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)
 
#define SDL_MUTEX_TIMEDOUT   1
 

Read/write lock functions

#define SDL_RWLOCK_TIMEDOUT   SDL_MUTEX_TIMEDOUT
 
typedef struct SDL_RWLock SDL_RWLock
 
int rwlock
 
SDL_RWLockSDL_CreateRWLock (void)
 
void SDL_LockRWLockForReading (SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock)
 
void SDL_LockRWLockForWriting (SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock)
 
int SDL_TryLockRWLockForReading (SDL_RWLock *rwlock) SDL_TRY_ACQUIRE_SHARED(0
 
int 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)
 

Mutex functions

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

Semaphore functions

typedef struct SDL_Semaphore SDL_Semaphore
 
SDL_SemaphoreSDL_CreateSemaphore (Uint32 initial_value)
 
void SDL_DestroySemaphore (SDL_Semaphore *sem)
 
int SDL_WaitSemaphore (SDL_Semaphore *sem)
 
int SDL_TryWaitSemaphore (SDL_Semaphore *sem)
 
int SDL_WaitSemaphoreTimeout (SDL_Semaphore *sem, Sint32 timeoutMS)
 
int SDL_PostSemaphore (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)
 
int SDL_SignalCondition (SDL_Condition *cond)
 
int SDL_BroadcastCondition (SDL_Condition *cond)
 
int SDL_WaitCondition (SDL_Condition *cond, SDL_Mutex *mutex)
 
int SDL_WaitConditionTimeout (SDL_Condition *cond, SDL_Mutex *mutex, Sint32 timeoutMS)
 

Detailed Description

Functions to provide thread synchronization primitives.

Definition in file SDL_mutex.h.

