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author Paper <paper@tflc.us>
date Mon, 05 Jan 2026 02:15:46 -0500
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0:e9bb126753e7 1:20d02a178406
1 /*
2 Simple DirectMedia Layer
3 Copyright (C) 1997-2025 Sam Lantinga <slouken@libsdl.org>
4
5 This software is provided 'as-is', without any express or implied
6 warranty. In no event will the authors be held liable for any damages
7 arising from the use of this software.
8
9 Permission is granted to anyone to use this software for any purpose,
10 including commercial applications, and to alter it and redistribute it
11 freely, subject to the following restrictions:
12
13 1. The origin of this software must not be misrepresented; you must not
14 claim that you wrote the original software. If you use this software
15 in a product, an acknowledgment in the product documentation would be
16 appreciated but is not required.
17 2. Altered source versions must be plainly marked as such, and must not be
18 misrepresented as being the original software.
19 3. This notice may not be removed or altered from any source distribution.
20 */
21
22 #ifndef SDL_mutex_h_
23 #define SDL_mutex_h_
24
25 /**
26 * # CategoryMutex
27 *
28 * SDL offers several thread synchronization primitives. This document can't
29 * cover the complicated topic of thread safety, but reading up on what each
30 * of these primitives are, why they are useful, and how to correctly use them
31 * is vital to writing correct and safe multithreaded programs.
32 *
33 * - Mutexes: SDL_CreateMutex()
34 * - Read/Write locks: SDL_CreateRWLock()
35 * - Semaphores: SDL_CreateSemaphore()
36 * - Condition variables: SDL_CreateCondition()
37 *
38 * SDL also offers a datatype, SDL_InitState, which can be used to make sure
39 * only one thread initializes/deinitializes some resource that several
40 * threads might try to use for the first time simultaneously.
41 */
42
43 #include <SDL3/SDL_stdinc.h>
44 #include <SDL3/SDL_atomic.h>
45 #include <SDL3/SDL_error.h>
46 #include <SDL3/SDL_thread.h>
47
48 #ifdef SDL_WIKI_DOCUMENTATION_SECTION
49
50 /**
51 * Enable thread safety attributes, only with clang.
52 *
53 * The attributes can be safely erased when compiling with other compilers.
54 *
55 * To enable analysis, set these environment variables before running cmake:
56 *
57 * ```bash
58 * export CC=clang
59 * export CFLAGS="-DSDL_THREAD_SAFETY_ANALYSIS -Wthread-safety"
60 * ```
61 */
62 #define SDL_THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))
63
64 #elif defined(SDL_THREAD_SAFETY_ANALYSIS) && defined(__clang__) && (!defined(SWIG))
65 #define SDL_THREAD_ANNOTATION_ATTRIBUTE__(x) __attribute__((x))
66 #else
67 #define SDL_THREAD_ANNOTATION_ATTRIBUTE__(x) /* no-op */
68 #endif
69
70 /**
71 * Wrapper around Clang thread safety analysis annotations.
72 *
73 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
74 *
75 * \since This macro is available since SDL 3.2.0.
76 */
77 #define SDL_CAPABILITY(x) \
78 SDL_THREAD_ANNOTATION_ATTRIBUTE__(capability(x))
79
80 /**
81 * Wrapper around Clang thread safety analysis annotations.
82 *
83 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
84 *
85 * \since This macro is available since SDL 3.2.0.
86 */
87 #define SDL_SCOPED_CAPABILITY \
88 SDL_THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
89
90 /**
91 * Wrapper around Clang thread safety analysis annotations.
92 *
93 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
94 *
95 * \since This macro is available since SDL 3.2.0.
96 */
97 #define SDL_GUARDED_BY(x) \
98 SDL_THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
99
100 /**
101 * Wrapper around Clang thread safety analysis annotations.
102 *
103 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
104 *
105 * \since This macro is available since SDL 3.2.0.
106 */
107 #define SDL_PT_GUARDED_BY(x) \
108 SDL_THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))
109
110 /**
111 * Wrapper around Clang thread safety analysis annotations.
112 *
113 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
114 *
115 * \since This macro is available since SDL 3.2.0.
116 */
117 #define SDL_ACQUIRED_BEFORE(x) \
118 SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(x))
119
120 /**
121 * Wrapper around Clang thread safety analysis annotations.
122 *
123 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
124 *
125 * \since This macro is available since SDL 3.2.0.
126 */
127 #define SDL_ACQUIRED_AFTER(x) \
128 SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(x))
129
130 /**
131 * Wrapper around Clang thread safety analysis annotations.
132 *
133 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
134 *
135 * \since This macro is available since SDL 3.2.0.
136 */
137 #define SDL_REQUIRES(x) \
138 SDL_THREAD_ANNOTATION_ATTRIBUTE__(requires_capability(x))
139
140 /**
141 * Wrapper around Clang thread safety analysis annotations.
142 *
143 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
144 *
145 * \since This macro is available since SDL 3.2.0.
