SDL 3.0
SDL_mutex.h File Reference
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Data Structures

struct  SDL_InitState
 

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)
 

Thread-safe initialization state functions

enum  SDL_InitStatus {
  SDL_INIT_STATUS_UNINITIALIZED ,
  SDL_INIT_STATUS_INITIALIZING ,
  SDL_INIT_STATUS_INITIALIZED ,
  SDL_INIT_STATUS_UNINITIALIZING
}
 
bool SDL_ShouldInit (SDL_InitState *state)
 
bool SDL_ShouldQuit (SDL_InitState *state)
 
void SDL_SetInitialized (SDL_InitState *state, bool initialized)
 

Mutex functions

typedef struct SDL_Mutex SDL_Mutex
 
bool mutex
 
SDL_MutexSDL_CreateMutex (void)
 
void SDL_LockMutex (SDL_Mutex *mutex) SDL_ACQUIRE(mutex)
 
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
 
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)
 
bool SDL_TryLockRWLockForReading (SDL_RWLock *rwlock) SDL_TRY_ACQUIRE_SHARED(0
 
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)
 
bool SDL_TryWaitSemaphore (SDL_Semaphore *sem)
 
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)
 
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))

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 145 of file SDL_mutex.h.

263 {
264#endif
265
266/**
267 * \name Mutex functions
268 */
269/* @{ */
270
271/**
272 * A means to serialize access to a resource between threads.
273 *
274 * Mutexes (short for "mutual exclusion") are a synchronization primitive that
275 * allows exactly one thread to proceed at a time.
276 *
277 * Wikipedia has a thorough explanation of the concept:
278 *
279 * https://en.wikipedia.org/wiki/Mutex
280 *
281 * \since This struct is available since SDL 3.1.3.
282 */
283typedef struct SDL_Mutex SDL_Mutex;
284
285/**
286 * Create a new mutex.
287 *
288 * All newly-created mutexes begin in the _unlocked_ state.
289 *
290 * Calls to SDL_LockMutex() will not return while the mutex is locked by
291 * another thread. See SDL_TryLockMutex() to attempt to lock without blocking.
292 *
293 * SDL mutexes are reentrant.
294 *
295 * \returns the initialized and unlocked mutex or NULL on failure; call
296 * SDL_GetError() for more information.
297 *
298 * \since This function is available since SDL 3.1.3.
299 *
300 * \sa SDL_DestroyMutex
301 * \sa SDL_LockMutex
302 * \sa SDL_TryLockMutex
303 * \sa SDL_UnlockMutex
304 */
305extern SDL_DECLSPEC SDL_Mutex * SDLCALL SDL_CreateMutex(void);
306
307/**
308 * Lock the mutex.
309 *
310 * This will block until the mutex is available, which is to say it is in the
311 * unlocked state and the OS has chosen the caller as the next thread to lock
312 * it. Of all threads waiting to lock the mutex, only one may do so at a time.
313 *
314 * It is legal for the owning thread to lock an already-locked mutex. It must
315 * unlock it the same number of times before it is actually made available for
316 * other threads in the system (this is known as a "recursive mutex").
317 *
318 * This function does not fail; if mutex is NULL, it will return immediately
319 * having locked nothing. If the mutex is valid, this function will always
320 * block until it can lock the mutex, and return with it locked.
321 *
322 * \param mutex the mutex to lock.
323 *
324 * \since This function is available since SDL 3.1.3.
325 *
326 * \sa SDL_TryLockMutex
327 * \sa SDL_UnlockMutex
328 */
329extern SDL_DECLSPEC void SDLCALL SDL_LockMutex(SDL_Mutex *mutex) SDL_ACQUIRE(mutex);
330
331/**
332 * Try to lock a mutex without blocking.
333 *
334 * This works just like SDL_LockMutex(), but if the mutex is not available,
335 * this function returns false immediately.
336 *
337 * This technique is useful if you need exclusive access to a resource but
338 * don't want to wait for it, and will return to it to try again later.
339 *
340 * This function returns true if passed a NULL mutex.
341 *
342 * \param mutex the mutex to try to lock.
343 * \returns true on success, false if the mutex would block.
344 *
345 * \since This function is available since SDL 3.1.3.
346 *
347 * \sa SDL_LockMutex
348 * \sa SDL_UnlockMutex
349 */
350extern SDL_DECLSPEC bool SDLCALL SDL_TryLockMutex(SDL_Mutex *mutex) SDL_TRY_ACQUIRE(0, mutex);
351
352/**
353 * Unlock the mutex.
354 *
355 * It is legal for the owning thread to lock an already-locked mutex. It must
356 * unlock it the same number of times before it is actually made available for
357 * other threads in the system (this is known as a "recursive mutex").
358 *
359 * It is illegal to unlock a mutex that has not been locked by the current
360 * thread, and doing so results in undefined behavior.
361 *
362 * \param mutex the mutex to unlock.
363 *
364 * \since This function is available since SDL 3.1.3.
365 *
366 * \sa SDL_LockMutex
367 * \sa SDL_TryLockMutex
368 */
369extern SDL_DECLSPEC void SDLCALL SDL_UnlockMutex(SDL_Mutex *mutex) SDL_RELEASE(mutex);
370
371/**
372 * Destroy a mutex created with SDL_CreateMutex().
373 *
374 * This function must be called on any mutex that is no longer needed. Failure
375 * to destroy a mutex will result in a system memory or resource leak. While
376 * it is safe to destroy a mutex that is _unlocked_, it is not safe to attempt
377 * to destroy a locked mutex, and may result in undefined behavior depending
378 * on the platform.
379 *
380 * \param mutex the mutex to destroy.
381 *
382 * \since This function is available since SDL 3.1.3.
383 *