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 * Synchronization functions which can time out return this value
119 * if they time out.
120 */
121#define SDL_MUTEX_TIMEDOUT 1
122
123
124/**
125 * \name Mutex functions
126 */
127/* @{ */
128
129/* The SDL mutex structure, defined in SDL_sysmutex.c */
130struct SDL_Mutex;
131typedef struct SDL_Mutex SDL_Mutex;
132
133/**
134 * Create a new mutex.
135 *
136 * All newly-created mutexes begin in the _unlocked_ state.
137 *
138 * Calls to SDL_LockMutex() will not return while the mutex is locked by
139 * another thread. See SDL_TryLockMutex() to attempt to lock without blocking.
140 *
141 * SDL mutexes are reentrant.
142 *
143 * \returns the initialized and unlocked mutex or NULL on failure; call
144 * SDL_GetError() for more information.
145 *
146 * \since This function is available since SDL 3.0.0.
147 *
148 * \sa SDL_DestroyMutex
149 * \sa SDL_LockMutex
150 * \sa SDL_TryLockMutex
151 * \sa SDL_UnlockMutex
152 */
153extern DECLSPEC SDL_Mutex *SDLCALL SDL_CreateMutex(void);
154
155/**
156 * Lock the mutex.
157 *
158 * This will block until the mutex is available, which is to say it is in the
159 * unlocked state and the OS has chosen the caller as the next thread to lock
160 * it. Of all threads waiting to lock the mutex, only one may do so at a time.
161 *
162 * It is legal for the owning thread to lock an already-locked mutex. It must
163 * unlock it the same number of times before it is actually made available for
164 * other threads in the system (this is known as a "recursive mutex").
165 *
166 * This function does not fail; if mutex is NULL, it will return immediately
167 * having locked nothing. If the mutex is valid, this function will always
168 * block until it can lock the mutex, and return with it locked.
169 *
170 * \param mutex the mutex to lock
171 *
172 * \since This function is available since SDL 3.0.0.
173 */
174extern DECLSPEC void SDLCALL SDL_LockMutex(SDL_Mutex *mutex) SDL_ACQUIRE(mutex);
175
176/**
177 * Try to lock a mutex without blocking.
178 *
179 * This works just like SDL_LockMutex(), but if the mutex is not available,
180 * this function returns `SDL_MUTEX_TIMEDOUT` immediately.
181 *
182 * This technique is useful if you need exclusive access to a resource but
183 * don't want to wait for it, and will return to it to try again later.
184 *
185 * This function does not fail; if mutex is NULL, it will return 0 immediately
186 * having locked nothing. If the mutex is valid, this function will always
187 * either lock the mutex and return 0, or return SDL_MUTEX_TIMEOUT and lock
188 * nothing.
189 *
190 * \param mutex the mutex to try to lock
191 * \returns 0 or `SDL_MUTEX_TIMEDOUT`
192 *
193 * \since This function is available since SDL 3.0.0.
194 *
195 * \sa SDL_CreateMutex
196 * \sa SDL_DestroyMutex
197 * \sa SDL_LockMutex
198 * \sa SDL_UnlockMutex
199 */
200extern DECLSPEC int SDLCALL SDL_TryLockMutex(SDL_Mutex *mutex) SDL_TRY_ACQUIRE(0, mutex);
201
202/**
203 * Unlock the mutex.
204 *
205 * It is legal for the owning thread to lock an already-locked mutex. It must
206 * unlock it the same number of times before it is actually made available for
207 * other threads in the system (this is known as a "recursive mutex").
208 *
209 * It is illegal to unlock a mutex that has not been locked by the current
210 * thread, and doing so results in undefined behavior.
211 *
212 * \param mutex the mutex to unlock.
213 *
214 * \since This function is available since SDL 3.0.0.
215 */
216extern DECLSPEC void SDLCALL SDL_UnlockMutex(SDL_Mutex *mutex) SDL_RELEASE(mutex);
217
218/**
219 * Destroy a mutex created with SDL_CreateMutex().
220 *
221 * This function must be called on any mutex that is no longer needed. Failure
222 * to destroy a mutex will result in a system memory or resource leak. While
223 * it is safe to destroy a mutex that is _unlocked_, it is not safe to attempt
224 * to destroy a locked mutex, and may result in undefined behavior depending
225 * on the platform.
226 *
227 * \param mutex the mutex to destroy
228 *
229 * \since This function is available since SDL 3.0.0.
230 *
231 * \sa SDL_CreateMutex
232 * \sa SDL_LockMutex
233 * \sa SDL_TryLockMutex
234 * \sa SDL_UnlockMutex
235 */
236extern DECLSPEC void SDLCALL SDL_DestroyMutex(SDL_Mutex *mutex);
237
238/* @} *//* Mutex functions */
239
240
241/**
242 * \name Read/write lock functions
243 */
244/* @{ */
245
246/* The SDL read/write lock structure, defined in SDL_sysrwlock.c */
247struct SDL_RWLock;
248typedef struct SDL_RWLock SDL_RWLock;
249
250/*
251 * Synchronization functions which can time out return this value
252 * if they time out.
253 */
254#define SDL_RWLOCK_TIMEDOUT SDL_MUTEX_TIMEDOUT
255
256
257/**
258 * Create a new read/write lock.
259 *
260 * A read/write lock is useful for situations where you have multiple threads
261 * trying to access a resource that is rarely updated. All threads requesting
262 * a read-only lock will be allowed to run in parallel; if a thread requests a
263 * write lock, it will be provided exclusive access. This makes it safe for
264 * multiple threads to use a resource at the same time if they promise not to
