Re^2: How to tell a child what to do?

[Eyck]

You are surprisingly right,

I somehow always regarded

$pid = open(KID_TO_WRITE, "|-");

trick as a way to talk with only one child, but if we rewrite it like this:

$fh = new FileHandle;
my $sleep_count = 0;

do {
        $pid = open($fh, "|-");
        unless (defined $pid) {
                warn "cannot fork: $!";
                die "bailing out" if $sleep_count++ > 6;
                sleep 10;
        }
} until defined $pid;

my (@some_data)=qw[a be ce];
if ($pid) {
         print $fh @some_data;
         close($fh) || warn "kid exited $?";
} else {
        while (<STDIN>) {
                print "GOT: $_\n"; # child's STDIN is parent's KID
        }
        exit;  # don't forget this
};

then we get to hold whole array of different $fd's, each for talking with one child. This would be clean and reliable, exactly what I wanted.

Thanx.

[Eyck]

on second thought..this doesn't work that well with more then one fd open...it hangs on close($fd). Maybe there's an error in my code:

print "I'm $$\n;";
use FileHandle;

$fh = new FileHandle;
$fh1 = new FileHandle;
my $sleep_count = 0;

do {
        $pid = open($fh, "|-");
        unless (defined $pid) {
                warn "cannot fork: $!";
                die "bailing out" if $sleep_count++ > 6;
                sleep 10;
        }
} until defined $pid;
if ($pid) {
        print "I'm master($$) $pid...\n";
} else {
        print "Waiting for commands($$)..\n";
        while (<STDIN>) {
                print "GOT: $_\n"; # child's STDIN is parent's KID
        }
        exit;  # don't forget this
};


do {
        $pid1 = open($fh1, "|-");
        unless (defined $pid1) {
                warn "cannot fork: $!";
                die "bailing out" if $sleep_count++ > 6;
                sleep 10;
        }
} until defined $pid1;
if ($pid1) {
        print "I'm master($$) $pid1...\n";
} else {
        print "Waiting for commands($$)..\n";
        while (<STDIN>) {
                print "GOT: $_\n"; # child's STDIN is parent's KID
        }
        exit;  # don't forget this
};


my (@some_data)=qw[a be ce];
print "($$)PID: $pid\n";
print $fh @some_data;
print "($$) printing done, let's close:\n";
close($fh) || warn "kid exited $?";

print "($$)PID: $pid1\n";
print $fh1 @some_data;
print "($$) printing done, let's close:\n";
close($fh1) || warn "kid exited $?";


print "END FH TEST\n\n\n";

[Anonymous Monk]

I wrote it slightly differently, and it seems to work for me:

#!/usr/bin/perl

use strict;
use warnings;

print "I'm the master ($$)\n";

my %pids;
my $children = 2;

for my $x (1 .. $children) {
    my ($fh, $pid);
    my $tries = 6;
    do {$pid = open $fh, "|-";
        unless (defined $pid) {
            warn "fork: $!\n";
            die "bailing out" unless $tries--; 
            sleep 5;
        }
    } until defined $pid;
    if ($pid) {
        print "I'm master ($$) of child ($pid)\n";
        $pids {$pid} = $fh;
    }
    else {
        printf "I'm a child ($$) of master (%d)\n", getppid;
        while (<>) {
            chomp;
            printf "Child ($$) received: [%s]\n", $_;
        }
        print "Child ($$) exiting\n";
        exit;
    }
}
my $count = 0;
while (my ($pid, $fh) = each %pids) {
    my $data = sprintf "[[%02d]]", ++$count;
    printf "Sending data %s to child (%d)\n", $data, $pid;
    print $fh $data, "\n";
}
while (my ($pid, $fh) = each %pids) {
    printf "Closing handle to child (%d)\n", $pid;
    close $fh or warn "Failed to close handle for child ($pid)\n";
}
    
print "Last line\n";

__END__
I'm the master (19054)
I'm a child (19055) of master (19054)
I'm master (19054) of child (19055)
I'm a child (19056) of master (19054)
I'm master (19054) of child (19056)
Sending data [[01]] to child (19056)
Sending data [[02]] to child (19055)
Closing handle to child (19056)
Child (19056) received: [[[01]]]
Child (19056) exiting
Closing handle to child (19055)
Child (19055) received: [[[02]]]
Child (19055) exiting
Last line

[Eyck]

Great. This is perfect.

However, I don't know why my version fails, which worries me.

Thanks again, I've got enough to tinker with now.