146 */
147 #define SDL_REQUIRES_SHARED(x) \
148 SDL_THREAD_ANNOTATION_ATTRIBUTE__(requires_shared_capability(x))
149
150 /**
151 * Wrapper around Clang thread safety analysis annotations.
152 *
153 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
154 *
155 * \since This macro is available since SDL 3.2.0.
156 */
157 #define SDL_ACQUIRE(x) \
158 SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquire_capability(x))
159
160 /**
161 * Wrapper around Clang thread safety analysis annotations.
162 *
163 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
164 *
165 * \since This macro is available since SDL 3.2.0.
166 */
167 #define SDL_ACQUIRE_SHARED(x) \
168 SDL_THREAD_ANNOTATION_ATTRIBUTE__(acquire_shared_capability(x))
169
170 /**
171 * Wrapper around Clang thread safety analysis annotations.
172 *
173 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
174 *
175 * \since This macro is available since SDL 3.2.0.
176 */
177 #define SDL_RELEASE(x) \
178 SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_capability(x))
179
180 /**
181 * Wrapper around Clang thread safety analysis annotations.
182 *
183 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
184 *
185 * \since This macro is available since SDL 3.2.0.
186 */
187 #define SDL_RELEASE_SHARED(x) \
188 SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_shared_capability(x))
189
190 /**
191 * Wrapper around Clang thread safety analysis annotations.
192 *
193 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
194 *
195 * \since This macro is available since SDL 3.2.0.
196 */
197 #define SDL_RELEASE_GENERIC(x) \
198 SDL_THREAD_ANNOTATION_ATTRIBUTE__(release_generic_capability(x))
199
200 /**
201 * Wrapper around Clang thread safety analysis annotations.
202 *
203 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
204 *
205 * \since This macro is available since SDL 3.2.0.
206 */
207 #define SDL_TRY_ACQUIRE(x, y) \
208 SDL_THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_capability(x, y))
209
210 /**
211 * Wrapper around Clang thread safety analysis annotations.
212 *
213 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
214 *
215 * \since This macro is available since SDL 3.2.0.
216 */
217 #define SDL_TRY_ACQUIRE_SHARED(x, y) \
218 SDL_THREAD_ANNOTATION_ATTRIBUTE__(try_acquire_shared_capability(x, y))
219
220 /**
221 * Wrapper around Clang thread safety analysis annotations.
222 *
223 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
224 *
225 * \since This macro is available since SDL 3.2.0.
226 */
227 #define SDL_EXCLUDES(x) \
228 SDL_THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(x))
229
230 /**
231 * Wrapper around Clang thread safety analysis annotations.
232 *
233 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
234 *
235 * \since This macro is available since SDL 3.2.0.
236 */
237 #define SDL_ASSERT_CAPABILITY(x) \
238 SDL_THREAD_ANNOTATION_ATTRIBUTE__(assert_capability(x))
239
240 /**
241 * Wrapper around Clang thread safety analysis annotations.
242 *
243 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
244 *
245 * \since This macro is available since SDL 3.2.0.
246 */
247 #define SDL_ASSERT_SHARED_CAPABILITY(x) \
248 SDL_THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_capability(x))
249
250 /**
251 * Wrapper around Clang thread safety analysis annotations.
252 *
253 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
254 *
255 * \since This macro is available since SDL 3.2.0.
256 */
257 #define SDL_RETURN_CAPABILITY(x) \
258 SDL_THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))
259
260 /**
261 * Wrapper around Clang thread safety analysis annotations.
262 *
263 * Please see https://clang.llvm.org/docs/ThreadSafetyAnalysis.html#mutex-h
264 *
265 * \since This macro is available since SDL 3.2.0.
266 */
267 #define SDL_NO_THREAD_SAFETY_ANALYSIS \
268 SDL_THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
269
270 /******************************************************************************/
271
272
273 #include <SDL3/SDL_begin_code.h>
274 /* Set up for C function definitions, even when using C++ */
275 #ifdef __cplusplus
276 extern "C" {
277 #endif
278
279 /**
280 * \name Mutex functions
281 */
282 /* @{ */
283
284 /**
285 * A means to serialize access to a resource between threads.
286 *
287 * Mutexes (short for "mutual exclusion") are a synchronization primitive that
288 * allows exactly one thread to proceed at a time.
289 *
290 * Wikipedia has a thorough explanation of the concept:
291 *
292 * https://en.wikipedia.org/wiki/Mutex
293 *
294 * \since This struct is available since SDL 3.2.0.
295 */
296 typedef struct SDL_Mutex SDL_Mutex;
297
298 /**
299 * Create a new mutex.
300 *
301 * All newly-created mutexes begin in the _unlocked_ state.
302 *
303 * Calls to SDL_LockMutex() will not return while the mutex is locked by
304 * another thread. See SDL_TryLockMutex() to attempt to lock without blocking.
305 *
306 * SDL mutexes are reentrant.
