SDL 3.0
SDL_mutex.h File Reference
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Macros

#define SDL_THREAD_ANNOTATION_ATTRIBUTE__(x)   /* no-op */
 
#define SDL_CAPABILITY(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(capability(x))
 
#define SDL_SCOPED_CAPABILITY    SDL_THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
 
#define SDL_GUARDED_BY(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
 
#define SDL_PT_GUARDED_BY(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))
 
#define SDL_ACQUIRED_BEFORE(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(x))
 
#define SDL_ACQUIRED_AFTER(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(x))
 
#define SDL_REQUIRES(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(requires_capability(x))
 
#define SDL_REQUIRES_SHARED(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(requires_shared_capability(x))
 
#define SDL_ACQUIRE(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquire_capability(x))
 
#define SDL_ACQUIRE_SHARED(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquire_shared_capability(x))
 
#define SDL_RELEASE(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_capability(x))
 
#define SDL_RELEASE_SHARED(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_shared_capability(x))
 
#define SDL_RELEASE_GENERIC(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_generic_capability(x))
 
#define SDL_TRY_ACQUIRE(x, y)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_capability(x, y))
 
#define SDL_TRY_ACQUIRE_SHARED(x, y)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_shared_capability(x, y))
 
#define SDL_EXCLUDES(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(x))
 
#define SDL_ASSERT_CAPABILITY(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(assert_capability(x))
 
#define SDL_ASSERT_SHARED_CAPABILITY(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_capability(x))
 
#define SDL_RETURN_CAPABILITY(x)    SDL_THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))
 
#define SDL_NO_THREAD_SAFETY_ANALYSIS    SDL_THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
 

Mutex functions

typedef struct SDL_Mutex SDL_Mutex
 
SDL_bool mutex
 
SDL_MutexSDL_CreateMutex (void)
 
void SDL_LockMutex (SDL_Mutex *mutex) SDL_ACQUIRE(mutex)
 
SDL_bool SDL_TryLockMutex (SDL_Mutex *mutex) SDL_TRY_ACQUIRE(0
 
void SDL_UnlockMutex (SDL_Mutex *mutex) SDL_RELEASE(mutex)
 
void SDL_DestroyMutex (SDL_Mutex *mutex)
 

Read/write lock functions

typedef struct SDL_RWLock SDL_RWLock
 
SDL_bool rwlock
 
SDL_RWLockSDL_CreateRWLock (void)
 
void SDL_LockRWLockForReading (SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock)
 
void SDL_LockRWLockForWriting (SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock)
 
SDL_bool SDL_TryLockRWLockForReading (SDL_RWLock *rwlock) SDL_TRY_ACQUIRE_SHARED(0
 
SDL_bool SDL_TryLockRWLockForWriting (SDL_RWLock *rwlock) SDL_TRY_ACQUIRE(0
 
void SDL_UnlockRWLock (SDL_RWLock *rwlock) SDL_RELEASE_GENERIC(rwlock)
 
void SDL_DestroyRWLock (SDL_RWLock *rwlock)
 

Semaphore functions

typedef struct SDL_Semaphore SDL_Semaphore
 
SDL_SemaphoreSDL_CreateSemaphore (Uint32 initial_value)
 
void SDL_DestroySemaphore (SDL_Semaphore *sem)
 
void SDL_WaitSemaphore (SDL_Semaphore *sem)
 
SDL_bool SDL_TryWaitSemaphore (SDL_Semaphore *sem)
 
SDL_bool SDL_WaitSemaphoreTimeout (SDL_Semaphore *sem, Sint32 timeoutMS)
 
void SDL_SignalSemaphore (SDL_Semaphore *sem)
 
Uint32 SDL_GetSemaphoreValue (SDL_Semaphore *sem)
 

Condition variable functions

typedef struct SDL_Condition SDL_Condition
 
SDL_ConditionSDL_CreateCondition (void)
 
void SDL_DestroyCondition (SDL_Condition *cond)
 
void SDL_SignalCondition (SDL_Condition *cond)
 
void SDL_BroadcastCondition (SDL_Condition *cond)
 
void SDL_WaitCondition (SDL_Condition *cond, SDL_Mutex *mutex)
 
SDL_bool SDL_WaitConditionTimeout (SDL_Condition *cond, SDL_Mutex *mutex, Sint32 timeoutMS)
 

Macro Definition Documentation

◆ SDL_ACQUIRE

#define SDL_ACQUIRE (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquire_capability(x))

Definition at line 73 of file SDL_mutex.h.

