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SDL Wiki


Wait for a thread to finish.


void SDL_WaitThread(SDL_Thread * thread, int *status);

Function Parameters


the SDL_Thread pointer that was returned from the SDL_CreateThread() call that started this thread


pointer to an integer that will receive the value returned from the thread function by its 'return', or NULL to not receive such value back.


Threads that haven't been detached will remain (as a "zombie") until this function cleans them up. Not doing so is a resource leak.

Once a thread has been cleaned up through this function, the SDL_Thread that references it becomes invalid and should not be referenced again. As such, only one thread may call SDL_WaitThread() on another.

The return code for the thread function is placed in the area pointed to by status, if status is not NULL.

You may not wait on a thread that has been used in a call to SDL_DetachThread(). Use either that function or this one, but not both, or behavior is undefined.

It is safe to pass a NULL thread to this function; it is a no-op.

Note that the thread pointer is freed by this function and is not valid afterward.

Code Examples

#include <stdio.h>
#include "SDL_thread.h"
#include "SDL_timer.h"

// Very simple thread - counts 0 to 9 delaying 50ms between increments
static int TestThread(void *ptr)
    int cnt;

    for (cnt = 0; cnt < 10; ++cnt) {
        printf("\nThread counter: %d", cnt);

    // Return the final value to the SDL_WaitThread function above
    return cnt;

int main(int argc, char *argv[])
    SDL_Thread *thread;
    int         threadReturnValue;

    printf("\nSimple SDL_CreateThread test:");

    // Simply create a thread
    thread = SDL_CreateThread(TestThread, "TestThread", (void *)NULL);

    if (NULL == thread) {
        printf("\nSDL_CreateThread failed: %s\n", SDL_GetError());
    } else {
        // Wait for the thread to complete. The thread functions return code will
        //       be placed in the "threadReturnValue" variable when it completes.
        SDL_WaitThread(thread, &threadReturnValue);
        printf("\nThread returned value: %d", threadReturnValue);

    return 0;

CategoryAPI, CategoryThread

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