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/**
23 * # CategoryAtomic
24 *
25 * Atomic operations.
26 *
27 * IMPORTANT: If you are not an expert in concurrent lockless programming, you
28 * should not be using any functions in this file. You should be protecting
29 * your data structures with full mutexes instead.
30 *
31 * ***Seriously, here be dragons!***
32 *
33 * You can find out a little more about lockless programming and the subtle
34 * issues that can arise here:
35 * https://learn.microsoft.com/en-us/windows/win32/dxtecharts/lockless-programming
36 *
37 * There's also lots of good information here:
38 *
39 * - https://www.1024cores.net/home/lock-free-algorithms
40 * - https://preshing.com/
41 *
42 * These operations may or may not actually be implemented using processor
43 * specific atomic operations. When possible they are implemented as true
44 * processor specific atomic operations. When that is not possible the are
45 * implemented using locks that *do* use the available atomic operations.
46 *
47 * All of the atomic operations that modify memory are full memory barriers.
48 */
49
50#ifndef SDL_atomic_h_
51#define SDL_atomic_h_
52
53#include <SDL3/SDL_stdinc.h>
54#include <SDL3/SDL_platform_defines.h>
55
56#include <SDL3/SDL_begin_code.h>
57
58/* Set up for C function definitions, even when using C++ */
59#ifdef __cplusplus
60extern "C" {
61#endif
62
63/**
64 * An atomic spinlock.
65 *
66 * The atomic locks are efficient spinlocks using CPU instructions, but are
67 * vulnerable to starvation and can spin forever if a thread holding a lock
68 * has been terminated. For this reason you should minimize the code executed
69 * inside an atomic lock and never do expensive things like API or system
70 * calls while holding them.
71 *
72 * They are also vulnerable to starvation if the thread holding the lock is
73 * lower priority than other threads and doesn't get scheduled. In general you
74 * should use mutexes instead, since they have better performance and
75 * contention behavior.
76 *
77 * The atomic locks are not safe to lock recursively.
78 *
79 * Porting Note: The spin lock functions and type are required and can not be
80 * emulated because they are used in the atomic emulation code.
81 */
82typedef int SDL_SpinLock;
83
84/**
85 * Try to lock a spin lock by setting it to a non-zero value.
86 *
87 * ***Please note that spinlocks are dangerous if you don't know what you're
88 * doing. Please be careful using any sort of spinlock!***
89 *
90 * \param lock a pointer to a lock variable.
91 * \returns true if the lock succeeded, false if the lock is already held.
92 *
93 * \threadsafety It is safe to call this function from any thread.
94 *
95 * \since This function is available since SDL 3.2.0.
96 *
97 * \sa SDL_LockSpinlock
98 * \sa SDL_UnlockSpinlock
99 */
100extern SDL_DECLSPEC bool SDLCALL SDL_TryLockSpinlock(SDL_SpinLock *lock);
101
102/**
103 * Lock a spin lock by setting it to a non-zero value.
104 *
105 * ***Please note that spinlocks are dangerous if you don't know what you're
106 * doing. Please be careful using any sort of spinlock!***
107 *
108 * \param lock a pointer to a lock variable.
109 *
110 * \threadsafety It is safe to call this function from any thread.
111 *
112 * \since This function is available since SDL 3.2.0.
113 *
114 * \sa SDL_TryLockSpinlock
115 * \sa SDL_UnlockSpinlock
116 */
117extern SDL_DECLSPEC void SDLCALL SDL_LockSpinlock(SDL_SpinLock *lock);
118
119/**
120 * Unlock a spin lock by setting it to 0.
121 *
122 * Always returns immediately.
123 *
124 * ***Please note that spinlocks are dangerous if you don't know what you're
125 * doing. Please be careful using any sort of spinlock!***
126 *
127 * \param lock a pointer to a lock variable.
128 *
129 * \threadsafety It is safe to call this function from any thread.
130 *
131 * \since This function is available since SDL 3.2.0.
