> perl -v 
5.8.4
[download]

Dear monks, On a production system where updates to Perl versions are not possible, I came across this SIG{ALRM} robber. Yes, dear monks, LWP stands accused. My question: can I go to bed with this robber?

Consider this code:

 eval {
        local $SIG{ALRM} = sub { die "Network Timeout/Error\n" };
        alarm($maxNetworkDelay);
        $ip=URL_encode($ip);
        $encodedMAC=URL_encode($mac);
        my $macr="https://somescript/login;
        $request = HTTP::Request->new(GET => $macr);
        $ua = LWP::UserAgent->new( timeout =>  $maxNetworkDelay );
        $response = $ua->request($request);
        $respcon = $response->content;
        alarm(0);
    };
<strike>
    if($@){
        ilog("Network Delay/Error for .");
        return (-1);
    }#
</strike>

    if($response->status_line =~ /^500/ ){
        ilog("Network Delay/Error for .");
        return (-1);
    }
[download]

I have read whatever there is publicly and from what I understood, decided to write the above since DNS errors/network latency/wrong domain name are _ALL_ trapped by the above code.

As you can see, when using eval with LWP, _your_ error catching mechanism ( the parts struck out ) will not work since LWP internally has a mechanism of its own. What we can test, however is whether LWP has caught the alarm I have triggered.

I am seeking to understand the what is going on. The above code works all the time to satisfaction. My questions are:

1. It looks like a process can have only one SIG{ALRM}

2. An alarm set is caught by the whatever alarm handling mechanism that is in scope - in our case, the alarm handling mechanism in LWP.

3. Once caught. $@ is read, handled, and reset.

4. Finally,do the monks approve of this?

---

In reply to The curious case of LWP - the SIG{ALRM} robber by MonkeyMonk

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