SDL  2.0
SDL_mutex.h File Reference
#include "SDL_stdinc.h"
#include "SDL_error.h"
#include "begin_code.h"
#include "close_code.h"
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Macros

#define SDL_MUTEX_TIMEDOUT   1
 
#define SDL_MUTEX_MAXWAIT   (~(Uint32)0)
 

Mutex functions

#define SDL_mutexP(m)   SDL_LockMutex(m)
 
#define SDL_mutexV(m)   SDL_UnlockMutex(m)
 
typedef struct SDL_mutex SDL_mutex
 
SDL_mutexSDL_CreateMutex (void)
 
int SDL_LockMutex (SDL_mutex *mutex)
 
int SDL_TryLockMutex (SDL_mutex *mutex)
 
int SDL_UnlockMutex (SDL_mutex *mutex)
 
void SDL_DestroyMutex (SDL_mutex *mutex)
 

Semaphore functions

typedef struct SDL_semaphore SDL_sem
 
SDL_semSDL_CreateSemaphore (Uint32 initial_value)
 
void SDL_DestroySemaphore (SDL_sem *sem)
 
int SDL_SemWait (SDL_sem *sem)
 
int SDL_SemTryWait (SDL_sem *sem)
 
int SDL_SemWaitTimeout (SDL_sem *sem, Uint32 ms)
 
int SDL_SemPost (SDL_sem *sem)
 
Uint32 SDL_SemValue (SDL_sem *sem)
 

Condition variable functions

typedef struct SDL_cond SDL_cond
 
SDL_condSDL_CreateCond (void)
 
void SDL_DestroyCond (SDL_cond *cond)
 
int SDL_CondSignal (SDL_cond *cond)
 
int SDL_CondBroadcast (SDL_cond *cond)
 
int SDL_CondWait (SDL_cond *cond, SDL_mutex *mutex)
 
int SDL_CondWaitTimeout (SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
 

Detailed Description

Functions to provide thread synchronization primitives.

Definition in file SDL_mutex.h.

Macro Definition Documentation

◆ SDL_MUTEX_MAXWAIT

#define SDL_MUTEX_MAXWAIT   (~(Uint32)0)

This is the timeout value which corresponds to never time out.

Definition at line 49 of file SDL_mutex.h.

◆ SDL_MUTEX_TIMEDOUT

#define SDL_MUTEX_TIMEDOUT   1

Synchronization functions which can time out return this value if they time out.

Definition at line 44 of file SDL_mutex.h.

◆ SDL_mutexP

#define SDL_mutexP (   m)    SDL_LockMutex(m)

Definition at line 100 of file SDL_mutex.h.

◆ SDL_mutexV

#define SDL_mutexV (   m)    SDL_UnlockMutex(m)

Definition at line 142 of file SDL_mutex.h.

Typedef Documentation

◆ SDL_cond

typedef struct SDL_cond SDL_cond

Definition at line 323 of file SDL_mutex.h.

◆ SDL_mutex

typedef struct SDL_mutex SDL_mutex

Definition at line 1 of file SDL_mutex.h.

◆ SDL_sem

typedef struct SDL_semaphore SDL_sem

Definition at line 162 of file SDL_mutex.h.

Function Documentation

◆ SDL_CondBroadcast()

int SDL_CondBroadcast ( SDL_cond cond)

Restart all threads that are waiting on the condition variable.

Parameters
condthe condition variable to signal
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_CondSignal
SDL_CondWait
SDL_CondWaitTimeout
SDL_CreateCond
SDL_DestroyCond

◆ SDL_CondSignal()

int SDL_CondSignal ( SDL_cond cond)

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

Parameters
condthe condition variable to signal
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_CondBroadcast
SDL_CondWait
SDL_CondWaitTimeout
SDL_CreateCond
SDL_DestroyCond

◆ SDL_CondWait()

int SDL_CondWait ( SDL_cond cond,
SDL_mutex mutex 
)

Wait until a condition variable is signaled.

This function unlocks the specified mutex and waits for another thread to call SDL_CondSignal() or SDL_CondBroadcast() on the condition variable cond. Once the condition variable is signaled, the mutex is re-locked and the function returns.

The mutex must be locked before calling this function.

This function is the equivalent of calling SDL_CondWaitTimeout() with a time length of SDL_MUTEX_MAXWAIT.