132 *
133 * \sa SDL_LockSpinlock
134 * \sa SDL_TryLockSpinlock
135 */
136extern SDL_DECLSPEC void SDLCALL SDL_UnlockSpinlock(SDL_SpinLock *lock);
137
138
139#ifdef SDL_WIKI_DOCUMENTATION_SECTION
140
141/**
142 * Mark a compiler barrier.
143 *
144 * A compiler barrier prevents the compiler from reordering reads and writes
145 * to globally visible variables across the call.
146 *
147 * This macro only prevents the compiler from reordering reads and writes, it
148 * does not prevent the CPU from reordering reads and writes. However, all of
149 * the atomic operations that modify memory are full memory barriers.
150 *
151 * \threadsafety Obviously this macro is safe to use from any thread at any
152 * time, but if you find yourself needing this, you are probably
153 * dealing with some very sensitive code; be careful!
154 *
155 * \since This macro is available since SDL 3.2.0.
156 */
157#define SDL_CompilerBarrier() DoCompilerSpecificReadWriteBarrier()
158
159#elif defined(_MSC_VER) && (_MSC_VER > 1200) && !defined(__clang__)
160void _ReadWriteBarrier(void);
161#pragma intrinsic(_ReadWriteBarrier)
162#define SDL_CompilerBarrier() _ReadWriteBarrier()
163#elif (defined(__GNUC__) && !defined(SDL_PLATFORM_EMSCRIPTEN)) || (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x5120))
164/* This is correct for all CPUs when using GCC or Solaris Studio 12.1+. */
165#define SDL_CompilerBarrier() __asm__ __volatile__ ("" : : : "memory")
166#elif defined(__WATCOMC__)
167extern __inline void SDL_CompilerBarrier(void);
168#pragma aux SDL_CompilerBarrier = "" parm [] modify exact [];
169#else
170#define SDL_CompilerBarrier() \
171{ SDL_SpinLock _tmp = 0; SDL_LockSpinlock(&_tmp); SDL_UnlockSpinlock(&_tmp); }
172#endif
173
174/**
175 * Insert a memory release barrier (function version).
176 *
177 * Please refer to SDL_MemoryBarrierRelease for details. This is a function
178 * version, which might be useful if you need to use this functionality from a
179 * scripting language, etc. Also, some of the macro versions call this
180 * function behind the scenes, where more heavy lifting can happen inside of
181 * SDL. Generally, though, an app written in C/C++/etc should use the macro
182 * version, as it will be more efficient.
183 *
184 * \threadsafety Obviously this function is safe to use from any thread at any
185 * time, but if you find yourself needing this, you are probably
186 * dealing with some very sensitive code; be careful!
187 *
188 * \since This function is available since SDL 3.2.0.
189 *
190 * \sa SDL_MemoryBarrierRelease
191 */
192extern SDL_DECLSPEC void SDLCALL SDL_MemoryBarrierReleaseFunction(void);
193
194/**
195 * Insert a memory acquire barrier (function version).
196 *
197 * Please refer to SDL_MemoryBarrierRelease for details. This is a function
198 * version, which might be useful if you need to use this functionality from a
199 * scripting language, etc. Also, some of the macro versions call this
200 * function behind the scenes, where more heavy lifting can happen inside of
201 * SDL. Generally, though, an app written in C/C++/etc should use the macro
202 * version, as it will be more efficient.
203 *
204 * \threadsafety Obviously this function is safe to use from any thread at any
205 * time, but if you find yourself needing this, you are probably
206 * dealing with some very sensitive code; be careful!
207 *
208 * \since This function is available since SDL 3.2.0.
209 *
210 * \sa SDL_MemoryBarrierAcquire
211 */
212extern SDL_DECLSPEC void SDLCALL SDL_MemoryBarrierAcquireFunction(void);
213
214
215#ifdef SDL_WIKI_DOCUMENTATION_SECTION
216
217/**
218 * Insert a memory release barrier (macro version).
