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SDL standard library

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SDL_mutex.h File Reference

SDL_mutex.h File Reference

Functions to provide thread synchronization primitives. More...

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Mutex functions

typedef struct SDL_mutex SDL_mutex
DECLSPEC SDL_mutex *SDLCALL SDL_CreateMutex (void)
 Create a mutex, initialized unlocked.
DECLSPEC int SDLCALL SDL_LockMutex (SDL_mutex *mutex)
DECLSPEC int SDLCALL SDL_TryLockMutex (SDL_mutex *mutex)
 Try to lock the mutex.
DECLSPEC int SDLCALL SDL_UnlockMutex (SDL_mutex *mutex)
DECLSPEC void SDLCALL SDL_DestroyMutex (SDL_mutex *mutex)
 Destroy a mutex.

Semaphore functions

typedef struct SDL_semaphore SDL_sem
DECLSPEC SDL_sem *SDLCALL SDL_CreateSemaphore (Uint32 initial_value)
 Create a semaphore, initialized with value, returns NULL on failure.
DECLSPEC void SDLCALL SDL_DestroySemaphore (SDL_sem *sem)
 Destroy a semaphore.
DECLSPEC int SDLCALL SDL_SemWait (SDL_sem *sem)
 This function suspends the calling thread until the semaphore pointed to by sem has a positive count.
DECLSPEC int SDLCALL SDL_SemTryWait (SDL_sem *sem)
 Non-blocking variant of SDL_SemWait().
DECLSPEC int SDLCALL SDL_SemWaitTimeout (SDL_sem *sem, Uint32 ms)
 Variant of SDL_SemWait() with a timeout in milliseconds.
DECLSPEC int SDLCALL SDL_SemPost (SDL_sem *sem)
 Atomically increases the semaphore's count (not blocking).
DECLSPEC Uint32 SDLCALL SDL_SemValue (SDL_sem *sem)
 Returns the current count of the semaphore.

Condition variable functions

typedef struct SDL_cond SDL_cond
DECLSPEC SDL_cond *SDLCALL SDL_CreateCond (void)
 Create a condition variable.
DECLSPEC void SDLCALL SDL_DestroyCond (SDL_cond *cond)
 Destroy a condition variable.
DECLSPEC int SDLCALL SDL_CondSignal (SDL_cond *cond)
 Restart one of the threads that are waiting on the condition variable.
DECLSPEC int SDLCALL SDL_CondBroadcast (SDL_cond *cond)
 Restart all threads that are waiting on the condition variable.
DECLSPEC int SDLCALL SDL_CondWait (SDL_cond *cond, SDL_mutex *mutex)
 Wait on the condition variable, unlocking the provided mutex.
DECLSPEC int SDLCALL SDL_CondWaitTimeout (SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
 Waits for at most ms milliseconds, and returns 0 if the condition variable is signaled, SDL_MUTEX_TIMEDOUT if the condition is not signaled in the allotted time, and -1 on error.

Detailed Description

Functions to provide thread synchronization primitives.

Definition in file SDL_mutex.h.

Function Documentation

DECLSPEC int SDLCALL SDL_CondBroadcast ( SDL_cond *  cond )

Restart all threads that are waiting on the condition variable.

Returns:
0 or -1 on error.
DECLSPEC int SDLCALL SDL_CondSignal ( SDL_cond *  cond )

Restart one of the threads that are waiting on the condition variable.

Returns:
0 or -1 on error.
DECLSPEC int SDLCALL SDL_CondWait ( SDL_cond *  cond,
SDL_mutex *  mutex 
)

Wait on the condition variable, unlocking the provided mutex.

Warning:
The mutex must be locked before entering this function!

The mutex is re-locked once the condition variable is signaled.

Returns:
0 when it is signaled, or -1 on error.
DECLSPEC int SDLCALL SDL_CondWaitTimeout ( SDL_cond *  cond,
SDL_mutex *  mutex,
Uint32  ms 
)

Waits for at most ms milliseconds, and returns 0 if the condition variable is signaled, SDL_MUTEX_TIMEDOUT if the condition is not signaled in the allotted time, and -1 on error.

Warning:
On some platforms this function is implemented by looping with a delay of 1 ms, and so should be avoided if possible.
DECLSPEC SDL_cond* SDLCALL SDL_CreateCond ( void   )

Create a condition variable.

Typical use of condition variables:

Thread A: SDL_LockMutex(lock); while ( ! condition ) { SDL_CondWait(cond, lock); } SDL_UnlockMutex(lock);

Thread B: SDL_LockMutex(lock); ... condition = true; ... SDL_CondSignal(cond); SDL_UnlockMutex(lock);

There is some discussion whether to signal the condition variable with the mutex locked or not. There is some potential performance benefit to unlocking first on some platforms, but there are some potential race conditions depending on how your code is structured.

In general it's safer to signal the condition variable while the mutex is locked.

DECLSPEC SDL_mutex* SDLCALL SDL_CreateMutex ( void   )

Create a mutex, initialized unlocked.

DECLSPEC SDL_sem* SDLCALL SDL_CreateSemaphore ( Uint32  initial_value )

Create a semaphore, initialized with value, returns NULL on failure.

DECLSPEC void SDLCALL SDL_DestroyCond ( SDL_cond *  cond )

Destroy a condition variable.

DECLSPEC void SDLCALL SDL_DestroyMutex ( SDL_mutex *  mutex )

Destroy a mutex.

DECLSPEC void SDLCALL SDL_DestroySemaphore ( SDL_sem *  sem )

Destroy a semaphore.

DECLSPEC int SDLCALL SDL_SemPost ( SDL_sem *  sem )

Atomically increases the semaphore's count (not blocking).

Returns:
0, or -1 on error.
DECLSPEC int SDLCALL SDL_SemTryWait ( SDL_sem *  sem )

Non-blocking variant of SDL_SemWait().

Returns:
0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait would block, and -1 on error.
DECLSPEC Uint32 SDLCALL SDL_SemValue ( SDL_sem *  sem )

Returns the current count of the semaphore.

DECLSPEC int SDLCALL SDL_SemWait ( SDL_sem *  sem )

This function suspends the calling thread until the semaphore pointed to by sem has a positive count.

It then atomically decreases the semaphore count.

DECLSPEC int SDLCALL SDL_SemWaitTimeout ( SDL_sem *  sem,
Uint32  ms 
)

Variant of SDL_SemWait() with a timeout in milliseconds.

Returns:
0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait does not succeed in the allotted time, and -1 on error.
Warning:
On some platforms this function is implemented by looping with a delay of 1 ms, and so should be avoided if possible.
DECLSPEC int SDLCALL SDL_TryLockMutex ( SDL_mutex *  mutex )

Try to lock the mutex.

Returns:
0, SDL_MUTEX_TIMEDOUT, or -1 on error
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