Network Programming IV - Asynchronous Request Handling: ThreadingMixIn and ForkingMixIn
This chapter is based on socketserver - A framework for network servers.
We'll see how we make asynchronous request using ThreadingMixIn and ForkingMixIn.
In the previous chapter, we used TCPServer which process requests synchronously. That means each request must be completed before the next request can be started. This isn't suitable if each request takes a long time to complete, because it requires a lot of computation, or because it returns a lot of data which the client is slow to process.
The solution to this is to create a separate process or thread to handle each request. The ForkingMixIn and ThreadingMixIn mix-in classes can be used to support asynchronous behavior.
# async.py import socket import threading import SocketServer class ThreadedTCPRequestHandler(SocketServer.BaseRequestHandler): def handle(self): data = str(self.request.recv(1024)) cur_thread = threading.current_thread() response = bytes("{}: {}".format(cur_thread.name, data)) self.request.sendall(response) class ThreadedTCPServer(SocketServer.ThreadingMixIn, SocketServer.TCPServer): pass def client(ip, port, message): sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.connect((ip, port)) try: sock.sendall(bytes(message)) response = str(sock.recv(1024)) print("Received: {}".format(response)) finally: sock.close() if __name__ == "__main__": # port 0 means to select an arbitrary unused port HOST, PORT = "localhost", 0 server = ThreadedTCPServer((HOST, PORT), ThreadedTCPRequestHandler) ip, port = server.server_address # start a thread with the server. # the thread will then start one more thread for each request. server_thread = threading.Thread(target=server.serve_forever) # exit the server thread when the main thread terminates server_thread.daemon = True server_thread.start() print("Server loop running in thread:", server_thread.name) client(ip, port, "Hello World 1") client(ip, port, "Hello World 2") client(ip, port, "Hello World 3") server.shutdown()
When inheriting from ThreadingMixIn for threaded connection behavior, we should explicitly declare how we want our threads to behave on an abrupt shutdown. The ThreadingMixIn class defines an attribute daemon_threads, which indicates whether or not the server should wait for thread termination. We should set the flag explicitly if we would like threads to behave autonomously. The default value is False, meaning that Python will not exit until all threads created by ThreadingMixIn have exited. In the code, we set it True, which means Python will exit the server thread when the main thread terminates not waiting for other threads' exit.
Forking and threading TCPServer can be created using the ForkingMixIn and ThreadingMixIn mix-in classes. For instance, a threading TCP server class is created as follows:
class ThreadingTCPServer(ThreadingMixIn, TCPServer): pass
The mix-in class must come first, since it overrides a method defined in TCPServer. Setting the various attributes also change the behavior of the underlying server mechanism.
To implement a service, we must derive a class from BaseRequestHandler and redefine its handle() method:
class ThreadedTCPRequestHandler(SocketServer.BaseRequestHandler): def handle(self): data = str(self.request.recv(1024)) cur_thread = threading.current_thread() response = bytes("{}: {}".format(cur_thread.name, data)) self.request.sendall(response)
The output from a run should look like this:
$ python async.py ('Server loop running in thread:', 'Thread-1') Received: Thread-2: Hello World 1 Received: Thread-3: Hello World 2 Received: Thread-4: Hello World 3
Python Network Programming
Network Programming - Server & Client A : Basics
Network Programming - Server & Client B : File Transfer
Network Programming II - Chat Server & Client
Network Programming III - SocketServer
Network Programming IV - SocketServer Asynchronous request
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