114 {
115#endif
116
117/**
118 * \name Mutex functions
119 */
120/* @{ */
121
122/**
123 * A means to serialize access to a resource between threads.
124 *
125 * Mutexes (short for "mutual exclusion") are a synchronization primitive that
126 * allows exactly one thread to proceed at a time.
127 *
128 * Wikipedia has a thorough explanation of the concept:
129 *
130 * https://en.wikipedia.org/wiki/Mutex
131 *
132 * \since This struct is available since SDL 3.0.0.
133 */
134typedef struct SDL_Mutex SDL_Mutex;
135
136/**
137 * Create a new mutex.
138 *
139 * All newly-created mutexes begin in the _unlocked_ state.
140 *
141 * Calls to SDL_LockMutex() will not return while the mutex is locked by
142 * another thread. See SDL_TryLockMutex() to attempt to lock without blocking.
143 *
144 * SDL mutexes are reentrant.
145 *
146 * \returns the initialized and unlocked mutex or NULL on failure; call
147 * SDL_GetError() for more information.
148 *
149 * \since This function is available since SDL 3.0.0.
150 *
151 * \sa SDL_DestroyMutex
152 * \sa SDL_LockMutex
153 * \sa SDL_TryLockMutex
154 * \sa SDL_UnlockMutex
155 */
156extern SDL_DECLSPEC SDL_Mutex * SDLCALL SDL_CreateMutex(void);
157
158/**
159 * Lock the mutex.
160 *
161 * This will block until the mutex is available, which is to say it is in the
162 * unlocked state and the OS has chosen the caller as the next thread to lock
163 * it. Of all threads waiting to lock the mutex, only one may do so at a time.
164 *
165 * It is legal for the owning thread to lock an already-locked mutex. It must
166 * unlock it the same number of times before it is actually made available for
167 * other threads in the system (this is known as a "recursive mutex").
168 *
169 * This function does not fail; if mutex is NULL, it will return immediately
170 * having locked nothing. If the mutex is valid, this function will always
171 * block until it can lock the mutex, and return with it locked.
172 *
173 * \param mutex the mutex to lock.
174 *
175 * \since This function is available since SDL 3.0.0.
176 *
177 * \sa SDL_TryLockMutex
178 * \sa SDL_UnlockMutex
179 */
180extern SDL_DECLSPEC void SDLCALL SDL_LockMutex(SDL_Mutex *mutex) SDL_ACQUIRE(mutex);
181
182/**
183 * Try to lock a mutex without blocking.
184 *
185 * This works just like SDL_LockMutex(), but if the mutex is not available,
186 * this function returns SDL_FALSE immediately.
187 *
188 * This technique is useful if you need exclusive access to a resource but
189 * don't want to wait for it, and will return to it to try again later.
190 *
191 * This function returns SDL_TRUE if passed a NULL mutex.
192 *
193 * \param mutex the mutex to try to lock.
194 * \returns SDL_TRUE on success, SDL_FALSE if the mutex would block.
195 *
196 * \since This function is available since SDL 3.0.0.
197 *
198 * \sa SDL_LockMutex
199 * \sa SDL_UnlockMutex
200 */
201extern SDL_DECLSPEC SDL_bool SDLCALL SDL_TryLockMutex(SDL_Mutex *mutex) SDL_TRY_ACQUIRE(0, mutex);
202
203/**
204 * Unlock the mutex.
205 *
206 * It is legal for the owning thread to lock an already-locked mutex. It must
207 * unlock it the same number of times before it is actually made available for
208 * other threads in the system (this is known as a "recursive mutex").
209 *
210 * It is illegal to unlock a mutex that has not been locked by the current
211 * thread, and doing so results in undefined behavior.
212 *
213 * \param mutex the mutex to unlock.
214 *
215 * \since This function is available since SDL 3.0.0.
216 *
217 * \sa SDL_LockMutex
218 * \sa SDL_TryLockMutex
219 */
220extern SDL_DECLSPEC void SDLCALL SDL_UnlockMutex(SDL_Mutex *mutex) SDL_RELEASE(mutex);
221
222/**
223 * Destroy a mutex created with SDL_CreateMutex().
224 *
225 * This function must be called on any mutex that is no longer needed. Failure
226 * to destroy a mutex will result in a system memory or resource leak. While
227 * it is safe to destroy a mutex that is _unlocked_, it is not safe to attempt
228 * to destroy a locked mutex, and may result in undefined behavior depending
229 * on the platform.
230 *
231 * \param mutex the mutex to destroy.
232 *
233 * \since This function is available since SDL 3.0.0.
234 *
235 * \sa SDL_CreateMutex
236 */
237extern SDL_DECLSPEC void SDLCALL SDL_DestroyMutex(SDL_Mutex *mutex);
238
239/* @} *//* Mutex functions */
240
241
242/**
243 * \name Read/write lock functions
244 */
245/* @{ */
246
247/**
248 * A mutex that allows read-only threads to run in parallel.
249 *
250 * A rwlock is roughly the same concept as SDL_Mutex, but allows threads that
251 * request read-only access to all hold the lock at the same time. If a thread
252 * requests write access, it will block until all read-only threads have
253 * released the lock, and no one else can hold the thread (for reading or
254 * writing) at the same time as the writing thread.
255 *
256 * This can be more efficient in cases where several threads need to access
257 * data frequently, but changes to that data are rare.
258 *
259 * There are other rules that apply to rwlocks that don't apply to mutexes,
260 * about how threads are scheduled and when they can be recursively locked.
261 * These are documented in the other rwlock functions.
262 *
263 * \since This struct is available since SDL 3.0.0.
264 */
265typedef struct SDL_RWLock SDL_RWLock;
266
267/**
268 * Create a new read/write lock.
269 *
270 * A read/write lock is useful for situations where you have multiple threads
271 * trying to access a resource that is rarely updated. All threads requesting
272 * a read-only lock will be allowed to run in parallel; if a thread requests a
273 * write lock, it will be provided exclusive access. This makes it safe for
274 * multiple threads to use a resource at the same time if they promise not to
275 * change it, and when it has to be changed, the rwlock will serve as a
276 * gateway to make sure those changes can be made safely.
277 *
278 * In the right situation, a rwlock can be more efficient than a mutex, which
279 * only lets a single thread proceed at a time, even if it won't be modifying
280 * the data.
281 *
282 * All newly-created read/write locks begin in the _unlocked_ state.
283 *
284 * Calls to SDL_LockRWLockForReading() and SDL_LockRWLockForWriting will not
285 * return while the rwlock is locked _for writing_ by another thread. See
286 * SDL_TryLockRWLockForReading() and SDL_TryLockRWLockForWriting() to attempt
287 * to lock without blocking.
288 *
289 * SDL read/write locks are only recursive for read-only locks! They are not
290 * guaranteed to be fair, or provide access in a FIFO manner! They are not
291 * guaranteed to favor writers. You may not lock a rwlock for both read-only
292 * and write access at the same time from the same thread (so you can't
293 * promote your read-only lock to a write lock without unlocking first).
294 *
295 * \returns the initialized and unlocked read/write lock or NULL on failure;
296 * call SDL_GetError() for more information.
297 *
298 * \since This function is available since SDL 3.0.0.
299 *
300 * \sa SDL_DestroyRWLock
301 * \sa SDL_LockRWLockForReading
302 * \sa SDL_LockRWLockForWriting
303 * \sa SDL_TryLockRWLockForReading
304 * \sa SDL_TryLockRWLockForWriting
305 * \sa SDL_UnlockRWLock
306 */
307extern SDL_DECLSPEC SDL_RWLock * SDLCALL SDL_CreateRWLock(void);
308
309/**
310 * Lock the read/write lock for _read only_ operations.
311 *
312 * This will block until the rwlock is available, which is to say it is not
313 * locked for writing by any other thread. Of all threads waiting to lock the
314 * rwlock, all may do so at the same time as long as they are requesting
315 * read-only access; if a thread wants to lock for writing, only one may do so
316 * at a time, and no other threads, read-only or not, may hold the lock at the
317 * same time.
318 *
319 * It is legal for the owning thread to lock an already-locked rwlock for
320 * reading. It must unlock it the same number of times before it is actually
321 * made available for other threads in the system (this is known as a
322 * "recursive rwlock").
323 *
324 * Note that locking for writing is not recursive (this is only available to
325 * read-only locks).
326 *
327 * It is illegal to request a read-only lock from a thread that already holds
328 * the write lock. Doing so results in undefined behavior. Unlock the write
329 * lock before requesting a read-only lock. (But, of course, if you have the
330 * write lock, you don't need further locks to read in any case.)
331 *
332 * This function does not fail; if rwlock is NULL, it will return immediately
333 * having locked nothing. If the rwlock is valid, this function will always
334 * block until it can lock the mutex, and return with it locked.
335 *
