SDL_CreateThread

Use this function to create a new thread with the same properties as the parent thread.

Syntax

SDL_Thread* SDL_CreateThread(SDL_ThreadFunction fn,
                             void*              data)

Function Parameters

Return Value

Returns the new thread pointer on success, NULL if the new thread could not be created. This is a pointer to an SDL defined device independent thread information structure. The returned thread pointer will be used for any subsuequent calls to manage this thread.

green

Code Examples

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

int TestThread( void *ptr );

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

        printf("\nSimple SDL_CreateThread test:");

        // Simply create a thread
        thread = SDL_CreateThread( TestThread, (void *)NULL);
        if( NULL == thread )
           printf("\nSDL_CreateThread failed: %s\n", SDL_GetError());
        else
           SDL_Delay(1000);

        return 1;
}

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

        for(cnt=0;cnt<10;cnt++)
        {
                printf( "\nThread counter: %d", cnt);
                SDL_Delay(50);
        }

        return 1;
}

Output:

Simple SDL_CreateThread test:
Thread counter: 0
Thread counter: 1
Thread counter: 2
Thread counter: 3
Thread counter: 4
Thread counter: 5
Thread counter: 6
Thread counter: 7
Thread counter: 8
Thread counter: 9

Remarks

*
SDL_CreateThread() creates a new thread of execution that shares all of its parent's global memory, signal handlers, file descriptors, etc, and runs the function fn, passing it the void pointer data. The thread quits when fn returns.
*

fn is the function passed to SDL_CreateThread() ^{and has the following syntax}. _{It is passed a void* user context parameter and returns an int.}

• int (SDLCALL * SDL_ThreadFunction) (void *data)
  green

Always use the caller's _beginthread() and _endthread() APIs to start a new thread. This way, if it's the SDL.DLL which uses this API, then the RTL of SDL.DLL will be used to create the new thread, and if it's the application, then the RTL of the application will be used. green

green

*
green

(SDL 1.2.7) Even after the procedure started in the thread returns, there still exist some resources allocated to the thread. To free these resources use SDL_WaitThread() to wait for the thread to finish and obtain the status code of the thread. If not done so, SDL_CreateThread() will hang after about 1010 successfully created threads (tested on GNU/Linux). This is consistent with POSIX threads behavior where unless threads are explicitly detached using pthread_detach() or created using a pthread_attr initialized using pthread_attr_setdetachstate() passed at pthread_create(), they must be waited for using pthread_join() for their resources to be released. The SDL threads abstraction library does not provide the functions to detach a thread ^or to launch a thread in detached mode.

(SDL 1.2.8) On win32, keystrokes are caught in correctly in a thread, but SDL_EnableUNICODE green

does not work correctly. Specifically, .unicode contains the same value as .sym, not the modified version for SHFT, CTRL, etc.

(SDL 1.2.9) On win32 (this wasn't observed on unix), the initial thread must be the one polling the SDL events. Otherwise, keyboard events are no longer caught. Moreover, it is recommended to use SDL_mixer and SDL blitting functions from within that initial thread as well, otherwise the system becomes unstable (also only under win32) despite the proper use of mutexes and conditional variables. This unfortunately limits a lot ^of the usefulness of threads when the software is also expected to run on win32.
*

green

Related Functions

• SDL_GetThreadID ???

• SDL_ThreadID ???

• SDL_WaitThread ???

CategoryAPI, CategoryThread