the problem is that waitpid exits (with -1) the moment the Alarm handler is executed
That's not a problem, it's a feature :) If you install a handler for a signal, and the handler gets invoked during interruptible system call (waitpid is interruptible), the system call fails with errno ($! in Perl) set to EINTR.

So you can install a handler for SIGINT, and abort waiting by pressing Control-C instead of 'A'. Then check if $! equals POSIX::EINTR.

If you must use 'A' rather than Control-C, you can use POSIX::Termios to change the interrupt character. Something like that (maybe there is a better way, but it should at least give you some food for thought): 
use strict;
use warnings;

use POSIX ();

my $new_interrupt_char = 'A';
my $seconds_to_sleep   = 5;

if ( POSIX::isatty( POSIX::STDIN_FILENO ) ) {

    my $term = POSIX::Termios->new();
    $term->getattr( POSIX::STDIN_FILENO );
    my $old_interrupt_char = $term->getcc( POSIX::VINTR );
    $term->setcc( POSIX::VINTR, ord $new_interrupt_char );
    $term->setattr( POSIX::STDIN_FILENO );
    END {
        # restore the interrupt char to default (Control-C)
        if ( defined $term ) {
            $term->setcc( POSIX::VINTR, $old_interrupt_char );
            $term->setattr( POSIX::STDIN_FILENO );
        }
    }
}

$SIG{INT} = sub {
    print "SIGINT handler called\n";
};

my $slept = sleep $seconds_to_sleep;   # use waitpid instead of sleep
if ( $slept != $seconds_to_sleep and $! == POSIX::EINTR ) {
    print "Sleep was interrupted, slept $slept secs\n";
}

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In reply to Re: Allowing user to abort waitpid by Anonymous Monk
in thread Allowing user to abort waitpid by lab007

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