SDL 2.0
SDL_thread.h
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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_thread_h_
23#define SDL_thread_h_
24
25/**
26 * # CategoryThread
27 *
28 * Header for the SDL thread management routines.
29 */
30
31#include "SDL_stdinc.h"
32#include "SDL_error.h"
33
34/* Thread synchronization primitives */
35#include "SDL_atomic.h"
36#include "SDL_mutex.h"
37
38#if (defined(__WIN32__) || defined(__GDK__)) && !defined(__WINRT__)
39#include <process.h> /* _beginthreadex() and _endthreadex() */
40#endif
41#if defined(__OS2__) /* for _beginthread() and _endthread() */
42#ifndef __EMX__
43#include <process.h>
44#else
45#include <stdlib.h>
46#endif
47#endif
48
49#include "begin_code.h"
50/* Set up for C function definitions, even when using C++ */
51#ifdef __cplusplus
52extern "C" {
53#endif
54
55/* The SDL thread structure, defined in SDL_thread.c */
56struct SDL_Thread;
57typedef struct SDL_Thread SDL_Thread;
58
59/* The SDL thread ID */
60typedef unsigned long SDL_threadID;
61
62/* Thread local storage ID, 0 is the invalid ID */
63typedef unsigned int SDL_TLSID;
64
65/**
66 * The SDL thread priority.
67 *
68 * SDL will make system changes as necessary in order to apply the thread
69 * priority. Code which attempts to control thread state related to priority
70 * should be aware that calling SDL_SetThreadPriority may alter such state.
71 * SDL_HINT_THREAD_PRIORITY_POLICY can be used to control aspects of this
72 * behavior.
73 *
74 * On many systems you require special privileges to set high or time critical
75 * priority.
76 */
83
84/**
85 * The function passed to SDL_CreateThread().
86 *
87 * \param data what was passed as `data` to SDL_CreateThread().
88 * \returns a value that can be reported through SDL_WaitThread().
89 */
90typedef int (SDLCALL * SDL_ThreadFunction) (void *data);
91
92
93#if (defined(__WIN32__) || defined(__GDK__)) && !defined(__WINRT__)
94/**
95 * \file SDL_thread.h
96 *
97 * We compile SDL into a DLL. This means, that it's the DLL which
98 * creates a new thread for the calling process with the SDL_CreateThread()
99 * API. There is a problem with this, that only the RTL of the SDL2.DLL will
100 * be initialized for those threads, and not the RTL of the calling
101 * application!
102 *
103 * To solve this, we make a little hack here.
104 *
105 * We'll always use the caller's _beginthread() and _endthread() APIs to
106 * start a new thread. This way, if it's the SDL2.DLL which uses this API,
107 * then the RTL of SDL2.DLL will be used to create the new thread, and if it's
108 * the application, then the RTL of the application will be used.
109 *
110 * So, in short:
111 * Always use the _beginthread() and _endthread() of the calling runtime
112 * library!
113 */
114#define SDL_PASSED_BEGINTHREAD_ENDTHREAD
115
117 (void *, unsigned, unsigned (__stdcall *func)(void *),
118 void * /*arg*/, unsigned, unsigned * /* threadID */);
119typedef void (__cdecl * pfnSDL_CurrentEndThread) (unsigned code);
120
121#ifndef SDL_beginthread
122#define SDL_beginthread _beginthreadex
123#endif
124#ifndef SDL_endthread
125#define SDL_endthread _endthreadex
126#endif
127
128extern DECLSPEC SDL_Thread *SDLCALL
129SDL_CreateThread(SDL_ThreadFunction fn, const char *name, void *data,
130 pfnSDL_CurrentBeginThread pfnBeginThread,
131 pfnSDL_CurrentEndThread pfnEndThread);
132
133extern DECLSPEC SDL_Thread *SDLCALL
135 const char *name, const size_t stacksize, void *data,
136 pfnSDL_CurrentBeginThread pfnBeginThread,
137 pfnSDL_CurrentEndThread pfnEndThread);
138
139
140#if defined(SDL_CreateThread) && SDL_DYNAMIC_API
141#undef SDL_CreateThread
142#define SDL_CreateThread(fn, name, data) SDL_CreateThread_REAL(fn, name, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
143#undef SDL_CreateThreadWithStackSize
144#define SDL_CreateThreadWithStackSize(fn, name, stacksize, data) SDL_CreateThreadWithStackSize_REAL(fn, name, stacksize, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
145#else
146#define SDL_CreateThread(fn, name, data) SDL_CreateThread(fn, name, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
147#define SDL_CreateThreadWithStackSize(fn, name, stacksize, data) SDL_CreateThreadWithStackSize(fn, name, stacksize, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
148#endif
149
150#elif defined(__OS2__)
151/*
152 * just like the windows case above: We compile SDL2
153 * into a dll with Watcom's runtime statically linked.