336 * \param rwlock the read/write lock to lock.
337 *
338 * \since This function is available since SDL 3.0.0.
339 *
340 * \sa SDL_LockRWLockForWriting
341 * \sa SDL_TryLockRWLockForReading
342 * \sa SDL_UnlockRWLock
343 */
344extern SDL_DECLSPEC void SDLCALL SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock);
345
346/**
347 * Lock the read/write lock for _write_ operations.
348 *
349 * This will block until the rwlock is available, which is to say it is not
350 * locked for reading or writing by any other thread. Only one thread may hold
351 * the lock when it requests write access; all other threads, whether they
352 * also want to write or only want read-only access, must wait until the
353 * writer thread has released the lock.
354 *
355 * It is illegal for the owning thread to lock an already-locked rwlock for
356 * writing (read-only may be locked recursively, writing can not). Doing so
357 * results in undefined behavior.
358 *
359 * It is illegal to request a write lock from a thread that already holds a
360 * read-only lock. Doing so results in undefined behavior. Unlock the
361 * read-only lock before requesting a write lock.
362 *
363 * This function does not fail; if rwlock is NULL, it will return immediately
364 * having locked nothing. If the rwlock is valid, this function will always
365 * block until it can lock the mutex, and return with it locked.
366 *
367 * \param rwlock the read/write lock to lock.
368 *
369 * \since This function is available since SDL 3.0.0.
370 *
371 * \sa SDL_LockRWLockForReading
372 * \sa SDL_TryLockRWLockForWriting
373 * \sa SDL_UnlockRWLock
374 */
375extern SDL_DECLSPEC void SDLCALL SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock);
376
377/**
378 * Try to lock a read/write lock _for reading_ without blocking.
379 *
380 * This works just like SDL_LockRWLockForReading(), but if the rwlock is not
381 * available, then this function returns SDL_FALSE immediately.
382 *
383 * This technique is useful if you need access to a resource but don't want to
384 * wait for it, and will return to it to try again later.
385 *
386 * Trying to lock for read-only access can succeed if other threads are
387 * holding read-only locks, as this won't prevent access.
388 *
389 * This function returns SDL_TRUE if passed a NULL rwlock.
390 *
391 * \param rwlock the rwlock to try to lock.
392 * \returns SDL_TRUE on success, SDL_FALSE if the lock would block.
393 *
394 * \since This function is available since SDL 3.0.0.
395 *
396 * \sa SDL_LockRWLockForReading
397 * \sa SDL_TryLockRWLockForWriting
398 * \sa SDL_UnlockRWLock
399 */
401
402/**
403 * Try to lock a read/write lock _for writing_ without blocking.
404 *
405 * This works just like SDL_LockRWLockForWriting(), but if the rwlock is not
406 * available, then this function returns SDL_FALSE immediately.
407 *
408 * This technique is useful if you need exclusive access to a resource but
409 * don't want to wait for it, and will return to it to try again later.
410 *
411 * It is illegal for the owning thread to lock an already-locked rwlock for
412 * writing (read-only may be locked recursively, writing can not). Doing so
413 * results in undefined behavior.
414 *
415 * It is illegal to request a write lock from a thread that already holds a
416 * read-only lock. Doing so results in undefined behavior. Unlock the
417 * read-only lock before requesting a write lock.
418 *
419 * This function returns SDL_TRUE if passed a NULL rwlock.
420 *
421 * \param rwlock the rwlock to try to lock.
422 * \returns SDL_TRUE on success, SDL_FALSE if the lock would block.
423 *
424 * \since This function is available since SDL 3.0.0.
425 *
426 * \sa SDL_LockRWLockForWriting
427 * \sa SDL_TryLockRWLockForReading
428 * \sa SDL_UnlockRWLock
429 */
431
432/**
433 * Unlock the read/write lock.
434 *
435 * Use this function to unlock the rwlock, whether it was locked for read-only
436 * or write operations.
437 *
438 * It is legal for the owning thread to lock an already-locked read-only lock.
439 * It must unlock it the same number of times before it is actually made
440 * available for other threads in the system (this is known as a "recursive
441 * rwlock").
442 *
443 * It is illegal to unlock a rwlock that has not been locked by the current
444 * thread, and doing so results in undefined behavior.
445 *
446 * \param rwlock the rwlock to unlock.
447 *
448 * \since This function is available since SDL 3.0.0.
449 *
450 * \sa SDL_LockRWLockForReading
451 * \sa SDL_LockRWLockForWriting
452 * \sa SDL_TryLockRWLockForReading
453 * \sa SDL_TryLockRWLockForWriting
454 */
455extern SDL_DECLSPEC void SDLCALL SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_RELEASE_GENERIC(rwlock);
456
457/**
458 * Destroy a read/write lock created with SDL_CreateRWLock().
459 *
460 * This function must be called on any read/write lock that is no longer
461 * needed. Failure to destroy a rwlock will result in a system memory or
462 * resource leak. While it is safe to destroy a rwlock that is _unlocked_, it
463 * is not safe to attempt to destroy a locked rwlock, and may result in
464 * undefined behavior depending on the platform.
465 *
466 * \param rwlock the rwlock to destroy.
467 *
468 * \since This function is available since SDL 3.0.0.
469 *
470 * \sa SDL_CreateRWLock
471 */
472extern SDL_DECLSPEC void SDLCALL SDL_DestroyRWLock(SDL_RWLock *rwlock);
473
474/* @} *//* Read/write lock functions */
475
476
477/**
478 * \name Semaphore functions
479 */
480/* @{ */
481
482/**
483 * A means to manage access to a resource, by count, between threads.
484 *
485 * Semaphores (specifically, "counting semaphores"), let X number of threads
486 * request access at the same time, each thread granted access decrementing a
487 * counter. When the counter reaches zero, future requests block until a prior
488 * thread releases their request, incrementing the counter again.
489 *
490 * Wikipedia has a thorough explanation of the concept:
491 *
492 * https://en.wikipedia.org/wiki/Semaphore_(programming)
493 *
494 * \since This struct is available since SDL 3.0.0.
495 */
496typedef struct SDL_Semaphore SDL_Semaphore;
497
498/**
499 * Create a semaphore.
500 *
501 * This function creates a new semaphore and initializes it with the value
502 * `initial_value`. Each wait operation on the semaphore will atomically
503 * decrement the semaphore value and potentially block if the semaphore value
504 * is 0. Each post operation will atomically increment the semaphore value and
505 * wake waiting threads and allow them to retry the wait operation.
506 *
507 * \param initial_value the starting value of the semaphore.
508 * \returns a new semaphore or NULL on failure; call SDL_GetError() for more
509 * information.
510 *
511 * \since This function is available since SDL 3.0.0.
512 *
513 * \sa SDL_DestroySemaphore
514 * \sa SDL_SignalSemaphore
515 * \sa SDL_TryWaitSemaphore
516 * \sa SDL_GetSemaphoreValue
517 * \sa SDL_WaitSemaphore
518 * \sa SDL_WaitSemaphoreTimeout
519 */
520extern SDL_DECLSPEC SDL_Semaphore * SDLCALL SDL_CreateSemaphore(Uint32 initial_value);
521
522/**
523 * Destroy a semaphore.
524 *
525 * It is not safe to destroy a semaphore if there are threads currently
526 * waiting on it.
527 *
528 * \param sem the semaphore to destroy.
529 *
530 * \since This function is available since SDL 3.0.0.
531 *
532 * \sa SDL_CreateSemaphore
533 */
534extern SDL_DECLSPEC void SDLCALL SDL_DestroySemaphore(SDL_Semaphore *sem);
535
536/**
537 * Wait until a semaphore has a positive value and then decrements it.
538 *
539 * This function suspends the calling thread until the semaphore pointed to by
540 * `sem` has a positive value, and then atomically decrement the semaphore
541 * value.
542 *
543 * This function is the equivalent of calling SDL_WaitSemaphoreTimeout() with
544 * a time length of -1.
545 *
546 * \param sem the semaphore wait on.
547 *
548 * \since This function is available since SDL 3.0.0.
549 *
550 * \sa SDL_SignalSemaphore
551 * \sa SDL_TryWaitSemaphore
552 * \sa SDL_WaitSemaphoreTimeout
553 */
554extern SDL_DECLSPEC void SDLCALL SDL_WaitSemaphore(SDL_Semaphore *sem);
555
556/**
557 * See if a semaphore has a positive value and decrement it if it does.
558 *
559 * This function checks to see if the semaphore pointed to by `sem` has a
560 * positive value and atomically decrements the semaphore value if it does. If
561 * the semaphore doesn't have a positive value, the function immediately
562 * returns SDL_FALSE.
563 *
564 * \param sem the semaphore to wait on.
565 * \returns SDL_TRUE if the wait succeeds, SDL_FALSE if the wait would block.
566 *
567 * \since This function is available since SDL 3.0.0.
568 *
569 * \sa SDL_SignalSemaphore
570 * \sa SDL_WaitSemaphore
571 * \sa SDL_WaitSemaphoreTimeout
