Question

I am writing a multithreaded socket application in Python using the socket module.
the server listens for connections and when it gets one it spawns a thread for that socket.

the server thread sends some data to the client. but the client is not yet ready to receive it. I thought this would have caused the server to wait until the client starts recv but instead returns immediately

the client then calls recv which is blocking and no data is ever received.

client socket constructor

self.__clientSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
self.__clientSocket.connect((server, port))

server socket constructor

        self.servSock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.servSock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        #self.servSock.settimeout(None)
        self.servSock.setblocking(1)
        self.servSock.bind((self.addr,self.port))
        self.servSock.listen(5)

listening accept thread

    try:
        (cs, address) = self.servSock.accept()
    except socket.timeout:
        return
    threadName = '\r\nClient %s:%s\r\n' % (cs, address)
    print threadName
    clientSocketHandler = ClientSocket()
    clientSocketHandler.setClientSocket(cs)
    self.clients.newThread(self.clientFunc, {clientSocketHandler : "1"}, threadName).start()

server and clients send/rec methods from inside ClientSocket

receivedData = self.__clientSocket.recv(1024*1024)

self.__clientSocket.send(s)

any ideas why send() is returning straight away?

Answer 1

any ideas why send() is returning straight away?

all send() does is fill the network buffer and return the ammount of bytes sent.

if you want a send that blocks just recv an acknowledgement message from the client.