265 * change it, and when it has to be changed, the rwlock will serve as a
266 * gateway to make sure those changes can be made safely.
267 *
268 * In the right situation, a rwlock can be more efficient than a mutex, which
269 * only lets a single thread proceed at a time, even if it won't be modifying
270 * the data.
271 *
272 * All newly-created read/write locks begin in the _unlocked_ state.
273 *
274 * Calls to SDL_LockRWLockForReading() and SDL_LockRWLockForWriting will not
275 * return while the rwlock is locked _for writing_ by another thread. See
276 * SDL_TryLockRWLockForReading() and SDL_TryLockRWLockForWriting() to attempt
277 * to lock without blocking.
278 *
279 * SDL read/write locks are only recursive for read-only locks! They are not
280 * guaranteed to be fair, or provide access in a FIFO manner! They are not
281 * guaranteed to favor writers. You may not lock a rwlock for both read-only
282 * and write access at the same time from the same thread (so you can't
283 * promote your read-only lock to a write lock without unlocking first).
284 *
285 * \returns the initialized and unlocked read/write lock or NULL on failure;
286 * call SDL_GetError() for more information.
287 *
288 * \since This function is available since SDL 3.0.0.
289 *
290 * \sa SDL_DestroyRWLock
291 * \sa SDL_LockRWLockForReading
292 * \sa SDL_TryLockRWLockForReading
293 * \sa SDL_LockRWLockForWriting
294 * \sa SDL_TryLockRWLockForWriting
295 * \sa SDL_UnlockRWLock
296 */
297extern DECLSPEC SDL_RWLock *SDLCALL SDL_CreateRWLock(void);
298
299/**
300 * Lock the read/write lock for _read only_ operations.
301 *
302 * This will block until the rwlock is available, which is to say it is not
303 * locked for writing by any other thread. Of all threads waiting to lock the
304 * rwlock, all may do so at the same time as long as they are requesting
305 * read-only access; if a thread wants to lock for writing, only one may do so
306 * at a time, and no other threads, read-only or not, may hold the lock at the
307 * same time.
308 *
309 * It is legal for the owning thread to lock an already-locked rwlock for
310 * reading. It must unlock it the same number of times before it is actually
311 * made available for other threads in the system (this is known as a
312 * "recursive rwlock").
313 *
314 * Note that locking for writing is not recursive (this is only available to
315 * read-only locks).
316 *
317 * It is illegal to request a read-only lock from a thread that already holds
318 * the write lock. Doing so results in undefined behavior. Unlock the write
319 * lock before requesting a read-only lock. (But, of course, if you have the
320 * write lock, you don't need further locks to read in any case.)
321 *
322 * This function does not fail; if rwlock is NULL, it will return immediately
323 * having locked nothing. If the rwlock is valid, this function will always
324 * block until it can lock the mutex, and return with it locked.
325 *
326 * \param rwlock the read/write lock to lock
327 *
328 * \since This function is available since SDL 3.0.0.
329 *
330 * \sa SDL_UnlockRWLock
331 */
333
334/**
335 * Lock the read/write lock for _write_ operations.
336 *
337 * This will block until the rwlock is available, which is to say it is not
338 * locked for reading or writing by any other thread. Only one thread may hold
339 * the lock when it requests write access; all other threads, whether they
340 * also want to write or only want read-only access, must wait until the
341 * writer thread has released the lock.
342 *
343 * It is illegal for the owning thread to lock an already-locked rwlock for
344 * writing (read-only may be locked recursively, writing can not). Doing so
345 * results in undefined behavior.
346 *
347 * It is illegal to request a write lock from a thread that already holds a
348 * read-only lock. Doing so results in undefined behavior. Unlock the
349 * read-only lock before requesting a write lock.
350 *
351 * This function does not fail; if rwlock is NULL, it will return immediately
352 * having locked nothing. If the rwlock is valid, this function will always
353 * block until it can lock the mutex, and return with it locked.
354 *
355 * \param rwlock the read/write lock to lock
356 *
357 * \since This function is available since SDL 3.0.0.
358 *
359 * \sa SDL_UnlockRWLock
360 */
361extern DECLSPEC void SDLCALL SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock);
362
363/**
364 * Try to lock a read/write lock _for reading_ without blocking.
365 *
366 * This works just like SDL_LockRWLockForReading(), but if the rwlock is not
367 * available, then this function returns `SDL_RWLOCK_TIMEDOUT` immediately.
368 *
369 * This technique is useful if you need access to a resource but don't want to
370 * wait for it, and will return to it to try again later.
371 *
372 * Trying to lock for read-only access can succeed if other threads are
373 * holding read-only locks, as this won't prevent access.
374 *
375 * This function does not fail; if rwlock is NULL, it will return 0
376 * immediately having locked nothing. If rwlock is valid, this function will
