def main():
    ...
    launcher = service.process_launcher()
    for api in CONF.enabled_apis:
        should_use_ssl = api in CONF.enabled_ssl_apis
        if api == 'ec2':
            server = service.WSGIService(api, use_ssl=should_use_ssl,
                                         max_url_len=16384)
        else:
            # Initiate a WSGI server.
            server = service.WSGIService(api, use_ssl=should_use_ssl)
        launcher.launch_service(server, workers=server.workers or 1)
    launcher.wait()

    def start(self):
        """Start serving a WSGI application.

        :returns: None
        """

        wsgi_kwargs = {
            'func': eventlet.wsgi.server,
            'sock': self._socket,
            'site': self.app,
            'protocol': self._protocol,
            'custom_pool': self._pool,
            'log': self._wsgi_logger,
            'log_format': CONF.wsgi_log_format,
            'debug': False
            }

        if self._max_url_len:
            wsgi_kwargs['url_length_limit'] = self._max_url_len

        self._server = eventlet.spawn(**wsgi_kwargs)

def server(sock, site,
           ......,
           capitalize_response_headers=True):
    """Start up a WSGI server handling requests from the supplied server
    socket.  This function loops forever.  The *sock* object will be
    closed after server exits, but the underlying file descriptor will
    remain open, so if you have a dup() of *sock*, it will remain usable.

    :param sock: Server socket, must be already bound to a port and listening.
    :param site: WSGI application function.

    ......
    """

    ......

    try:
        serv.log.info("(%s) wsgi starting up on %s" % (
            serv.pid, socket_repr(sock)))
        while True:
            try:
                client_socket = sock.accept()
                client_socket[0].settimeout(serv.socket_timeout)
                serv.log.debug("(%s) accepted %r" % (
                    serv.pid, client_socket[1]))
                try:
                    pool.spawn_n(serv.process_request, client_socket)
                    ......
    finally:
        pool.waitall()
        ......

while True:
	client_socket = sock.accept()
	pool.spawn_n(serv.process_request, client_socket)

def main():
    ......
    server = service.Service.create(binary='nova-compute',
                                    topic=CONF.compute_topic,
                                    db_allowed=CONF.conductor.use_local)
    service.serve(server)
    service.wait()

class MessageHandlingServer(object):
    """Server for handling messages.

    Connect a transport to a dispatcher that knows how process the
    message using an executor that knows how the app wants to create
    new tasks.
    """

    ......

    def start(self):
        """Start handling incoming messages.

        This method causes the server to begin polling the transport for
        incoming messages and passing them to the dispatcher. Message
        processing will continue until the stop() method is called.

        The executor controls how the server integrates with the applications
        I/O handling strategy - it may choose to poll for messages in a new
        process, thread or co-operatively scheduled coroutine or simply by
        registering a callback with an event loop. Similarly, the executor may
        choose to dispatch messages in a new thread, coroutine or simply the
        current thread. An RPCServer subclass is available for each I/O
        strategy supported by the library, so choose the subclass appropriate
        for your program.
        """
        if self._executor is not None:
            return
        try:
            listener = self.dispatcher._listen(self.transport)
        except driver_base.TransportDriverError as ex:
            raise ServerListenError(self.target, ex)

        self._executor = self._executor_cls(self.conf, listener,
                                            self.dispatcher)
        self._executor.start()

    def wait(self):
        """Wait for message processing to complete.

        After calling stop(), there may still be some some existing messages
        which have not been completely processed. The wait() method blocks
        until all message processing has completed.
        """
        if self._executor is not None:
            self._executor.wait()

    ....

class EventletExecutor(base.ExecutorBase):

    """A message executor which integrates with eventlet.

    This is an executor which polls for incoming messages from a greenthread
    and dispatches each message in its own greenthread.

    The stop() method kills the message polling greenthread and the wait()
    method waits for all message dispatch greenthreads to complete.
    """

    ......

    def start(self):
        if self._thread is not None:
            return

        @excutils.forever_retry_uncaught_exceptions
        def _executor_thread():
            try:
                while True:
                    incoming = self.listener.poll()
                    spawn_with(ctxt=self.dispatcher(incoming),
                               pool=self._greenpool)
            except greenlet.GreenletExit:
                return

        self._thread = eventlet.spawn(_executor_thread)

while True:
    incoming = self.listener.poll()
    spawn_with(ctxt=self.dispatcher(incoming),
               pool=self._greenpool)