Re^3: Closing socket handle of child process (complicated?)

Thank you for your reply, I didn't post the entire code as I didn't want to take up too much space, instead of posting the entire daemon code, I thought it might be better to post the code for the helper program. This program (helper) acts as an intermediary between my Perl TK program and a forking server which accepts connection requests from helper. helper also has a bidirectional pipe connected to communicate with the TK program. My aim is to send a text command to the helper such as Close_Server which when detected would close the socket connection with the forking server. The problem was that due to blocking I couldnt implement listening to STDIN (this is the piped output from TK program) and listening to the socket in the same while loop without using select (as you suggest). I've tried to use fork which works great but killing the child process does not close the socket, the data still keeps coming through. The only way to stop this is by killing the entire process.

#!/usr/bin/perl
#
#  IP administrator helper.
#

use 5.005;
use IPADM;
use IO::Socket;
use strict;
use vars qw/$sock/;

do {print "Usage:  helper host port\n"; exit} unless @ARGV == 2;
my $neighbourSocket = join ":", $ARGV[0], $ARGV[1];
my $int_count;

#Flush back to parent
STDOUT->autoflush(1);           # unbuffer output

$SIG{PIPE} = sub {print "2 Pipe Error.\n$EOF\n"; exit;};
$SIG{TERM} = sub {exit; };
#ignore child processes to prevent zombies
$SIG{CHLD} = 'IGNORE';

my $sock = IO::Socket::INET->new( PeerAddr => $ARGV[0],
          Proto => 'tcp', PeerPort => $ARGV[1]);
print +((defined $sock) ? "0 Connect OK:$$" : "3 Connect Failed:$$"), 
+"\n$EOF\n";

my $kidpid;
    # split the program into two processes, identical twins
    die "can't fork: $!" unless defined($kidpid = fork());    
    # if parent
    if ($kidpid) {                      
            # parent copies the socket to standard output
        #Read from parent (STDIN), this is received from TK program vi
+a a pipe
            while(<STDIN>) {
            # if the close server command from TK program is detected,
+ break from loop            
            last if /Close_Server/;
            }
        # kill the child process
        kill("TERM" => $kidpid);        
    }
    # if child
    else {
        # Loop forever until socket is closed (I cant close it!!)
        while (1) {
            # Create array to collect output from server
                my(@data) = ();
            # Add the addressing information to start of array
                push @data, "$neighbourSocket\n";    
            #collect data from daemon until EOF is reached, at this po
+int it can be piped back to TK program
                while (<$sock>) {    
                push @data, $_;        # accumulate command's reply
                last if /^$EOF$/;
                    }
           # Catch daemon failure, send output back to TK program for 
+processing
            print (/^$EOF$/ ? @data : "4 Daemon Failure\n$EOF\n");
        } # whilend
    }
close $sock;
exit;
[download]

Any guidance would be much appreciated, Paul

Comment on Re^3: Closing socket handle of child process (complicated?) Download Code

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Re^4: Closing socket handle of child process (shutdown, %SIG) by tye (Sage) on Jan 03, 2012 at 16:33 UTC
You could have the parent call shutdown: `while( <$connection> ) { last if /Close_Server/; } kill( "TERM" => $kidpid ); shutdown( $connection, 1 ); # we should stop writing to socket` [download] That might cause the child to get a "RESET" response if it continues to write after that point (which should cause the TCP stack to refuse to forward future write requests, even if the program ignored the failure and continued to try to write data). But it might just be that the child is ignoring SIGTERM. You could set up a $SIG{TERM} handler in hopes of preventing that problem. I recall that children ignore the signals that their parents were ignoring. But I'm surprised to not find documentation of that fact right now. I think that setting $SIG{TERM} would override that but I have a nagging doubt about that. - tye	[reply] [d/l]

Replies are listed 'Best First'.

Re^4: Closing socket handle of child process (shutdown, %SIG)
by tye (Sage) on Jan 03, 2012 at 16:33 UTC

You could have the parent call shutdown:

    while( <$connection> ) {
        last if /Close_Server/;
    }
    kill( "TERM" => $kidpid );
    shutdown( $connection, 1 ); # we should stop writing to socket
[download]

That might cause the child to get a "RESET" response if it continues to write after that point (which should cause the TCP stack to refuse to forward future write requests, even if the program ignored the failure and continued to try to write data).

But it might just be that the child is ignoring SIGTERM. You could set up a $SIG{TERM} handler in hopes of preventing that problem.

I recall that children ignore the signals that their parents were ignoring. But I'm surprised to not find documentation of that fact right now. I think that setting $SIG{TERM} would override that but I have a nagging doubt about that.

- tye

[reply]
[d/l]