Perl: eval timer in while

Question

I try to achieve a timer with several loops as below

while ( $try < 3) {
    eval {
        local $SIG{ALRM} = {};
        alarm 3;
        $ret = # sending request and wait for response
        alarm 0;
    }
    last if defined($ret);
    $try++;
}

But actually, when the alarm expired, the whole 'while' loop got interrupted, and the loop didn't happen at all.

Where I got the thing wrong?

Miller · Accepted Answer · 2014-03-20 00:57:02Z

1

You need to set an ALRM Handler, just like the alarm docs demonstrate:

for (1..3) {    
    print "Loop $_\n";

    eval {
        local $SIG{ALRM} = sub { die "alarm\n" };
        alarm 5;

        my $count = int rand 10;
        print "Is $count < 5?\n"; 
        sleep $count;

        alarm 0; #cancel the alarm if does not hang
    };

    if ($@) {
        die unless $@ eq "alarm\n";   # propagate unexpected errors
    } else {
        print "Our code succeeded\n";
        last;
    }
}

edited Mar 20, 2014 at 0:57

answered Mar 20, 2014 at 0:46

Miller

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4 Comments

Yang Over a year ago

I wrote a handler at first time, but looked not working either. I'll try it again.

Miller Over a year ago

What I've demonstrated should work just fine. Can even just copy/paste this into a script to confirm before trying to integrate it into your code.

Yang Over a year ago

Yes, thanks. I used "timeout\n" instead of "alarm\n". After I changed to "alarm\n", everything is working. Thanks. So for my dumb, "alarm\n" looks quite fixed.

Yang Over a year ago

En, not exactly the case about 'alarm\n'. I found '$@' is not certain in my case, so when I tried to check the output of the exception, it always dies. I guess in my context (some super class or something else) throw some output at the same time to make '$@' not certain.

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