219 *
220 * Memory barriers are designed to prevent reads and writes from being
221 * reordered by the compiler and being seen out of order on multi-core CPUs.
222 *
223 * A typical pattern would be for thread A to write some data and a flag, and
224 * for thread B to read the flag and get the data. In this case you would
225 * insert a release barrier between writing the data and the flag,
226 * guaranteeing that the data write completes no later than the flag is
227 * written, and you would insert an acquire barrier between reading the flag
228 * and reading the data, to ensure that all the reads associated with the flag
229 * have completed.
230 *
231 * In this pattern you should always see a release barrier paired with an
232 * acquire barrier and you should gate the data reads/writes with a single
233 * flag variable.
234 *
235 * For more information on these semantics, take a look at the blog post:
236 * http://preshing.com/20120913/acquire-and-release-semantics
237 *
238 * This is the macro version of this functionality; if possible, SDL will use
239 * compiler intrinsics or inline assembly, but some platforms might need to
240 * call the function version of this, SDL_MemoryBarrierReleaseFunction to do
241 * the heavy lifting. Apps that can use the macro should favor it over the
242 * function.
243 *
244 * \threadsafety Obviously this macro is safe to use from any thread at any
245 * time, but if you find yourself needing this, you are probably
246 * dealing with some very sensitive code; be careful!
247 *
248 * \since This macro is available since SDL 3.2.0.
249 *
250 * \sa SDL_MemoryBarrierAcquire
251 * \sa SDL_MemoryBarrierReleaseFunction
252 */
253#define SDL_MemoryBarrierRelease() SDL_MemoryBarrierReleaseFunction()
254
255/**
256 * Insert a memory acquire barrier (macro version).
257 *
258 * Please see SDL_MemoryBarrierRelease for the details on what memory barriers
259 * are and when to use them.
260 *
261 * This is the macro version of this functionality; if possible, SDL will use
262 * compiler intrinsics or inline assembly, but some platforms might need to
263 * call the function version of this, SDL_MemoryBarrierAcquireFunction, to do
264 * the heavy lifting. Apps that can use the macro should favor it over the
265 * function.
266 *
267 * \threadsafety Obviously this macro is safe to use from any thread at any
268 * time, but if you find yourself needing this, you are probably
269 * dealing with some very sensitive code; be careful!
270 *
271 * \since This macro is available since SDL 3.2.0.
272 *
273 * \sa SDL_MemoryBarrierRelease
274 * \sa SDL_MemoryBarrierAcquireFunction
275 */
276#define SDL_MemoryBarrierAcquire() SDL_MemoryBarrierAcquireFunction()
277
278#elif defined(__GNUC__) && (defined(__powerpc__) || defined(__ppc__))
279#define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("lwsync" : : : "memory")
280#define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("lwsync" : : : "memory")
281#elif defined(__GNUC__) && defined(__aarch64__)
282#define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("dmb ish" : : : "memory")
283#define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("dmb ish" : : : "memory")
284#elif defined(__GNUC__) && defined(__arm__)
285#if 0 /* defined(SDL_PLATFORM_LINUX) || defined(SDL_PLATFORM_ANDROID) */
286/* Information from:
287 https://chromium.googlesource.com/chromium/chromium/+/trunk/base/atomicops_internals_arm_gcc.h#19
288
289 The Linux kernel provides a helper function which provides the right code for a memory barrier,
290 hard-coded at address 0xffff0fa0
291*/
292typedef void (*SDL_KernelMemoryBarrierFunc)();
293#define SDL_MemoryBarrierRelease() ((SDL_KernelMemoryBarrierFunc)0xffff0fa0)()
294#define SDL_MemoryBarrierAcquire() ((SDL_KernelMemoryBarrierFunc)0xffff0fa0)()
295#else
296#if defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__) || defined(__ARM_ARCH_7EM__) || defined(__ARM_ARCH_7R__) || defined(__ARM_ARCH_7M__) || defined(__ARM_ARCH_7S__) || defined(__ARM_ARCH_8A__)