377 * always either lock the rwlock and return 0, or return SDL_RWLOCK_TIMEOUT
378 * and lock nothing.
379 *
380 * \param rwlock the rwlock to try to lock
381 * \returns 0 or `SDL_RWLOCK_TIMEDOUT`
382 *
383 * \since This function is available since SDL 3.0.0.
384 *
385 * \sa SDL_CreateRWLock
386 * \sa SDL_DestroyRWLock
387 * \sa SDL_TryLockRWLockForReading
388 * \sa SDL_UnlockRWLock
389 */
391
392/**
393 * Try to lock a read/write lock _for writing_ without blocking.
394 *
395 * This works just like SDL_LockRWLockForWriting(), but if the rwlock is not
396 * available, this function returns `SDL_RWLOCK_TIMEDOUT` immediately.
397 *
398 * This technique is useful if you need exclusive access to a resource but
399 * don't want to wait for it, and will return to it to try again later.
400 *
401 * It is illegal for the owning thread to lock an already-locked rwlock for
402 * writing (read-only may be locked recursively, writing can not). Doing so
403 * results in undefined behavior.
404 *
405 * It is illegal to request a write lock from a thread that already holds a
406 * read-only lock. Doing so results in undefined behavior. Unlock the
407 * read-only lock before requesting a write lock.
408 *
409 * This function does not fail; if rwlock is NULL, it will return 0
410 * immediately having locked nothing. If rwlock is valid, this function will
411 * always either lock the rwlock and return 0, or return SDL_RWLOCK_TIMEOUT
412 * and lock nothing.
413 *
414 * \param rwlock the rwlock to try to lock
415 * \returns 0 or `SDL_RWLOCK_TIMEDOUT`
416 *
417 * \since This function is available since SDL 3.0.0.
418 *
419 * \sa SDL_CreateRWLock
420 * \sa SDL_DestroyRWLock
421 * \sa SDL_TryLockRWLockForWriting
422 * \sa SDL_UnlockRWLock
423 */
424extern DECLSPEC int SDLCALL SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE(0, rwlock);
425
426/**
427 * Unlock the read/write lock.
428 *
429 * Use this function to unlock the rwlock, whether it was locked for read-only
430 * or write operations.
431 *
432 * It is legal for the owning thread to lock an already-locked read-only lock.
433 * It must unlock it the same number of times before it is actually made
434 * available for other threads in the system (this is known as a "recursive
435 * rwlock").
436 *
437 * It is illegal to unlock a rwlock that has not been locked by the current
438 * thread, and doing so results in undefined behavior.
439 *
440 * \param rwlock the rwlock to unlock.
441 *
442 * \since This function is available since SDL 3.0.0.
443 */
444extern DECLSPEC void SDLCALL SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_RELEASE_GENERIC(rwlock);
445
446/**
447 * Destroy a read/write lock created with SDL_CreateRWLock().
448 *
449 * This function must be called on any read/write lock that is no longer
450 * needed. Failure to destroy a rwlock will result in a system memory or
451 * resource leak. While it is safe to destroy a rwlock that is _unlocked_, it
452 * is not safe to attempt to destroy a locked rwlock, and may result in
453 * undefined behavior depending on the platform.
454 *
455 * \param rwlock the rwlock to destroy
456 *
457 * \since This function is available since SDL 3.0.0.
458 *
459 * \sa SDL_CreateRWLock
460 * \sa SDL_LockRWLockForReading
461 * \sa SDL_LockRWLockForWriting
462 * \sa SDL_TryLockRWLockForReading
463 * \sa SDL_TryLockRWLockForWriting
464 * \sa SDL_UnlockRWLock
465 */
466extern DECLSPEC void SDLCALL SDL_DestroyRWLock(SDL_RWLock *rwlock);
467
468/* @} *//* Read/write lock functions */
469
470
471/**
472 * \name Semaphore functions
473 */
474/* @{ */
475
476/* The SDL semaphore structure, defined in SDL_syssem.c */
477struct SDL_Semaphore;
478typedef struct SDL_Semaphore SDL_Semaphore;
479
480/**
481 * Create a semaphore.
482 *
483 * This function creates a new semaphore and initializes it with the value
484 * `initial_value`. Each wait operation on the semaphore will atomically
485 * decrement the semaphore value and potentially block if the semaphore value
486 * is 0. Each post operation will atomically increment the semaphore value and
487 * wake waiting threads and allow them to retry the wait operation.
488 *
489 * \param initial_value the starting value of the semaphore
490 * \returns a new semaphore or NULL on failure; call SDL_GetError() for more
491 * information.
492 *
493 * \since This function is available since SDL 3.0.0.
494 *
495 * \sa SDL_DestroySemaphore
496 * \sa SDL_PostSemaphore
497 * \sa SDL_TryWaitSemaphore
498 * \sa SDL_GetSemaphoreValue
499 * \sa SDL_WaitSemaphore
500 * \sa SDL_WaitSemaphoreTimeout
501 */
502extern DECLSPEC SDL_Semaphore *SDLCALL SDL_CreateSemaphore(Uint32 initial_value);
503
504/**
505 * Destroy a semaphore.
506 *
507 * It is not safe to destroy a semaphore if there are threads currently
508 * waiting on it.
509 *
510 * \param sem the semaphore to destroy
511 *
512 * \since This function is available since SDL 3.0.0.
513 *
514 * \sa SDL_CreateSemaphore
515 * \sa SDL_PostSemaphore
516 * \sa SDL_TryWaitSemaphore
517 * \sa SDL_GetSemaphoreValue
518 * \sa SDL_WaitSemaphore
519 * \sa SDL_WaitSemaphoreTimeout
520 */
521extern DECLSPEC void SDLCALL SDL_DestroySemaphore(SDL_Semaphore *sem);