572 */
573extern SDL_DECLSPEC SDL_bool SDLCALL SDL_TryWaitSemaphore(SDL_Semaphore *sem);
574
575/**
576 * Wait until a semaphore has a positive value and then decrements it.
577 *
578 * This function suspends the calling thread until either the semaphore
579 * pointed to by `sem` has a positive value or the specified time has elapsed.
580 * If the call is successful it will atomically decrement the semaphore value.
581 *
582 * \param sem the semaphore to wait on.
583 * \param timeoutMS the length of the timeout, in milliseconds, or -1 to wait
584 * indefinitely.
585 * \returns SDL_TRUE if the wait succeeds or SDL_FALSE if the wait times out.
586 *
587 * \since This function is available since SDL 3.0.0.
588 *
589 * \sa SDL_SignalSemaphore
590 * \sa SDL_TryWaitSemaphore
591 * \sa SDL_WaitSemaphore
592 */
593extern SDL_DECLSPEC SDL_bool SDLCALL SDL_WaitSemaphoreTimeout(SDL_Semaphore *sem, Sint32 timeoutMS);
594
595/**
596 * Atomically increment a semaphore's value and wake waiting threads.
597 *
598 * \param sem the semaphore to increment.
599 *
600 * \since This function is available since SDL 3.0.0.
601 *
602 * \sa SDL_TryWaitSemaphore
603 * \sa SDL_WaitSemaphore
604 * \sa SDL_WaitSemaphoreTimeout
605 */
606extern SDL_DECLSPEC void SDLCALL SDL_SignalSemaphore(SDL_Semaphore *sem);
607
608/**
609 * Get the current value of a semaphore.
610 *
611 * \param sem the semaphore to query.
612 * \returns the current value of the semaphore.
613 *
614 * \since This function is available since SDL 3.0.0.
615 */
616extern SDL_DECLSPEC Uint32 SDLCALL SDL_GetSemaphoreValue(SDL_Semaphore *sem);
617
618/* @} *//* Semaphore functions */
619
620
621/**
622 * \name Condition variable functions
623 */
624/* @{ */
625
626/**
627 * A means to block multiple threads until a condition is satisfied.
628 *
629 * Condition variables, paired with an SDL_Mutex, let an app halt multiple
630 * threads until a condition has occurred, at which time the app can release
631 * one or all waiting threads.
632 *
633 * Wikipedia has a thorough explanation of the concept:
634 *
635 * https://en.wikipedia.org/wiki/Condition_variable
636 *
637 * \since This struct is available since SDL 3.0.0.
638 */
639typedef struct SDL_Condition SDL_Condition;
640
641/**
642 * Create a condition variable.
643 *
644 * \returns a new condition variable or NULL on failure; call SDL_GetError()
645 * for more information.
646 *
647 * \since This function is available since SDL 3.0.0.
648 *
649 * \sa SDL_BroadcastCondition
650 * \sa SDL_SignalCondition
651 * \sa SDL_WaitCondition
652 * \sa SDL_WaitConditionTimeout
653 * \sa SDL_DestroyCondition
654 */
655extern SDL_DECLSPEC SDL_Condition * SDLCALL SDL_CreateCondition(void);
656
657/**
658 * Destroy a condition variable.
659 *
660 * \param cond the condition variable to destroy.
661 *
662 * \since This function is available since SDL 3.0.0.
663 *
664 * \sa SDL_CreateCondition
665 */
666extern SDL_DECLSPEC void SDLCALL SDL_DestroyCondition(SDL_Condition *cond);
667
668/**
669 * Restart one of the threads that are waiting on the condition variable.
670 *
671 * \param cond the condition variable to signal.
672 *
673 * \threadsafety It is safe to call this function from any thread.
674 *
675 * \since This function is available since SDL 3.0.0.
676 *
677 * \sa SDL_BroadcastCondition
678 * \sa SDL_WaitCondition
679 * \sa SDL_WaitConditionTimeout
680 */
681extern SDL_DECLSPEC void SDLCALL SDL_SignalCondition(SDL_Condition *cond);
682
683/**
684 * Restart all threads that are waiting on the condition variable.
685 *
686 * \param cond the condition variable to signal.
687 *
688 * \threadsafety It is safe to call this function from any thread.
689 *
690 * \since This function is available since SDL 3.0.0.
691 *
692 * \sa SDL_SignalCondition
693 * \sa SDL_WaitCondition
694 * \sa SDL_WaitConditionTimeout
695 */
696extern SDL_DECLSPEC void SDLCALL SDL_BroadcastCondition(SDL_Condition *cond);
697
698/**
699 * Wait until a condition variable is signaled.
700 *
701 * This function unlocks the specified `mutex` and waits for another thread to
702 * call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition
703 * variable `cond`. Once the condition variable is signaled, the mutex is
704 * re-locked and the function returns.
705 *
706 * The mutex must be locked before calling this function. Locking the mutex
707 * recursively (more than once) is not supported and leads to undefined
708 * behavior.
709 *
710 * This function is the equivalent of calling SDL_WaitConditionTimeout() with
711 * a time length of -1.
712 *
713 * \param cond the condition variable to wait on.
714 * \param mutex the mutex used to coordinate thread access.
715 *
716 * \threadsafety It is safe to call this function from any thread.
717 *
718 * \since This function is available since SDL 3.0.0.
719 *
720 * \sa SDL_BroadcastCondition
721 * \sa SDL_SignalCondition
722 * \sa SDL_WaitConditionTimeout
723 */
724extern SDL_DECLSPEC void SDLCALL SDL_WaitCondition(SDL_Condition *cond, SDL_Mutex *mutex);
725
726/**
727 * Wait until a condition variable is signaled or a certain time has passed.
728 *
729 * This function unlocks the specified `mutex` and waits for another thread to
730 * call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition
731 * variable `cond`, or for the specified time to elapse. Once the condition
732 * variable is signaled or the time elapsed, the mutex is re-locked and the
733 * function returns.
734 *
735 * The mutex must be locked before calling this function. Locking the mutex
736 * recursively (more than once) is not supported and leads to undefined
737 * behavior.
738 *
739 * \param cond the condition variable to wait on.
740 * \param mutex the mutex used to coordinate thread access.
741 * \param timeoutMS the maximum time to wait, in milliseconds, or -1 to wait
742 * indefinitely.
743 * \returns SDL_TRUE if the condition variable is signaled, SDL_FALSE if the
744 * condition is not signaled in the allotted time.
745 *
746 * \threadsafety It is safe to call this function from any thread.
747 *
748 * \since This function is available since SDL 3.0.0.
749 *
750 * \sa SDL_BroadcastCondition
751 * \sa SDL_SignalCondition
752 * \sa SDL_WaitCondition
753 */
754extern SDL_DECLSPEC SDL_bool SDLCALL SDL_WaitConditionTimeout(SDL_Condition *cond,
755 SDL_Mutex *mutex, Sint32 timeoutMS);
756
757/* @} *//* Condition variable functions */
758
759
760/* Ends C function definitions when using C++ */
761#ifdef __cplusplus
762}
763#endif
764#include <SDL3/SDL_close_code.h>
765
766#endif /* SDL_mutex_h_ */
void SDL_DestroyRWLock(SDL_RWLock *rwlock)
void SDL_WaitCondition(SDL_Condition *cond, SDL_Mutex *mutex)
SDL_bool SDL_TryWaitSemaphore(SDL_Semaphore *sem)
#define SDL_ACQUIRE(x)
Definition SDL_mutex.h:73
#define SDL_TRY_ACQUIRE(x, y)
Definition SDL_mutex.h:88
SDL_bool SDL_WaitConditionTimeout(SDL_Condition *cond, SDL_Mutex *mutex, Sint32 timeoutMS)
SDL_RWLock * SDL_CreateRWLock(void)
void SDL_DestroySemaphore(SDL_Semaphore *sem)
SDL_bool SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE(0
#define SDL_TRY_ACQUIRE_SHARED(x, y)
Definition SDL_mutex.h:91
#define SDL_ACQUIRE_SHARED(x)
Definition SDL_mutex.h:76
void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_RELEASE(mutex)
void SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock)
struct SDL_Mutex SDL_Mutex
Definition SDL_mutex.h:135
void SDL_SignalCondition(SDL_Condition *cond)
#define SDL_RELEASE_GENERIC(x)
Definition SDL_mutex.h:85
SDL_bool SDL_TryLockMutex(SDL_Mutex *mutex) SDL_TRY_ACQUIRE(0
SDL_Semaphore * SDL_CreateSemaphore(Uint32 initial_value)
void SDL_LockMutex(SDL_Mutex *mutex) SDL_ACQUIRE(mutex)
SDL_bool SDL_TryLockRWLockForReading(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE_SHARED(0
void SDL_SignalSemaphore(SDL_Semaphore *sem)
Uint32 SDL_GetSemaphoreValue(SDL_Semaphore *sem)
struct SDL_Semaphore SDL_Semaphore
Definition SDL_mutex.h:497
SDL_bool mutex
Definition SDL_mutex.h:202
void SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_RELEASE_GENERIC(rwlock)
SDL_bool SDL_WaitSemaphoreTimeout(SDL_Semaphore *sem, Sint32 timeoutMS)
struct SDL_RWLock SDL_RWLock
Definition SDL_mutex.h:266
void SDL_WaitSemaphore(SDL_Semaphore *sem)
void SDL_DestroyCondition(SDL_Condition *cond)
void SDL_DestroyMutex(SDL_Mutex *mutex)
SDL_Condition * SDL_CreateCondition(void)
SDL_bool rwlock
Definition SDL_mutex.h:401
#define SDL_RELEASE(x)
Definition SDL_mutex.h:79
SDL_Mutex * SDL_CreateMutex(void)
void SDL_BroadcastCondition(SDL_Condition *cond)
void SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock)
struct SDL_Condition SDL_Condition
Definition SDL_mutex.h:640
int32_t Sint32
Definition SDL_stdinc.h:344
uint32_t Uint32
Definition SDL_stdinc.h:353
bool SDL_bool
Definition SDL_stdinc.h:301

