Perl Monks, any help will be much appreciated....I've got a server that use IO::Pipe to open up filehandles to forked sub processes and then loaded into an IO::Select object for reading. The issue I'm having is that filehandles generated by IO::Pipe do not seem to be handled properly by the can_read() method of IO::Select when the can_read is the condition in a while loop. The code below will read the first filehandle made available, however the while loop then exits, even with two filehandles still in the select set (as confirmed by the count() method).

This code was working using open "-|" and STDOUT, but debugging messages in sub-modules forced the need to use explicit filehandles in the child process and I converted to IO::Pipe. Please note that this is a simplified test version of the production application, that's why it doesn't make real world sense. This is being run on Solaris 2.8 on a standard install of Perl 5.6.1. Also, read_line() is a homegrown sysread() wrapper I wrote. Thanks in advance! Brian Goad 

use IO::Select;
use IO::Pipe;
use IO::Handle;
@connect = ("3","2","1");

    # "main" child
    my $select_ch = new IO::Select;
    foreach $msg (@connect)
    {
      # for each write, fork a child
      if($msg)
      {
        # fork and open child for reading
        my $pipe = new IO::Pipe;

        if(my $pid = fork() )
        {
          #parent
          $fh = $pipe->reader();
          $debug && print "$$ forked $pid\n";
          $fh->blocking(0); # set non-blocking I/O
          $debug && print "adding filehandle ($fh)\n";
          $select_ch->add($fh);
        }
        else
        {
           #child
           my $childhandle = $pipe->writer();
           sleep $msg;
           print $childhandle "$msg,response,$mt\n";
           exit 0; #kill the child process
        }
      }
    } # done with processing this read

    # here we read for responses from the filehandles
    my @readyfiles; #array for select to populate
    my $rh; # a readable filehandle
    while( @readyfiles = $select_ch->can_read() )
    {
       foreach $rh (@readyfiles)
       {
           # read from filehandle, send back string 
           my $child_resp_string = '';
           print "calling read_line\n";
           my $bytes = read_line(\$child_resp_string,$rh);
           $debug && print "returned $child_resp_string\n";
           # only one read per handle, so close
           $select_ch->remove($rh);
           $rh->close;
           my $cnt = $select_ch->count();
           $debug && print "$cnt handles left to read\n";
       }
    }
    print "exiting...\n";
    exit 0;

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In reply to IO::Pipe and IO::Select by brinogordon

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