[Freeciv-Dev] Re: (PR#3391) SDL client polls the network

["Raimar Falke via RT" <rt@xxxxxxxxxxxxxx>]

On Tue, Feb 11, 2003 at 05:04:04PM -0800, Jason Short via RT wrote:
> 
> Currently the SDL client monitors the network connection by polling
> every 100 milliseconds for data.  This leads to a lot of lag in updates.
> 
> The correct thing to do is to get an interrupt or callback that is
> activated when network data is available.  This is what the other
> clients do (although it is possible that the underlying libraries just
> do polling, we would hope not).  However, in my brief research I don't
> see how to do this with SDL.  Is it possible that this functionality is
> not portable?  How could anyone ever program on a system that didn't
> provide this?

Rafal asked me yesterday the question. I searched a bit and found
nothing. The canonical solution looks like this:
 Thread 1:
    1) select on network input
    2) push an event in the SDL event queue
    3) goto 1)
 Thread 2:
    1) wait for SDL event queue
    2) act according to the event (mouse, network)
    3) goto 1)

The other is polling (see our current code).

I completely agree that this is a big design error in SDL.

Lets take a look 
(http://www.libsdl.org/cgi/cvsweb.cgi/SDL12/src/events/SDL_events.c?rev=1.9&content-type=text/x-cvsweb-markup):

/* Run the system dependent event loops */
void SDL_PumpEvents(void)
{
  if (!SDL_EventThread) {
    SDL_VideoDevice *video = current_video;
    SDL_VideoDevice *this  = current_video;

    /* Get events from the video subsystem */
    if (video) {
      video->PumpEvents(this);
    }

    /* Queue pending key-repeat events */
    SDL_CheckKeyRepeat();

#ifndef DISABLE_JOYSTICK
    /* Check for joystick state change */
    if (SDL_numjoysticks && (SDL_eventstate & SDL_JOYEVENTMASK)) {
      SDL_JoystickUpdate();
    }
#endif
  }
}

int SDL_WaitEvent(SDL_Event * event)
{
   while (1) {
      SDL_PumpEvents();
      switch (SDL_PeepEvents(event, 1, SDL_GETEVENT, SDL_ALLEVENTS)) {
        case -1: return 0;
        case 1:  return 1;
        case 0:  SDL_Delay(10);
      }
   }
}

So this is even worse. It has a built in polling every 10ms.

        Raimar

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