◆ SDL_ACQUIRE_SHARED

#define SDL_ACQUIRE_SHARED (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquire_shared_capability(x))

Definition at line 76 of file SDL_mutex.h.

◆ SDL_ACQUIRED_AFTER

#define SDL_ACQUIRED_AFTER (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(x))

Definition at line 64 of file SDL_mutex.h.

◆ SDL_ACQUIRED_BEFORE

#define SDL_ACQUIRED_BEFORE (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(x))

Definition at line 61 of file SDL_mutex.h.

◆ SDL_ASSERT_CAPABILITY

#define SDL_ASSERT_CAPABILITY (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(assert_capability(x))

Definition at line 97 of file SDL_mutex.h.

◆ SDL_ASSERT_SHARED_CAPABILITY

#define SDL_ASSERT_SHARED_CAPABILITY (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_capability(x))

Definition at line 100 of file SDL_mutex.h.

◆ SDL_CAPABILITY

#define SDL_CAPABILITY (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(capability(x))

Definition at line 49 of file SDL_mutex.h.

◆ SDL_EXCLUDES

#define SDL_EXCLUDES (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(x))

Definition at line 94 of file SDL_mutex.h.

◆ SDL_GUARDED_BY

#define SDL_GUARDED_BY (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))

Definition at line 55 of file SDL_mutex.h.

◆ SDL_NO_THREAD_SAFETY_ANALYSIS

#define SDL_NO_THREAD_SAFETY_ANALYSIS    SDL_THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)

Definition at line 106 of file SDL_mutex.h.

◆ SDL_PT_GUARDED_BY

#define SDL_PT_GUARDED_BY (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))

Definition at line 58 of file SDL_mutex.h.

◆ SDL_RELEASE

#define SDL_RELEASE (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_capability(x))

Definition at line 79 of file SDL_mutex.h.

◆ SDL_RELEASE_GENERIC

#define SDL_RELEASE_GENERIC (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_generic_capability(x))

Definition at line 85 of file SDL_mutex.h.

