[winGRASS] Re: [GRASS5] Windows native Xdriver

[Glynn Clements]

Mike Thomas wrote:

> > > As /dev doesn't exist on my computer, this wonn't work for me (and I suspect
> > > many Cygwin users).
> >
> > Cygwin implements device files such as /dev/tty, /dev/null and
> > /dev/windows internally. Try "ls -l /dev/windows"; it works, even
> > though there isn't a /dev/directory.
> 
> Spot on, thanks.  I appreciate your patient technical explanations - my
> personal programming preferences lie far away from the world of sockets and
> Unix emulation on Windows!
> 
> Getting back to your earlier request for feedback on Windows NT, using:
> 
>     fd = open ("/dev/windows", O_NONBLOCK, 0);
> 
> on my Windows XP computer is an improvement as it allows 3 Xdriver window
> refreshes (generated by covering and then uncovering the window with the
> Grass console window) before the XDriver degenerates into the buffered event
> behaviour described earlier.
> .
> This is probably being caused by the repeated opening using up some internal
> fd buffer - caching the fd by making it static cures the problem:
> 
> -------------------------------------------------------------------
> int
> XConnectionNumber(Display* display)
> {
>  static int fd = 0;
>  NT_debug ("XConnectionNumber\n");
>  if ( 0 == fd ) {
>    fd = open ("/dev/windows", O_NONBLOCK, 0);
>    if ( -1 == fd ) {
>      NT_log ("XConnectionNumber unable to open /dev/windows, errno = %d\n",
> errno);
>    }
>  }
>  return ( fd );
> }
> -------------------------------------------------------------------

Aha!

Technically, a better solution would be to do the above in
XOpenDisplay, and store the descriptor in "display->fd". Then,
XConnectionNumber() would become:

	int XConnectionNumber(Display* display)
	{
		return display->fd;
	}

which is basically the definition used by X proper. Actually, in X,
its the other way around:

lib/X11/Macros.c:
	int XConnectionNumber(dpy) Display *dpy; { return (ConnectionNumber(dpy)); }

lib/X11/Xlib.h:
	#define ConnectionNumber(dpy) 	(((_XPrivDisplay)dpy)->fd)

> This, of course assumes that nobody will close the fd.  Is that likely?

Yes. Under X, closing the descriptor which is returned from
XConnectionNumber() would close the connection to the X server, which
would usually be fatal for the client.

-- 
Glynn Clements <glynn.clements at virgin.net>