154 */
155#define SDL_PASSED_BEGINTHREAD_ENDTHREAD
156
157typedef int (*pfnSDL_CurrentBeginThread)(void (*func)(void *), void *, unsigned, void * /*arg*/);
158typedef void (*pfnSDL_CurrentEndThread)(void);
159
160#ifndef SDL_beginthread
161#define SDL_beginthread _beginthread
162#endif
163#ifndef SDL_endthread
164#define SDL_endthread _endthread
165#endif
166
167extern DECLSPEC SDL_Thread *SDLCALL
168SDL_CreateThread(SDL_ThreadFunction fn, const char *name, void *data,
169 pfnSDL_CurrentBeginThread pfnBeginThread,
170 pfnSDL_CurrentEndThread pfnEndThread);
171extern DECLSPEC SDL_Thread *SDLCALL
172SDL_CreateThreadWithStackSize(SDL_ThreadFunction fn, const char *name, const size_t stacksize, void *data,
173 pfnSDL_CurrentBeginThread pfnBeginThread,
174 pfnSDL_CurrentEndThread pfnEndThread);
175
176#if defined(SDL_CreateThread) && SDL_DYNAMIC_API
177#undef SDL_CreateThread
178#define SDL_CreateThread(fn, name, data) SDL_CreateThread_REAL(fn, name, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
179#undef SDL_CreateThreadWithStackSize
180#define SDL_CreateThreadWithStackSize(fn, name, stacksize, data) SDL_CreateThreadWithStackSize_REAL(fn, name, stacksize, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
181#else
182#define SDL_CreateThread(fn, name, data) SDL_CreateThread(fn, name, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
183#define SDL_CreateThreadWithStackSize(fn, name, stacksize, data) SDL_CreateThreadWithStackSize(fn, name, stacksize, data, (pfnSDL_CurrentBeginThread)SDL_beginthread, (pfnSDL_CurrentEndThread)SDL_endthread)
184#endif
185
186#else
187
188/**
189 * Create a new thread with a default stack size.
190 *
191 * This is equivalent to calling:
192 *
193 * ```c
194 * SDL_CreateThreadWithStackSize(fn, name, 0, data);
195 * ```
196 *
197 * \param fn the SDL_ThreadFunction function to call in the new thread.
198 * \param name the name of the thread.
199 * \param data a pointer that is passed to `fn`.
200 * \returns an opaque pointer to the new thread object on success, NULL if the
201 * new thread could not be created; call SDL_GetError() for more
202 * information.
203 *
204 * \since This function is available since SDL 2.0.0.
205 *
206 * \sa SDL_CreateThreadWithStackSize
207 * \sa SDL_WaitThread
208 */
209extern DECLSPEC SDL_Thread *SDLCALL
210SDL_CreateThread(SDL_ThreadFunction fn, const char *name, void *data);
211
212/**
213 * Create a new thread with a specific stack size.
214 *
215 * SDL makes an attempt to report `name` to the system, so that debuggers can
216 * display it. Not all platforms support this.