◆ SDL_RELEASE_SHARED

#define SDL_RELEASE_SHARED (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_shared_capability(x))

Definition at line 82 of file SDL_mutex.h.

◆ SDL_REQUIRES

#define SDL_REQUIRES (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(requires_capability(x))

Definition at line 67 of file SDL_mutex.h.

◆ SDL_REQUIRES_SHARED

#define SDL_REQUIRES_SHARED (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(requires_shared_capability(x))

Definition at line 70 of file SDL_mutex.h.

◆ SDL_RETURN_CAPABILITY

#define SDL_RETURN_CAPABILITY (   x)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))

Definition at line 103 of file SDL_mutex.h.

◆ SDL_SCOPED_CAPABILITY

#define SDL_SCOPED_CAPABILITY    SDL_THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)

Definition at line 52 of file SDL_mutex.h.

◆ SDL_THREAD_ANNOTATION_ATTRIBUTE__

#define SDL_THREAD_ANNOTATION_ATTRIBUTE__ (   x)    /* no-op */

CategoryMutex

Functions to provide thread synchronization primitives.

Definition at line 46 of file SDL_mutex.h.

◆ SDL_TRY_ACQUIRE

#define SDL_TRY_ACQUIRE (   x,
 
)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_capability(x, y))

Definition at line 88 of file SDL_mutex.h.

◆ SDL_TRY_ACQUIRE_SHARED

#define SDL_TRY_ACQUIRE_SHARED (   x,
 
)     SDL_THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_shared_capability(x, y))

Definition at line 91 of file SDL_mutex.h.

Typedef Documentation

◆ SDL_Condition

typedef struct SDL_Condition SDL_Condition

A means to block multiple threads until a condition is satisfied.

Condition variables, paired with an SDL_Mutex, let an app halt multiple threads until a condition has occurred, at which time the app can release one or all waiting threads.

Wikipedia has a thorough explanation of the concept:

https://en.wikipedia.org/wiki/Condition_variable

Since
This struct is available since SDL 3.0.0.

Definition at line 640 of file SDL_mutex.h.

◆ SDL_Mutex

typedef struct SDL_Mutex SDL_Mutex

A means to serialize access to a resource between threads.

Mutexes (short for "mutual exclusion") are a synchronization primitive that allows exactly one thread to proceed at a time.

Wikipedia has a thorough explanation of the concept:

https://en.wikipedia.org/wiki/Mutex

Since
This struct is available since SDL 3.0.0.

Definition at line 135 of file SDL_mutex.h.

◆ SDL_RWLock

typedef struct SDL_RWLock SDL_RWLock

A mutex that allows read-only threads to run in parallel.

A rwlock is roughly the same concept as SDL_Mutex, but allows threads that request read-only access to all hold the lock at the same time. If a thread requests write access, it will block until all read-only threads have released the lock, and no one else can hold the thread (for reading or writing) at the same time as the writing thread.

This can be more efficient in cases where several threads need to access data frequently, but changes to that data are rare.

There are other rules that apply to rwlocks that don't apply to mutexes, about how threads are scheduled and when they can be recursively locked. These are documented in the other rwlock functions.

Since
This struct is available since SDL 3.0.0.

Definition at line 266 of file SDL_mutex.h.

◆ SDL_Semaphore

typedef struct SDL_Semaphore SDL_Semaphore

A means to manage access to a resource, by count, between threads.

Semaphores (specifically, "counting semaphores"), let X number of threads request access at the same time, each thread granted access decrementing a counter. When the counter reaches zero, future requests block until a prior thread releases their request, incrementing the counter again.

Wikipedia has a thorough explanation of the concept:

https://en.wikipedia.org/wiki/Semaphore_(programming)

Since
This struct is available since SDL 3.0.0.

Definition at line 497 of file SDL_mutex.h.

Function Documentation

◆ SDL_BroadcastCondition()

void SDL_BroadcastCondition ( SDL_Condition cond)
extern

Restart all threads that are waiting on the condition variable.

Parameters
condthe condition variable to signal.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_SignalCondition
SDL_WaitCondition
SDL_WaitConditionTimeout

◆ SDL_CreateCondition()

SDL_Condition * SDL_CreateCondition ( void  )
extern

Create a condition variable.

Returns
a new condition variable or NULL on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 3.0.0.
See also
SDL_BroadcastCondition
SDL_SignalCondition
SDL_WaitCondition
SDL_WaitConditionTimeout
SDL_DestroyCondition

◆ SDL_CreateMutex()

SDL_Mutex * SDL_CreateMutex ( void  )
extern

Create a new mutex.

All newly-created mutexes begin in the unlocked state.

Calls to SDL_LockMutex() will not return while the mutex is locked by another thread. See SDL_TryLockMutex() to attempt to lock without blocking.

SDL mutexes are reentrant.

Returns
the initialized and unlocked mutex or NULL on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 3.0.0.
See also
SDL_DestroyMutex
SDL_LockMutex
SDL_TryLockMutex
SDL_UnlockMutex

◆ SDL_CreateRWLock()

SDL_RWLock * SDL_CreateRWLock ( void  )
extern

Create a new read/write lock.

A read/write lock is useful for situations where you have multiple threads trying to access a resource that is rarely updated. All threads requesting a read-only lock will be allowed to run in parallel; if a thread requests a write lock, it will be provided exclusive access. This makes it safe for multiple threads to use a resource at the same time if they promise not to change it, and when it has to be changed, the rwlock will serve as a gateway to make sure those changes can be made safely.

In the right situation, a rwlock can be more efficient than a mutex, which only lets a single thread proceed at a time, even if it won't be modifying the data.

All newly-created read/write locks begin in the unlocked state.

Calls to SDL_LockRWLockForReading() and SDL_LockRWLockForWriting will not return while the rwlock is locked for writing by another thread. See SDL_TryLockRWLockForReading() and SDL_TryLockRWLockForWriting() to attempt to lock without blocking.

SDL read/write locks are only recursive for read-only locks! They are not guaranteed to be fair, or provide access in a FIFO manner! They are not guaranteed to favor writers. You may not lock a rwlock for both read-only and write access at the same time from the same thread (so you can't promote your read-only lock to a write lock without unlocking first).

Returns
the initialized and unlocked read/write lock or NULL on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 3.0.0.
See also
SDL_DestroyRWLock
SDL_LockRWLockForReading
SDL_LockRWLockForWriting
SDL_TryLockRWLockForReading
SDL_TryLockRWLockForWriting
SDL_UnlockRWLock

◆ SDL_CreateSemaphore()

SDL_Semaphore * SDL_CreateSemaphore ( Uint32  initial_value)
extern

Create a semaphore.

This function creates a new semaphore and initializes it with the value initial_value. Each wait operation on the semaphore will atomically decrement the semaphore value and potentially block if the semaphore value is 0. Each post operation will atomically increment the semaphore value and wake waiting threads and allow them to retry the wait operation.

