jbryan has asked for the wisdom of the Perl Monks concerning the following question:

Silly me - I forgot to import File::Touch. So when I added line 85 (as seen here) my script did not exit with an "Undefined subroutine" error (as perl -e 'touch("/tmp/test")' does) - no, it rudely crashes my entire friggin X server!

The question is: why? And what am I really calling when I call touch() if I didn't use File::Touch? (The next rev on that file linked above does use File::Touch - and, wonder of wonders, X doesn't crash.) But the question remains - why in the world does calling touch() without File::Touch being used cause X to crash? (This crash happens on two different machines, both running CentOS, both running NVidia display drivers.)

My program works now that I use File::Touch, the emergency is over - now I'm just mad - mad that something simple like that causes X to crash - with no rhyme or reason, no messages in /var/log/messages, /var/log/Xorg*.log - nothing. Like I said, this is more personal pride at figuring out why than a need to fix it - the program works, now I want to know why it broke to begin with. Any pointers, wise monks?

Replies are listed 'Best First'.
Re: touch() crashes Xorg
by irirgem (Novice) on Sep 29, 2012 at 03:55 UTC
    Interesting question
    I don't have a direct answer, but do have some ideas...

    File::Touch uses the following sub to do the work: 
        if (-e $file){
        my $sb = stat($file) or croak("Could not stat ($file): $!");
        $atime = $sb->atime;
        $mtime = $sb->mtime;
    } else {
        unless ($self->{_no_create}){
        sysopen my $fh,$file,$SYSOPEN_MODE or croak("Can't create $fil
+e : $!");
        close $fh or croak("Can't close $file : $!");
        $atime = $time;
        $mtime = $time;
        }
    }

    [download]
    ExtUtils::Command uses: 
    sub touch {
    my $t    = time;
    expand_wildcards();
    foreach my $file (@ARGV) {
        open(FILE,">>$file") || die "Cannot write $file:$!";
        close(FILE);
        utime($t,$t,$file);
    }
}

    [download]
    However I can't seem to find what touch() is being used in the case above, but as you can see, the two modules above use a different method to do the work... maybe in that lies the mystery.
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      Interesting - thanks for showing that code. However, as far as I know, until I added 'use File::Touch', neither of those modules were in use - and nothing (that I know of) should have exported a symbol called 'touch' into my namespace.

      I guess the question might be - is there some debug/devel tool that I can use to tell me what I would call if I called touch in that context? E.g. perhaps the source file that the symbol originates from?

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Re: touch() crashes Xorg
by Anonymous Monk on Sep 29, 2012 at 06:25 UTC

    calling touch() without File::Touch being used cause X to crash?

    Because you have bad RAM? Ancient unsupported perl version? Ancient unsupported OS version? Something else?

    Crash isn't specific enough :)

[reply]

      You're absolutely right - crash is not specific enough. My apologies. To be specific, I have no logs that show any details of the "crash" as I call it - I can only tell you exactly what I observe.

      1. I run my script (perl tests/propogate.t)
      2. Script starts (output on STDOUT observed)
      3. Entire display goes black
      4. NVIDIA logo appears (using nvidia drivers)
      5. Gnome login manager appears, prompting me to login
      6. I login to Gnome again, open konsole and cd to devel directory again
      7. Go back to 1 - process is 100% repeatable

      A couple of notes:

      • To find out that it was the call to touch() causing the crash, I reverted to previous rev of the file and re-added in lines one-by-one till the "crash" occurred
      • This occurs on a quite-recent version of Perl (5.10.1)
      • This happens not just on this machine, but on two other machines at exactly the same spot. (The only commonality I can find is all three use "name-brand" NVIDIA display drivers. All three run CentOS, but each a slightly different version. All CentOS versions > 5.1)

      If it was just one machine, I might submit to the bad RAM theory - but three machines, all in the same spot? (Two desktops, one laptop.)

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        Can you post a small script that reproduces the error? That might help us to see what the issue is, or at least to be able to reproduce it.

        --MidLifeXis

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Re: touch() crashes Xorg
by Anonymous Monk on Sep 29, 2012 at 16:02 UTC
    Lacking log, have you run tried getting output via ktrace (in FreeBSD at least), ltrace, strace, trace-cmd, truss, and the like?
[reply]
      My knowledge and awareness of such commands is limited at best. I shall go forth and Google. Thanks for the arrow toward enlightenment, mate!
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