217 *
218 * Thread naming is a little complicated: Most systems have very small limits
219 * for the string length (Haiku has 32 bytes, Linux currently has 16, Visual
220 * C++ 6.0 has _nine_!), and possibly other arbitrary rules. You'll have to
221 * see what happens with your system's debugger. The name should be UTF-8 (but
222 * using the naming limits of C identifiers is a better bet). There are no
223 * requirements for thread naming conventions, so long as the string is
224 * null-terminated UTF-8, but these guidelines are helpful in choosing a name:
225 *
226 * https://stackoverflow.com/questions/149932/naming-conventions-for-threads
227 *
228 * If a system imposes requirements, SDL will try to munge the string for it
229 * (truncate, etc), but the original string contents will be available from
230 * SDL_GetThreadName().
231 *
232 * The size (in bytes) of the new stack can be specified. Zero means "use the
233 * system default" which might be wildly different between platforms. x86
234 * Linux generally defaults to eight megabytes, an embedded device might be a
235 * few kilobytes instead. You generally need to specify a stack that is a
236 * multiple of the system's page size (in many cases, this is 4 kilobytes, but
237 * check your system documentation).
238 *
239 * In SDL 2.1, stack size will be folded into the original SDL_CreateThread
240 * function, but for backwards compatibility, this is currently a separate
241 * function.
242 *
243 * \param fn the SDL_ThreadFunction function to call in the new thread.
244 * \param name the name of the thread.
245 * \param stacksize the size, in bytes, to allocate for the new thread stack.
246 * \param data a pointer that is passed to `fn`.
247 * \returns an opaque pointer to the new thread object on success, NULL if the
248 * new thread could not be created; call SDL_GetError() for more
249 * information.
250 *
251 * \since This function is available since SDL 2.0.9.
252 *
253 * \sa SDL_WaitThread
254 */
255extern DECLSPEC SDL_Thread *SDLCALL
256SDL_CreateThreadWithStackSize(SDL_ThreadFunction fn, const char *name, const size_t stacksize, void *data);
257
258#endif
259
260/**
261 * Get the thread name as it was specified in SDL_CreateThread().
262 *
263 * This is internal memory, not to be freed by the caller, and remains valid
264 * until the specified thread is cleaned up by SDL_WaitThread().
265 *
266 * \param thread the thread to query.
267 * \returns a pointer to a UTF-8 string that names the specified thread, or
268 * NULL if it doesn't have a name.
269 *
270 * \since This function is available since SDL 2.0.0.
271 *
272 * \sa SDL_CreateThread
273 */
274extern DECLSPEC const char *SDLCALL SDL_GetThreadName(SDL_Thread *thread);
275
276/**
277 * Get the thread identifier for the current thread.
278 *
279 * This thread identifier is as reported by the underlying operating system.
280 * If SDL is running on a platform that does not support threads the return
281 * value will always be zero.
282 *
283 * This function also returns a valid thread ID when called from the main
284 * thread.
285 *
286 * \returns the ID of the current thread.
287 *
288 * \since This function is available since SDL 2.0.0.
289 *
290 * \sa SDL_GetThreadID
291 */
292extern DECLSPEC SDL_threadID SDLCALL SDL_ThreadID(void);
293
294/**
295 * Get the thread identifier for the specified thread.
296 *
297 * This thread identifier is as reported by the underlying operating system.
298 * If SDL is running on a platform that does not support threads the return
299 * value will always be zero.
300 *
301 * \param thread the thread to query.
302 * \returns the ID of the specified thread, or the ID of the current thread if
303 * `thread` is NULL.
304 *
305 * \since This function is available since SDL 2.0.0.
306 *
307 * \sa SDL_ThreadID
308 */
309extern DECLSPEC SDL_threadID SDLCALL SDL_GetThreadID(SDL_Thread * thread);
310
311/**
312 * Set the priority for the current thread.
313 *
314 * Note that some platforms will not let you alter the priority (or at least,
315 * promote the thread to a higher priority) at all, and some require you to be
316 * an administrator account. Be prepared for this to fail.
