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

by Eyck (Priest)
on Sep 21, 2005 at 10:12 UTC ( #493713=note: print w/ replies, xml ) Need Help??


in reply to Re: How to tell a child what to do?
in thread How to tell a child what to do?

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.


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Re^3: How to tell a child what to do?
by Eyck (Priest) on Sep 21, 2005 at 10:36 UTC
    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 "($$) printing done, let's close:\n"; close($fh1) || warn "kid exited $?"; print "END FH TEST\n\n\n";
      I wrote it slightly differently, and it seems to work for me:
      #!/usr/bin/perl use strict; use warnings; print "I'm the master ($$)\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

        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.

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