I am forking a process and need to wait for it to complete, but also need to let the user hit A to abort at any time. My Perl skills are quite limited. Environment: RH 3 (legacy server, with Perl 5.8.0).

I have tried to use an Alarm handler to check for keyboard input every second, so that I can kill the child pid from there if the user presses A, but the problem is that waitpid exits (with -1) the moment the Alarm handler is executed (without any keyboard input, and without executing the kill statement).

Below is a sample to illustrate the issue.

Help would be much appreciated!

#!/usr/bin/perl

use strict;
use Term::ReadKey;

$SIG{ALRM} = "AlarmHandler";

my $childPid = fork();
die unless defined($childPid);
if ( ! $childPid ) {
    # in child
    sleep 10;
    exit 0;
}

# in parent
print "\nPlease do xyz (or hit A to abort).\n";
alarm (1); # Check for keystroke every second
if (waitpid($childPid, 0) > 0) {
    my ($rc, $sig, $core) = ($? >> 8, $? & 127, $? & 128);
    if ($core) {
        print "PID $childPid dumped core\n";
    } elsif ($sig == 9){
        print "PID $childPid was killed!\n";
    } else {
        print "PID $childPid returned $rc";
    }
} else {
    print "Where did PID $childPid go??"; # When AlarmHandler runs, wa
+itpid exits with -1, so gets here.
}
alarm (0);                
exit 0;

sub AlarmHandler()
{ 
    open(TTY, "</dev/tty") or die "Failed to open /dev/tty: $!";
    my $input = ReadLine -1, *TTY;
    if ($input ne "") {
        if ($input =~ /a.*/i) {
            print "\n\rAborting xyz\n\r";
            kill $childPid;
        }
    }
    close(TTY) or die "Failed to close /dev/tty: $!";
    alarm (1); # set alarm again
}

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In reply to Allowing user to abort waitpid by lab007

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