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(This is the documentation for SDL3, which is under heavy development and the API is changing! SDL2 is the current stable version!)


Lock the read/write lock for read only operations.


int SDL_LockRWLockForReading(SDL_RWLock *rwlock) SDL_ACQUIRE_SHARED(rwlock);

Function Parameters

rwlock the read/write lock to lock

Return Value

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


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 is available since SDL 3.0.0.


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