307 *
308 * \returns the initialized and unlocked mutex or NULL on failure; call
309 * SDL_GetError() for more information.
310 *
311 * \since This function is available since SDL 3.2.0.
312 *
313 * \sa SDL_DestroyMutex
314 * \sa SDL_LockMutex
315 * \sa SDL_TryLockMutex
316 * \sa SDL_UnlockMutex
317 */
318 extern SDL_DECLSPEC SDL_Mutex * SDLCALL SDL_CreateMutex(void);
319
320 /**
321 * Lock the mutex.
322 *
323 * This will block until the mutex is available, which is to say it is in the
324 * unlocked state and the OS has chosen the caller as the next thread to lock
325 * it. Of all threads waiting to lock the mutex, only one may do so at a time.
326 *
327 * It is legal for the owning thread to lock an already-locked mutex. It must
328 * unlock it the same number of times before it is actually made available for
329 * other threads in the system (this is known as a "recursive mutex").
330 *
331 * This function does not fail; if mutex is NULL, it will return immediately
332 * having locked nothing. If the mutex is valid, this function will always
333 * block until it can lock the mutex, and return with it locked.
334 *
335 * \param mutex the mutex to lock.
336 *
337 * \since This function is available since SDL 3.2.0.
338 *
339 * \sa SDL_TryLockMutex
340 * \sa SDL_UnlockMutex
341 */
342 extern SDL_DECLSPEC void SDLCALL SDL_LockMutex(SDL_Mutex *mutex) SDL_ACQUIRE(mutex);
343
344 /**
345 * Try to lock a mutex without blocking.
346 *
347 * This works just like SDL_LockMutex(), but if the mutex is not available,
348 * this function returns false immediately.
349 *
350 * This technique is useful if you need exclusive access to a resource but
351 * don't want to wait for it, and will return to it to try again later.
352 *
353 * This function returns true if passed a NULL mutex.
354 *
355 * \param mutex the mutex to try to lock.
356 * \returns true on success, false if the mutex would block.
357 *
358 * \since This function is available since SDL 3.2.0.
359 *
360 * \sa SDL_LockMutex
361 * \sa SDL_UnlockMutex
362 */
363 extern SDL_DECLSPEC bool SDLCALL SDL_TryLockMutex(SDL_Mutex *mutex) SDL_TRY_ACQUIRE(true, mutex);
364
365 /**
366 * Unlock the mutex.
367 *
368 * It is legal for the owning thread to lock an already-locked mutex. It must
369 * unlock it the same number of times before it is actually made available for
370 * other threads in the system (this is known as a "recursive mutex").
371 *
372 * It is illegal to unlock a mutex that has not been locked by the current
373 * thread, and doing so results in undefined behavior.
374 *
375 * \param mutex the mutex to unlock.
376 *
377 * \since This function is available since SDL 3.2.0.
378 *
379 * \sa SDL_LockMutex
380 * \sa SDL_TryLockMutex
381 */
382 extern SDL_DECLSPEC void SDLCALL SDL_UnlockMutex(SDL_Mutex *mutex) SDL_RELEASE(mutex);
383
384 /**
385 * Destroy a mutex created with SDL_CreateMutex().
386 *
387 * This function must be called on any mutex that is no longer needed. Failure
388 * to destroy a mutex will result in a system memory or resource leak. While
389 * it is safe to destroy a mutex that is _unlocked_, it is not safe to attempt
390 * to destroy a locked mutex, and may result in undefined behavior depending
391 * on the platform.
392 *
393 * \param mutex the mutex to destroy.
394 *
395 * \since This function is available since SDL 3.2.0.
396 *
397 * \sa SDL_CreateMutex
398 */
399 extern SDL_DECLSPEC void SDLCALL SDL_DestroyMutex(SDL_Mutex *mutex);
400
401 /* @} *//* Mutex functions */
402
403
404 /**
405 * \name Read/write lock functions
406 */
407 /* @{ */
408
409 /**
410 * A mutex that allows read-only threads to run in parallel.
411 *
412 * A rwlock is roughly the same concept as SDL_Mutex, but allows threads that
413 * request read-only access to all hold the lock at the same time. If a thread
414 * requests write access, it will block until all read-only threads have
415 * released the lock, and no one else can hold the thread (for reading or
416 * writing) at the same time as the writing thread.
417 *
418 * This can be more efficient in cases where several threads need to access
419 * data frequently, but changes to that data are rare.
420 *
421 * There are other rules that apply to rwlocks that don't apply to mutexes,
422 * about how threads are scheduled and when they can be recursively locked.
423 * These are documented in the other rwlock functions.
424 *
425 * \since This struct is available since SDL 3.2.0.
426 */
427 typedef struct SDL_RWLock SDL_RWLock;
428
429 /**
430 * Create a new read/write lock.
