SDL_mutex.h (6665B)
1/* 2 Simple DirectMedia Layer 3 Copyright (C) 1997-2020 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 * \file SDL_mutex.h 27 * 28 * Functions to provide thread synchronization primitives. 29 */ 30 31#include "SDL_stdinc.h" 32#include "SDL_error.h" 33 34#include "begin_code.h" 35/* Set up for C function definitions, even when using C++ */ 36#ifdef __cplusplus 37extern "C" { 38#endif 39 40/** 41 * Synchronization functions which can time out return this value 42 * if they time out. 43 */ 44#define SDL_MUTEX_TIMEDOUT 1 45 46/** 47 * This is the timeout value which corresponds to never time out. 48 */ 49#define SDL_MUTEX_MAXWAIT (~(Uint32)0) 50 51 52/** 53 * \name Mutex functions 54 */ 55/* @{ */ 56 57/* The SDL mutex structure, defined in SDL_sysmutex.c */ 58struct SDL_mutex; 59typedef struct SDL_mutex SDL_mutex; 60 61/** 62 * Create a mutex, initialized unlocked. 63 */ 64extern DECLSPEC SDL_mutex *SDLCALL SDL_CreateMutex(void); 65 66/** 67 * Lock the mutex. 68 * 69 * \return 0, or -1 on error. 70 */ 71#define SDL_mutexP(m) SDL_LockMutex(m) 72extern DECLSPEC int SDLCALL SDL_LockMutex(SDL_mutex * mutex); 73 74/** 75 * Try to lock the mutex 76 * 77 * \return 0, SDL_MUTEX_TIMEDOUT, or -1 on error 78 */ 79extern DECLSPEC int SDLCALL SDL_TryLockMutex(SDL_mutex * mutex); 80 81/** 82 * Unlock the mutex. 83 * 84 * \return 0, or -1 on error. 85 * 86 * \warning It is an error to unlock a mutex that has not been locked by 87 * the current thread, and doing so results in undefined behavior. 88 */ 89#define SDL_mutexV(m) SDL_UnlockMutex(m) 90extern DECLSPEC int SDLCALL SDL_UnlockMutex(SDL_mutex * mutex); 91 92/** 93 * Destroy a mutex. 94 */ 95extern DECLSPEC void SDLCALL SDL_DestroyMutex(SDL_mutex * mutex); 96 97/* @} *//* Mutex functions */ 98 99 100/** 101 * \name Semaphore functions 102 */ 103/* @{ */ 104 105/* The SDL semaphore structure, defined in SDL_syssem.c */ 106struct SDL_semaphore; 107typedef struct SDL_semaphore SDL_sem; 108 109/** 110 * Create a semaphore, initialized with value, returns NULL on failure. 111 */ 112extern DECLSPEC SDL_sem *SDLCALL SDL_CreateSemaphore(Uint32 initial_value); 113 114/** 115 * Destroy a semaphore. 116 */ 117extern DECLSPEC void SDLCALL SDL_DestroySemaphore(SDL_sem * sem); 118 119/** 120 * This function suspends the calling thread until the semaphore pointed 121 * to by \c sem has a positive count. It then atomically decreases the 122 * semaphore count. 123 */ 124extern DECLSPEC int SDLCALL SDL_SemWait(SDL_sem * sem); 125 126/** 127 * Non-blocking variant of SDL_SemWait(). 128 * 129 * \return 0 if the wait succeeds, ::SDL_MUTEX_TIMEDOUT if the wait would 130 * block, and -1 on error. 131 */ 132extern DECLSPEC int SDLCALL SDL_SemTryWait(SDL_sem * sem); 133 134/** 135 * Variant of SDL_SemWait() with a timeout in milliseconds. 136 * 137 * \return 0 if the wait succeeds, ::SDL_MUTEX_TIMEDOUT if the wait does not 138 * succeed in the allotted time, and -1 on error. 139 * 140 * \warning On some platforms this function is implemented by looping with a 141 * delay of 1 ms, and so should be avoided if possible. 142 */ 143extern DECLSPEC int SDLCALL SDL_SemWaitTimeout(SDL_sem * sem, Uint32 ms); 144 145/** 146 * Atomically increases the semaphore's count (not blocking). 147 * 148 * \return 0, or -1 on error. 149 */ 150extern DECLSPEC int SDLCALL SDL_SemPost(SDL_sem * sem); 151 152/** 153 * Returns the current count of the semaphore. 154 */ 155extern DECLSPEC Uint32 SDLCALL SDL_SemValue(SDL_sem * sem); 156 157/* @} *//* Semaphore functions */ 158 159 160/** 161 * \name Condition variable functions 162 */ 163/* @{ */ 164 165/* The SDL condition variable structure, defined in SDL_syscond.c */ 166struct SDL_cond; 167typedef struct SDL_cond SDL_cond; 168 169/** 170 * Create a condition variable. 171 * 172 * Typical use of condition variables: 173 * 174 * Thread A: 175 * SDL_LockMutex(lock); 176 * while ( ! condition ) { 177 * SDL_CondWait(cond, lock); 178 * } 179 * SDL_UnlockMutex(lock); 180 * 181 * Thread B: 182 * SDL_LockMutex(lock); 183 * ... 184 * condition = true; 185 * ... 186 * SDL_CondSignal(cond); 187 * SDL_UnlockMutex(lock); 188 * 189 * There is some discussion whether to signal the condition variable 190 * with the mutex locked or not. There is some potential performance 191 * benefit to unlocking first on some platforms, but there are some 192 * potential race conditions depending on how your code is structured. 193 * 194 * In general it's safer to signal the condition variable while the 195 * mutex is locked. 196 */ 197extern DECLSPEC SDL_cond *SDLCALL SDL_CreateCond(void); 198 199/** 200 * Destroy a condition variable. 201 */ 202extern DECLSPEC void SDLCALL SDL_DestroyCond(SDL_cond * cond); 203 204/** 205 * Restart one of the threads that are waiting on the condition variable. 206 * 207 * \return 0 or -1 on error. 208 */ 209extern DECLSPEC int SDLCALL SDL_CondSignal(SDL_cond * cond); 210 211/** 212 * Restart all threads that are waiting on the condition variable. 213 * 214 * \return 0 or -1 on error. 215 */ 216extern DECLSPEC int SDLCALL SDL_CondBroadcast(SDL_cond * cond); 217 218/** 219 * Wait on the condition variable, unlocking the provided mutex. 220 * 221 * \warning The mutex must be locked before entering this function! 222 * 223 * The mutex is re-locked once the condition variable is signaled. 224 * 225 * \return 0 when it is signaled, or -1 on error. 226 */ 227extern DECLSPEC int SDLCALL SDL_CondWait(SDL_cond * cond, SDL_mutex * mutex); 228 229/** 230 * Waits for at most \c ms milliseconds, and returns 0 if the condition 231 * variable is signaled, ::SDL_MUTEX_TIMEDOUT if the condition is not 232 * signaled in the allotted time, and -1 on error. 233 * 234 * \warning On some platforms this function is implemented by looping with a 235 * delay of 1 ms, and so should be avoided if possible. 236 */ 237extern DECLSPEC int SDLCALL SDL_CondWaitTimeout(SDL_cond * cond, 238 SDL_mutex * mutex, Uint32 ms); 239 240/* @} *//* Condition variable functions */ 241 242 243/* Ends C function definitions when using C++ */ 244#ifdef __cplusplus 245} 246#endif 247#include "close_code.h" 248 249#endif /* SDL_mutex_h_ */ 250 251/* vi: set ts=4 sw=4 expandtab: */