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SDL2-FFI-0.08
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/ SDL2::mutex

NAME

SDL2::mutex - Functions to Provide Thread Synchronization Primitives

SYNOPSIS

    use SDL2 qw[:mutex];

DESCRIPTION

Functions in this group provide thread synchronization primitives for multi-threaded programing.

There are three primitives available in SDL:

Mutex
Semaphore
Condition Variable

The SDL mutex is implemented as a recursive mutex so you can nest lock and unlock calls to the same mutex.

Functions

These functions may be imported by name or with the :mutex tag.

SDL_CreateMutex( )

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 undef on failure; call SDL_GetError( ) for more information.

SDL_LockMutex( ... )

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").

Expected parameters include:

mutex - the mutex to lock

Returns 0 on success, or -1 on error.

SDL_TryLockMutex( ... )

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.

Expected parameters include:

mutex - the mutex to attempt to lock

Returns 0, SDL_MUTEX_TIMEDOUT, or -1 on error; call SDL_GetError( ) for more information.

SDL_UnlockMutex( ... )

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.

Expected parameters include:

mutex - the mutex to unlock

Returns 0 on success, or -1 on error.

SDL_DestroyMutex( ... )

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.

Expected parameters include:

mutex - the mutex to destroy

SDL_CreateSemaphore( ... )

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.

Expected parameters include:

initial_value - the starting value of the semaphore

Returns a new semaphore or undef on failure; call SDL_GetError( ) for more information.

SDL_DestroySemaphore( ... )

Destroy a semaphore.

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

Expected parameters include:

sem - the semaphore to destroy

SDL_SemWait( ... )

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.

Expected parameters include:

sem - the semaphore to wait on

Returns 0 on success or a negative error code on failure; call SDL_GetError( ) for more information.

SDL_SemTryWait( ... )

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.

Expected parameters include:

sem - the 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.

SDL_SemWaitTimeout( ... )

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.

Expected parameters include:

sem - the semaphore to wait on
ms - the 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.

SDL_SemPost( ... )

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

Expected parameters include:

sem - the semaphore to increment

Returns 0 on success or a negative error code on failure; call SDL_GetError( ) for more information.

SDL_SemValue( ... )

Get the current value of a semaphore.

Expected parameters include:

sem - the semaphore to query

Returns the current value of the semaphore.

SDL_CreateCond( )

Create a condition variable.

Returns a new condition variable or undef on failure; call SDL_GetError( ) for more information.

SDL_DestroyCond( ... )

Destroy a condition variable.

Expected parameters include:

cond - the condition variable to destroy

SDL_CondSignal( ... )

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

Expected parameters include:

cond - the condition variable to signal

Returns 0 on success or a negative error code on failure; call SDL_GetError( ) for more information.

SDL_CondBroadcast( ... )

Restart all threads that are waiting on the condition variable.

Expected parameters include:

cond - the condition variable to signal

Returns 0 on success or a negative error code on failure; call SDL_GetError( ) for more information.

SDL_CondWait( ... )

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.

Expected parameters include:

cond - the condition variable to wait on
mutex - the 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.

SDL_CondWaitTimeout( ... )

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.

Expected parameters include:

cond - the condition variable to wait on
mutex - the mutex used to coordinate thread access
ms - the 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.

Defined Variables and Enumerations

These variables may be imported by name or with the :mutex tag. Enumerations may be imported with the given tag.

SDL_MUTEX_TIMEDOUT

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

SDL_MUTEX_MAXWAIT

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

LICENSE

Copyright (C) Sanko Robinson.

This library is free software; you can redistribute it and/or modify it under the terms found in the Artistic License 2. Other copyrights, terms, and conditions may apply to data transmitted through this module.

AUTHOR

Sanko Robinson <sanko@cpan.org>