522
523/**
524 * Wait until a semaphore has a positive value and then decrements it.
525 *
526 * This function suspends the calling thread until either the semaphore
527 * pointed to by `sem` has a positive value or the call is interrupted by a
528 * signal or error. If the call is successful it will atomically decrement the
529 * semaphore value.
530 *
531 * This function is the equivalent of calling SDL_WaitSemaphoreTimeout() with
532 * a time length of -1.
533 *
534 * \param sem the semaphore wait on
535 * \returns 0 on success or a negative error code on failure; call
536 * SDL_GetError() for more information.
537 *
538 * \since This function is available since SDL 3.0.0.
539 *
540 * \sa SDL_CreateSemaphore
541 * \sa SDL_DestroySemaphore
542 * \sa SDL_PostSemaphore
543 * \sa SDL_TryWaitSemaphore
544 * \sa SDL_GetSemaphoreValue
545 * \sa SDL_WaitSemaphore
546 * \sa SDL_WaitSemaphoreTimeout
547 */
548extern DECLSPEC int SDLCALL SDL_WaitSemaphore(SDL_Semaphore *sem);
549
550/**
551 * See if a semaphore has a positive value and decrement it if it does.
552 *
553 * This function checks to see if the semaphore pointed to by `sem` has a
554 * positive value and atomically decrements the semaphore value if it does. If
555 * the semaphore doesn't have a positive value, the function immediately
556 * returns SDL_MUTEX_TIMEDOUT.
557 *
558 * \param sem the semaphore to wait on
559 * \returns 0 if the wait succeeds, `SDL_MUTEX_TIMEDOUT` if the wait would
560 * block, or a negative error code on failure; call SDL_GetError()
561 * for more information.
562 *
563 * \since This function is available since SDL 3.0.0.
564 *
565 * \sa SDL_CreateSemaphore
566 * \sa SDL_DestroySemaphore
567 * \sa SDL_PostSemaphore
568 * \sa SDL_GetSemaphoreValue
569 * \sa SDL_WaitSemaphore
570 * \sa SDL_WaitSemaphoreTimeout
571 */
572extern DECLSPEC int SDLCALL SDL_TryWaitSemaphore(SDL_Semaphore *sem);
573
574/**
575 * Wait until a semaphore has a positive value and then decrements it.
576 *
577 * This function suspends the calling thread until either the semaphore
578 * pointed to by `sem` has a positive value, the call is interrupted by a
579 * signal or error, or the specified time has elapsed. If the call is
580 * 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
584 * \returns 0 if the wait succeeds, `SDL_MUTEX_TIMEDOUT` if the wait does not
585 * succeed in the allotted time, or a negative error code on failure;
586 * call SDL_GetError() for more information.
587 *
588 * \since This function is available since SDL 3.0.0.
589 *
590 * \sa SDL_CreateSemaphore
591 * \sa SDL_DestroySemaphore
592 * \sa SDL_PostSemaphore
593 * \sa SDL_TryWaitSemaphore
594 * \sa SDL_GetSemaphoreValue
595 * \sa SDL_WaitSemaphore
596 */
597extern DECLSPEC int SDLCALL SDL_WaitSemaphoreTimeout(SDL_Semaphore *sem, Sint32 timeoutMS);
598
599/**
600 * Atomically increment a semaphore's value and wake waiting threads.
601 *
602 * \param sem the semaphore to increment
603 * \returns 0 on success or a negative error code on failure; call
604 * SDL_GetError() for more information.
605 *
606 * \since This function is available since SDL 3.0.0.
607 *
608 * \sa SDL_CreateSemaphore
609 * \sa SDL_DestroySemaphore
610 * \sa SDL_TryWaitSemaphore
611 * \sa SDL_GetSemaphoreValue
612 * \sa SDL_WaitSemaphore
613 * \sa SDL_WaitSemaphoreTimeout
614 */
615extern DECLSPEC int SDLCALL SDL_PostSemaphore(SDL_Semaphore *sem);
616
617/**
618 * Get the current value of a semaphore.
619 *
620 * \param sem the semaphore to query
621 * \returns the current value of the semaphore.
622 *
623 * \since This function is available since SDL 3.0.0.
624 *
625 * \sa SDL_CreateSemaphore
626 */
627extern DECLSPEC Uint32 SDLCALL SDL_GetSemaphoreValue(SDL_Semaphore *sem);
628
629/* @} *//* Semaphore functions */
630
631
632/**
633 * \name Condition variable functions
634 */
635/* @{ */
636
637/* The SDL condition variable structure, defined in SDL_syscond.c */
638struct SDL_Condition;
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 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_BroadcastCondition
665 * \sa SDL_SignalCondition
666 * \sa SDL_WaitCondition
667 * \sa SDL_WaitConditionTimeout
668 * \sa SDL_CreateCondition
669 */
670extern DECLSPEC void SDLCALL SDL_DestroyCondition(SDL_Condition *cond);
671
672/**
673 * Restart one of the threads that are waiting on the condition variable.
674 *
675 * \param cond the condition variable to signal
676 * \returns 0 on success or a negative error code on failure; call
677 * SDL_GetError() for more information.
678 *
679 * \since This function is available since SDL 3.0.0.
680 *
681 * \sa SDL_BroadcastCondition
682 * \sa SDL_WaitCondition
683 * \sa SDL_WaitConditionTimeout
684 * \sa SDL_CreateCondition
685 * \sa SDL_DestroyCondition
686 */
687extern DECLSPEC int SDLCALL SDL_SignalCondition(SDL_Condition *cond);
688
689/**
690 * Restart all threads that are waiting on the condition variable.
691 *
692 * \param cond the condition variable to signal
693 * \returns 0 on success or a negative error code on failure; call
694 * SDL_GetError() for more information.
695 *
696 * \since This function is available since SDL 3.0.0.