317 *
318 * \param priority the SDL_ThreadPriority to set.
319 * \returns 0 on success or a negative error code on failure; call
320 * SDL_GetError() for more information.
321 *
322 * \since This function is available since SDL 2.0.0.
323 */
324extern DECLSPEC int SDLCALL SDL_SetThreadPriority(SDL_ThreadPriority priority);
325
326/**
327 * Wait for a thread to finish.
328 *
329 * Threads that haven't been detached will remain (as a "zombie") until this
330 * function cleans them up. Not doing so is a resource leak.
331 *
332 * Once a thread has been cleaned up through this function, the SDL_Thread
333 * that references it becomes invalid and should not be referenced again. As
334 * such, only one thread may call SDL_WaitThread() on another.
335 *
336 * The return code for the thread function is placed in the area pointed to by
337 * `status`, if `status` is not NULL.
338 *
339 * You may not wait on a thread that has been used in a call to
340 * SDL_DetachThread(). Use either that function or this one, but not both, or
341 * behavior is undefined.
342 *
343 * It is safe to pass a NULL thread to this function; it is a no-op.
344 *
345 * Note that the thread pointer is freed by this function and is not valid
346 * afterward.
347 *
348 * \param thread the SDL_Thread pointer that was returned from the
349 * SDL_CreateThread() call that started this thread.
350 * \param status pointer to an integer that will receive the value returned
351 * from the thread function by its 'return', or NULL to not
352 * receive such value back.
353 *
354 * \since This function is available since SDL 2.0.0.
355 *
356 * \sa SDL_CreateThread
357 * \sa SDL_DetachThread
358 */
359extern DECLSPEC void SDLCALL SDL_WaitThread(SDL_Thread * thread, int *status);
360
361/**
362 * Let a thread clean up on exit without intervention.
363 *
364 * A thread may be "detached" to signify that it should not remain until
365 * another thread has called SDL_WaitThread() on it. Detaching a thread is
366 * useful for long-running threads that nothing needs to synchronize with or
367 * further manage. When a detached thread is done, it simply goes away.
368 *
369 * There is no way to recover the return code of a detached thread. If you
370 * need this, don't detach the thread and instead use SDL_WaitThread().
371 *
372 * Once a thread is detached, you should usually assume the SDL_Thread isn't
373 * safe to reference again, as it will become invalid immediately upon the
374 * detached thread's exit, instead of remaining until someone has called
375 * SDL_WaitThread() to finally clean it up. As such, don't detach the same
376 * thread more than once.
377 *
378 * If a thread has already exited when passed to SDL_DetachThread(), it will
379 * stop waiting for a call to SDL_WaitThread() and clean up immediately. It is
380 * not safe to detach a thread that might be used with SDL_WaitThread().
381 *
382 * You may not call SDL_WaitThread() on a thread that has been detached. Use
383 * either that function or this one, but not both, or behavior is undefined.
384 *
385 * It is safe to pass NULL to this function; it is a no-op.
386 *
387 * \param thread the SDL_Thread pointer that was returned from the
388 * SDL_CreateThread() call that started this thread.
389 *
390 * \since This function is available since SDL 2.0.2.
391 *
392 * \sa SDL_CreateThread
393 * \sa SDL_WaitThread
394 */
395extern DECLSPEC void SDLCALL SDL_DetachThread(SDL_Thread * thread);
396
397/**
398 * Create a piece of thread-local storage.
399 *
400 * This creates an identifier that is globally visible to all threads but
401 * refers to data that is thread-specific.
402 *
403 * \returns the newly created thread local storage identifier or 0 on error.
404 *
405 * \since This function is available since SDL 2.0.0.
406 *
407 * \sa SDL_TLSGet
408 * \sa SDL_TLSSet
409 */
410extern DECLSPEC SDL_TLSID SDLCALL SDL_TLSCreate(void);
411
412/**
413 * Get the current thread's value associated with a thread local storage ID.