384 * \sa SDL_CreateMutex
385 */
386extern SDL_DECLSPEC void SDLCALL SDL_DestroyMutex(SDL_Mutex *mutex);
387
388/* @} *//* Mutex functions */
389
390
391/**
392 * \name Read/write lock functions
393 */
394/* @{ */
395
396/**
397 * A mutex that allows read-only threads to run in parallel.
398 *
399 * A rwlock is roughly the same concept as SDL_Mutex, but allows threads that
400 * request read-only access to all hold the lock at the same time. If a thread
401 * requests write access, it will block until all read-only threads have
402 * released the lock, and no one else can hold the thread (for reading or
403 * writing) at the same time as the writing thread.
404 *
405 * This can be more efficient in cases where several threads need to access
406 * data frequently, but changes to that data are rare.
407 *
408 * There are other rules that apply to rwlocks that don't apply to mutexes,
409 * about how threads are scheduled and when they can be recursively locked.
410 * These are documented in the other rwlock functions.
411 *
412 * \since This struct is available since SDL 3.1.3.
413 */
414typedef struct SDL_RWLock SDL_RWLock;
415
416/**
417 * Create a new read/write lock.
418 *
419 * A read/write lock is useful for situations where you have multiple threads
420 * trying to access a resource that is rarely updated. All threads requesting
421 * a read-only lock will be allowed to run in parallel; if a thread requests a
422 * write lock, it will be provided exclusive access. This makes it safe for
423 * multiple threads to use a resource at the same time if they promise not to
424 * change it, and when it has to be changed, the rwlock will serve as a
425 * gateway to make sure those changes can be made safely.
426 *
427 * In the right situation, a rwlock can be more efficient than a mutex, which
428 * only lets a single thread proceed at a time, even if it won't be modifying
429 * the data.
430 *
431 * All newly-created read/write locks begin in the _unlocked_ state.
432 *
433 * Calls to SDL_LockRWLockForReading() and SDL_LockRWLockForWriting will not
434 * return while the rwlock is locked _for writing_ by another thread. See
435 * SDL_TryLockRWLockForReading() and SDL_TryLockRWLockForWriting() to attempt
436 * to lock without blocking.
437 *
438 * SDL read/write locks are only recursive for read-only locks! They are not
439 * guaranteed to be fair, or provide access in a FIFO manner! They are not
440 * guaranteed to favor writers. You may not lock a rwlock for both read-only
441 * and write access at the same time from the same thread (so you can't
442 * promote your read-only lock to a write lock without unlocking first).
443 *
444 * \returns the initialized and unlocked read/write lock or NULL on failure;
445 * call SDL_GetError() for more information.
446 *
447 * \since This function is available since SDL 3.1.3.
448 *
449 * \sa SDL_DestroyRWLock
450 * \sa SDL_LockRWLockForReading
451 * \sa SDL_LockRWLockForWriting
452 * \sa SDL_TryLockRWLockForReading
453 * \sa SDL_TryLockRWLockForWriting
454 * \sa SDL_UnlockRWLock
455 */
456extern SDL_DECLSPEC SDL_RWLock * SDLCALL SDL_CreateRWLock(void);
457
458/**
459 * Lock the read/write lock for _read only_ operations.
460 *
461 * This will block until the rwlock is available, which is to say it is not
462 * locked for writing by any other thread. Of all threads waiting to lock the
463 * rwlock, all may do so at the same time as long as they are requesting
464 * read-only access; if a thread wants to lock for writing, only one may do so
465 * at a time, and no other threads, read-only or not, may hold the lock at the
466 * same time.
467 *
468 * It is legal for the owning thread to lock an already-locked rwlock for
469 * reading. It must unlock it the same number of times before it is actually
470 * made available for other threads in the system (this is known as a
471 * "recursive rwlock").
472 *
473 * Note that locking for writing is not recursive (this is only available to
474 * read-only locks).
475 *
476 * It is illegal to request a read-only lock from a thread that already holds
477 * the write lock. Doing so results in undefined behavior. Unlock the write
478 * lock before requesting a read-only lock. (But, of course, if you have the
479 * write lock, you don't need further locks to read in any case.)
480 *
481 * This function does not fail; if rwlock is NULL, it will return immediately
482 * having locked nothing. If the rwlock is valid, this function will always
483 * block until it can lock the mutex, and return with it locked.
484 *
485 * \param rwlock the read/write lock to lock.
486 *
487 * \since This function is available since SDL 3.1.3.
488 *
489 * \sa SDL_LockRWLockForWriting
490 * \sa SDL_TryLockRWLockForReading
491 * \sa SDL_UnlockRWLock
492 */
493extern SDL_DECLSPEC void SDLCALL SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock);
494
495/**
496 * Lock the read/write lock for _write_ operations.
497 *
498 * This will block until the rwlock is available, which is to say it is not
499 * locked for reading or writing by any other thread. Only one thread may hold
500 * the lock when it requests write access; all other threads, whether they
501 * also want to write or only want read-only access, must wait until the
502 * writer thread has released the lock.
503 *
504 * It is illegal for the owning thread to lock an already-locked rwlock for
