Message Passing b/w processes , that works both in windows and Linux

shijumic has asked for the wisdom of the Perl Monks concerning the following question:

Hi,
I was trying to write a perl script that creates a number of child processes, and try to communicate b/w parent and child processes using pipes instead of socketpair. I wrote a script to communicate b/w processes bidirectionally using pipes ,but it doesn't work as intended, Would someone take a look at the following script and tell me what I'm doing wrong here.
Since I need to run the same script in windows,I think I can't use socketpair like below for bidirectional communication rt?

socketpair(CHILD, PARENT, AF_UNIX, SOCK_STREAM, PF_UNSPEC)
                                or  die "socketpair: $!";
[download]

or Is there any perl module that has effective methods of message passing b/w processes.
Any help would be greatly appreciated..
Thanks,
Shijumic..


#!/usr/bin/perl -w
    # pipe1 - bidirectional communication using two pipe pairs
    #         designed for the socketpair-challenged

    use IO::Handle;

    pipe(PARENT_RDR, CHILD_WTR);
    pipe(CHILD_RDR,  PARENT_WTR);

    CHILD_WTR->autoflush(1);
    PARENT_WTR->autoflush(1);

    if ($pid = fork) {

       close PARENT_RDR; close PARENT_WTR;

       send_message(CHILD_WTR,HELLO,1234);

       my ($code1,$msg1) = receive_message(CHILD_RDR);
       print "Parent Received:" . $code1 . "\t" . $msg1 . "\n";

       close CHILD_RDR; close CHILD_WTR;

       waitpid($pid,0);
    }
    else {

        die "cannot fork: $!" unless defined $pid;
        close CHILD_RDR; close CHILD_WTR;

        my ($code,$msg) = receive_message(PARENT_RDR);

        print "Child Received:" . $code . "\t" . $msg . "\n";

        send_message(PARENT_WTR,Hi,1234);

       close PARENT_RDR; close PARENT_WTR;
       exit;

    }


    sub send_message {

     my $handle  = shift;
     my $code    = shift;
     my $msg   = shift;

     $message = join(':' , $code,$msg);

     print $handle $message;

    }

   sub receive_message {

      my $handle = shift;
      my $msg;

      chomp($msg = <$handle>);

      ($code,$msg) = split (/:/,$msg);

      return ($code,$msg);
    }
[download]

Comment on Message Passing b/w processes , that works both in windows and Linux Select or Download Code

Replies are listed 'Best First'.
Re: Message Passing b/w processes , that works both in windows and Linux by ikegami (Patriarch) on Jun 08, 2009 at 22:02 UTC
For starters, `fork` creates a thread (not a process) in Windows. Is that a problem? I wrote a script to communicate b/w processes bidirectionally using pipes ,but it doesn't work as intended The script you posted runs on neither linux nor Windows until you fix the issue with reading until a newline is encountered when none is sent. Then, it works fine on both linux and Windows. Since I need to run the same script in windows,I think I can't use socketpair like below for bidirectional communication rt? I'm pretty sure you can, but you might have to change from `AF_UNIX` to `AF_INET`.	[reply] [d/l] [select]
Re^2: Message Passing b/w processes , that works both in windows and Linux by shijumic (Novice) on Jun 08, 2009 at 22:45 UTC
Thanks much for your rely. Would you please explain me,how to fix the issue with reading until a newline is encountered when none is sent in the above script. Thanks -Shijumic	[reply]
Re^3: Message Passing b/w processes , that works both in windows and Linux (read) by tye (Sage) on Jun 09, 2009 at 00:25 UTC
You use read($sock) not `<$sock>` (or sysread or recv). Note that you might also run into the problem I was able to work around at Re^2: ActiveState woes : Is it EOF-blind? (perl bug). And you probably want to replace fork with either Win32::Process::Create( $^X, qq(perl "$0" ...), ... ) or `system( 1, $^X, $0, ... )` (this Win32-specific use of system is documented in perlport). So write a wrapper that uses fork if not on Win32. - tye	[reply] [d/l] [select]
Re^4: Message Passing b/w processes , that works both in windows and Linux (read) by ikegami (Patriarch) on Jun 09, 2009 at 01:24 UTC
Re^5: Message Passing b/w processes , that works both in windows and Linux (newlines) by tye (Sage) on Jun 09, 2009 at 01:58 UTC
Re^3: Message Passing b/w processes , that works both in windows and Linux by ikegami (Patriarch) on Jun 09, 2009 at 00:10 UTC
Since the readers are waiting for a newline, I sent one by changing `print $handle $message;` to `print $handle "$message\n";`	[reply] [d/l] [select]
Re: Message Passing b/w processes , that works both in windows and Linux by repellent (Priest) on Jun 09, 2009 at 18:14 UTC
I have been trying to do that with IPC::Exe, so please give it a try and let me know what you think. The module has quite a thorough test suite thrown at it. It's been a long effort but I know I can still improve on it.	[reply]