Invalid argument exception in socket.accept() if I restart immediately after a previous run quit

Question

I have a client server architecture written in python. Most of the time it works fine, but sometimes, after I stop the server and restart it immediately afterwards, I get the following error:

Accept failed due to : 22 Message Invalid argument, error: [Errno 22] Invalid argument

However, if I wait a few minutes and the start the same script again with no changes it works fine.

This is the loop I use on the server to accept incoming connections from clients:

try:
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.bind(('',port))
    s.listen(1)
except:
    #logError()

while True:
    try:
        conn, address = s.accept() #THIS ACCEPT FAILS SOMETIMES
        multiprocessing.Process(target=HandleConnection, args=(conn, address, messageQueue, taskQueue, IOLock, numberOfConnections, numberOfConnectionsLock,resultsDirectory)).start()
    except socket.error, msg:
      #logError()  -> this except catches the error

Does the port get blocked for some time after I run the server? If so, is there are way to query if the port is blocked and wait until it's unblocked if I want to start the server up again immediately after it just quit?

Answer 1

You need to set SO_REUSEADDR before binding.

setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

Failing to do so may prevent the socket from binding, thus the error when accepting. You would have noticed this error if you hadn't choked exceptions in the first block.