505 * writing (read-only may be locked recursively, writing can not). Doing so
506 * results in undefined behavior.
507 *
508 * It is illegal to request a write lock from a thread that already holds a
509 * read-only lock. Doing so results in undefined behavior. Unlock the
510 * read-only lock before requesting a write lock.
511 *
512 * This function does not fail; if rwlock is NULL, it will return immediately
513 * having locked nothing. If the rwlock is valid, this function will always
514 * block until it can lock the mutex, and return with it locked.
515 *
516 * \param rwlock the read/write lock to lock.
517 *
518 * \since This function is available since SDL 3.1.3.
519 *
520 * \sa SDL_LockRWLockForReading
521 * \sa SDL_TryLockRWLockForWriting
522 * \sa SDL_UnlockRWLock
523 */
524extern SDL_DECLSPEC void SDLCALL SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock);
525
526/**
527 * Try to lock a read/write lock _for reading_ without blocking.
528 *
529 * This works just like SDL_LockRWLockForReading(), but if the rwlock is not
530 * available, then this function returns false immediately.
531 *
532 * This technique is useful if you need access to a resource but don't want to
533 * wait for it, and will return to it to try again later.
534 *
535 * Trying to lock for read-only access can succeed if other threads are
536 * holding read-only locks, as this won't prevent access.
537 *
538 * This function returns true if passed a NULL rwlock.
539 *
540 * \param rwlock the rwlock to try to lock.
541 * \returns true on success, false if the lock would block.
542 *
543 * \since This function is available since SDL 3.1.3.
544 *
545 * \sa SDL_LockRWLockForReading
546 * \sa SDL_TryLockRWLockForWriting
547 * \sa SDL_UnlockRWLock
548 */
549extern SDL_DECLSPEC bool SDLCALL SDL_TryLockRWLockForReading(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE_SHARED(0, rwlock);
550
551/**
552 * Try to lock a read/write lock _for writing_ without blocking.
553 *
554 * This works just like SDL_LockRWLockForWriting(), but if the rwlock is not
555 * available, then this function returns false immediately.
556 *
557 * This technique is useful if you need exclusive access to a resource but
558 * don't want to wait for it, and will return to it to try again later.
559 *
560 * It is illegal for the owning thread to lock an already-locked rwlock for
561 * writing (read-only may be locked recursively, writing can not). Doing so
562 * results in undefined behavior.
563 *
564 * It is illegal to request a write lock from a thread that already holds a
565 * read-only lock. Doing so results in undefined behavior. Unlock the
566 * read-only lock before requesting a write lock.
567 *
568 * This function returns true if passed a NULL rwlock.
569 *
570 * \param rwlock the rwlock to try to lock.
571 * \returns true on success, false if the lock would block.
572 *
573 * \since This function is available since SDL 3.1.3.
574 *
575 * \sa SDL_LockRWLockForWriting
576 * \sa SDL_TryLockRWLockForReading
577 * \sa SDL_UnlockRWLock
578 */
579extern SDL_DECLSPEC bool SDLCALL SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE(0, rwlock);
580
581/**
582 * Unlock the read/write lock.
583 *
584 * Use this function to unlock the rwlock, whether it was locked for read-only
585 * or write operations.
586 *
587 * It is legal for the owning thread to lock an already-locked read-only lock.
588 * It must unlock it the same number of times before it is actually made
589 * available for other threads in the system (this is known as a "recursive
590 * rwlock").
591 *
592 * It is illegal to unlock a rwlock that has not been locked by the current
593 * thread, and doing so results in undefined behavior.
594 *
595 * \param rwlock the rwlock to unlock.
596 *
597 * \since This function is available since SDL 3.1.3.
598 *
599 * \sa SDL_LockRWLockForReading
600 * \sa SDL_LockRWLockForWriting
601 * \sa SDL_TryLockRWLockForReading
602 * \sa SDL_TryLockRWLockForWriting
603 */
604extern SDL_DECLSPEC void SDLCALL SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_RELEASE_GENERIC(rwlock);
605
606/**
607 * Destroy a read/write lock created with SDL_CreateRWLock().
608 *
609 * This function must be called on any read/write lock that is no longer
610 * needed. Failure to destroy a rwlock will result in a system memory or
611 * resource leak. While it is safe to destroy a rwlock that is _unlocked_, it
612 * is not safe to attempt to destroy a locked rwlock, and may result in
613 * undefined behavior depending on the platform.
614 *
615 * \param rwlock the rwlock to destroy.
616 *
617 * \since This function is available since SDL 3.1.3.
618 *
619 * \sa SDL_CreateRWLock
620 */
621extern SDL_DECLSPEC void SDLCALL SDL_DestroyRWLock(SDL_RWLock *rwlock);
622
623/* @} *//* Read/write lock functions */
624
625
626/**
627 * \name Semaphore functions
628 */
629/* @{ */
630
631/**
632 * A means to manage access to a resource, by count, between threads.
633 *
634 * Semaphores (specifically, "counting semaphores"), let X number of threads
635 * request access at the same time, each thread granted access decrementing a
636 * counter. When the counter reaches zero, future requests block until a prior
637 * thread releases their request, incrementing the counter again.
638 *
639 * Wikipedia has a thorough explanation of the concept:
640 *