697 *
698 * \sa SDL_SignalCondition
699 * \sa SDL_WaitCondition
700 * \sa SDL_WaitConditionTimeout
701 * \sa SDL_CreateCondition
702 * \sa SDL_DestroyCondition
703 */
704extern DECLSPEC int SDLCALL SDL_BroadcastCondition(SDL_Condition *cond);
705
706/**
707 * Wait until a condition variable is signaled.
708 *
709 * This function unlocks the specified `mutex` and waits for another thread to
710 * call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition
711 * variable `cond`. Once the condition variable is signaled, the mutex is
712 * re-locked and the function returns.
713 *
714 * The mutex must be locked before calling this function. Locking the mutex
715 * recursively (more than once) is not supported and leads to undefined
716 * behavior.
717 *
718 * This function is the equivalent of calling SDL_WaitConditionTimeout() with
719 * a time length of -1.
720 *
721 * \param cond the condition variable to wait on
722 * \param mutex the mutex used to coordinate thread access
723 * \returns 0 when it is signaled or a negative error code on failure; call
724 * SDL_GetError() for more information.
725 *
726 * \since This function is available since SDL 3.0.0.
727 *
728 * \sa SDL_BroadcastCondition
729 * \sa SDL_SignalCondition
730 * \sa SDL_WaitConditionTimeout
731 * \sa SDL_CreateCondition
732 * \sa SDL_DestroyCondition
733 */
734extern DECLSPEC int SDLCALL SDL_WaitCondition(SDL_Condition *cond, SDL_Mutex *mutex);
735
736/**
737 * Wait until a condition variable is signaled or a certain time has passed.
738 *
739 * This function unlocks the specified `mutex` and waits for another thread to
740 * call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition
741 * variable `cond`, or for the specified time to elapse. Once the condition
742 * variable is signaled or the time elapsed, the mutex is re-locked and the
743 * function returns.
744 *
745 * The mutex must be locked before calling this function. Locking the mutex
746 * recursively (more than once) is not supported and leads to undefined
747 * behavior.
748 *
749 * \param cond the condition variable to wait on
750 * \param mutex the mutex used to coordinate thread access
751 * \param timeoutMS the maximum time to wait, in milliseconds, or -1 to wait
752 * indefinitely
753 * \returns 0 if the condition variable is signaled, `SDL_MUTEX_TIMEDOUT` if
754 * the condition is not signaled in the allotted time, or a negative
755 * error code on failure; call SDL_GetError() for more information.
756 *
757 * \since This function is available since SDL 3.0.0.
758 *
759 * \sa SDL_BroadcastCondition
760 * \sa SDL_SignalCondition
761 * \sa SDL_WaitCondition
762 * \sa SDL_CreateCondition
763 * \sa SDL_DestroyCondition
764 */
765extern DECLSPEC int SDLCALL SDL_WaitConditionTimeout(SDL_Condition *cond,
766 SDL_Mutex *mutex, Sint32 timeoutMS);
767
768/* @} *//* Condition variable functions */
769
770
771/* Ends C function definitions when using C++ */
772#ifdef __cplusplus
773}
774#endif
775#include <SDL3/SDL_close_code.h>
776
777#endif /* SDL_mutex_h_ */
void SDL_DestroyRWLock(SDL_RWLock *rwlock)
int rwlock
Definition SDL_mutex.h:391
#define SDL_ACQUIRE(x)
Definition SDL_mutex.h:73
int SDL_TryLockMutex(SDL_Mutex *mutex) SDL_TRY_ACQUIRE(0
#define SDL_TRY_ACQUIRE(x, y)
Definition SDL_mutex.h:88
SDL_RWLock * SDL_CreateRWLock(void)
void SDL_DestroySemaphore(SDL_Semaphore *sem)
#define SDL_TRY_ACQUIRE_SHARED(x, y)
Definition SDL_mutex.h:91
#define SDL_ACQUIRE_SHARED(x)
Definition SDL_mutex.h:76
int SDL_PostSemaphore(SDL_Semaphore *sem)
void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_RELEASE(mutex)
int SDL_WaitCondition(SDL_Condition *cond, SDL_Mutex *mutex)
void SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock)
int SDL_SignalCondition(SDL_Condition *cond)
struct SDL_Mutex SDL_Mutex
Definition SDL_mutex.h:132
int SDL_TryLockRWLockForReading(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE_SHARED(0
#define SDL_RELEASE_GENERIC(x)
Definition SDL_mutex.h:85
SDL_Semaphore * SDL_CreateSemaphore(Uint32 initial_value)
void SDL_LockMutex(SDL_Mutex *mutex) SDL_ACQUIRE(mutex)
int SDL_WaitSemaphoreTimeout(SDL_Semaphore *sem, Sint32 timeoutMS)
int SDL_TryWaitSemaphore(SDL_Semaphore *sem)
Uint32 SDL_GetSemaphoreValue(SDL_Semaphore *sem)
struct SDL_Semaphore SDL_Semaphore
Definition SDL_mutex.h:479
int mutex
Definition SDL_mutex.h:201
int SDL_WaitConditionTimeout(SDL_Condition *cond, SDL_Mutex *mutex, Sint32 timeoutMS)
void SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_RELEASE_GENERIC(rwlock)
int SDL_BroadcastCondition(SDL_Condition *cond)
struct SDL_RWLock SDL_RWLock
Definition SDL_mutex.h:249
void SDL_DestroyCondition(SDL_Condition *cond)
void SDL_DestroyMutex(SDL_Mutex *mutex)
SDL_Condition * SDL_CreateCondition(void)
#define SDL_RELEASE(x)
Definition SDL_mutex.h:79
SDL_Mutex * SDL_CreateMutex(void)
int SDL_WaitSemaphore(SDL_Semaphore *sem)
void SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock)
int SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE(0
struct SDL_Condition SDL_Condition
Definition SDL_mutex.h:640
int32_t Sint32
Definition SDL_stdinc.h:167
uint32_t Uint32
Definition SDL_stdinc.h:173

