[ns] Problems using ns object in OTcl

["Mark Janssen" <M.P.C.Janssen@phys.uu.nl>]

Hi all,

I am having troubles using ns object (eg agents and nodes) in my own custom
OTcl class Entity.
I want to be able to create a new entity which then consists of a node a TCP
agent and a TCPSink. If I can write this wrapper class I maybe able to catch
the done of the TCP agent and use this to implement client server behaviour.
However when I try to use the agents in this class I get an error message
from ns:

trace: can't attach _o10 for writing.

My guess is that the class doesn't contain pointers to the objects but
copies of them. Any ideas of whats wrong and how I could accomplish what I
am trying to do are very much appreciated.

Below my tcl-script and the error message

Regards,
Mark Janssen

----- test.tcl -----

#Create a simulator object
set ns [new Simulator]

#Define different colors for data flows
$ns color 1 Blue


Class Entity

Entity instproc init {sender receiver node} {

 $self set sender_ $sender
 $self set receiver_ $receiver
 $self set node_ $node

}
Entity instproc start {} {
  global ns
  $self instvar sender_
  $self instvar receiver_
  $self instvar node_
  $ns attach-agent $sender_  $node_
  $ns attach-agent $receiver_ $node_

}

Entity instproc done {} {
  global ns
  $ns trace-annotate "Done"
  puts "Done"
}

#Open the nam trace file
set nf [open out.nam w]
$ns namtrace-all $nf

#Open the trace file
set f [open out.tr w]
$ns trace-all $f

#Define a 'finish' procedure
proc finish {} {
        global ns nf f
        $ns flush-trace
 close $f
 #Close the trace file
        close $nf
 #Execute nam on the trace file
        exec nam out.nam &
        exit 0
}

set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
$ns duplex-link $n0 $n1 1Mb 80ms DropTail
$ns duplex-link $n1 $n2 1Mb 80ms DropTail

set tcp1 [new Agent/TCP]
set sink1 [new Agent/TCPSink]
set server1 [new Entity $tcp1 $sink1 $n0]

set tcp2 [new Agent/TCP]
set sink2 [new Agent/TCPSink]
set server2 [new Entity $tcp2 $sink2 $n2]

$server1 start
$server2 start

$ns connect [$server1 set sender_] [$server2 set receiver_]

#Call the finish procedure after 5 seconds of simulation time
$ns at 0.1 "[$server1 set sender_] send 1000"
$ns at 5.0 "finish"
#Run the simulation
$ns run
----- test.tcl -----

----- err.log -----
[mjanssen@laptop myscripts]$ ns test.tcl
trace: can't attach _o10 for writing
    (_o59 cmd line 1)
    invoked from within
"_o59 cmd attach _o10"
    invoked from within
"catch "$self cmd $args" ret"
    (procedure "_o59" line 2)
    (SplitObject unknown line 2)
    invoked from within
"$node attach $agent"
    (procedure "_o3" line 2)
    (Simulator attach-agent line 2)
    invoked from within
"$ns attach-agent $sender_  $node_"
    (procedure "_o61" line 6)
    (Entity start line 6)
    invoked from within
"$server1 start "
    (file "mark.tcl" line 69)
[mjanssen@laptop myscripts]$
----- err.log -----

------------
Mark Janssen
Institute of Computational Physics
Room MG307
Telephone 030-2537724