I create a couple of windows to display YUV data from 2 separate pthreads.  When the 2nd window is created I get a seg fault in the call to  "SDL_PollEvent (&event)" the seg fault happens 2 places:

SDL_x11events.c: 

...
    if (_this->suspend_screensaver) {
        Uint32 now = SDL_GetTicks();
        if (!data->screensaver_activity

At this point, "data" is NULL.

and

SDL_x11mouse.c:

            data = (SDL_WindowData *)window->driverdata;

            if (x11_cursor != None) {
    if( data->xwindow )
                X11_XDefineCursor(display, data->xwindow, x11_cursor );
            } else {
                X11_XUndefineCursor(display, data->xwindow);
            }

again, driverdata is NULL.

It looks to me like the PumpEvents funciton is being called too early when the 2nd window is created.  The first window has been set up properly but the 2nd window has NULL in the driverdata field.

I can work round it by catching the NULL case and ignoring the call.

Here is the code I used to create the windows:

void DisplayTask (void *arg)
{
	unsigned int ctxId = *(unsigned int *)arg;

    SDL_Surface *fontSurface[2];
    SDL_Texture *fontTex[2];
    SDL_Surface *alteraSurface[2] = { NULL, NULL };
    SDL_Texture *alteraTex[2] = { NULL, NULL };

	printf("DisplayTask_SDL: started, context id = %d\n", ctxId );
    

    static SDL_Window *win[MAX_CONTEXT];
    static SDL_Renderer *ren[MAX_CONTEXT];
    static SDL_Texture *tex[MAX_CONTEXT] = { NULL, NULL };

    SDL_Color white = { 0xFF, 0xFF, 0xFF, 0 };


        win[ctxId] = SDL_CreateWindow ("Altera HEVC Demo", 0, 0, WIDTH, HEIGHT, SDL_WINDOW_SHOWN);


    if (win[ctxId] == NULL)
    {

        printf ("Can't create window\n");
        SDL_Quit ();

        exit (-1);
    }

    ren[ctxId] = SDL_CreateRenderer (win[ctxId], -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC);

    if (ren[ctxId] == NULL)
    {
        printf ("Can't create renderer\n");
        SDL_DestroyWindow (win[ctxId]);
        SDL_Quit ();
        exit (-1);
    }

    tex[ctxId] = SDL_CreateTexture (ren[ctxId], SDL_PIXELFORMAT_YV12, SDL_TEXTUREACCESS_STREAMING, WIDTH, HEIGHT);

    if (!tex[ctxId])
    {
        printf ("Tex create failed ror %p\n", ren[ctxId]);
        exit (-2);
    }

...
}


I have a separate thread that is doing this:


void *SDL_InputThread( void *arg )
{
	static SDL_Event event;

        sem_wait (&inputSem );

	SDL_ShowCursor (0);

	memset( &event, 0, sizeof( SDL_Event ));

	while(bRunning) 
	{
		if (SDL_PollEvent (&event))	// only do this for 1 context
		{
		    switch (event.type)
		    {