Documentation

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.

Thread safety

It is safe to call this function from any thread.

See also

sDL_DestroyMutex, sDL_LockMutex, sDL_TryLockMutex, sDL_UnlockMutex

C declaration

SDL_CreateMutex, defined at SDL3/SDL_mutex.h 320:41

Since: 3.2.0

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").

This function does not fail; if mutex is NULL, it will return immediately having locked nothing. If the mutex is valid, this function will always block until it can lock the mutex, and return with it locked.

Thread safety

It is safe to call this function from any thread.

See also

sDL_TryLockMutex, sDL_UnlockMutex

C declaration

SDL_LockMutex, defined at SDL3/SDL_mutex.h 346:34

Since: 3.2.0

Try to lock a mutex without blocking.

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

This function returns true if passed a NULL mutex.

Returns

true on success, false if the mutex would block.

Thread safety

It is safe to call this function from any thread.

See also

sDL_LockMutex, sDL_UnlockMutex

C declaration

SDL_TryLockMutex, defined at SDL3/SDL_mutex.h 369:34

Since: 3.2.0

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

Thread safety

This call must be paired with a previous locking call on the same thread.

See also

sDL_LockMutex, sDL_TryLockMutex

C declaration

SDL_UnlockMutex, defined at SDL3/SDL_mutex.h 391:34

Since: 3.2.0

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.

Thread safety

It is safe to call this function from any thread.

See also

sDL_CreateMutex

C declaration

SDL_DestroyMutex, defined at SDL3/SDL_mutex.h 410:34

Since: 3.2.0

Create a new read/write lock.

A read/write lock is useful for situations where you have multiple threads trying to access a resource that is rarely updated. All threads requesting a read-only lock will be allowed to run in parallel; if a thread requests a write lock, it will be provided exclusive access. This makes it safe for multiple threads to use a resource at the same time if they promise not to change it, and when it has to be changed, the rwlock will serve as a gateway to make sure those changes can be made safely.

In the right situation, a rwlock can be more efficient than a mutex, which only lets a single thread proceed at a time, even if it won't be modifying the data.

All newly-created read/write locks begin in the unlocked state.

Calls to SDL_LockRWLockForReading() and SDL_LockRWLockForWriting will not return while the rwlock is locked for writing by another thread. See SDL_TryLockRWLockForReading() and SDL_TryLockRWLockForWriting() to attempt to lock without blocking.

SDL read/write locks are only recursive for read-only locks! They are not guaranteed to be fair, or provide access in a FIFO manner! They are not guaranteed to favor writers. You may not lock a rwlock for both read-only and write access at the same time from the same thread (so you can't promote your read-only lock to a write lock without unlocking first).

Returns

the initialized and unlocked read/write lock or NULL on failure; call SDL_GetError() for more information.

Thread safety

It is safe to call this function from any thread.

See also

sDL_DestroyRWLock, sDL_LockRWLockForReading, sDL_LockRWLockForWriting, sDL_TryLockRWLockForReading, sDL_TryLockRWLockForWriting, sDL_UnlockRWLock

C declaration

SDL_CreateRWLock, defined at SDL3/SDL_mutex.h 482:42

Since: 3.2.0

Lock the read/write lock for read only operations.

This will block until the rwlock is available, which is to say it is not locked for writing by any other thread. Of all threads waiting to lock the rwlock, all may do so at the same time as long as they are requesting read-only access; if a thread wants to lock for writing, only one may do so at a time, and no other threads, read-only or not, may hold the lock at the same time.

It is legal for the owning thread to lock an already-locked rwlock for reading. 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 rwlock").

Note that locking for writing is not recursive (this is only available to read-only locks).

It is illegal to request a read-only lock from a thread that already holds the write lock. Doing so results in undefined behavior. Unlock the write lock before requesting a read-only lock. (But, of course, if you have the write lock, you don't need further locks to read in any case.)

This function does not fail; if rwlock is NULL, it will return immediately having locked nothing. If the rwlock is valid, this function will always block until it can lock the mutex, and return with it locked.

Thread safety

It is safe to call this function from any thread.

See also

sDL_LockRWLockForWriting, sDL_TryLockRWLockForReading, sDL_UnlockRWLock

C declaration

SDL_LockRWLockForReading, defined at SDL3/SDL_mutex.h 521:34

Since: 3.2.0

Lock the read/write lock for write operations.

This will block until the rwlock is available, which is to say it is not locked for reading or writing by any other thread. Only one thread may hold the lock when it requests write access; all other threads, whether they also want to write or only want read-only access, must wait until the writer thread has released the lock.

It is illegal for the owning thread to lock an already-locked rwlock for writing (read-only may be locked recursively, writing can not). Doing so results in undefined behavior.

