I have limited Java Socket experience and all of it using TCP. I am trying to learn UDP. I am running a multiple process application that is using UDP multicasting. After some brief research (and my nascent understanding of the topic), I thought multicasting would be the proper approach.
Metaphorically I want all the processes to share the same “room” and should at “shout at” each other. So when process 1 sends a message “hello” I want all process 2..n to receive that packet and vice versa.
At first it all seemed to be working but then I realized I have a bug (if you can call it that). I start up the first process, and when I startup the second one, the first process receives the second’s message but not vice versa.
I was wondering, when I do MulticastSocket receive() on process 1, is that effecitvely taking that DatagramPacket off a stack that then process 2 doesn’t see when it does it’s recieve()?
The problem is not in the choice of protocol – TCP/IP won’t help, and neither would UDP broadcast.
The problem is an operating system’s network stacks doesn’t buffer network traffic when there is nothing currently listening for it. And that is what happening with respect to the second process.
In short, your scheme cannot work.
One alternative is to have a “new” process multicast a “Who is there” message, and have all of the others respond with a multicast or directed packet. However, you are reinventing the wheel here. This problem has been solved many times before with various “middleware” stacks.