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From: daniel@cs.UAlberta.CA (Daniel Lanovaz)
Newsgroups: comp.windows.x.motif
Subject: Re: XmUpdateDisplay fails
Message-ID: <1991Apr8.162933.21613@cs.UAlberta.CA>
Date: 8 Apr 91 16:29:33 GMT
References: <1991Apr5.153900.22674@athena.mit.edu> <20738@paperboy.OSF.ORG>
Sender: news@cs.UAlberta.CA (News Administrator)
Distribution: inet
Organization: University of Alberta, Edmonton, Canada
Lines: 63

In article <20738@paperboy.OSF.ORG> dbrooks@osf.org (David Brooks) writes:
>alice@athena.mit.edu (Timothy R Wall) writes:
>|> I use XmUpdateDisplay to refresh my application before starting a long
>|> load from disk and subsequent calculation.  Immediately after
>|> XmUpdateDisplay I call a routine to change the cursor, which calls
>|> XFlush; I see the cursor change, but no screen update.  What's wrong?
>
>This turns out not to be the case.  The server may have delivered the
>events, but the client hasn't received them yet.  There's a timing issue,
>which may (or not) involve the window manager, and some of us are looking
>into a better solution.  For now, you can try:
>
>	XSync(XtDisplay(toplevel), 0);
>	usleep(<some-number-found-empirically>);
>	XmUpdateDisplay(toplevel);
>
>where <some-number-found-empirically> on my workstation is 60000.

Is it possible to process events sent from the server while in a compute-
bound system module by having the events interrupt your process while it is
computing?  I have experimented with something like the following.  It seems
to work with the programs I use it in, but there may be problems I don't
see (for instance, what to do if the SIGIO interrupt was not generated by
the ConnectionNumber(Display) socket)?

    InstallEventHandler(topLevel);
    DoSomeVeryLongCalculation();
    RemoveEventHandler(topLevel);

    XEventHandler(/* Some parameters here */)
    {
        XEvent anEvent;

        while(XtPending()) {
            XtNextEvent(&anEvent);
            XtDispatchEvent(&anEvent);
        }
    }

    InstallEventHandler(Widget topLevel)
    {
        Display *theDisplay = XtDisplay(topLevel);
        int connectNumber   = ConnectionNumber(theDisplay);

        signal(SIGIO, XEventHandler);

        if (fcntl(connectionNumber, F_SETFL, FASYNC) < 0) {
            perror("Some error message");
            return ERROR_OF_SOME_SORT;
        }

        if (fcntl(connectionNumber, F_SETOWN, getpid()) < 0) {
            perror("Some error message");
            return ERROR_OF_SOME_SORT;
        }

        XFlush(theDisplay);

        return EVERTHING_WENT_OK;
    }

Daniel
daniel@cs.ualberta.ca