641 * https://en.wikipedia.org/wiki/Semaphore_(programming)
642 *
643 * \since This struct is available since SDL 3.1.3.
644 */
645typedef struct SDL_Semaphore SDL_Semaphore;
646
647/**
648 * Create a semaphore.
649 *
650 * This function creates a new semaphore and initializes it with the value
651 * `initial_value`. Each wait operation on the semaphore will atomically
652 * decrement the semaphore value and potentially block if the semaphore value
653 * is 0. Each post operation will atomically increment the semaphore value and
654 * wake waiting threads and allow them to retry the wait operation.
655 *
656 * \param initial_value the starting value of the semaphore.
657 * \returns a new semaphore or NULL on failure; call SDL_GetError() for more
658 * information.
659 *
660 * \since This function is available since SDL 3.1.3.
661 *
662 * \sa SDL_DestroySemaphore
663 * \sa SDL_SignalSemaphore
664 * \sa SDL_TryWaitSemaphore
665 * \sa SDL_GetSemaphoreValue
666 * \sa SDL_WaitSemaphore
667 * \sa SDL_WaitSemaphoreTimeout
668 */
669extern SDL_DECLSPEC SDL_Semaphore * SDLCALL SDL_CreateSemaphore(Uint32 initial_value);
670
671/**
672 * Destroy a semaphore.
673 *
674 * It is not safe to destroy a semaphore if there are threads currently
675 * waiting on it.
676 *
677 * \param sem the semaphore to destroy.
678 *
679 * \since This function is available since SDL 3.1.3.
680 *
681 * \sa SDL_CreateSemaphore
682 */
683extern SDL_DECLSPEC void SDLCALL SDL_DestroySemaphore(SDL_Semaphore *sem);
684
685/**
686 * Wait until a semaphore has a positive value and then decrements it.
687 *
688 * This function suspends the calling thread until the semaphore pointed to by
689 * `sem` has a positive value, and then atomically decrement the semaphore
690 * value.
691 *
692 * This function is the equivalent of calling SDL_WaitSemaphoreTimeout() with
693 * a time length of -1.
694 *
695 * \param sem the semaphore wait on.
696 *
697 * \since This function is available since SDL 3.1.3.
698 *
699 * \sa SDL_SignalSemaphore
700 * \sa SDL_TryWaitSemaphore
701 * \sa SDL_WaitSemaphoreTimeout
702 */
703extern SDL_DECLSPEC void SDLCALL SDL_WaitSemaphore(SDL_Semaphore *sem);
704
705/**
706 * See if a semaphore has a positive value and decrement it if it does.
707 *
708 * This function checks to see if the semaphore pointed to by `sem` has a
709 * positive value and atomically decrements the semaphore value if it does. If
710 * the semaphore doesn't have a positive value, the function immediately
711 * returns false.
712 *
713 * \param sem the semaphore to wait on.
714 * \returns true if the wait succeeds, false if the wait would block.
715 *
716 * \since This function is available since SDL 3.1.3.
717 *
718 * \sa SDL_SignalSemaphore
719 * \sa SDL_WaitSemaphore
720 * \sa SDL_WaitSemaphoreTimeout
721 */
722extern SDL_DECLSPEC bool SDLCALL SDL_TryWaitSemaphore(SDL_Semaphore *sem);
723
724/**
725 * Wait until a semaphore has a positive value and then decrements it.
726 *
727 * This function suspends the calling thread until either the semaphore
728 * pointed to by `sem` has a positive value or the specified time has elapsed.
729 * If the call is successful it will atomically decrement the semaphore value.
730 *
731 * \param sem the semaphore to wait on.
732 * \param timeoutMS the length of the timeout, in milliseconds, or -1 to wait
733 * indefinitely.
734 * \returns true if the wait succeeds or false if the wait times out.
735 *
736 * \since This function is available since SDL 3.1.3.
737 *
738 * \sa SDL_SignalSemaphore
739 * \sa SDL_TryWaitSemaphore
740 * \sa SDL_WaitSemaphore
741 */
742extern SDL_DECLSPEC bool SDLCALL SDL_WaitSemaphoreTimeout(SDL_Semaphore *sem, Sint32 timeoutMS);
743
744/**
745 * Atomically increment a semaphore's value and wake waiting threads.
746 *
747 * \param sem the semaphore to increment.
748 *
749 * \since This function is available since SDL 3.1.3.
750 *
751 * \sa SDL_TryWaitSemaphore
752 * \sa SDL_WaitSemaphore
753 * \sa SDL_WaitSemaphoreTimeout
754 */
755extern SDL_DECLSPEC void SDLCALL SDL_SignalSemaphore(SDL_Semaphore *sem);
756
757/**
758 * Get the current value of a semaphore.
759 *
760 * \param sem the semaphore to query.
761 * \returns the current value of the semaphore.
762 *
763 * \since This function is available since SDL 3.1.3.
764 */
765extern SDL_DECLSPEC Uint32 SDLCALL SDL_GetSemaphoreValue(SDL_Semaphore *sem);
766
767/* @} *//* Semaphore functions */
768
769
770/**
771 * \name Condition variable functions
772 */
773/* @{ */
774
775/**
776 * A means to block multiple threads until a condition is satisfied.
777 *
778 * Condition variables, paired with an SDL_Mutex, let an app halt multiple
779 * threads until a condition has occurred, at which time the app can release
780 * one or all waiting threads.
781 *
782 * Wikipedia has a thorough explanation of the concept:
783 *
784 * https://en.wikipedia.org/wiki/Condition_variable
785 *
786 * \since This struct is available since SDL 3.1.3.
787 */
788typedef struct SDL_Condition SDL_Condition;
789
790/**
791 * Create a condition variable.
792 *
793 * \returns a new condition variable or NULL on failure; call SDL_GetError()
794 * for more information.
795 *
796 * \since This function is available since SDL 3.1.3.
797 *
798 * \sa SDL_BroadcastCondition
799 * \sa SDL_SignalCondition
800 * \sa SDL_WaitCondition
801 * \sa SDL_WaitConditionTimeout
802 * \sa SDL_DestroyCondition