Parameters
condthe condition variable to wait on
mutexthe mutex used to coordinate thread access
Returns
0 when it is signaled or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_CondBroadcast
SDL_CondSignal
SDL_CondWaitTimeout
SDL_CreateCond
SDL_DestroyCond

◆ SDL_CondWaitTimeout()

int SDL_CondWaitTimeout ( SDL_cond cond,
SDL_mutex mutex,
Uint32  ms 
)

Wait until a condition variable is signaled or a certain time has passed.

This function unlocks the specified mutex and waits for another thread to call SDL_CondSignal() or SDL_CondBroadcast() on the condition variable cond, or for the specified time to elapse. Once the condition variable is signaled or the time elapsed, the mutex is re-locked and the function returns.

The mutex must be locked before calling this function.

Parameters
condthe condition variable to wait on
mutexthe mutex used to coordinate thread access
msthe maximum time to wait, in milliseconds, or SDL_MUTEX_MAXWAIT to wait indefinitely
Returns
0 if the condition variable is signaled, SDL_MUTEX_TIMEDOUT if the condition is not signaled in the allotted time, or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_CondBroadcast
SDL_CondSignal
SDL_CondWait
SDL_CreateCond
SDL_DestroyCond

◆ SDL_CreateCond()

SDL_cond* SDL_CreateCond ( void  )

Create a condition variable.

Returns
a new condition variable or NULL on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_CondBroadcast
SDL_CondSignal
SDL_CondWait
SDL_CondWaitTimeout
SDL_DestroyCond

◆ SDL_CreateMutex()

SDL_mutex* SDL_CreateMutex ( void  )

Create a new mutex.

All newly-created mutexes begin in the unlocked state.

Calls to SDL_LockMutex() will not return while the mutex is locked by another thread. See SDL_TryLockMutex() to attempt to lock without blocking.

SDL mutexes are reentrant.

Returns
the initialized and unlocked mutex or NULL on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_DestroyMutex
SDL_LockMutex
SDL_TryLockMutex
SDL_UnlockMutex

◆ SDL_CreateSemaphore()

SDL_sem* SDL_CreateSemaphore ( Uint32  initial_value)

Create a semaphore.

This function creates a new semaphore and initializes it with the value initial_value. Each wait operation on the semaphore will atomically decrement the semaphore value and potentially block if the semaphore value is 0. Each post operation will atomically increment the semaphore value and wake waiting threads and allow them to retry the wait operation.

Parameters
initial_valuethe starting value of the semaphore
Returns
a new semaphore or NULL on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_DestroySemaphore
SDL_SemPost
SDL_SemTryWait
SDL_SemValue
SDL_SemWait
SDL_SemWaitTimeout

◆ SDL_DestroyCond()

void SDL_DestroyCond ( SDL_cond cond)

Destroy a condition variable.

Parameters
condthe condition variable to destroy
Since
This function is available since SDL 2.0.0.
See also
SDL_CondBroadcast
SDL_CondSignal
SDL_CondWait
SDL_CondWaitTimeout
SDL_CreateCond

◆ SDL_DestroyMutex()

void SDL_DestroyMutex ( SDL_mutex mutex)

Destroy a mutex created with SDL_CreateMutex().

This function must be called on any mutex that is no longer needed. Failure to destroy a mutex will result in a system memory or resource leak. While it is safe to destroy a mutex that is unlocked, it is not safe to attempt to destroy a locked mutex, and may result in undefined behavior depending on the platform.

Parameters
mutexthe mutex to destroy
Since
This function is available since SDL 2.0.0.
See also
SDL_CreateMutex
SDL_LockMutex
SDL_TryLockMutex
SDL_UnlockMutex

◆ SDL_DestroySemaphore()

void SDL_DestroySemaphore ( SDL_sem sem)

Destroy a semaphore.

It is not safe to destroy a semaphore if there are threads currently waiting on it.

Parameters
semthe semaphore to destroy
Since
This function is available since SDL 2.0.0.
See also
SDL_CreateSemaphore
SDL_SemPost
SDL_SemTryWait
SDL_SemValue
SDL_SemWait
SDL_SemWaitTimeout

◆ SDL_LockMutex()

int SDL_LockMutex ( SDL_mutex mutex)

Lock the mutex.

This will block until the mutex is available, which is to say it is in the unlocked state and the OS has chosen the caller as the next thread to lock it. Of all threads waiting to lock the mutex, only one may do so at a time.