◆ 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_MUTEX_TIMEDOUT

#define SDL_MUTEX_TIMEDOUT   1

Synchronization functions which can time out return this value if they time out.

Definition at line 122 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_RWLOCK_TIMEDOUT

#define SDL_RWLOCK_TIMEDOUT   SDL_MUTEX_TIMEDOUT

Definition at line 255 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 */

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

Definition at line 640 of file SDL_mutex.h.

◆ SDL_Mutex

typedef struct SDL_Mutex SDL_Mutex

Definition at line 132 of file SDL_mutex.h.

◆ SDL_RWLock

typedef struct SDL_RWLock SDL_RWLock

Definition at line 249 of file SDL_mutex.h.

◆ SDL_Semaphore

typedef struct SDL_Semaphore SDL_Semaphore

Definition at line 479 of file SDL_mutex.h.

Function Documentation

◆ SDL_BroadcastCondition()

int SDL_BroadcastCondition ( SDL_Condition cond)
extern

Restart all threads that are waiting on the condition variable.

Parameters
condthe condition variable to signal
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 3.0.0.
See also
SDL_SignalCondition
SDL_WaitCondition
SDL_WaitConditionTimeout
SDL_CreateCondition
SDL_DestroyCondition

◆ 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_TryLockRWLockForReading
SDL_LockRWLockForWriting
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_PostSemaphore
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_BroadcastCondition
SDL_SignalCondition
SDL_WaitCondition
SDL_WaitConditionTimeout
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_LockMutex
SDL_TryLockMutex
SDL_UnlockMutex

◆ 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_LockRWLockForReading
SDL_LockRWLockForWriting
SDL_TryLockRWLockForReading
SDL_TryLockRWLockForWriting
SDL_UnlockRWLock

◆ 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_PostSemaphore
SDL_TryWaitSemaphore
SDL_GetSemaphoreValue
SDL_WaitSemaphore
SDL_WaitSemaphoreTimeout

◆ 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.
See also
SDL_CreateSemaphore

◆ 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.