803 */
804extern SDL_DECLSPEC SDL_Condition * SDLCALL SDL_CreateCondition(void);
805
806/**
807 * Destroy a condition variable.
808 *
809 * \param cond the condition variable to destroy.
810 *
811 * \since This function is available since SDL 3.1.3.
812 *
813 * \sa SDL_CreateCondition
814 */
815extern SDL_DECLSPEC void SDLCALL SDL_DestroyCondition(SDL_Condition *cond);
816
817/**
818 * Restart one of the threads that are waiting on the condition variable.
819 *
820 * \param cond the condition variable to signal.
821 *
822 * \threadsafety It is safe to call this function from any thread.
823 *
824 * \since This function is available since SDL 3.1.3.
825 *
826 * \sa SDL_BroadcastCondition
827 * \sa SDL_WaitCondition
828 * \sa SDL_WaitConditionTimeout
829 */
830extern SDL_DECLSPEC void SDLCALL SDL_SignalCondition(SDL_Condition *cond);
831
832/**
833 * Restart all threads that are waiting on the condition variable.
834 *
835 * \param cond the condition variable to signal.
836 *
837 * \threadsafety It is safe to call this function from any thread.
838 *
839 * \since This function is available since SDL 3.1.3.
840 *
841 * \sa SDL_SignalCondition
842 * \sa SDL_WaitCondition
843 * \sa SDL_WaitConditionTimeout
844 */
845extern SDL_DECLSPEC void SDLCALL SDL_BroadcastCondition(SDL_Condition *cond);
846
847/**
848 * Wait until a condition variable is signaled.
849 *
850 * This function unlocks the specified `mutex` and waits for another thread to
851 * call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition
852 * variable `cond`. Once the condition variable is signaled, the mutex is
853 * re-locked and the function returns.
854 *
855 * The mutex must be locked before calling this function. Locking the mutex
856 * recursively (more than once) is not supported and leads to undefined
857 * behavior.
858 *
859 * This function is the equivalent of calling SDL_WaitConditionTimeout() with
860 * a time length of -1.
861 *
862 * \param cond the condition variable to wait on.
863 * \param mutex the mutex used to coordinate thread access.
864 *
865 * \threadsafety It is safe to call this function from any thread.
866 *
867 * \since This function is available since SDL 3.1.3.
868 *
869 * \sa SDL_BroadcastCondition
870 * \sa SDL_SignalCondition
871 * \sa SDL_WaitConditionTimeout
872 */
873extern SDL_DECLSPEC void SDLCALL SDL_WaitCondition(SDL_Condition *cond, SDL_Mutex *mutex);
874
875/**
876 * Wait until a condition variable is signaled or a certain time has passed.
877 *
878 * This function unlocks the specified `mutex` and waits for another thread to
879 * call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition
880 * variable `cond`, or for the specified time to elapse. Once the condition
881 * variable is signaled or the time elapsed, the mutex is re-locked and the
882 * function returns.
883 *
884 * The mutex must be locked before calling this function. Locking the mutex
885 * recursively (more than once) is not supported and leads to undefined
886 * behavior.
887 *
888 * \param cond the condition variable to wait on.
889 * \param mutex the mutex used to coordinate thread access.
890 * \param timeoutMS the maximum time to wait, in milliseconds, or -1 to wait
891 * indefinitely.
892 * \returns true if the condition variable is signaled, false if the condition
893 * is not signaled in the allotted time.
894 *
895 * \threadsafety It is safe to call this function from any thread.
896 *
897 * \since This function is available since SDL 3.1.3.
898 *
899 * \sa SDL_BroadcastCondition
900 * \sa SDL_SignalCondition
901 * \sa SDL_WaitCondition
902 */
903extern SDL_DECLSPEC bool SDLCALL SDL_WaitConditionTimeout(SDL_Condition *cond,
904 SDL_Mutex *mutex, Sint32 timeoutMS);
905
906/* @} *//* Condition variable functions */
907
908/**
909 * \name Thread-safe initialization state functions
910 */
911/* @{ */
912
913/**
914 * The current status of an SDL_InitState structure.
915 *
916 * \since This enum is available since SDL 3.1.3.
917 */
918typedef enum SDL_InitStatus
919{
925
926/**
927 * A structure used for thread-safe initialization and shutdown.
928 *
929 * Here is an example of using this:
930 *
931 * ```c
932 * static SDL_AtomicInitState init;
933 *
934 * bool InitSystem(void)
935 * {
936 * if (!SDL_ShouldInit(&init)) {
937 * // The system is initialized
938 * return true;
939 * }
940 *
941 * // At this point, you should not leave this function without calling SDL_SetInitialized()
942 *
943 * bool initialized = DoInitTasks();
944 * SDL_SetInitialized(&init, initialized);
945 * return initialized;
946 * }
947 *
948 * bool UseSubsystem(void)
949 * {
950 * if (SDL_ShouldInit(&init)) {
951 * // Error, the subsystem isn't initialized
952 * SDL_SetInitialized(&init, false);
953 * return false;
954 * }
955 *
956 * // Do work using the initialized subsystem
957 *
958 * return true;
959 * }
960 *
961 * void QuitSystem(void)
962 * {
963 * if (!SDL_ShouldQuit(&init)) {
964 * // The system is not initialized
965 * return;
966 * }
967 *
968 * // At this point, you should not leave this function without calling SDL_SetInitialized()
969 *
970 * DoQuitTasks();
971 * SDL_SetInitialized(&init, false);
972 * }
973 * ```
974 *
975 * Note that this doesn't protect any resources created during initialization,
976 * or guarantee that nobody is using those resources during cleanup. You