431 *
432 * A read/write lock is useful for situations where you have multiple threads
433 * trying to access a resource that is rarely updated. All threads requesting
434 * a read-only lock will be allowed to run in parallel; if a thread requests a
435 * write lock, it will be provided exclusive access. This makes it safe for
436 * multiple threads to use a resource at the same time if they promise not to
437 * change it, and when it has to be changed, the rwlock will serve as a
438 * gateway to make sure those changes can be made safely.
439 *
440 * In the right situation, a rwlock can be more efficient than a mutex, which
441 * only lets a single thread proceed at a time, even if it won't be modifying
442 * the data.
443 *
444 * All newly-created read/write locks begin in the _unlocked_ state.
445 *
446 * Calls to SDL_LockRWLockForReading() and SDL_LockRWLockForWriting will not
447 * return while the rwlock is locked _for writing_ by another thread. See
448 * SDL_TryLockRWLockForReading() and SDL_TryLockRWLockForWriting() to attempt
449 * to lock without blocking.
450 *
451 * SDL read/write locks are only recursive for read-only locks! They are not
452 * guaranteed to be fair, or provide access in a FIFO manner! They are not
453 * guaranteed to favor writers. You may not lock a rwlock for both read-only
454 * and write access at the same time from the same thread (so you can't
455 * promote your read-only lock to a write lock without unlocking first).
456 *
457 * \returns the initialized and unlocked read/write lock or NULL on failure;
458 * call SDL_GetError() for more information.
459 *
460 * \since This function is available since SDL 3.2.0.
461 *
462 * \sa SDL_DestroyRWLock
463 * \sa SDL_LockRWLockForReading
464 * \sa SDL_LockRWLockForWriting
465 * \sa SDL_TryLockRWLockForReading
466 * \sa SDL_TryLockRWLockForWriting
467 * \sa SDL_UnlockRWLock
468 */
469 extern SDL_DECLSPEC SDL_RWLock * SDLCALL SDL_CreateRWLock(void);
470
471 /**
472 * Lock the read/write lock for _read only_ operations.
473 *
474 * This will block until the rwlock is available, which is to say it is not
475 * locked for writing by any other thread. Of all threads waiting to lock the
476 * rwlock, all may do so at the same time as long as they are requesting
477 * read-only access; if a thread wants to lock for writing, only one may do so
478 * at a time, and no other threads, read-only or not, may hold the lock at the
479 * same time.
480 *
481 * It is legal for the owning thread to lock an already-locked rwlock for
482 * reading. It must unlock it the same number of times before it is actually
483 * made available for other threads in the system (this is known as a
484 * "recursive rwlock").
485 *
486 * Note that locking for writing is not recursive (this is only available to
487 * read-only locks).
488 *
489 * It is illegal to request a read-only lock from a thread that already holds
490 * the write lock. Doing so results in undefined behavior. Unlock the write
491 * lock before requesting a read-only lock. (But, of course, if you have the
492 * write lock, you don't need further locks to read in any case.)
493 *
494 * This function does not fail; if rwlock is NULL, it will return immediately
495 * having locked nothing. If the rwlock is valid, this function will always
496 * block until it can lock the mutex, and return with it locked.
497 *
498 * \param rwlock the read/write lock to lock.
499 *
500 * \since This function is available since SDL 3.2.0.
501 *
502 * \sa SDL_LockRWLockForWriting
503 * \sa SDL_TryLockRWLockForReading
504 * \sa SDL_UnlockRWLock
505 */
506 extern SDL_DECLSPEC void SDLCALL SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock);
507
508 /**
509 * Lock the read/write lock for _write_ operations.
510 *
511 * This will block until the rwlock is available, which is to say it is not
512 * locked for reading or writing by any other thread. Only one thread may hold
513 * the lock when it requests write access; all other threads, whether they
514 * also want to write or only want read-only access, must wait until the
515 * writer thread has released the lock.
516 *
517 * It is illegal for the owning thread to lock an already-locked rwlock for
518 * writing (read-only may be locked recursively, writing can not). Doing so
519 * results in undefined behavior.
520 *
521 * It is illegal to request a write lock from a thread that already holds a
522 * read-only lock. Doing so results in undefined behavior. Unlock the
523 * read-only lock before requesting a write lock.
524 *
525 * This function does not fail; if rwlock is NULL, it will return immediately
526 * having locked nothing. If the rwlock is valid, this function will always
527 * block until it can lock the mutex, and return with it locked.
528 *
529 * \param rwlock the read/write lock to lock.
530 *
531 * \since This function is available since SDL 3.2.0.
532 *
533 * \sa SDL_LockRWLockForReading
534 * \sa SDL_TryLockRWLockForWriting
535 * \sa SDL_UnlockRWLock
536 */
537 extern SDL_DECLSPEC void SDLCALL SDL_LockRWLockForWriting(SDL_RWLock *rwlock) SDL_ACQUIRE(rwlock);
538
539 /**
540 * Try to lock a read/write lock _for reading_ without blocking.
541 *
542 * This works just like SDL_LockRWLockForReading(), but if the rwlock is not
543 * available, then this function returns false immediately.
