====== (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 ==
int SDL_SemWait(SDL_sem *sem);
== 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 sem
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 [[SDL_MUTEX_MAXWAIT]]
.
== Version ==
This function is available since SDL 3.0.0.
== Code Examples ==
#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);
}
== Related Functions ==
:[[SDL_CreateSemaphore]]
:[[SDL_DestroySemaphore]]
:[[SDL_SemPost]]
:[[SDL_SemTryWait]]
:[[SDL_SemValue]]
:[[SDL_SemWait]]
:[[SDL_SemWaitTimeout]]
----
[[CategoryAPI]], [[CategoryMutex]]