Re^2: getting data to a signal handler

I figured out something that doesn't SEEM to use globals, but it probably does something much worse...

Run this and hit CTRL-C, it will print how many seconds it thinks it's been running

#! /usr/bin/perl -w -T

use strict;

my $var;

($var,$SIG{INT}) = voodoo();

sub voodoo {
        my $thing ;
        my $sub = sub {
                my $blob = \$thing;
                print $$blob."\n";
                exit;
        };
        return (\$thing,$sub);
}

for (my $i=0; $i<60 ;$i++) {
        $$var = $i;
        sleep 1;
}
[download]

Let me know what sort of terrible thing I've done...

Comment on Re^2: getting data to a signal handler Download Code

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Re^3: getting data to a signal handler by Zaxo (Archbishop) on Nov 19, 2005 at 03:13 UTC
You're forming a closure on $thing, as well as returning a reference to it. `voodoo()` indeed! One nice way to pretend you don't have a global variable when you do (I've talked about this one before): `{ my $foo; sub foo () :lvalue { $foo } } foo = 'bar'; print foo, $/;` [download] No sigil, that makes some people happy ;-) After Compline, Zaxo	[reply] [d/l]
Re: getting data to a signal handler by jonadab (Parson) on Nov 19, 2005 at 12:32 UTC
In general, lexical closures are a handy and useful technique, but I'm not entirely sure what interesting edge cases will emerge if you combine them with signal handlers. I wouldn't care to speculate on that without understanding the nittier and grittier details of how signal handlers are handled. What I would do is name the global in a fashion that prevents it from ever having a namespace collision and then just leave it global. For instance, I might call it something like $SIGINT_HANDLER_GLOBAL_ONE_FOR_NET_SERVER_POP3 (if it were the first global variable for the interrupt signal handler for Net::Server::POP3; as it happens that module doesn't have any such thing, but you get the idea).	[reply]