544 *
545 * This technique is useful if you need access to a resource but don't want to
546 * wait for it, and will return to it to try again later.
547 *
548 * Trying to lock for read-only access can succeed if other threads are
549 * holding read-only locks, as this won't prevent access.
550 *
551 * This function returns true if passed a NULL rwlock.
552 *
553 * \param rwlock the rwlock to try to lock.
554 * \returns true on success, false if the lock would block.
555 *
556 * \since This function is available since SDL 3.2.0.
557 *
558 * \sa SDL_LockRWLockForReading
559 * \sa SDL_TryLockRWLockForWriting
560 * \sa SDL_UnlockRWLock
561 */
562 extern SDL_DECLSPEC bool SDLCALL SDL_TryLockRWLockForReading(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE_SHARED(true, rwlock);
563
564 /**
565 * Try to lock a read/write lock _for writing_ without blocking.
566 *
567 * This works just like SDL_LockRWLockForWriting(), but if the rwlock is not
568 * available, then this function returns false immediately.
569 *
570 * This technique is useful if you need exclusive access to a resource but
571 * don't want to wait for it, and will return to it to try again later.
572 *
573 * It is illegal for the owning thread to lock an already-locked rwlock for
574 * writing (read-only may be locked recursively, writing can not). Doing so
575 * results in undefined behavior.
576 *
577 * It is illegal to request a write lock from a thread that already holds a
578 * read-only lock. Doing so results in undefined behavior. Unlock the
579 * read-only lock before requesting a write lock.
580 *
581 * This function returns true if passed a NULL rwlock.
582 *
583 * \param rwlock the rwlock to try to lock.
584 * \returns true on success, false if the lock would block.
585 *
586 * \since This function is available since SDL 3.2.0.
587 *
588 * \sa SDL_LockRWLockForWriting
589 * \sa SDL_TryLockRWLockForReading
590 * \sa SDL_UnlockRWLock
591 */
592 extern SDL_DECLSPEC bool SDLCALL SDL_TryLockRWLockForWriting(SDL_RWLock *rwlock) SDL_TRY_ACQUIRE(true, rwlock);
593
594 /**
595 * Unlock the read/write lock.
596 *
597 * Use this function to unlock the rwlock, whether it was locked for read-only
598 * or write operations.
599 *
600 * It is legal for the owning thread to lock an already-locked read-only lock.
601 * It must unlock it the same number of times before it is actually made
602 * available for other threads in the system (this is known as a "recursive
603 * rwlock").
604 *
605 * It is illegal to unlock a rwlock that has not been locked by the current
606 * thread, and doing so results in undefined behavior.
607 *
608 * \param rwlock the rwlock to unlock.
609 *
610 * \since This function is available since SDL 3.2.0.
611 *
612 * \sa SDL_LockRWLockForReading
613 * \sa SDL_LockRWLockForWriting
614 * \sa SDL_TryLockRWLockForReading
615 * \sa SDL_TryLockRWLockForWriting
616 */
617 extern SDL_DECLSPEC void SDLCALL SDL_UnlockRWLock(SDL_RWLock *rwlock) SDL_RELEASE_GENERIC(rwlock);
618
619 /**
620 * Destroy a read/write lock created with SDL_CreateRWLock().
621 *
622 * This function must be called on any read/write lock that is no longer
623 * needed. Failure to destroy a rwlock will result in a system memory or
624 * resource leak. While it is safe to destroy a rwlock that is _unlocked_, it
625 * is not safe to attempt to destroy a locked rwlock, and may result in
626 * undefined behavior depending on the platform.
627 *
628 * \param rwlock the rwlock to destroy.
629 *
630 * \since This function is available since SDL 3.2.0.
631 *
632 * \sa SDL_CreateRWLock
633 */
634 extern SDL_DECLSPEC void SDLCALL SDL_DestroyRWLock(SDL_RWLock *rwlock);
635
636 /* @} *//* Read/write lock functions */
637
638
639 /**
640 * \name Semaphore functions
641 */
642 /* @{ */
643
644 /**
645 * A means to manage access to a resource, by count, between threads.
646 *
647 * Semaphores (specifically, "counting semaphores"), let X number of threads
648 * request access at the same time, each thread granted access decrementing a
649 * counter. When the counter reaches zero, future requests block until a prior
650 * thread releases their request, incrementing the counter again.
651 *
652 * Wikipedia has a thorough explanation of the concept:
653 *
654 * https://en.wikipedia.org/wiki/Semaphore_(programming)
655 *
656 * \since This struct is available since SDL 3.2.0.
657 */
658 typedef struct SDL_Semaphore SDL_Semaphore;
659
660 /**
661 * Create a semaphore.
662 *
663 * This function creates a new semaphore and initializes it with the value
664 * `initial_value`. Each wait operation on the semaphore will atomically
665 * decrement the semaphore value and potentially block if the semaphore value
666 * is 0. Each post operation will atomically increment the semaphore value and
667 * wake waiting threads and allow them to retry the wait operation.
