multiplexer.tgz is a Tcl "multiplexer" - or, in other words, a server that handles one-to-many comunication. One client sends it some data, and it sends that to all the other clients.  Originally by [davidw], it is now part of [tcllib].

[CMcC] I have rewritten this as an incrtcl class called Mux, it can be found here: [http://sourceforge.net/projects/libtclpq/]

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[schlenk] A multiplexer can also be created with the new Tcl [chan create] command introduced with TIP 219.

This is a simple example multiplexer, which creates a new writable channel, which multiplexes its output to a number of external channels.

  package require Tcl 8.5
  package require snit

  snit::type multiplexer {
       constructor {mode args} {
           # Handle args ...
           set targets $args
           set dead 0
	   set chan [chan create $mode $self]
       }
       destructor {
           # ... delete internal state ...
           if {$dead} return
           set dead 1
           catch {close $chan}
       }

       method handle {} {return $chan}
       variable chan
       variable dead 0
       variable targets ""

       method finalize {dummy} {
           if {$dead} return
           set dead 1
           $self destroy
       }
       method initialize {dummy mode} {
         if {"read" in $mode} {
             error "Only writing is supported for this channel type"
         }
      	 return {initialize finalize write watch}
       }
       method read       {dummy count} {}
       method write      {dummy data} {
         # multiplex the written data,
         # may need extra handling if the encodings of the target
	 foreach targetchan $targets {
             set state [chan configure $targetchan]
             chan configure $targetchan -encoding binary \
                                	-translation binary \
                                	-eofchar {}
	     puts -nonewline $targetchan $data
	     chan configure $targetchan {expand}$state
	 }
	 string length $data
       }
       method seek       {dummy offset base} {}
       method configure  {dummy args} {}
       method watch      {dummy events} {}
       method blocking   {dummy isblocking} {}
   }

   proc multiplexer_open {args} {
       return [[multiplexer %AUTO% {expand}$args] handle]
   }
 
Usage example:

 set fd [open somefile.txt w+]
 set ch [multiplexer_open write stderr $fd]
 puts $ch "Some message"
 # did not implement buffering control, so flush explicitly...
 flush $ch
 
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[Category Design]