I’m stunned: weird problem with python and sockets + threads

Question

I have a python script that is a http-server: http://paste2.org/p/89701, when benchmarking it against ApacheBench (ab) with a concurrency level (-c switch) that is lower then or equal to the value i specified in the socket.listen()-call in the sourcecode everything works fine, but as soon as put the concurrency level in apache bench above the value in the socket.listen()-call performance drops through the floor, some example:

• socket.listen(10) and ab -n 50 -c 10 http://localhost/ = 1200req/s
• socket.listen(10) and ab -n 50 -c 11 http://localhost/ = 40req/s
• socket.listen(100) and ab -n 5000 -c 100 http://localhost/ = 1000req/s
• socket.listen(100) and ab -n 5000 -c 101 http://localhost/ = 32req/s

Nothing changes in the code between the two calls, I can’t figure out what is wrong - been at this problem for one day now. Also note that: The multiplexing version of the same code (I wrote to compare to the threaded version) works FINE no matter what socket.listen() is set to or what the concurrency (-c switch) in apache is set to.

I've spent a day on IRC/python docs, posted on comp.lang.python and on my blog - I can't find ANYONE that even has an idea what could be wrong. Help me!

Answer 1

For the heck of it I also implemented an asynchronous version:

import socket, Queue, select

class Request(object):
    def __init__(self, conn):
        self.conn = conn
        self.fileno = conn.fileno
        self.perform = self._perform().next

    def _perform(self):
        data = self.conn.recv(4048)
        while '\r\n\r\n' not in data:
            msg = self.conn.recv(4048)
            if msg:
                data += msg
                yield
            else:
                break
        reading.remove(self)
        writing.append(self)

        data = 'HTTP/1.1 200 OK\r\n\r\nHello World'
        while data:
            sent = self.conn.send(data)
            data = data[sent:]
            yield
        writing.remove(self)
        self.conn.close()

class Acceptor:
    def __init__(self):
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        sock.bind(('', 1234))
        sock.listen(10)
        self.sock = sock
        self.fileno = sock.fileno

    def perform(self):
        conn, addr = self.sock.accept()
        reading.append(Request(conn))

if __name__ == '__main__':
    reading = [Acceptor()]
    writing = list()

    while 1:
        readable, writable, error = select.select(reading, writing, [])
        for action in readable + writable:
            try: action.perform()
            except StopIteration: pass

which performs:

ab -n 10000 -c 10 http://127.0.0.1:1234/ --> 16822.13 [#/sec]
ab -n 10000 -c 11 http://127.0.0.1:1234/ --> 15704.41 [#/sec]