297#define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("dmb ish" : : : "memory")
298#define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("dmb ish" : : : "memory")
299#elif defined(__ARM_ARCH_6__) || defined(__ARM_ARCH_6J__) || defined(__ARM_ARCH_6K__) || defined(__ARM_ARCH_6T2__) || defined(__ARM_ARCH_6Z__) || defined(__ARM_ARCH_6ZK__)
300#ifdef __thumb__
301/* The mcr instruction isn't available in thumb mode, use real functions */
302#define SDL_MEMORY_BARRIER_USES_FUNCTION
303#define SDL_MemoryBarrierRelease() SDL_MemoryBarrierReleaseFunction()
304#define SDL_MemoryBarrierAcquire() SDL_MemoryBarrierAcquireFunction()
305#else
306#define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r"(0) : "memory")
307#define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("mcr p15, 0, %0, c7, c10, 5" : : "r"(0) : "memory")
308#endif /* __thumb__ */
309#else
310#define SDL_MemoryBarrierRelease() __asm__ __volatile__ ("" : : : "memory")
311#define SDL_MemoryBarrierAcquire() __asm__ __volatile__ ("" : : : "memory")
312#endif /* SDL_PLATFORM_LINUX || SDL_PLATFORM_ANDROID */
313#endif /* __GNUC__ && __arm__ */
314#else
315#if (defined(__SUNPRO_C) && (__SUNPRO_C >= 0x5120))
316/* This is correct for all CPUs on Solaris when using Solaris Studio 12.1+. */
317#include <mbarrier.h>
318#define SDL_MemoryBarrierRelease() __machine_rel_barrier()
319#define SDL_MemoryBarrierAcquire() __machine_acq_barrier()
320#else
321/* This is correct for the x86 and x64 CPUs, and we'll expand this over time. */
322#define SDL_MemoryBarrierRelease() SDL_CompilerBarrier()
323#define SDL_MemoryBarrierAcquire() SDL_CompilerBarrier()
324#endif
325#endif
326
327/* "REP NOP" is PAUSE, coded for tools that don't know it by that name. */
328#ifdef SDL_WIKI_DOCUMENTATION_SECTION
329
330/**
331 * A macro to insert a CPU-specific "pause" instruction into the program.
332 *
333 * This can be useful in busy-wait loops, as it serves as a hint to the CPU as
334 * to the program's intent; some CPUs can use this to do more efficient
335 * processing. On some platforms, this doesn't do anything, so using this
336 * macro might just be a harmless no-op.
337 *
338 * Note that if you are busy-waiting, there are often more-efficient
339 * approaches with other synchronization primitives: mutexes, semaphores,
340 * condition variables, etc.
341 *
342 * \threadsafety This macro is safe to use from any thread.
343 *
344 * \since This macro is available since SDL 3.2.0.
345 */
346#define SDL_CPUPauseInstruction() DoACPUPauseInACompilerAndArchitectureSpecificWay
347
348#elif (defined(__GNUC__) || defined(__clang__)) && (defined(__i386__) || defined(__x86_64__))
349 #define SDL_CPUPauseInstruction() __asm__ __volatile__("pause\n") /* Some assemblers can't do REP NOP, so go with PAUSE. */
350#elif (defined(__arm__) && defined(__ARM_ARCH) && __ARM_ARCH >= 7) || defined(__aarch64__)
351 #define SDL_CPUPauseInstruction() __asm__ __volatile__("yield" ::: "memory")
352#elif (defined(__powerpc__) || defined(__powerpc64__))
353 #define SDL_CPUPauseInstruction() __asm__ __volatile__("or 27,27,27");
354#elif (defined(__riscv) && __riscv_xlen == 64)
355 #define SDL_CPUPauseInstruction() __asm__ __volatile__(".insn i 0x0F, 0, x0, x0, 0x010");
356#elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
357 #define SDL_CPUPauseInstruction() _mm_pause() /* this is actually "rep nop" and not a SIMD instruction. No inline asm in MSVC x86-64! */
358#elif defined(_MSC_VER) && (defined(_M_ARM) || defined(_M_ARM64))
359 #define SDL_CPUPauseInstruction() __yield()
360#elif defined(__WATCOMC__) && defined(__386__)
361 extern __inline void SDL_CPUPauseInstruction(void);
362 #pragma aux SDL_CPUPauseInstruction = ".686p" ".xmm2" "pause"
363#else
364 #define SDL_CPUPauseInstruction()
365#endif
366
367
368/**
369 * A type representing an atomic integer value.