Parameters
initial_valuethe starting value of the semaphore.
Returns
a new semaphore or NULL on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 3.0.0.
See also
SDL_DestroySemaphore
SDL_SignalSemaphore
SDL_TryWaitSemaphore
SDL_GetSemaphoreValue
SDL_WaitSemaphore
SDL_WaitSemaphoreTimeout

◆ SDL_DestroyCondition()

void SDL_DestroyCondition ( SDL_Condition cond)
extern

Destroy a condition variable.

Parameters
condthe condition variable to destroy.
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateCondition

◆ SDL_DestroyMutex()

void SDL_DestroyMutex ( SDL_Mutex mutex)
extern

Destroy a mutex created with SDL_CreateMutex().

This function must be called on any mutex that is no longer needed. Failure to destroy a mutex will result in a system memory or resource leak. While it is safe to destroy a mutex that is unlocked, it is not safe to attempt to destroy a locked mutex, and may result in undefined behavior depending on the platform.

Parameters
mutexthe mutex to destroy.
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateMutex

◆ SDL_DestroyRWLock()

void SDL_DestroyRWLock ( SDL_RWLock rwlock)
extern

Destroy a read/write lock created with SDL_CreateRWLock().

This function must be called on any read/write lock that is no longer needed. Failure to destroy a rwlock will result in a system memory or resource leak. While it is safe to destroy a rwlock that is unlocked, it is not safe to attempt to destroy a locked rwlock, and may result in undefined behavior depending on the platform.

Parameters
rwlockthe rwlock to destroy.
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateRWLock

◆ SDL_DestroySemaphore()

void SDL_DestroySemaphore ( SDL_Semaphore sem)
extern

Destroy a semaphore.

It is not safe to destroy a semaphore if there are threads currently waiting on it.

Parameters
semthe semaphore to destroy.
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateSemaphore

◆ SDL_GetSemaphoreValue()

Uint32 SDL_GetSemaphoreValue ( SDL_Semaphore sem)
extern

Get the current value of a semaphore.

Parameters
semthe semaphore to query.
Returns
the current value of the semaphore.
Since
This function is available since SDL 3.0.0.

◆ SDL_LockMutex()

void SDL_LockMutex ( SDL_Mutex mutex)
extern

Lock the mutex.

This will block until the mutex is available, which is to say it is in the unlocked state and the OS has chosen the caller as the next thread to lock it. Of all threads waiting to lock the mutex, only one may do so at a time.

It is legal for the owning thread to lock an already-locked mutex. It must unlock it the same number of times before it is actually made available for other threads in the system (this is known as a "recursive mutex").

This function does not fail; if mutex is NULL, it will return immediately having locked nothing. If the mutex is valid, this function will always block until it can lock the mutex, and return with it locked.

Parameters
mutexthe mutex to lock.
Since
This function is available since SDL 3.0.0.
See also
SDL_TryLockMutex
SDL_UnlockMutex

◆ SDL_LockRWLockForReading()

void SDL_LockRWLockForReading ( SDL_RWLock rwlock)
extern

Lock the read/write lock for read only operations.

This will block until the rwlock is available, which is to say it is not locked for writing by any other thread. Of all threads waiting to lock the rwlock, all may do so at the same time as long as they are requesting read-only access; if a thread wants to lock for writing, only one may do so at a time, and no other threads, read-only or not, may hold the lock at the same time.

It is legal for the owning thread to lock an already-locked rwlock for reading. It must unlock it the same number of times before it is actually made available for other threads in the system (this is known as a "recursive rwlock").

Note that locking for writing is not recursive (this is only available to read-only locks).

It is illegal to request a read-only lock from a thread that already holds the write lock. Doing so results in undefined behavior. Unlock the write lock before requesting a read-only lock. (But, of course, if you have the write lock, you don't need further locks to read in any case.)

This function does not fail; if rwlock is NULL, it will return immediately having locked nothing. If the rwlock is valid, this function will always block until it can lock the mutex, and return with it locked.

Parameters
rwlockthe read/write lock to lock.
Since
This function is available since SDL 3.0.0.
See also
SDL_LockRWLockForWriting
SDL_TryLockRWLockForReading
SDL_UnlockRWLock

◆ SDL_LockRWLockForWriting()

void SDL_LockRWLockForWriting ( SDL_RWLock rwlock)
extern

Lock the read/write lock for write operations.

This will block until the rwlock is available, which is to say it is not locked for reading or writing by any other thread. Only one thread may hold the lock when it requests write access; all other threads, whether they also want to write or only want read-only access, must wait until the writer thread has released the lock.

It is illegal for the owning thread to lock an already-locked rwlock for writing (read-only may be locked recursively, writing can not). Doing so results in undefined behavior.

It is illegal to request a write lock from a thread that already holds a read-only lock. Doing so results in undefined behavior. Unlock the read-only lock before requesting a write lock.

This function does not fail; if rwlock is NULL, it will return immediately having locked nothing. If the rwlock is valid, this function will always block until it can lock the mutex, and return with it locked.

Parameters
rwlockthe read/write lock to lock.
Since
This function is available since SDL 3.0.0.
See also
SDL_LockRWLockForReading
SDL_TryLockRWLockForWriting
SDL_UnlockRWLock

◆ SDL_SignalCondition()

void SDL_SignalCondition ( SDL_Condition cond)
extern

Restart one of the threads that are waiting on the condition variable.

Parameters
condthe condition variable to signal.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_BroadcastCondition
SDL_WaitCondition
SDL_WaitConditionTimeout

◆ SDL_SignalSemaphore()

void SDL_SignalSemaphore ( SDL_Semaphore sem)
extern

Atomically increment a semaphore's value and wake waiting threads.

Parameters
semthe semaphore to increment.
Since
This function is available since SDL 3.0.0.
See also
SDL_TryWaitSemaphore
SDL_WaitSemaphore
SDL_WaitSemaphoreTimeout

◆ SDL_TryLockMutex()

SDL_bool SDL_TryLockMutex ( SDL_Mutex mutex)
extern

Try to lock a mutex without blocking.

This works just like SDL_LockMutex(), but if the mutex is not available, this function returns SDL_FALSE immediately.

This technique is useful if you need exclusive access to a resource but don't want to wait for it, and will return to it to try again later.

This function returns SDL_TRUE if passed a NULL mutex.

Parameters
mutexthe mutex to try to lock.
Returns
SDL_TRUE on success, SDL_FALSE if the mutex would block.
Since
This function is available since SDL 3.0.0.
See also
SDL_LockMutex
SDL_UnlockMutex

◆ SDL_TryLockRWLockForReading()

SDL_bool SDL_TryLockRWLockForReading ( SDL_RWLock rwlock)
extern

Try to lock a read/write lock for reading without blocking.

This works just like SDL_LockRWLockForReading(), but if the rwlock is not available, then this function returns SDL_FALSE immediately.

