queue - (OMNeT++) Why PacketQueue is always 0?

Question

I'm trying to code in OMNeT++ an app that gets the queue length from the node where it is invoked and sends it to another node.

The plan is to modify the UdpBasicApp.cc file invoked in a router and make it get the length of the queue of the DropTailQueue module.

Searching online I found that this is the right method...

cModule *mod = getModuleByPath("router3.eth[*].mac.queue");                  
queueing::PacketQueue *queue = check_and_cast<queueing::PacketQueue*>(mod);
int c = queue->getNumPackets();
EV << c;

...since the DropTailQueue extends the PacketQueue module. I put a print at the end to see if there was something wrong. When I run the simulation, using the modified UdpBasicApp module, c is always 0. I hardly doubt that the queue is always 0, but I don't know how to verify this doubt. If it's an error, why is it always 0?

question from:https://stackoverflow.com/questions/65874996/omnet-why-packetqueue-is-always-0

Answer 1

My guess is, that you are querying a different queue than you assume. You should not use patterns (i.e. *) in your model path, because that may match on multiple eth modules, and it's unspecified, which one will be returned.