977 * should use other mechanisms to protect those, if that's a concern for your
978 * code.
979 *
980 * \since This struct is available since SDL 3.1.3.
981 */
982typedef struct SDL_InitState
983{
986 void *reserved;
988
989/**
990 * Return whether initialization should be done.
991 *
992 * This function checks the passed in state and if initialization should be
993 * done, sets the status to `SDL_INIT_STATUS_INITIALIZING` and returns true.
994 * If another thread is already modifying this state, it will wait until
995 * that's done before returning.
996 *
997 * If this function returns true, the calling code must call
998 * SDL_SetInitialized() to complete the initialization.
999 *
1000 * \param state the initialization state to check.
1001 * \returns true if initialization needs to be done, false otherwise.
1002 *
1003 * \threadsafety It is safe to call this function from any thread.
1004 *
1005 * \since This function is available since SDL 3.1.3.
1006 *
1007 * \sa SDL_SetInitialized
1008 * \sa SDL_ShouldQuit
1009 */
1010extern SDL_DECLSPEC bool SDLCALL SDL_ShouldInit(SDL_InitState *state);
1011
1012/**
1013 * Return whether cleanup should be done.
1014 *
1015 * This function checks the passed in state and if cleanup should be done,
1016 * sets the status to `SDL_INIT_STATUS_UNINITIALIZING` and returns true.
1017 *
1018 * If this function returns true, the calling code must call
1019 * SDL_SetInitialized() to complete the cleanup.
1020 *
1021 * \param state the initialization state to check.
1022 * \returns true if cleanup needs to be done, false otherwise.
1023 *
1024 * \threadsafety It is safe to call this function from any thread.
1025 *
1026 * \since This function is available since SDL 3.1.3.
1027 *
1028 * \sa SDL_SetInitialized
1029 * \sa SDL_ShouldInit
1030 */
1031extern SDL_DECLSPEC bool SDLCALL SDL_ShouldQuit(SDL_InitState *state);
1032
1033/**
1034 * Finish an initialization state transition.
1035 *
1036 * This function sets the status of the passed in state to
1037 * `SDL_INIT_STATUS_INITIALIZED` or `SDL_INIT_STATUS_UNINITIALIZED` and allows
1038 * any threads waiting for the status to proceed.
1039 *
1040 * \param state the initialization state to check.
1041 * \param initialized the new initialization state.
1042 *
1043 * \threadsafety It is safe to call this function from any thread.
1044 *
1045 * \since This function is available since SDL 3.1.3.
1046 *
1047 * \sa SDL_ShouldInit
1048 * \sa SDL_ShouldQuit
1049 */
1050extern SDL_DECLSPEC void SDLCALL SDL_SetInitialized(SDL_InitState *state, bool initialized);
1051
1052/* @} *//* Thread-safe initialization state functions */
1053
1054/* Ends C function definitions when using C++ */
1055#ifdef __cplusplus
1056}
1057#endif
1058#include <SDL3/SDL_close_code.h>
1059
1060#endif /* SDL_mutex_h_ */
void SDL_DestroyRWLock(SDL_RWLock *rwlock)
bool SDL_WaitConditionTimeout(SDL_Condition *cond, SDL_Mutex *mutex, Sint32 timeoutMS)
void SDL_WaitCondition(SDL_Condition *cond, SDL_Mutex *mutex)
#define SDL_ACQUIRE(x)
Definition SDL_mutex.h:145
#define SDL_TRY_ACQUIRE(x, y)
Definition SDL_mutex.h:195
SDL_RWLock * SDL_CreateRWLock(void)
void SDL_DestroySemaphore(SDL_Semaphore *sem)
#define SDL_TRY_ACQUIRE_SHARED(x, y)
Definition SDL_mutex.h:205
bool SDL_TryLockRWLockForReading(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE_SHARED(0
bool SDL_ShouldInit(SDL_InitState *state)
#define SDL_ACQUIRE_SHARED(x)
Definition SDL_mutex.h:155
bool SDL_TryLockMutex(SDL_Mutex *mutex) SDL_TRY_ACQUIRE(0
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:284
void SDL_SignalCondition(SDL_Condition *cond)
bool SDL_WaitSemaphoreTimeout(SDL_Semaphore *sem, Sint32 timeoutMS)
bool rwlock
Definition SDL_mutex.h:550
#define SDL_RELEASE_GENERIC(x)
Definition SDL_mutex.h:185
SDL_Semaphore * SDL_CreateSemaphore(Uint32 initial_value)
void SDL_SetInitialized(SDL_InitState *state, bool initialized)
void SDL_LockMutex(SDL_Mutex *mutex) SDL_ACQUIRE(mutex)
void SDL_SignalSemaphore(SDL_Semaphore *sem)
bool SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE(0
Uint32 SDL_GetSemaphoreValue(SDL_Semaphore *sem)
struct SDL_Semaphore SDL_Semaphore
Definition SDL_mutex.h:646
void SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_RELEASE_GENERIC(rwlock)
struct SDL_RWLock SDL_RWLock
Definition SDL_mutex.h:415
bool SDL_TryWaitSemaphore(SDL_Semaphore *sem)
void SDL_WaitSemaphore(SDL_Semaphore *sem)
void SDL_DestroyCondition(SDL_Condition *cond)
void SDL_DestroyMutex(SDL_Mutex *mutex)
SDL_InitStatus
Definition SDL_mutex.h:920
@ SDL_INIT_STATUS_INITIALIZED
Definition SDL_mutex.h:923
@ SDL_INIT_STATUS_UNINITIALIZED
Definition SDL_mutex.h:921
@ SDL_INIT_STATUS_UNINITIALIZING
Definition SDL_mutex.h:924
@ SDL_INIT_STATUS_INITIALIZING
Definition SDL_mutex.h:922
SDL_Condition * SDL_CreateCondition(void)
#define SDL_RELEASE(x)
Definition SDL_mutex.h:165
SDL_Mutex * SDL_CreateMutex(void)
void SDL_BroadcastCondition(SDL_Condition *cond)
void SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock)
bool SDL_ShouldQuit(SDL_InitState *state)
bool mutex
Definition SDL_mutex.h:351
struct SDL_Condition SDL_Condition
Definition SDL_mutex.h:789
int32_t Sint32
Definition SDL_stdinc.h:452
uint32_t Uint32
Definition SDL_stdinc.h:461
Uint64 SDL_ThreadID
Definition SDL_thread.h:72
void * reserved
Definition SDL_mutex.h:987
SDL_AtomicInt status
Definition SDL_mutex.h:985
SDL_ThreadID thread
Definition SDL_mutex.h:986