668 *
669 * \param initial_value the starting value of the semaphore.
670 * \returns a new semaphore or NULL on failure; call SDL_GetError() for more
671 * information.
672 *
673 * \since This function is available since SDL 3.2.0.
674 *
675 * \sa SDL_DestroySemaphore
676 * \sa SDL_SignalSemaphore
677 * \sa SDL_TryWaitSemaphore
678 * \sa SDL_GetSemaphoreValue
679 * \sa SDL_WaitSemaphore
680 * \sa SDL_WaitSemaphoreTimeout
681 */
682 extern SDL_DECLSPEC SDL_Semaphore * SDLCALL SDL_CreateSemaphore(Uint32 initial_value);
683
684 /**
685 * Destroy a semaphore.
686 *
687 * It is not safe to destroy a semaphore if there are threads currently
688 * waiting on it.
689 *
690 * \param sem the semaphore to destroy.
691 *
692 * \since This function is available since SDL 3.2.0.
693 *
694 * \sa SDL_CreateSemaphore
695 */
696 extern SDL_DECLSPEC void SDLCALL SDL_DestroySemaphore(SDL_Semaphore *sem);
697
698 /**
699 * Wait until a semaphore has a positive value and then decrements it.
700 *
701 * This function suspends the calling thread until the semaphore pointed to by
702 * `sem` has a positive value, and then atomically decrement the semaphore
703 * value.
704 *
705 * This function is the equivalent of calling SDL_WaitSemaphoreTimeout() with
706 * a time length of -1.
707 *
708 * \param sem the semaphore wait on.
709 *
710 * \since This function is available since SDL 3.2.0.
711 *
712 * \sa SDL_SignalSemaphore
713 * \sa SDL_TryWaitSemaphore
714 * \sa SDL_WaitSemaphoreTimeout
715 */
716 extern SDL_DECLSPEC void SDLCALL SDL_WaitSemaphore(SDL_Semaphore *sem);
717
718 /**
719 * See if a semaphore has a positive value and decrement it if it does.
720 *
721 * This function checks to see if the semaphore pointed to by `sem` has a
722 * positive value and atomically decrements the semaphore value if it does. If
723 * the semaphore doesn't have a positive value, the function immediately
724 * returns false.
725 *
726 * \param sem the semaphore to wait on.
727 * \returns true if the wait succeeds, false if the wait would block.
728 *
729 * \since This function is available since SDL 3.2.0.
730 *
731 * \sa SDL_SignalSemaphore
732 * \sa SDL_WaitSemaphore
733 * \sa SDL_WaitSemaphoreTimeout
734 */
735 extern SDL_DECLSPEC bool SDLCALL SDL_TryWaitSemaphore(SDL_Semaphore *sem);
736
737 /**
738 * Wait until a semaphore has a positive value and then decrements it.
739 *
740 * This function suspends the calling thread until either the semaphore
741 * pointed to by `sem` has a positive value or the specified time has elapsed.
742 * If the call is successful it will atomically decrement the semaphore value.
743 *
744 * \param sem the semaphore to wait on.
745 * \param timeoutMS the length of the timeout, in milliseconds, or -1 to wait
746 * indefinitely.
747 * \returns true if the wait succeeds or false if the wait times out.
748 *
749 * \since This function is available since SDL 3.2.0.
750 *
751 * \sa SDL_SignalSemaphore
752 * \sa SDL_TryWaitSemaphore
753 * \sa SDL_WaitSemaphore
754 */
755 extern SDL_DECLSPEC bool SDLCALL SDL_WaitSemaphoreTimeout(SDL_Semaphore *sem, Sint32 timeoutMS);
756
757 /**
758 * Atomically increment a semaphore's value and wake waiting threads.
759 *
760 * \param sem the semaphore to increment.
761 *
762 * \since This function is available since SDL 3.2.0.
763 *
764 * \sa SDL_TryWaitSemaphore
765 * \sa SDL_WaitSemaphore
766 * \sa SDL_WaitSemaphoreTimeout
767 */
768 extern SDL_DECLSPEC void SDLCALL SDL_SignalSemaphore(SDL_Semaphore *sem);
769
770 /**
771 * Get the current value of a semaphore.
772 *
773 * \param sem the semaphore to query.
774 * \returns the current value of the semaphore.
775 *
776 * \since This function is available since SDL 3.2.0.
777 */
778 extern SDL_DECLSPEC Uint32 SDLCALL SDL_GetSemaphoreValue(SDL_Semaphore *sem);
779
780 /* @} *//* Semaphore functions */
781
782
783 /**
784 * \name Condition variable functions
785 */
786 /* @{ */
787
788 /**
789 * A means to block multiple threads until a condition is satisfied.
790 *
791 * Condition variables, paired with an SDL_Mutex, let an app halt multiple
792 * threads until a condition has occurred, at which time the app can release
793 * one or all waiting threads.
