RE: how to interact with an endless loop

[Dirk Bremer]

> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On 
> Behalf Of Su,
> Yu (Eugene)
> Sent: Thursday, October 06, 2005 3:08 PM
> To: perl-win32-users@listserv.ActiveState.com
> Subject: RE: how to interact with an endless loop
> 
> Hi All,
> 
> I want to write a simple perl script to start an endless loop 
> (for reading
> data from a periphery device, such as a measurement unit), 
> but I also want
> to be able to stop it anytime. Right now I use "Ctrl-Alt-Del" 
> to do it.
> There must be a better way. I has been trying to use open, 
> pipe...not seem
> to understand how to use them.
> 

Let me suggest another method. This method would have several
advantages. Within your loop, at certain times, you would need to poll
by calling a sub similar to this

#-----------------------------------------------------------------------
---#
# Check for a socket connection and process commands.
#
#-----------------------------------------------------------------------
---#
sub Connection()
{
    use IO::Socket;
    my $Status;
    
    # Open a socket to listen and respond to connections.
    $Log->WriteLog("Opening socket connection",0) if DEBUG;
    my $Socket = IO::Socket::INET->new(LocalHost => $SocketServer,
                                       Listen    => 5,
                                       LocalPort => $Port,
                                       Proto     => 'tcp',
                                       Reuse     => 1,
                                       Timeout   => $Interval);
    unless($Socket) {$Log->WriteLog("A socket cannot be opened $!",1);
return(0)}
    
    $Log->WriteLog("Waiting for a connection",0) if DEBUG;

    # Process queue and program commands.
    SESSION: while ($Comm = $Socket->accept())
    {
        my $Command;
        $Status = 0;
        $Log->WriteLog("Session established",0) if DEBUG;
        while (<$Comm>)
        {
            chomp;
            $Command = substr($_,0,3);

            $Log->WriteLog("Monitor.pl received request $_",0);
            print($Comm "Monitor.pl received request \'$_\'\n");
            
            # End this connection if a 'end' command is received.
            if ($Command eq 'end') {print($Comm "command complete\n");
last SESSION}

            # Perform the Help subroutine if the 'help' command is
received.
            if ($Command eq 'hel')
            {
                Help(1);
                print($Comm "command complete\n");
                next;
            }

            # Show all set options and their values.
            if ($Command eq 'opt')
            {
                for (sort keys %Options) {print($Comm "Option -$_ =
$Options{$_}\n")}
                print($Comm "command complete\n");
                next;
            }

            # Exit this program if a 'term' command is received.
            if ($Command eq 'ter') {print($Comm "command complete\n");
$Status = 1; last SESSION}

            # Invalid command.
            print($Comm "Invalid command\n");
            print($Comm "command complete\n");
        }
    }

    # Close session.
    $Log->WriteLog("Session ended",0) if DEBUG;
    close($Comm) if (defined $Comm);

    # Close socket.
    $Log->WriteLog("Closing socket connection",0) if DEBUG;
    close($Socket)if (defined $Socket);
    
    # Destroy object references.
    $Comm   = undef;
    $Socket = undef;

    exit(1) if ($Status);
    return(1);
}

You then need a simple client program that will open a connection to
your endless-loop program and will send simple strings that will be
interpreted as commands. Advantages include that the socket connection
will time-out at the $Interval number of seconds and will then resume
your loop. You will be able to use the client program on another PC to
issue commands to the endless-loop program that is running on another
PC.

A simple client program:

#! C:/perl/bin/perl -w
# SocketClient.pl 05/17/2003.

# Declare pragmas.
use diagnostics;
use strict;
use warnings;

# Declare modules.
use FindBin qw($Bin);
use lib $Bin;
use IO::Socket;

my ($Port, $Server);
if (@ARGV) {$Server = shift}
else       {$Server = 'target_server_name'}
if (@ARGV) {$Port = shift}
else       {$Port = 80}
my ($Answer, $Socket);

SOCKET: while ()
{
    # Attempt to open a socket connection to the specified server on the
    # specified port.
    print("Opening a socket connection to server $Server on port
$Port\n");
    $Socket = IO::Socket::INET->new(PeerAddr => $Server, PeerPort =>
$Port, Proto => 'tcp');

    # If the connection cannot be opened, wait ten seconds and try
again.
    unless($Socket) {sleep(10); next}

    # Process the connection.
    while ()
    {
        # Prompt the user for a command string.
        print("\nEnter command string>");
        $_ = <STDIN>;
        chomp;

        # Exit this program based upon user input.
        last SOCKET if ($_ eq 'exit');

        # Write the entered command to the socket connection.
        print($Socket "$_\n");

        # Wait for and then process the information returned from the
server.
        while ($Answer = <$Socket>)
        {
            chomp($Answer);
            print("Accepted from server: $Answer\n");

            # Exit this loop when the server replies that the submitted
            # command has completed.
            last if ($Answer eq 'command complete');
        }

        # Exit the socket connection if a end of terminate command was
entered.
        last SOCKET if ($_ eq 'term' or $_ eq 'end');
    }
}
# Close the socket connection.
close($Socket);

exit(1);

__END__

Dirk Bremer - Senior Systems Engineer - ESS/AMS - NISC Lake St. Louis MO
- USA Central Time Zone
636-755-2652 fax 636-755-2503

[EMAIL PROTECTED]
www.nisc.coop 

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