++zaxo - Wonderfully useful still these many years later!

I continue to be confused by the select... while kill $ppid, 0; even with the note about it in the description. Can someone elaborate some more to help me understand better?

Here is my modified version of the original code. I ended up making it more verbose, and added additional code for the parent to manage the children.

Please feel free to comment or suggest improvements!

Thanks

-Craig

#!/usr/bin/perl
use warnings;
use strict;

use Data::Dumper;

$::DEBUG = 1;        # 0=off

my $DKID;        # Daemon kid PID
my %CKIDS;        # Client kids PIDs

# Make a pipe (in/out filehandles are parent's process id)...
my ($ppid, $in, $out) = $$;
pipe ($in, $out) or die $!;

print STDERR "Parent is $ppid\n";

##################
# spawn daemon kid
##################
{
    local $|=1;

    # Fork daemon child...
    my $child;
    defined($child = fork) or die $!;

    # Parent & kid sort themselves out...
    if($child) {
        print STDERR "daemon child is $child\n" if $::DEBUG;
        $DKID=$child;
        last;
    }

    # Kid code...
    print STDERR "I am Daemon child $$\n" if $::DEBUG;
    close $out or die $!;    # deamon kid does not write, only reads

    # Daemon reads input side of pipe, forever...
    while (<$in>){
        #print "Daemon got: $_";
        print ".";
    }
    exit 0;
}

###################
# spawn client kids
###################
{
    select($out); local $|=1;

    # Spawn 10 client kids...
    for my $kid (1..10) {
        # Fork kid...
        my $child;
        defined($child = fork) or die $!;
    
        # Parent & kid sort themselves out...
        if($child) {        # Parent
            $CKIDS{$child} = $kid;
            next;        # Parent moves on
        }
        # Kid code...
        print STDERR "I am client child $$\n" if $::DEBUG;
        close $in;    # client kid does not read, only writes

        # Print out messages at random times...
        select(undef, undef, undef, rand(1000)/1000),
          print 'Child ', $kid,
            ' pid=', $$,
            ' message=', 0 | rand 10000,
            "\n"
          for 1..10;
        exit 0;
    }
}

#############
# Manage kids
#############

print STDERR "CKIDS DUMP:\n", Dumper(\%CKIDS), "\n" if $::DEBUG;

# Watch kids until all are gone...
my $ret;
while ( ($ret = waitpid(-1, 0)) > 0 ) {
    # Handle dead kid...
    print STDERR "\nPARENT: Child ret=$ret status: $?\n" if $::DEBUG;
    my $exit_value = $? >>8;
    my $signal_num = $? & 127;
    my $dumped_core = $? & 128;
    print STDERR "PARENT: Child exit=$exit_value, sig=$signal_num,
        core=$dumped_core\n" if $::DEBUG;

    # Remove from list if client kid...
    delete($CKIDS{$ret});
    print STDERR "CKIDS DUMP:\n", Dumper(\%CKIDS), "\n" if $::DEBUG;

    # If no more client kids, kill daemon kid...
    if(scalar(keys(%CKIDS)) <= 0) {
        # Will repeatadly hit this code if daemon kid doesn't die...
        print STDERR "All client kids gone, killing daemon kid...\n" i
+f $::DEBUG;
        kill('HUP', $DKID);
    }
}
print STDERR "PARENT: All kids gone, exiting\n";
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