fileevent in TCL is very slow - asynchronous

Question

I tried to write a code in TCL. The idea is to write code that does a proxy over cisco. My cisco is cisco 3700 version 12.4 and the version of TCL is 8.3. I work with GNS (Graphical Network Simulator), therefore all components are virtual(including the cisco).
In my code I opened 2 sockets with two diffrent computers: sock1 and sock2.
I configured these sockets in the following way:
fconfigure $sock1 -translation binary -buffering none -blocking 0
fconfigure $sock2 -translation binary -buffering none -blocking 0
Now I tried to transfer information between them (proxy).
As I read, the language is single-threaded and therefore I need to use events. So, I created two file event handlers that called a function:
fileevent $sock1 readable [list proxy $sock1 $sock2]
fileevent $sock2 readable [list proxy $sock2 $sock1]
The proxy function read data from the first socket and send it to the other socket.
The code works well: I transfred rdp and smb over this proxy. The problem is that it really slow: It takes something like 1000-1100 ms. Therefore I can't use remote desktop througth the proxy and even smbclient is very slow. The proxy function is really fast (I checked it and also I tried to print at the start and at the end of the function). Therefore, I assume that the interrupts from the os are very slow (or tcl executes the script slow). In addition I opened wireshark on both sides of the cisco and it takes second between the incoming message and the outgoing message.
Another information:
I want that some clients will communicate at the same time, therefore my TCL code defines a server socket:
set server_socket [socket -server handle_conn $port]
vwait is_finish
and the function "handle_conn" opens socket to the second side and create file event handlers:
proc handle_conn{sock1 addr port} {
CREATE THE SECOND SOCKET (sock2)
fileevent $sock1 readable [list proxy $sock1 $sock2]
fileevent $sock2 readable [list proxy $sock2 $sock1]
}
Therefore, I need asynchronous code (I tried to write a synchronous version: it works fast but the problem is that I can't create more than one connection at the same time (and for example my proxy doesn't work with program that need two ports or with two diffrent programs at the same time)).
I can't understand if the problem is with fconfigure, with events in tcl, with gns or another problem.
Hope for help!
Edit:
proc proxy {s1 s2} {
if {([eof $s1] || [eof $s2]) || ([catch {read $s1} data] || [catch {puts -nonewline $s2 $data}])} {
catch {close $s1}
catch {close $s2}
}

Answer 1

I find it curious that the code is slow for you; Tcl's fast enough to be used to implement full web servers handling complex content. It makes me suspect that something else is going on. For example, the proxy command sounds like it is mainly just copying bytes from one channel to another, but there are slow ways to do this and there are fast ways. One of the best methods is to put both channels in binary mode (fconfigure $chan -translation binary) and then use fcopy in asynchronous mode to move the bytes over; it has been internally optimised to use efficient buffer sizes and limit the amount of copying between memory buffers. Here's how a proxy command might look:
proc proxy {sourceChannel destinationChannel} {
fconfigure $sourceChannel -translation binary
fconfigure $destinationChannel -translation binary
fcopy $sourceChannel $destinationChannel -command [list \
copydone $sourceChannel $destinationChannel]
}
The copydone procedure gets called when everything is moved. Here's a basic example, but you might need to be a bit more careful since you've got copies going in both directions:
proc copydone {src dst numBytes {errorMsg ""}} {
# $numBytes bytes of data were moved
close $src
close $dst
if {$error != ""} {
puts stderr "error in fcopy: $error"
}
}
If it wasn't for the fact that you are running on a cisco device, I'd also suggest upgrading the version of Tcl in use. Formally, 8.3 hasn't been supported for a very long time.