414 *
415 * \param id the thread local storage ID.
416 * \returns the value associated with the ID for the current thread or NULL if
417 * no value has been set; call SDL_GetError() for more information.
418 *
419 * \since This function is available since SDL 2.0.0.
420 *
421 * \sa SDL_TLSCreate
422 * \sa SDL_TLSSet
423 */
424extern DECLSPEC void * SDLCALL SDL_TLSGet(SDL_TLSID id);
425
426typedef void (SDLCALL *SDL_TLSDestructorCallback)(void*);
427
428/**
429 * Set the current thread's value associated with a thread local storage ID.
430 *
431 * The function prototype for `destructor` is:
432 *
433 * ```c
434 * void destructor(void *value)
435 * ```
436 *
437 * where its parameter `value` is what was passed as `value` to SDL_TLSSet().
438 *
439 * \param id the thread local storage ID.
440 * \param value the value to associate with the ID for the current thread.
441 * \param destructor a function called when the thread exits, to free the
442 * value.
443 * \returns 0 on success or a negative error code on failure; call
444 * SDL_GetError() for more information.
445 *
446 * \since This function is available since SDL 2.0.0.
447 *
448 * \sa SDL_TLSCreate
449 * \sa SDL_TLSGet
450 */
451extern DECLSPEC int SDLCALL SDL_TLSSet(SDL_TLSID id, const void *value, SDL_TLSDestructorCallback destructor);
452
453/**
454 * Cleanup all TLS data for this thread.
455 *
456 * \since This function is available since SDL 2.0.16.
457 */
458extern DECLSPEC void SDLCALL SDL_TLSCleanup(void);
459
460/* Ends C function definitions when using C++ */
461#ifdef __cplusplus
462}
463#endif
464#include "close_code.h"
465
466#endif /* SDL_thread_h_ */
467
468/* vi: set ts=4 sw=4 expandtab: */
unsigned long uintptr_t
void * SDL_TLSGet(SDL_TLSID id)
unsigned int SDL_TLSID
Definition SDL_thread.h:63
void(__cdecl * pfnSDL_CurrentEndThread)(unsigned code)
Definition SDL_thread.h:119
void SDL_DetachThread(SDL_Thread *thread)
#define SDL_CreateThread(fn, name, data)
Definition SDL_thread.h:146
SDL_threadID SDL_GetThreadID(SDL_Thread *thread)
const char * SDL_GetThreadName(SDL_Thread *thread)
void(* SDL_TLSDestructorCallback)(void *)
Definition SDL_thread.h:426
SDL_TLSID SDL_TLSCreate(void)
#define SDL_CreateThreadWithStackSize(fn, name, stacksize, data)
Definition SDL_thread.h:147
void SDL_TLSCleanup(void)
struct SDL_Thread SDL_Thread
Definition SDL_thread.h:57
int SDL_SetThreadPriority(SDL_ThreadPriority priority)
void SDL_WaitThread(SDL_Thread *thread, int *status)
unsigned long SDL_threadID
Definition SDL_thread.h:60
SDL_ThreadPriority
Definition SDL_thread.h:77
@ SDL_THREAD_PRIORITY_TIME_CRITICAL
Definition SDL_thread.h:81
@ SDL_THREAD_PRIORITY_LOW
Definition SDL_thread.h:78
@ SDL_THREAD_PRIORITY_HIGH
Definition SDL_thread.h:80
@ SDL_THREAD_PRIORITY_NORMAL
Definition SDL_thread.h:79
int(* SDL_ThreadFunction)(void *data)
Definition SDL_thread.h:90
uintptr_t(__cdecl * pfnSDL_CurrentBeginThread)(void *, unsigned, unsigned(__stdcall *func)(void *), void *, unsigned, unsigned *)
Definition SDL_thread.h:117
SDL_threadID SDL_ThreadID(void)
int SDL_TLSSet(SDL_TLSID id, const void *value, SDL_TLSDestructorCallback destructor)