TCL:shared scope when using exec to launch 2 new tcl shells - multithreading

Question

Let's say I have a proc called upgrade that's is used to upgrade machines/devices. I want to upgrade 2 machines in parallel. Inside a proc called main, I use exec to launch 2 tcl shells that eventually call the upgrade proc. The thing is, before I launch the 2 tcl shells using exec, I have to connect to a traffic generator that only allows one connection instance to it.You can connect to it if you already have a connection to it.How to make the newly launched shells upgrade proc aware that a connection already exists and no need to connect to it? It seems that the newly created shells dont share the space and scope of the main proc.
Note that if I don't use exec and call upgrade in series, both upgrade calls know about the connection and the upgrades work.
Maybe I'm doing multi-processing in TCL wrong?
Thanks for your help

Answer 1

exec will not inherit any open file descriptors.
One possible solution: Have the subprocesses connect to the parent process. The parent process will accept the connections and pass all data directly through to the traffic generator and send any responses back to the appropriate subprocess.
Edit:
Another solution is to rewrite your upgrade procedure to process multiple upgrades at the same time. This might be easier than using exec.
The main problem is that you will need some way to determine which process or upgrade connection the data received from the traffic manager is meant for. This will be true whether you use the method outlined above, or if you rewrite your upgrade process so that it handles multiple upgrades at one time.
If you do not have a way to route incoming data from the traffic manager, what you want to do will be difficult.
This code is overly simplified. There is no error checking and it doesn't handle the closing of a socket.
Any operation on a socket should be enclosed in a try { } block, as a socket error can happen at any point in time.
Also, the connection needs to have its encoding set properly (if sending binary data).
# First, the server (the main process) must create the
# server socket and associate it with a connection handler.
# A read handler is set up to handle the incoming data.
proc readHandler {sock} {
global tmsock
if {[gets $sock data] >= 0} {
puts $tmsock $data
}
}
proc connectHandler {sock addr port} {
global socks
# save the socket the connection came in on.
# the array index should not be the port, but rather some
# data which can be used to route incoming messages from the
# traffic manager.
set socks($port) $sock
fconfigure $sock -buffering line -blocking false
fileevent $sock readable [list ::readHandler $sock]
}
socket -server ::connectHandler $myport
# The server also needs an event handler for data
# from the traffic manager.
proc tmReadHandler {} {
global tmsock
global socks
if {[gets $tmsock data] >= 0} {
# have to determine which process the data is for
set port unknown?
set sock $socks($port)
puts $sock $data
}
}
fileevent $tmsock readable [list ::tmReadHandler]