It is illegal to request a write lock from a thread that already holds a read-only lock. Doing so results in undefined behavior. Unlock the read-only lock before requesting a write lock.

This function does not fail; if rwlock is NULL, it will return immediately having locked nothing. If the rwlock is valid, this function will always block until it can lock the mutex, and return with it locked.

Thread safety

It is safe to call this function from any thread.

See also

sDL_LockRWLockForReading, sDL_TryLockRWLockForWriting, sDL_UnlockRWLock

C declaration

SDL_LockRWLockForWriting, defined at SDL3/SDL_mutex.h 554:34

Since: 3.2.0

Try to lock a read/write lock for reading without blocking.

This works just like SDL_LockRWLockForReading(), but if the rwlock is not available, then this function returns false immediately.

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

Trying to lock for read-only access can succeed if other threads are holding read-only locks, as this won't prevent access.

This function returns true if passed a NULL rwlock.

Returns

true on success, false if the lock would block.

Thread safety

It is safe to call this function from any thread.

See also

sDL_LockRWLockForReading, sDL_TryLockRWLockForWriting, sDL_UnlockRWLock

C declaration

SDL_TryLockRWLockForReading, defined at SDL3/SDL_mutex.h 581:34

Since: 3.2.0

Try to lock a read/write lock for writing without blocking.

This works just like SDL_LockRWLockForWriting(), but if the rwlock is not available, then this function returns false 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.

It is illegal for the owning thread to lock an already-locked rwlock for writing (read-only may be locked recursively, writing can not). Doing so results in undefined behavior.

It is illegal to request a write lock from a thread that already holds a read-only lock. Doing so results in undefined behavior. Unlock the read-only lock before requesting a write lock.

This function returns true if passed a NULL rwlock.

Returns

true on success, false if the lock would block.

Thread safety

It is safe to call this function from any thread.

See also

sDL_LockRWLockForWriting, sDL_TryLockRWLockForReading, sDL_UnlockRWLock

C declaration

SDL_TryLockRWLockForWriting, defined at SDL3/SDL_mutex.h 613:34

Since: 3.2.0

Unlock the read/write lock.

Use this function to unlock the rwlock, whether it was locked for read-only or write operations.

It is legal for the owning thread to lock an already-locked read-only lock. 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 rwlock").

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

Thread safety

This call must be paired with a previous locking call on the same thread.

See also

sDL_LockRWLockForReading, sDL_LockRWLockForWriting, sDL_TryLockRWLockForReading, sDL_TryLockRWLockForWriting

C declaration

SDL_UnlockRWLock, defined at SDL3/SDL_mutex.h 641:34

Since: 3.2.0

Destroy a read/write lock created with SDL_CreateRWLock().

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

Thread safety

It is safe to call this function from any thread.

See also

sDL_CreateRWLock

C declaration

SDL_DestroyRWLock, defined at SDL3/SDL_mutex.h 660:34

Since: 3.2.0

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.

Returns

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

Thread safety

It is safe to call this function from any thread.

See also

sDL_DestroySemaphore, sDL_SignalSemaphore, sDL_TryWaitSemaphore, sDL_GetSemaphoreValue, sDL_WaitSemaphore, sDL_WaitSemaphoreTimeout

C declaration

SDL_CreateSemaphore, defined at SDL3/SDL_mutex.h 710:45

Since: 3.2.0

Destroy a semaphore.

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

Thread safety

It is safe to call this function from any thread.

See also

sDL_CreateSemaphore

C declaration

SDL_DestroySemaphore, defined at SDL3/SDL_mutex.h 726:34

Since: 3.2.0

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

This function suspends the calling thread until the semaphore pointed to by sem has a positive value, and then atomically decrement the semaphore value.

This function is the equivalent of calling SDL_WaitSemaphoreTimeout() with a time length of -1.

Thread safety

It is safe to call this function from any thread.

See also

sDL_SignalSemaphore, sDL_TryWaitSemaphore, sDL_WaitSemaphoreTimeout

C declaration

SDL_WaitSemaphore, defined at SDL3/SDL_mutex.h 748:34

Since: 3.2.0

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 false.

Returns

true if the wait succeeds, false if the wait would block.

Thread safety

It is safe to call this function from any thread.

See also

sDL_SignalSemaphore, sDL_WaitSemaphore, sDL_WaitSemaphoreTimeout

C declaration

SDL_TryWaitSemaphore, defined at SDL3/SDL_mutex.h 769:34

Since: 3.2.0

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 specified time has elapsed. If the call is successful it will atomically decrement the semaphore value.

Returns

true if the wait succeeds or false if the wait times out.

Thread safety

It is safe to call this function from any thread.

