From my perspective, the select object just holds some bits indicating the state of the connection(s). So your $read_set can add many sockets....a whole giant internal array of them. It can loop over them constantly to see which sockets are open, in a recv/send state, etc. There is also the accept condition, so you can monitor everytime someone wants to connect to the socket.

. So you will see pseudo logic like:

while( my $sel = $select->can_read ){

      if($sel->accept){spawn a new connection maybe 
                                          by forking/threading or addi
+ng to the select array }

if( $sel->is_connected){ #check for connection status

if ($sel->can_write){  etc  }
}
}
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the problem comes with making the select work in a bi-directional manner, usually a forking server and or client is used so the socket can both send and recv simultaneously. If both client and server are set to either send or recv, it locks up the socket.