It is legal for the owning thread to lock an already-locked mutex. It must unlock it the same number of times before it is actually made available for other threads in the system (this is known as a "recursive mutex").

Parameters
mutexthe mutex to lock
Returns
0, or -1 on error.
Since
This function is available since SDL 2.0.0.

◆ SDL_SemPost()

int SDL_SemPost ( SDL_sem sem)

Atomically increment a semaphore's value and wake waiting threads.

Parameters
semthe semaphore to increment
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_CreateSemaphore
SDL_DestroySemaphore
SDL_SemTryWait
SDL_SemValue
SDL_SemWait
SDL_SemWaitTimeout

◆ SDL_SemTryWait()

int SDL_SemTryWait ( SDL_sem sem)

See if a semaphore has a positive value and decrement it if it does.

This function checks to see if the semaphore pointed to by sem has a positive value and atomically decrements the semaphore value if it does. If the semaphore doesn't have a positive value, the function immediately returns SDL_MUTEX_TIMEDOUT.

Parameters
semthe semaphore to wait on
Returns
0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait would block, or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_CreateSemaphore
SDL_DestroySemaphore
SDL_SemPost
SDL_SemValue
SDL_SemWait
SDL_SemWaitTimeout

◆ SDL_SemValue()

Uint32 SDL_SemValue ( SDL_sem sem)

Get the current value of a semaphore.

Parameters
semthe semaphore to query
Returns
the current value of the semaphore.
Since
This function is available since SDL 2.0.0.
See also
SDL_CreateSemaphore

◆ SDL_SemWait()

int SDL_SemWait ( SDL_sem sem)

Wait until a semaphore has a positive value and then decrements it.

This function suspends the calling thread until either the semaphore pointed to by sem has a positive value or the call is interrupted by a signal or error. If the call is successful it will atomically decrement the semaphore value.

This function is the equivalent of calling SDL_SemWaitTimeout() with a time length of SDL_MUTEX_MAXWAIT.

Parameters
semthe semaphore wait on
Returns
0 on success or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_CreateSemaphore
SDL_DestroySemaphore
SDL_SemPost
SDL_SemTryWait
SDL_SemValue
SDL_SemWait
SDL_SemWaitTimeout

◆ SDL_SemWaitTimeout()

int SDL_SemWaitTimeout ( SDL_sem sem,
Uint32  ms 
)

Wait until a semaphore has a positive value and then decrements it.

This function suspends the calling thread until either the semaphore pointed to by sem has a positive value, the call is interrupted by a signal or error, or the specified time has elapsed. If the call is successful it will atomically decrement the semaphore value.

Parameters
semthe semaphore to wait on
msthe length of the timeout, in milliseconds
Returns
0 if the wait succeeds, SDL_MUTEX_TIMEDOUT if the wait does not succeed in the allotted time, or a negative error code on failure; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_CreateSemaphore
SDL_DestroySemaphore
SDL_SemPost
SDL_SemTryWait
SDL_SemValue
SDL_SemWait

◆ SDL_TryLockMutex()

int SDL_TryLockMutex ( SDL_mutex mutex)

Try to lock a mutex without blocking.

This works just like SDL_LockMutex(), but if the mutex is not available, this function returns SDL_MUTEX_TIMEOUT immediately.

This technique is useful if you need exclusive access to a resource but don't want to wait for it, and will return to it to try again later.

Parameters
mutexthe mutex to try to lock
Returns
0, SDL_MUTEX_TIMEDOUT, or -1 on error; call SDL_GetError() for more information.
Since
This function is available since SDL 2.0.0.
See also
SDL_CreateMutex
SDL_DestroyMutex
SDL_LockMutex
SDL_UnlockMutex

◆ SDL_UnlockMutex()

int SDL_UnlockMutex ( SDL_mutex mutex)

Unlock the mutex.

It is legal for the owning thread to lock an already-locked mutex. It must unlock it the same number of times before it is actually made available for other threads in the system (this is known as a "recursive mutex").

It is an error to unlock a mutex that has not been locked by the current thread, and doing so results in undefined behavior.

It is also an error to unlock a mutex that isn't locked at all.

Parameters
mutexthe mutex to unlock.
Returns
0, or -1 on error.
Since
This function is available since SDL 2.0.0.