====== (This is the documentation for SDL3, which is under heavy development and the API is changing! [https://wiki.libsdl.org/SDL2/ SDL2] is the current stable version!) ======
= SDL_SemWait =

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

== Syntax ==

<syntaxhighlight lang='c'>
int SDL_SemWait(SDL_sem *sem);
</syntaxhighlight>

== Function Parameters ==

{|
|'''sem'''
|the semaphore wait on
|}

== Return Value ==

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

== Remarks ==

This function suspends the calling thread until either the semaphore
pointed to by <code>sem</code> has a positive value or the call is
interrupted by a signal or error. If the call is successful it will
atomically decrement the semaphore value.

This function is the equivalent of calling [[SDL_SemWaitTimeout]]() with a
time length of <code>[[SDL_MUTEX_MAXWAIT]]</code>.

== Version ==

This function is available since SDL 3.0.0.

== Code Examples ==

<!-- # Begin Semaphore Example -->
<syntaxhighlight lang='c'>
#define NB_WAITER 10

SDL_sem *sem;

// Increments the semaphore every 2s
int poster_thread() {
  for (int i = 0; i < NB_WAITER; i++) {
    SDL_SemPost(sem);
    SDL_Delay(2 * 1000);
  }
  return 0;
}

int waiter_thread() {
  int status;

  status = SDL_SemWait(sem);
  
  if (status == 0) {
    SDL_Log("Semaphore was decremented.\n");
  } else {
    SDL_LogError(SDL_LOG_CATEGORY_APPLICATION, "An error has occured while waiting: %s\n", SDL_GetError());
  }
  return 0;
}

int main() {
  sem = SDL_CreateSemaphore(0);
  create_and_wait_threads(); // 1 poster, 10 waiters
  SDL_DestroySemaphore(sem);
}
</syntaxhighlight>
<!-- # End Semaphore Example -->

== Related Functions ==

:[[SDL_CreateSemaphore]]
:[[SDL_DestroySemaphore]]
:[[SDL_SemPost]]
:[[SDL_SemTryWait]]
:[[SDL_SemValue]]
:[[SDL_SemWait]]
:[[SDL_SemWaitTimeout]]

----
[[CategoryAPI]], [[CategoryMutex]]