◆ SDL_ACQUIRE_SHARED

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 155 of file SDL_mutex.h.

◆ SDL_ACQUIRED_AFTER

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 115 of file SDL_mutex.h.

◆ SDL_ACQUIRED_BEFORE

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 105 of file SDL_mutex.h.

◆ SDL_ASSERT_CAPABILITY

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 225 of file SDL_mutex.h.

◆ SDL_ASSERT_SHARED_CAPABILITY

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 235 of file SDL_mutex.h.

◆ SDL_CAPABILITY

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 65 of file SDL_mutex.h.

◆ SDL_EXCLUDES

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 215 of file SDL_mutex.h.

◆ SDL_GUARDED_BY

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 85 of file SDL_mutex.h.

◆ SDL_NO_THREAD_SAFETY_ANALYSIS

#define SDL_NO_THREAD_SAFETY_ANALYSIS    SDL_THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 255 of file SDL_mutex.h.

◆ SDL_PT_GUARDED_BY

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 95 of file SDL_mutex.h.

◆ SDL_RELEASE

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 165 of file SDL_mutex.h.

◆ SDL_RELEASE_GENERIC

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 185 of file SDL_mutex.h.

◆ SDL_RELEASE_SHARED

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 175 of file SDL_mutex.h.

◆ SDL_REQUIRES

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 125 of file SDL_mutex.h.

◆ SDL_REQUIRES_SHARED

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 135 of file SDL_mutex.h.

◆ SDL_RETURN_CAPABILITY

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 245 of file SDL_mutex.h.

◆ SDL_SCOPED_CAPABILITY

#define SDL_SCOPED_CAPABILITY    SDL_THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 75 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 55 of file SDL_mutex.h.