This technique is useful if you need access to a resource but don't want to wait for it, and will return to it to try again later.

Trying to lock for read-only access can succeed if other threads are holding read-only locks, as this won't prevent access.

This function returns SDL_TRUE if passed a NULL rwlock.

Parameters
rwlockthe rwlock to try to lock.
Returns
SDL_TRUE on success, SDL_FALSE if the lock would block.
Since
This function is available since SDL 3.0.0.
See also
SDL_LockRWLockForReading
SDL_TryLockRWLockForWriting
SDL_UnlockRWLock

◆ SDL_TryLockRWLockForWriting()

SDL_bool SDL_TryLockRWLockForWriting ( SDL_RWLock rwlock)
extern

Try to lock a read/write lock for writing without blocking.

This works just like SDL_LockRWLockForWriting(), but if the rwlock is not available, then this function returns SDL_FALSE immediately.

This technique is useful if you need exclusive access to a resource but don't want to wait for it, and will return to it to try again later.

It is illegal for the owning thread to lock an already-locked rwlock for writing (read-only may be locked recursively, writing can not). Doing so results in undefined behavior.

It is illegal to request a write lock from a thread that already holds a read-only lock. Doing so results in undefined behavior. Unlock the read-only lock before requesting a write lock.

This function returns SDL_TRUE if passed a NULL rwlock.

Parameters
rwlockthe rwlock to try to lock.
Returns
SDL_TRUE on success, SDL_FALSE if the lock would block.
Since
This function is available since SDL 3.0.0.
See also
SDL_LockRWLockForWriting
SDL_TryLockRWLockForReading
SDL_UnlockRWLock

◆ SDL_TryWaitSemaphore()

SDL_bool SDL_TryWaitSemaphore ( SDL_Semaphore sem)
extern

See if a semaphore has a positive value and decrement it if it does.

This function checks to see if the semaphore pointed to by sem has a positive value and atomically decrements the semaphore value if it does. If the semaphore doesn't have a positive value, the function immediately returns SDL_FALSE.

Parameters
semthe semaphore to wait on.
Returns
SDL_TRUE if the wait succeeds, SDL_FALSE if the wait would block.
Since
This function is available since SDL 3.0.0.
See also
SDL_SignalSemaphore
SDL_WaitSemaphore
SDL_WaitSemaphoreTimeout

◆ SDL_UnlockMutex()

void SDL_UnlockMutex ( SDL_Mutex mutex)
extern

Unlock the mutex.

It is legal for the owning thread to lock an already-locked mutex. It must unlock it the same number of times before it is actually made available for other threads in the system (this is known as a "recursive mutex").

It is illegal to unlock a mutex that has not been locked by the current thread, and doing so results in undefined behavior.

Parameters
mutexthe mutex to unlock.
Since
This function is available since SDL 3.0.0.
See also
SDL_LockMutex
SDL_TryLockMutex

◆ SDL_UnlockRWLock()

void SDL_UnlockRWLock ( SDL_RWLock rwlock)
extern

Unlock the read/write lock.

Use this function to unlock the rwlock, whether it was locked for read-only or write operations.

It is legal for the owning thread to lock an already-locked read-only lock. It must unlock it the same number of times before it is actually made available for other threads in the system (this is known as a "recursive rwlock").

It is illegal to unlock a rwlock that has not been locked by the current thread, and doing so results in undefined behavior.

Parameters
rwlockthe rwlock to unlock.
Since
This function is available since SDL 3.0.0.
See also
SDL_LockRWLockForReading
SDL_LockRWLockForWriting
SDL_TryLockRWLockForReading
SDL_TryLockRWLockForWriting

◆ SDL_WaitCondition()

void SDL_WaitCondition ( SDL_Condition cond,
SDL_Mutex mutex 
)
extern

Wait until a condition variable is signaled.

This function unlocks the specified mutex and waits for another thread to call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition variable cond. Once the condition variable is signaled, the mutex is re-locked and the function returns.

The mutex must be locked before calling this function. Locking the mutex recursively (more than once) is not supported and leads to undefined behavior.

This function is the equivalent of calling SDL_WaitConditionTimeout() with a time length of -1.

Parameters
condthe condition variable to wait on.
mutexthe mutex used to coordinate thread access.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_BroadcastCondition
SDL_SignalCondition
SDL_WaitConditionTimeout

◆ SDL_WaitConditionTimeout()

SDL_bool SDL_WaitConditionTimeout ( SDL_Condition cond,
SDL_Mutex mutex,
Sint32  timeoutMS 
)
extern

Wait until a condition variable is signaled or a certain time has passed.

This function unlocks the specified mutex and waits for another thread to call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition variable cond, or for the specified time to elapse. Once the condition variable is signaled or the time elapsed, the mutex is re-locked and the function returns.

The mutex must be locked before calling this function. Locking the mutex recursively (more than once) is not supported and leads to undefined behavior.

Parameters
condthe condition variable to wait on.
mutexthe mutex used to coordinate thread access.
timeoutMSthe maximum time to wait, in milliseconds, or -1 to wait indefinitely.
Returns
SDL_TRUE if the condition variable is signaled, SDL_FALSE if the condition is not signaled in the allotted time.

\threadsafety It is safe to call this function from any thread.

Since
This function is available since SDL 3.0.0.
See also
SDL_BroadcastCondition
SDL_SignalCondition
SDL_WaitCondition

◆ SDL_WaitSemaphore()

void SDL_WaitSemaphore ( SDL_Semaphore sem)
extern

Wait until a semaphore has a positive value and then decrements it.

This function suspends the calling thread until the semaphore pointed to by sem has a positive value, and then atomically decrement the semaphore value.

This function is the equivalent of calling SDL_WaitSemaphoreTimeout() with a time length of -1.

Parameters
semthe semaphore wait on.
Since
This function is available since SDL 3.0.0.
See also
SDL_SignalSemaphore
SDL_TryWaitSemaphore
SDL_WaitSemaphoreTimeout

◆ SDL_WaitSemaphoreTimeout()

SDL_bool SDL_WaitSemaphoreTimeout ( SDL_Semaphore sem,
Sint32  timeoutMS 
)
extern

Wait until a semaphore has a positive value and then decrements it.

This function suspends the calling thread until either the semaphore pointed to by sem has a positive value or the specified time has elapsed. If the call is successful it will atomically decrement the semaphore value.

Parameters
semthe semaphore to wait on.
timeoutMSthe length of the timeout, in milliseconds, or -1 to wait indefinitely.
Returns
SDL_TRUE if the wait succeeds or SDL_FALSE if the wait times out.
Since
This function is available since SDL 3.0.0.
See also
SDL_SignalSemaphore
SDL_TryWaitSemaphore
SDL_WaitSemaphore

Variable Documentation

◆ mutex

SDL_bool mutex

Definition at line 202 of file SDL_mutex.h.

◆ rwlock

SDL_bool rwlock

Definition at line 401 of file SDL_mutex.h.