SDL_mutexV man page
SDL_mutexV — Unlock a mutex
#include "SDL.h" #include "SDL_thread.h"
int SDL_mutexV(SDL_mutex *mutex);
Unlocks the mutex, which was previously created with SDL_CreateMutex. Returns 0 on success, or -1 on an error.
SDL also defines a macro #define SDL_UnlockMutex(m) SDL_mutexV(m).