◆ SDL_TRY_ACQUIRE

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

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 195 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))

Wrapper around Clang thread safety analysis annotations.

Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h

Since
This macro is available since SDL 3.1.3.

Definition at line 205 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 3.1.3.

Definition at line 789 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 3.1.3.

Definition at line 284 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 3.1.3.

Definition at line 415 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 3.1.3.

Definition at line 646 of file SDL_mutex.h.

Enumeration Type Documentation

◆ SDL_InitStatus

The current status of an SDL_InitState structure.

Since
This enum is available since SDL 3.1.3.
Enumerator
SDL_INIT_STATUS_UNINITIALIZED 
SDL_INIT_STATUS_INITIALIZING 
SDL_INIT_STATUS_INITIALIZED 
SDL_INIT_STATUS_UNINITIALIZING 

Definition at line 919 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 3.1.3.
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 3.1.3.
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 3.1.3.
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 3.1.3.
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 3.1.3.
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 3.1.3.
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 3.1.3.
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 3.1.3.
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 3.1.3.
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 3.1.3.

◆ 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 3.1.3.
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 3.1.3.
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 3.1.3.
See also
SDL_LockRWLockForReading
SDL_TryLockRWLockForWriting
SDL_UnlockRWLock

◆ SDL_SetInitialized()

void SDL_SetInitialized ( SDL_InitState state,
bool  initialized 
)
extern

Finish an initialization state transition.

This function sets the status of the passed in state to SDL_INIT_STATUS_INITIALIZED or SDL_INIT_STATUS_UNINITIALIZED and allows any threads waiting for the status to proceed.

Parameters
statethe initialization state to check.
initializedthe new initialization state.

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

Since
This function is available since SDL 3.1.3.
See also
SDL_ShouldInit
SDL_ShouldQuit

◆ SDL_ShouldInit()

bool SDL_ShouldInit ( SDL_InitState state)
extern

Return whether initialization should be done.

This function checks the passed in state and if initialization should be done, sets the status to SDL_INIT_STATUS_INITIALIZING and returns true. If another thread is already modifying this state, it will wait until that's done before returning.

If this function returns true, the calling code must call SDL_SetInitialized() to complete the initialization.

Parameters
statethe initialization state to check.
Returns
true if initialization needs to be done, false otherwise.

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

Since
This function is available since SDL 3.1.3.
See also
SDL_SetInitialized
SDL_ShouldQuit

◆ SDL_ShouldQuit()

bool SDL_ShouldQuit ( SDL_InitState state)
extern

Return whether cleanup should be done.

This function checks the passed in state and if cleanup should be done, sets the status to SDL_INIT_STATUS_UNINITIALIZING and returns true.

If this function returns true, the calling code must call SDL_SetInitialized() to complete the cleanup.

Parameters
statethe initialization state to check.
Returns
true if cleanup needs to be done, false otherwise.

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

Since
This function is available since SDL 3.1.3.
See also
SDL_SetInitialized
SDL_ShouldInit

◆ 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 3.1.3.
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 3.1.3.
See also
SDL_TryWaitSemaphore
SDL_WaitSemaphore
SDL_WaitSemaphoreTimeout

◆ SDL_TryLockMutex()

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 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 true if passed a NULL mutex.

Parameters
mutexthe mutex to try to lock.
Returns
true on success, false if the mutex would block.
Since
This function is available since SDL 3.1.3.
See also
SDL_LockMutex
SDL_UnlockMutex

◆ SDL_TryLockRWLockForReading()

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 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 true if passed a NULL rwlock.

Parameters
rwlockthe rwlock to try to lock.
Returns
true on success, false if the lock would block.
Since
This function is available since SDL 3.1.3.
See also
SDL_LockRWLockForReading
SDL_TryLockRWLockForWriting
SDL_UnlockRWLock

◆ SDL_TryLockRWLockForWriting()

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 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 true if passed a NULL rwlock.

Parameters
rwlockthe rwlock to try to lock.
Returns
true on success, false if the lock would block.
Since
This function is available since SDL 3.1.3.
See also
SDL_LockRWLockForWriting
SDL_TryLockRWLockForReading
SDL_UnlockRWLock

◆ SDL_TryWaitSemaphore()

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 false.

Parameters
semthe semaphore to wait on.
Returns
true if the wait succeeds, false if the wait would block.
Since
This function is available since SDL 3.1.3.
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 3.1.3.
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 3.1.3.
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 3.1.3.
See also
SDL_BroadcastCondition
SDL_SignalCondition
SDL_WaitConditionTimeout

◆ SDL_WaitConditionTimeout()

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
true if the condition variable is signaled, 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 3.1.3.
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 3.1.3.
See also
SDL_SignalSemaphore
SDL_TryWaitSemaphore
SDL_WaitSemaphoreTimeout

◆ SDL_WaitSemaphoreTimeout()

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
true if the wait succeeds or false if the wait times out.
Since
This function is available since SDL 3.1.3.
See also
SDL_SignalSemaphore
SDL_TryWaitSemaphore
SDL_WaitSemaphore

Variable Documentation

◆ mutex

bool mutex

Definition at line 351 of file SDL_mutex.h.

◆ rwlock

bool rwlock

Definition at line 550 of file SDL_mutex.h.