794 *
795 * Wikipedia has a thorough explanation of the concept:
796 *
797 * https://en.wikipedia.org/wiki/Condition_variable
798 *
799 * \since This struct is available since SDL 3.2.0.
800 */
801 typedef struct SDL_Condition SDL_Condition;
802
803 /**
804 * Create a condition variable.
805 *
806 * \returns a new condition variable or NULL on failure; call SDL_GetError()
807 * for more information.
808 *
809 * \since This function is available since SDL 3.2.0.
810 *
811 * \sa SDL_BroadcastCondition
812 * \sa SDL_SignalCondition
813 * \sa SDL_WaitCondition
814 * \sa SDL_WaitConditionTimeout
815 * \sa SDL_DestroyCondition
816 */
817 extern SDL_DECLSPEC SDL_Condition * SDLCALL SDL_CreateCondition(void);
818
819 /**
820 * Destroy a condition variable.
821 *
822 * \param cond the condition variable to destroy.
823 *
824 * \since This function is available since SDL 3.2.0.
825 *
826 * \sa SDL_CreateCondition
827 */
828 extern SDL_DECLSPEC void SDLCALL SDL_DestroyCondition(SDL_Condition *cond);
829
830 /**
831 * Restart one of the threads that are waiting on the condition variable.
832 *
833 * \param cond the condition variable to signal.
834 *
835 * \threadsafety It is safe to call this function from any thread.
836 *
837 * \since This function is available since SDL 3.2.0.
838 *
839 * \sa SDL_BroadcastCondition
840 * \sa SDL_WaitCondition
841 * \sa SDL_WaitConditionTimeout
842 */
843 extern SDL_DECLSPEC void SDLCALL SDL_SignalCondition(SDL_Condition *cond);
844
845 /**
846 * Restart all threads that are waiting on the condition variable.
847 *
848 * \param cond the condition variable to signal.
849 *
850 * \threadsafety It is safe to call this function from any thread.
851 *
852 * \since This function is available since SDL 3.2.0.
853 *
854 * \sa SDL_SignalCondition
855 * \sa SDL_WaitCondition
856 * \sa SDL_WaitConditionTimeout
857 */
858 extern SDL_DECLSPEC void SDLCALL SDL_BroadcastCondition(SDL_Condition *cond);
859
860 /**
861 * Wait until a condition variable is signaled.
862 *
863 * This function unlocks the specified `mutex` and waits for another thread to
864 * call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition
865 * variable `cond`. Once the condition variable is signaled, the mutex is
866 * re-locked and the function returns.
867 *
868 * The mutex must be locked before calling this function. Locking the mutex
869 * recursively (more than once) is not supported and leads to undefined
870 * behavior.
871 *
872 * This function is the equivalent of calling SDL_WaitConditionTimeout() with
873 * a time length of -1.
874 *
875 * \param cond the condition variable to wait on.
876 * \param mutex the mutex used to coordinate thread access.
877 *
878 * \threadsafety It is safe to call this function from any thread.
879 *
880 * \since This function is available since SDL 3.2.0.
881 *
882 * \sa SDL_BroadcastCondition
883 * \sa SDL_SignalCondition
884 * \sa SDL_WaitConditionTimeout
885 */
886 extern SDL_DECLSPEC void SDLCALL SDL_WaitCondition(SDL_Condition *cond, SDL_Mutex *mutex);
887
888 /**
889 * Wait until a condition variable is signaled or a certain time has passed.
890 *
891 * This function unlocks the specified `mutex` and waits for another thread to
892 * call SDL_SignalCondition() or SDL_BroadcastCondition() on the condition
893 * variable `cond`, or for the specified time to elapse. Once the condition
894 * variable is signaled or the time elapsed, the mutex is re-locked and the
895 * function returns.
896 *
897 * The mutex must be locked before calling this function. Locking the mutex
898 * recursively (more than once) is not supported and leads to undefined
899 * behavior.
900 *
901 * \param cond the condition variable to wait on.
902 * \param mutex the mutex used to coordinate thread access.
903 * \param timeoutMS the maximum time to wait, in milliseconds, or -1 to wait
904 * indefinitely.
905 * \returns true if the condition variable is signaled, false if the condition
906 * is not signaled in the allotted time.
907 *
908 * \threadsafety It is safe to call this function from any thread.
909 *
910 * \since This function is available since SDL 3.2.0.
911 *
912 * \sa SDL_BroadcastCondition
913 * \sa SDL_SignalCondition
914 * \sa SDL_WaitCondition
915 */
916 extern SDL_DECLSPEC bool SDLCALL SDL_WaitConditionTimeout(SDL_Condition *cond,
917 SDL_Mutex *mutex, Sint32 timeoutMS);
918
919 /* @} *//* Condition variable functions */
920
921 /**
922 * \name Thread-safe initialization state functions
923 */
924 /* @{ */
925
926 /**
927 * The current status of an SDL_InitState structure.
928 *
929 * \since This enum is available since SDL 3.2.0.