◆ 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_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_UnlockRWLock

◆ SDL_PostSemaphore()

int SDL_PostSemaphore ( SDL_Semaphore sem)
extern

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

Parameters
semthe semaphore to increment
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateSemaphore
SDL_DestroySemaphore
SDL_TryWaitSemaphore
SDL_GetSemaphoreValue
SDL_WaitSemaphore
SDL_WaitSemaphoreTimeout

◆ SDL_SignalCondition()

int SDL_SignalCondition ( SDL_Condition cond)
extern

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

Parameters
condthe condition variable to signal
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 3.0.0.
See also
SDL_BroadcastCondition
SDL_WaitCondition
SDL_WaitConditionTimeout
SDL_CreateCondition
SDL_DestroyCondition

◆ SDL_TryLockMutex()

int 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_MUTEX_TIMEDOUT 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 does not fail; if mutex is NULL, it will return 0 immediately having locked nothing. If the mutex is valid, this function will always either lock the mutex and return 0, or return SDL_MUTEX_TIMEOUT and lock nothing.

Parameters
mutexthe mutex to try to lock
Returns
0 or SDL_MUTEX_TIMEDOUT
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateMutex
SDL_DestroyMutex
SDL_LockMutex
SDL_UnlockMutex

◆ SDL_TryLockRWLockForReading()

int 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_RWLOCK_TIMEDOUT 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 does not fail; if rwlock is NULL, it will return 0 immediately having locked nothing. If rwlock is valid, this function will always either lock the rwlock and return 0, or return SDL_RWLOCK_TIMEOUT and lock nothing.

Parameters
rwlockthe rwlock to try to lock
Returns
0 or SDL_RWLOCK_TIMEDOUT
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateRWLock
SDL_DestroyRWLock
SDL_TryLockRWLockForReading
SDL_UnlockRWLock

◆ SDL_TryLockRWLockForWriting()

int 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, this function returns SDL_RWLOCK_TIMEDOUT 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 does not fail; if rwlock is NULL, it will return 0 immediately having locked nothing. If rwlock is valid, this function will always either lock the rwlock and return 0, or return SDL_RWLOCK_TIMEOUT and lock nothing.

Parameters
rwlockthe rwlock to try to lock
Returns
0 or SDL_RWLOCK_TIMEDOUT
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateRWLock
SDL_DestroyRWLock
SDL_TryLockRWLockForWriting
SDL_UnlockRWLock

◆ SDL_TryWaitSemaphore()

int 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_MUTEX_TIMEDOUT.

Parameters
semthe semaphore to wait on
Returns
0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait would block, or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateSemaphore
SDL_DestroySemaphore
SDL_PostSemaphore
SDL_GetSemaphoreValue
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.

◆ 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.

◆ SDL_WaitCondition()

int 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
Returns
0 when it is signaled or a negative error code 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_WaitConditionTimeout
SDL_CreateCondition
SDL_DestroyCondition

◆ SDL_WaitConditionTimeout()

int 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
0 if the condition variable is signaled, SDL_MUTEX_TIMEDOUT if the condition is not signaled in the allotted time, or a negative error code 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_CreateCondition
SDL_DestroyCondition

◆ SDL_WaitSemaphore()

int 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 either the semaphore pointed to by sem has a positive value or the call is interrupted by a signal or error. If the call is successful it will 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
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateSemaphore
SDL_DestroySemaphore
SDL_PostSemaphore
SDL_TryWaitSemaphore
SDL_GetSemaphoreValue
SDL_WaitSemaphore
SDL_WaitSemaphoreTimeout

◆ SDL_WaitSemaphoreTimeout()

int 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, the call is interrupted by a signal or error, 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
Returns
0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait does not succeed in the allotted time, or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 3.0.0.
See also
SDL_CreateSemaphore
SDL_DestroySemaphore
SDL_PostSemaphore
SDL_TryWaitSemaphore
SDL_GetSemaphoreValue
SDL_WaitSemaphore

Variable Documentation

◆ mutex

int mutex

Definition at line 201 of file SDL_mutex.h.

◆ rwlock

int rwlock

Definition at line 391 of file SDL_mutex.h.