If I trigger an alarm, subsequent reading from a filedescriptor seems broken in an odd way :

$ ./alarmfail.pl 1
TIMEOUT=1
SLEEP=5

(sub1):begin_pos:0
#MAIN, a
#MAIN, b
#MAIN, c
(sub1):sleeping...
(sub1):timed_out!
(sub1):end_pos:52

(sub2):begin_pos:0
(sub2):end_pos:1

(sub2):begin_pos:0
(sub2):end_pos:1

Code works as expected when alarm isn't triggered :

$ ./alarmfail.pl 10
TIMEOUT=10
SLEEP=5

(sub1):begin_pos:0
#MAIN, a
#MAIN, b
#MAIN, c
(sub1):sleeping...
(sub1):end_pos:52

(sub2):begin_pos:0
#MAIN, a
#MAIN, b
#MAIN, c
(sub2):end_pos:52

(sub2):begin_pos:0
#MAIN, a
#MAIN, b
#MAIN, c
(sub2):end_pos:52

Note: The code is an example only, I'm unable to move the inline '#MAIN' tags to a __DATA__ section in my legacy codebase. So perhaps this is a quirk of opening a filehandle to the script itself?

#!/usr/bin/env perl
# Example code to show how reading from file descriptors fails after a
+n alarm is triggered?
use strict;
use warnings;

my $timeout = defined($ARGV[0]) ? $ARGV[0] : 2;
my $sleep = 5;
print "TIMEOUT=$timeout\n";
print "SLEEP=$sleep\n\n";

#MAIN, a
#MAIN, b
#MAIN, c

sub sub1 {
    open(FD1, "$0") or die "ERROR: Could not open $0 : $!\n";
    $. = defined($.) ? $. : 0;
    print "(sub1):begin_pos:$.\n";
    while (<FD1>){
        next if ! /^#MAIN|^#DATA/;
        print $_;
    }
    eval {
        local $SIG{ALRM} = sub { die "alarm\n"; };
        alarm $timeout;
        print "(sub1):sleeping...\n";
        my $cmd = `sleep $sleep 2>&1;echo slept`;
        alarm 0;
    };
    if ($@){
        print "(sub1):timed_out!\n";
    } else {
        # did not time out
    }
    print "(sub1):end_pos:$.\n\n";
    close FD1 or die "$!\n";
}

sub sub2 {
    open(FD2, "$0") or die "ERROR: Could not open $0 : $!\n";
    print "(sub2):begin_pos:$.\n";
    while (<FD2>){
        next if ! /^#MAIN|^#DATA/;
        print $_;
    }
    print "(sub2):end_pos:$.\n\n";
    close FD2 or die "$!\n";
}

&sub1;
&sub2;
&sub2;
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