930 */
931 typedef enum SDL_InitStatus
932 {
933 SDL_INIT_STATUS_UNINITIALIZED,
934 SDL_INIT_STATUS_INITIALIZING,
935 SDL_INIT_STATUS_INITIALIZED,
936 SDL_INIT_STATUS_UNINITIALIZING
937 } SDL_InitStatus;
938
939 /**
940 * A structure used for thread-safe initialization and shutdown.
941 *
942 * Here is an example of using this:
943 *
944 * ```c
945 * static SDL_InitState init;
946 *
947 * bool InitSystem(void)
948 * {
949 * if (!SDL_ShouldInit(&init)) {
950 * // The system is initialized
951 * return true;
952 * }
953 *
954 * // At this point, you should not leave this function without calling SDL_SetInitialized()
955 *
956 * bool initialized = DoInitTasks();
957 * SDL_SetInitialized(&init, initialized);
958 * return initialized;
959 * }
960 *
961 * bool UseSubsystem(void)
962 * {
963 * if (SDL_ShouldInit(&init)) {
964 * // Error, the subsystem isn't initialized
965 * SDL_SetInitialized(&init, false);
966 * return false;
967 * }
968 *
969 * // Do work using the initialized subsystem
970 *
971 * return true;
972 * }
973 *
974 * void QuitSystem(void)
975 * {
976 * if (!SDL_ShouldQuit(&init)) {
977 * // The system is not initialized
978 * return;
979 * }
980 *
981 * // At this point, you should not leave this function without calling SDL_SetInitialized()
982 *
983 * DoQuitTasks();
984 * SDL_SetInitialized(&init, false);
985 * }
986 * ```
987 *
988 * Note that this doesn't protect any resources created during initialization,
989 * or guarantee that nobody is using those resources during cleanup. You
990 * should use other mechanisms to protect those, if that's a concern for your
991 * code.
992 *
993 * \since This struct is available since SDL 3.2.0.
994 */
995 typedef struct SDL_InitState
996 {
997 SDL_AtomicInt status;
998 SDL_ThreadID thread;
999 void *reserved;
1000 } SDL_InitState;
1001
1002 /**
1003 * Return whether initialization should be done.
1004 *
1005 * This function checks the passed in state and if initialization should be
1006 * done, sets the status to `SDL_INIT_STATUS_INITIALIZING` and returns true.
1007 * If another thread is already modifying this state, it will wait until
1008 * that's done before returning.
1009 *
1010 * If this function returns true, the calling code must call
1011 * SDL_SetInitialized() to complete the initialization.
1012 *
1013 * \param state the initialization state to check.
1014 * \returns true if initialization needs to be done, false otherwise.
1015 *
1016 * \threadsafety It is safe to call this function from any thread.
1017 *
1018 * \since This function is available since SDL 3.2.0.
1019 *
1020 * \sa SDL_SetInitialized
1021 * \sa SDL_ShouldQuit
1022 */
1023 extern SDL_DECLSPEC bool SDLCALL SDL_ShouldInit(SDL_InitState *state);
1024
1025 /**
1026 * Return whether cleanup should be done.
1027 *
1028 * This function checks the passed in state and if cleanup should be done,
1029 * sets the status to `SDL_INIT_STATUS_UNINITIALIZING` and returns true.
1030 *
1031 * If this function returns true, the calling code must call
1032 * SDL_SetInitialized() to complete the cleanup.
1033 *
1034 * \param state the initialization state to check.
1035 * \returns true if cleanup needs to be done, false otherwise.
1036 *
1037 * \threadsafety It is safe to call this function from any thread.
1038 *
1039 * \since This function is available since SDL 3.2.0.
1040 *
1041 * \sa SDL_SetInitialized
1042 * \sa SDL_ShouldInit
1043 */
1044 extern SDL_DECLSPEC bool SDLCALL SDL_ShouldQuit(SDL_InitState *state);
1045
1046 /**
1047 * Finish an initialization state transition.
1048 *
1049 * This function sets the status of the passed in state to
1050 * `SDL_INIT_STATUS_INITIALIZED` or `SDL_INIT_STATUS_UNINITIALIZED` and allows
1051 * any threads waiting for the status to proceed.
1052 *
1053 * \param state the initialization state to check.
1054 * \param initialized the new initialization state.
1055 *
1056 * \threadsafety It is safe to call this function from any thread.
1057 *
1058 * \since This function is available since SDL 3.2.0.
1059 *
1060 * \sa SDL_ShouldInit
1061 * \sa SDL_ShouldQuit
1062 */
1063 extern SDL_DECLSPEC void SDLCALL SDL_SetInitialized(SDL_InitState *state, bool initialized);
1064
1065 /* @} *//* Thread-safe initialization state functions */
1066
1067 /* Ends C function definitions when using C++ */
1068 #ifdef __cplusplus
1069 }
1070 #endif
1071 #include <SDL3/SDL_close_code.h>
1072
1073 #endif /* SDL_mutex_h_ */