python - 如何使异步不阻塞？

Question

我正在使用以下链接中的以下代码。我的理解是 asyncore.loop() 将打印 LOOP_DONE 而不是等待数据被传递。相反，只有在读取了所有数据后才打印 LOOP_DONE。为什么 loop() 阻塞？

http://broadcast.oreilly.com/2009/03/pymotw-asyncore.html

import asyncore
import logging
import socket
from cStringIO import StringIO
import urlparse
class HttpClient(asyncore.dispatcher):

    def __init__(self, url):
        self.url = url
        self.logger = logging.getLogger(self.url)
        self.parsed_url = urlparse.urlparse(url)
        asyncore.dispatcher.__init__(self)
        self.write_buffer = 'GET %s HTTP/1.0\r\n\r\n' % self.url
        self.read_buffer = StringIO()
        self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
        address = (self.parsed_url.netloc, 80)
        self.logger.debug('connecting to %s', address)
        self.connect(address)

    def handle_connect(self):
        self.logger.debug('handle_connect()')

    def handle_close(self):
        self.logger.debug('handle_close()')
        self.close()

    def writable(self):
        is_writable = (len(self.write_buffer) > 0)
        if is_writable:
            self.logger.debug('writable() -> %s', is_writable)
        return is_writable

    def readable(self):
        self.logger.debug('readable() -> True')
        return True

    def handle_write(self):
        sent = self.send(self.write_buffer)
        self.logger.debug('handle_write() -> "%s"', self.write_buffer[:sent])
        self.write_buffer = self.write_buffer[sent:]

    def handle_read(self):
        data = self.recv(8192)
        self.logger.debug('handle_read() -> %d bytes', len(data))
        self.read_buffer.write(data)

if __name__ == '__main__':
    logging.basicConfig(level=logging.DEBUG,
                        format='%(name)s: %(message)s',
                        )
    clients = []
    for i in range(10):
        clients.append(HttpClient('http://www.python.org/'))
    #clients = [
    #    HttpClient('http://www.python.org/'),
    #    HttpClient('http://www.doughellmann.com/PyMOTW/contents.html'),
    #]

    logging.debug('LOOP STARTING')
    asyncore.loop()
    logging.debug('LOOP DONE')

    for c in clients:
        response_body = c.read_buffer.getvalue()
        print c.url, 'got', len(response_body), 'bytes'