370 *
371 * This can be used to manage a value that is synchronized across multiple
372 * CPUs without a race condition; when an app sets a value with
373 * SDL_SetAtomicInt all other threads, regardless of the CPU it is running on,
374 * will see that value when retrieved with SDL_GetAtomicInt, regardless of CPU
375 * caches, etc.
376 *
377 * This is also useful for atomic compare-and-swap operations: a thread can
378 * change the value as long as its current value matches expectations. When
379 * done in a loop, one can guarantee data consistency across threads without a
380 * lock (but the usual warnings apply: if you don't know what you're doing, or
381 * you don't do it carefully, you can confidently cause any number of
382 * disasters with this, so in most cases, you _should_ use a mutex instead of
383 * this!).
384 *
385 * This is a struct so people don't accidentally use numeric operations on it
386 * directly. You have to use SDL atomic functions.
387 *
388 * \since This struct is available since SDL 3.2.0.
389 *
390 * \sa SDL_CompareAndSwapAtomicInt
391 * \sa SDL_GetAtomicInt
392 * \sa SDL_SetAtomicInt
393 * \sa SDL_AddAtomicInt
394 */
395typedef struct SDL_AtomicInt { int value; } SDL_AtomicInt;
396
397/**
398 * Set an atomic variable to a new value if it is currently an old value.
399 *
400 * ***Note: If you don't know what this function is for, you shouldn't use
401 * it!***
402 *
403 * \param a a pointer to an SDL_AtomicInt variable to be modified.
404 * \param oldval the old value.
405 * \param newval the new value.
406 * \returns true if the atomic variable was set, false otherwise.
407 *
408 * \threadsafety It is safe to call this function from any thread.
409 *
410 * \since This function is available since SDL 3.2.0.
411 *
412 * \sa SDL_GetAtomicInt
413 * \sa SDL_SetAtomicInt
414 */
415extern SDL_DECLSPEC bool SDLCALL SDL_CompareAndSwapAtomicInt(SDL_AtomicInt *a, int oldval, int newval);
416
417/**
418 * Set an atomic variable to a value.
419 *
420 * This function also acts as a full memory barrier.
421 *
422 * ***Note: If you don't know what this function is for, you shouldn't use
423 * it!***
424 *
425 * \param a a pointer to an SDL_AtomicInt variable to be modified.
426 * \param v the desired value.
427 * \returns the previous value of the atomic variable.
428 *
429 * \threadsafety It is safe to call this function from any thread.
430 *
431 * \since This function is available since SDL 3.2.0.
432 *
433 * \sa SDL_GetAtomicInt
434 */
435extern SDL_DECLSPEC int SDLCALL SDL_SetAtomicInt(SDL_AtomicInt *a, int v);
436
437/**
438 * Get the value of an atomic variable.
439 *
440 * ***Note: If you don't know what this function is for, you shouldn't use
441 * it!***
442 *
443 * \param a a pointer to an SDL_AtomicInt variable.
444 * \returns the current value of an atomic variable.
445 *
446 * \threadsafety It is safe to call this function from any thread.
447 *
448 * \since This function is available since SDL 3.2.0.
449 *
450 * \sa SDL_SetAtomicInt
451 */
452extern SDL_DECLSPEC int SDLCALL SDL_GetAtomicInt(SDL_AtomicInt *a);
453
454/**
455 * Add to an atomic variable.
