###### (This is the documentation for SDL3, which is under heavy development and the API is changing! [SDL2](https://wiki.libsdl.org/SDL2/) is the current stable version!) # SDL_CreateRWLock Create a new read/write lock. ## Syntax ```c SDL_RWLock* SDL_CreateRWLock(void); ``` ## Return Value Returns the initialized and unlocked read/write lock or NULL on failure; call [SDL_GetError](SDL_GetError)() for more information. ## Remarks 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](SDL_LockRWLockForReading)() and [SDL_LockRWLockForWriting](SDL_LockRWLockForWriting) will not return while the rwlock is locked _for writing_ by another thread. See [SDL_TryLockRWLockForReading](SDL_TryLockRWLockForReading)() and [SDL_TryLockRWLockForWriting](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). ## Version This function is available since SDL 3.0.0. ## Related Functions * [SDL_DestroyRWLock](SDL_DestroyRWLock) * [SDL_LockRWLockForReading](SDL_LockRWLockForReading) * [SDL_LockRWLockForWriting](SDL_LockRWLockForWriting) * [SDL_TryLockRWLockForReading](SDL_TryLockRWLockForReading) * [SDL_TryLockRWLockForWriting](SDL_TryLockRWLockForWriting) * [SDL_UnlockRWLock](SDL_UnlockRWLock) ---- [CategoryAPI](CategoryAPI)