See also

sDL_SignalSemaphore, sDL_TryWaitSemaphore, sDL_WaitSemaphore

C declaration

SDL_WaitSemaphoreTimeout, defined at SDL3/SDL_mutex.h 791:34

Since: 3.2.0

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

Thread safety

It is safe to call this function from any thread.

See also

sDL_TryWaitSemaphore, sDL_WaitSemaphore, sDL_WaitSemaphoreTimeout

C declaration

SDL_SignalSemaphore, defined at SDL3/SDL_mutex.h 806:34

Since: 3.2.0

Get the current value of a semaphore.

Returns

the current value of the semaphore.

Thread safety

It is safe to call this function from any thread.

C declaration

SDL_GetSemaphoreValue, defined at SDL3/SDL_mutex.h 818:36

Since: 3.2.0

Create a condition variable.

Returns

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

Thread safety

It is safe to call this function from any thread.

See also

sDL_BroadcastCondition, sDL_SignalCondition, sDL_WaitCondition, sDL_WaitConditionTimeout, sDL_DestroyCondition

C declaration

SDL_CreateCondition, defined at SDL3/SDL_mutex.h 859:45

Since: 3.2.0

Destroy a condition variable.

Thread safety

It is safe to call this function from any thread.

See also

sDL_CreateCondition

C declaration

SDL_DestroyCondition, defined at SDL3/SDL_mutex.h 872:34

Since: 3.2.0

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

Thread safety

It is safe to call this function from any thread.

See also

sDL_BroadcastCondition, sDL_WaitCondition, sDL_WaitConditionTimeout

C declaration

SDL_SignalCondition, defined at SDL3/SDL_mutex.h 887:34

Since: 3.2.0

Restart all threads that are waiting on the condition variable.

Thread safety

It is safe to call this function from any thread.

See also

sDL_SignalCondition, sDL_WaitCondition, sDL_WaitConditionTimeout

C declaration

SDL_BroadcastCondition, defined at SDL3/SDL_mutex.h 902:34

Since: 3.2.0

Wait until a condition variable is signaled.

This function unlocks the specified mutex and waits for another thread to call SDL_SignalCondition() or SDL_BroadcastCondition() 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. Locking the mutex recursively (more than once) is not supported and leads to undefined behavior.

This function is the equivalent of calling SDL_WaitConditionTimeout() with a time length of -1.

Thread safety

It is safe to call this function from any thread.

See also

sDL_BroadcastCondition, sDL_SignalCondition, sDL_WaitConditionTimeout

C declaration

SDL_WaitCondition, defined at SDL3/SDL_mutex.h 930:34

Since: 3.2.0

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_SignalCondition() or SDL_BroadcastCondition() 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. Locking the mutex recursively (more than once) is not supported and leads to undefined behavior.

Returns

true if the condition variable is signaled, false if the condition is not signaled in the allotted time.

Thread safety

It is safe to call this function from any thread.

See also

sDL_BroadcastCondition, sDL_SignalCondition, sDL_WaitCondition

C declaration

SDL_WaitConditionTimeout, defined at SDL3/SDL_mutex.h 960:34

Since: 3.2.0

Return whether initialization should be done.

This function checks the passed in state and if initialization should be done, sets the status to SDL_INIT_STATUS_INITIALIZING and returns true. If another thread is already modifying this state, it will wait until that's done before returning.

If this function returns true, the calling code must call SDL_SetInitialized() to complete the initialization.

Returns

true if initialization needs to be done, false otherwise.

Thread safety

It is safe to call this function from any thread.

See also

sDL_SetInitialized, sDL_ShouldQuit

C declaration

SDL_ShouldInit, defined at SDL3/SDL_mutex.h 1067:34

Since: 3.2.0

Return whether cleanup should be done.

This function checks the passed in state and if cleanup should be done, sets the status to SDL_INIT_STATUS_UNINITIALIZING and returns true.

If this function returns true, the calling code must call SDL_SetInitialized() to complete the cleanup.

Returns

true if cleanup needs to be done, false otherwise.

Thread safety

It is safe to call this function from any thread.

See also

sDL_SetInitialized, sDL_ShouldInit

C declaration

SDL_ShouldQuit, defined at SDL3/SDL_mutex.h 1088:34

Since: 3.2.0

Finish an initialization state transition.

This function sets the status of the passed in state to SDL_INIT_STATUS_INITIALIZED or SDL_INIT_STATUS_UNINITIALIZED and allows any threads waiting for the status to proceed.

Thread safety

It is safe to call this function from any thread.

See also

sDL_ShouldInit, sDL_ShouldQuit

C declaration

SDL_SetInitialized, defined at SDL3/SDL_mutex.h 1107:34

Since: 3.2.0