456 *
457 * This function also acts as a full memory barrier.
458 *
459 * ***Note: If you don't know what this function is for, you shouldn't use
460 * it!***
461 *
462 * \param a a pointer to an SDL_AtomicInt variable to be modified.
463 * \param v the desired value to add.
464 * \returns the previous value of the atomic variable.
465 *
466 * \threadsafety It is safe to call this function from any thread.
467 *
468 * \since This function is available since SDL 3.2.0.
469 *
470 * \sa SDL_AtomicDecRef
471 * \sa SDL_AtomicIncRef
472 */
473extern SDL_DECLSPEC int SDLCALL SDL_AddAtomicInt(SDL_AtomicInt *a, int v);
474
475#ifndef SDL_AtomicIncRef
476
477/**
478 * Increment an atomic variable used as a reference count.
479 *
480 * ***Note: If you don't know what this macro is for, you shouldn't use it!***
481 *
482 * \param a a pointer to an SDL_AtomicInt to increment.
483 * \returns the previous value of the atomic variable.
484 *
485 * \threadsafety It is safe to call this macro from any thread.
486 *
487 * \since This macro is available since SDL 3.2.0.
488 *
489 * \sa SDL_AtomicDecRef
490 */
491#define SDL_AtomicIncRef(a) SDL_AddAtomicInt(a, 1)
492#endif
493
494#ifndef SDL_AtomicDecRef
495
496/**
497 * Decrement an atomic variable used as a reference count.
498 *
499 * ***Note: If you don't know what this macro is for, you shouldn't use it!***
500 *
501 * \param a a pointer to an SDL_AtomicInt to decrement.
502 * \returns true if the variable reached zero after decrementing, false
503 * otherwise.
504 *
505 * \threadsafety It is safe to call this macro from any thread.
506 *
507 * \since This macro is available since SDL 3.2.0.
508 *
509 * \sa SDL_AtomicIncRef
510 */
511#define SDL_AtomicDecRef(a) (SDL_AddAtomicInt(a, -1) == 1)
512#endif
513
514/**
515 * A type representing an atomic unsigned 32-bit value.
516 *
517 * This can be used to manage a value that is synchronized across multiple
518 * CPUs without a race condition; when an app sets a value with
519 * SDL_SetAtomicU32 all other threads, regardless of the CPU it is running on,
520 * will see that value when retrieved with SDL_GetAtomicU32, regardless of CPU
521 * caches, etc.
522 *
523 * This is also useful for atomic compare-and-swap operations: a thread can
524 * change the value as long as its current value matches expectations. When
525 * done in a loop, one can guarantee data consistency across threads without a
526 * lock (but the usual warnings apply: if you don't know what you're doing, or
527 * you don't do it carefully, you can confidently cause any number of
528 * disasters with this, so in most cases, you _should_ use a mutex instead of
529 * this!).
530 *
531 * This is a struct so people don't accidentally use numeric operations on it
532 * directly. You have to use SDL atomic functions.
533 *
534 * \since This struct is available since SDL 3.2.0.
535 *
536 * \sa SDL_CompareAndSwapAtomicU32
537 * \sa SDL_GetAtomicU32
538 * \sa SDL_SetAtomicU32
539 */
540typedef struct SDL_AtomicU32 { Uint32 value; } SDL_AtomicU32;
541
542/**
543 * Set an atomic variable to a new value if it is currently an old value.
544 *
545 * ***Note: If you don't know what this function is for, you shouldn't use
546 * it!***
547 *
548 * \param a a pointer to an SDL_AtomicU32 variable to be modified.
549 * \param oldval the old value.
550 * \param newval the new value.
551 * \returns true if the atomic variable was set, false otherwise.
552 *
553 * \threadsafety It is safe to call this function from any thread.
554 *
555 * \since This function is available since SDL 3.2.0.
