#!/bin/env perl

use 5.010;
use warnings;
use strict;
use Carp;
use File::Basename;
use IO::Socket;
use IO::Select;
use IO::File;                   
use POSIX qw{WNOHANG setsid};   
use POSIX qw{SIGHUP SIGTERM SIGUSR1};

my $sigset = POSIX::SigSet->new();

# SIGCHLD (17) child-process ended
#
my $CHLDaction
  = POSIX::SigAction->new( 'sigCHLD_handler', $sigset, &POSIX::SA_NODEFER );
POSIX::sigaction( &POSIX::SIGCHLD, $CHLDaction );

sub sigCHLD_handler {
    say "Enter sigCHLD handler";
}

say "Perl version: $^V";

my $active_readers = 0;
my $current_reader_limit = 10;

while (1) {
    if ($active_readers < $current_reader_limit) {
        # Launch enough new readers to bring us up to the current limit
        while ($active_readers < $current_reader_limit) {
            ++$active_readers;
            
            my $service_pid;
            if ( !defined( $service_pid = fork ) ) {
                say "Couldn't fork. Exit.";
                exit;
            }
            
            # CHILD process
            #
            elsif ( 0 == $service_pid ) {
                my $command = "echo Hello from child $active_readers " . 'pid $$';
                exec $command;
            }
            # PARENT process
            say "Spawned child $active_readers pid $service_pid"
        }
    }

    sleep;
    say "Out of sleep, begin reaping";
    while ( ( my $kid = waitpid( -1, WNOHANG ) ) > 0 ) {
        --$active_readers;
        say "Reaping child process $kid, active readers now $active_readers";
    }
    say "Finished reaping";
}

##</code><code>##

$ tom_strip
Perl version: v5.16.2
Spawned child 1 pid 18734
Spawned child 2 pid 18735
Spawned child 3 pid 18736
Spawned child 4 pid 18737
Spawned child 5 pid 18738
Spawned child 6 pid 18739
Spawned child 7 pid 18740
Spawned child 8 pid 18741
Spawned child 9 pid 18742
Spawned child 10 pid 18743
Hello from child 1 pid 18734
Enter sigCHLD handler
Out of sleep, begin reaping
Hello from child 2 pid 18735
Reaping child process 18734, active readers now 9
Finished reaping
Hello from child 3 pid 18736
Enter sigCHLD handler
Hello from child 4 pid 18737
Enter sigCHLD handler
Hello from child 5 pid 18738
Enter sigCHLD handler
Hello from child 6 pid 18739
Enter sigCHLD handler
Enter sigCHLD handler
Hello from child 7 pid 18740
Enter sigCHLD handler
Hello from child 9 pid 18742
Hello from child 8 pid 18741
Hello from child 10 pid 18743
Hello from child 10 pid 18748