SDL_SemPost man page
SDL_SemPost — Unlock a semaphore.
#include "SDL.h" #include "SDL_thread.h"
int SDL_SemPost(SDL_sem *sem);
SDL_SemPost unlocks the semaphore pointed to by sem and atomically increments the semaphores value. Threads that were blocking on the semaphore may be scheduled after this call succeeds.
SDL_SemPost should be called after a semaphore is locked by a successful call to SDL_SemWait, SDL_SemTryWait or SDL_SemWaitTimeout.
Returns 0 if successful or -1 if there was an error (leaving the semaphore unchanged).
SDL_CreateSemaphore, SDL_DestroySemaphore, SDL_SemWait, SDL_SemTryWait, SDL_SemWaitTimeout, SDL_SemValue