it(&sConditionVariableHash); 438 while (ConditionVariable* variable = it.Next()) { 439 // count waiting threads 440 int count = variable->fEntries.Count(); 441 442 kprintf("%p %p %-20s %15d\n", variable, variable->fObject, 443 variable->fObjectType, count); 444 } 445 } 446 447 448 void 449 ConditionVariable::Dump() const 450 { 451 kprintf("condition variable %p\n", this); 452 kprintf(" object: %p (%s)\n", fObject, fObjectType); 453 kprintf(" threads:"); 454 455 for (EntryList::ConstIterator it = fEntries.GetIterator(); 456 ConditionVariableEntry* entry = it.Next();) { 457 kprintf(" %" B_PRId32, entry->fThread->id); 458 } 459 kprintf("\n"); 460 } 461 462 463 // #pragma mark - 464 465 466 void 467 condition_variable_init() 468 { 469 new(&sConditionVariableHash) ConditionVariableHash; 470 471 status_t error = sConditionVariableHash.Init(kConditionVariableHashSize); 472 if (error != B_OK) { 473 panic("condition_variable_init(): Failed to init hash table: %s", 474 strerror(error)); 475 } 476 477 add_debugger_command_etc("cvar", &dump_condition_variable, 478 "Dump condition variable info", 479 "<address>\n" 480 "Prints info for the specified condition variable.\n" 481 " <address> - Address of the condition variable or the object it is\n" 482 " associated with.\n", 0); 483 add_debugger_command_etc("cvars", &list_condition_variables, 484 "List condition variables", 485 "\n" 486 "Lists all existing condition variables\n", 0); 487 } 488