[aklug] Re: SPUG: Pull out of a blocking subroutine?

From: Christopher Howard <choward@indicium.us>
Date: Mon Jan 11 2010 - 17:11:55 AKST

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Skylos wrote:
> Sure.
>
> http://www.sdsc.edu/~moreland/courses/IntroPerl/docs/manual/pod/perlfunc/alarm.html
>
> eval {
> local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
> alarm $timeout;
> $nread = sysread SOCKET, $buffer, $size;
> alarm 0;
> };
> if ($@) {
> die unless $@ eq "alarm\n"; # propagate unexpected errors
> # timed out
> }
> else {
> # didn't
> }
>
> Skylos
>
> "If only I could get rid of hunger by rubbing my belly" - Diogenes
>
>
> On Mon, Jan 11, 2010 at 5:27 PM, Christopher Howard <choward@indicium.us
> <mailto:choward@indicium.us>> wrote:
>
> Hi. I'm still working on integrating LEGO::NXT into my project. Problem
> I've hit though is that apparently there are no actual functions for
> checking communication status with the robot.
>
> There is other function I thought I could use to detect (implicitly) if
> communication is still established. Problem is that they are /all/
> blocking. Documentation basically says that the author hasn't got around
> to making non-blocking functions yet, and I don't really have time to
> reprogram his module myself.
>
> So, my perverted, evil question: Is there some hackish way to pull out
> of a blocking subroutine? Say, if it has returned after three seconds or
> something like that?
>
> --
> Christopher Howard
> http://indicium.us
> http://theologia.indicium.us
> http://robots.arsc.edu
>
>
> _____________________________________________________________
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>
>

This sounds like exactly what I need, but it doesn't seem to be working.
 It still freezes at the call to Does it make any difference that I am
not making a simple system call, but instead a call to a function in a
module?

while(1)
{
    eval {

        local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required

        alarm 5;
        # $Scoop_a is my robot object

        $ret =
$Scoop_a->nxt->get_battery_level($LEGO::NXT::Constants::NXT_RET);
        alarm 0;
    };
    if ($@) {
        die unless $@ eq "alarm\n"; # propagate unexpected errors

        # timed out

    }
    else {
        # didn't

    }
    print "We made it through!";
    sleep 2;
}

- --
Christopher Howard
http://indicium.us
http://theologia.indicium.us
http://robots.arsc.edu
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Received on Mon Jan 11 17:13:57 2010

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