in reply to IPC via named pipes, losing some messages

Here's how to make the reads block so you don't have to constantly re-open the pipe: 
open(RW, "+<pipe") or die "unable to open pipe: $!\n";
open(FH, "<pipe") or die "open pipe: $!\n";
while (<FH>) {
    # process line
}

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The trick is to always have the pipe opened for writing so that you'll never get EOF when reading it.

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Re^2: IPC via named pipes, losing some messages
by ftumsh (Scribe) on Apr 15, 2008 at 13:52 UTC
    Thanks everyone for your help. I finally cracked it yesterday. The trick is to open the pipe for read/write, bypass perlio and have a blocking read. The code below shows how it's done. I could possibly have moved to sockets, but pipes are as old as the hills so it should be possible to use them and on top of that the writer could be a bash script. Having said that, I did find out how to have bash write to a socket... 
    # Non blocking open
open (FH, "+<", $config->{'pipe'} ) || die "Unable to open $config->{'
+pipe'}";

my $rin = '';
my $rout = '';
vec( $rin, fileno(FH), 1) = 1; # No, I have no idea either

# Loop forever.
while (1) {

    # Wait for the pipe to change status
    my $nfound = select( $rout = $rin, undef, undef, undef ); # blocki
+ng select

    my $data;
    # Non blocking select only returns a value while there is somethin
+g in the pipe
    while ( select( $rout = $rin, undef, undef, 0 ) ) {
        sysread FH, my $buf, 2048;
        $data .= $buf;
    }

    Log( { logfile => $log_file, text => 'trace: START: '. ( $data || 
+'$data no val' ) }) if TRACE;

    # 9/4/8 A request is C,DIR,1ROSE
    # Multiple requests can come through on one read ie C,FOO,1ROSEC,B
+AR,1ROSE
    for ( split /ROSE/, $data ? $data : '' ) {
        if ( /^RELOAD/ ) {
            # Reread the config file
            Log({logfile=>$log_file, text=> qq{RELOAD: Reloading confi
+g}});
            load_config();
        }
        else {
            process_input( { data => $_ } ) if $_;
        }
    }

} # while 1

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[reply]
[d/l]

      "ROSE" has got to be the weirdest line ending I've ever seen.

      I took the liberty of cleaning up your code a bit.

      • I fixed a bug where a single message could be considered two.
      • I eliminated the select which needlessly served to empty the pipe.
      • I replaced split since you have a record terminator rather than a record separator. 
      # Non blocking open
open (FH, "+<", $config->{'pipe'} ) || die "Unable to open $config->{'
+pipe'}";

my $buf = '';

# Loop forever.
while (1) {
    my $rv = sysread( FH, $buf, 2048, length($buf) );
    die("Error reading from pipe: $!\n") if !defined($rv);

    # 9/4/8 A request is C,DIR,1ROSE
    # Multiple requests can come through on one read ie C,FOO,1ROSEC,B
+AR,1ROSE
    while ($buf =~ s/(.*?ROSE)//s) {
       my $rec = $1;
       Log( { logfile => $log_file, text => "trace: START: $rec" }) if
+ TRACE;

        if ( $rec =~ /^RELOAD,/ ) {
            # Reread the config file
            Log({logfile=>$log_file, text=> qq{RELOAD: Reloading confi
+g}});
            load_config();
        }
        else {
            process_input( { data => $rec } );
        }
    }

} # while 1

      [download]
[reply]
[d/l]
[select]
        Thanks for that. I'm going to test it next week. I would do it sooner but I'm off tomorrow and I don't like sending software live before I'm away. It tends to generate tedious wtf have you done now telephone calls... Could you explain what you mean in your bullet points, 1 and 3 please? John
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