Many thanks for your response - let me take this by the numbers:

1,2,3) It was actually a typo, caused by me editing out superfluous code/comments/debugs, and a manual typing error. That line should have been:

  $openStreamsSock{$streamRequest++} = $sock->accept();
[download]

$streamRequest is just stream counter. New client connection sockets are added to the hash, with the $streamRequest the unique key.

4) Thanks for the coding economy!

5) You're right, I wasn't depopulating $fin (now $rin, to match standard), but at the top of the loop I reinitialized $fin and then set it up again by adding the listening socket and all currently open sockets. That should have taken care of initializing it correctly each time I get to the select.

Here's the updated code, adding in checking EBITS:

      while (1)
      {
        # Set up bit vectors for polling
        my $rin = '';
        my $ein = '';
        my $rout;
        my $eout;
        vec ($rin,  fileno ($sock)         , 1) = 1;
        vec ($ein,  fileno ($sock)         , 1) = 1;
        foreach my $streamID (keys %openStreamsSock)
        {
          vec ($fin,  fileno($openStreamsSock{$streamID})   , 1) = 1;
          vec ($ein,  fileno($openStreamsSock{$streamID})   , 1) = 1;
        }

        # Wait for incoming message
        my $nfound = select ($rout=$rin, undef, $eout=$ein, 5);
        if ($nfound) 
        {
          # Check client streams, close any in error
          foreach my $streamID (keys %openStreamsSock)
          {
            if (vec($eout, fileno($openStreamsSock{$streamID}),1))
            {
              close ($openStreamsSock{$streamID});
              delete ($openStreamsSock{$streamID});
            }
          }

          if (vec($rout, fileno($sock),1))
          {
            $openStreamsSock{$streamRequest++} = $sock->accept();
          }
          else
          {
            foreach my $streamID (keys %openStreamsSock)
            {
              if (vec($rout, fileno($openStreamsSock{$streamID}),1))
              {
                # read data off the socket; not a message here, just r
+aw data
                $msgSize = sysread ($openStreamsSock{$streamID},
                                    $msgReceived, 1048576);

                if (defined ($msgSize) && ($msgSize > 0))
                {
                  writeStreamData ($streamID, $msgReceived);
                }
                else
                {
                  # $msgSize being 0 indicates end of stream, or
                  # $msgSize being undef indicates error, so close
                  close ($openStreamsSock{$streamID});
                  delete ($openStreamsSock{$streamID});
                }
              }
            }
          }
        }
        else
        {
          print "$0: Normal timeout of select...\n";
        }
      }
[download]

I'll have to look at your example a bit - it looks like you're using some different constructs. Thanks again!