556 *
557 * \sa SDL_GetAtomicU32
558 * \sa SDL_SetAtomicU32
559 */
560extern SDL_DECLSPEC bool SDLCALL SDL_CompareAndSwapAtomicU32(SDL_AtomicU32 *a, Uint32 oldval, Uint32 newval);
561
562/**
563 * Set an atomic variable to a value.
564 *
565 * This function also acts as a full memory barrier.
566 *
567 * ***Note: If you don't know what this function is for, you shouldn't use
568 * it!***
569 *
570 * \param a a pointer to an SDL_AtomicU32 variable to be modified.
571 * \param v the desired value.
572 * \returns the previous value of the atomic variable.
573 *
574 * \threadsafety It is safe to call this function from any thread.
575 *
576 * \since This function is available since SDL 3.2.0.
577 *
578 * \sa SDL_GetAtomicU32
579 */
580extern SDL_DECLSPEC Uint32 SDLCALL SDL_SetAtomicU32(SDL_AtomicU32 *a, Uint32 v);
581
582/**
583 * Get the value of an atomic variable.
584 *
585 * ***Note: If you don't know what this function is for, you shouldn't use
586 * it!***
587 *
588 * \param a a pointer to an SDL_AtomicU32 variable.
589 * \returns the current value of an atomic variable.
590 *
591 * \threadsafety It is safe to call this function from any thread.
592 *
593 * \since This function is available since SDL 3.2.0.
594 *
595 * \sa SDL_SetAtomicU32
596 */
597extern SDL_DECLSPEC Uint32 SDLCALL SDL_GetAtomicU32(SDL_AtomicU32 *a);
598
599/**
600 * Set a pointer to a new value if it is currently an old value.
601 *
602 * ***Note: If you don't know what this function is for, you shouldn't use
603 * it!***
604 *
605 * \param a a pointer to a pointer.
606 * \param oldval the old pointer value.
607 * \param newval the new pointer value.
608 * \returns true if the pointer was set, false otherwise.
609 *
610 * \threadsafety It is safe to call this function from any thread.
611 *
612 * \since This function is available since SDL 3.2.0.
613 *
614 * \sa SDL_CompareAndSwapAtomicInt
615 * \sa SDL_GetAtomicPointer
616 * \sa SDL_SetAtomicPointer
617 */
618extern SDL_DECLSPEC bool SDLCALL SDL_CompareAndSwapAtomicPointer(void **a, void *oldval, void *newval);
619
620/**
621 * Set a pointer to a value atomically.
622 *
623 * ***Note: If you don't know what this function is for, you shouldn't use
624 * it!***
625 *
626 * \param a a pointer to a pointer.
627 * \param v the desired pointer value.
628 * \returns the previous value of the pointer.
629 *
630 * \threadsafety It is safe to call this function from any thread.
631 *
632 * \since This function is available since SDL 3.2.0.
633 *
634 * \sa SDL_CompareAndSwapAtomicPointer
635 * \sa SDL_GetAtomicPointer
636 */
637extern SDL_DECLSPEC void * SDLCALL SDL_SetAtomicPointer(void **a, void *v);
638
639/**
640 * Get the value of a pointer atomically.
641 *
642 * ***Note: If you don't know what this function is for, you shouldn't use
643 * it!***
644 *
645 * \param a a pointer to a pointer.
646 * \returns the current value of a pointer.
647 *
648 * \threadsafety It is safe to call this function from any thread.
649 *
650 * \since This function is available since SDL 3.2.0.
651 *
652 * \sa SDL_CompareAndSwapAtomicPointer
653 * \sa SDL_SetAtomicPointer
654 */
655extern SDL_DECLSPEC void * SDLCALL SDL_GetAtomicPointer(void **a);
656
657/* Ends C function definitions when using C++ */
658#ifdef __cplusplus
659}
660#endif
661
662#include <SDL3/SDL_close_code.h>
663
664#endif /* SDL_atomic_h_ */
665