asyncore python挂起

我尝试使用asyncore做简单的异步http客户端：
这段代码工作正常,输出是(快速)：

www.gmail.com  :  recv http code:  301
www.yandex.ru  :  recv http code:  200
www.python.org  :  recv http code:  200
www.google.ru  :  recv http code:  200
www.gravatar.com  :  recv http code:  302
www.com.com  :  recv http code:  302
www.yahoo.com  :  recv http code:  302
www.bom.com  :  recv http code:  301

但是,与我不存在主机的取消注释：

#c = AsyncHTTP('http://www.no-such-host.ru') #!this line breaks execution!

执行中断,代码挂起一段时间,输出部分数据并挂起,没有最后的数据输出：

connection error: [Errno -5] No address associated with hostname
www.gmail.com  :  recv http code:  301
www.yandex.ru  :  recv http code:  200
www.yahoo.com  :  recv http code:  302
www.com.com  :  recv http code:  302
www.bom.com  :  recv http code:  301
www.gravatar.com  :  recv http code:  302

…
一些主机在这里丢失,并在开始时长时间延迟.

为什么会这样,以及如何解决这个问题？

# coding=utf-8
import asyncore
import string,socket
import StringIO
import mimetools,urlparse

class AsyncHTTP(asyncore.dispatcher):
    # HTTP requestor

    def __init__(self,uri):
        asyncore.dispatcher.__init__(self)

        self.uri = uri


        # turn the uri into a valid request
        scheme,host,path,params,query,fragment = urlparse.urlparse(uri)
        assert scheme == "http","only supports HTTP requests"
        try:
            host,port = string.split(host,":",1)
            port = int(port)
        except (TypeError,ValueError):
            port = 80 # default port
        if not path:
            path = "/"
        if params:
            path = path + ";" + params
        if query:
            path = path + "?" + query

        self.request = "GET %s HTTP/1.0\r\nHost: %s\r\n\r\n" % (path,host)

        self.host = host
        self.port = port

        self.status = None
        self.header = None
        self.http_code = None
        self.data = ""

        # get things going!
        self.create_socket(socket.AF_INET,socket.soCK_STREAM)
        #self.connect((host,port))
        #return
        try:
            self.connect((host,port))
        except Exception,e:
            self.close()
            self.handle_connect_expt(e)

    def handle_connect(self):
        self.send(self.request)

    def handle_expt(self):
        print "handle_expt error!"
        self.close()

    def handle_error(self):
        print "handle_error error!"
        self.close()

    def handle_connect_expt(self,expt):
        print "connection error:",expt

    def handle_code(self):        
        print self.host," : ","recv http code: ",self.http_code


    def handle_read(self):
        data = self.recv(2048)
        #print data
        if not self.header:
            self.data = self.data + data
            try:
                i = string.index(self.data,"\r\n\r\n")
            except ValueError:
                return # continue
            else:
                # parse header
                fp = StringIO.StringIO(self.data[:i+4])
                # status line is "HTTP/version status message"
                status = fp.readline()
                self.status = string.split(status," ",2)
                self.http_code = self.status[1]
                self.handle_code()      

                # followed by a rfc822-style message header
                self.header = mimetools.Message(fp)
                # followed by a newline,and the payload (if any)
                data = self.data[i+4:]
                self.data = ""
                #header recived
                #self.close()


    def handle_close(self):
        self.close()




c = AsyncHTTP('http://www.python.org')
c = AsyncHTTP('http://www.yandex.ru')
c = AsyncHTTP('http://www.google.ru')
c = AsyncHTTP('http://www.gmail.com')
c = AsyncHTTP('http://www.gravatar.com')
c = AsyncHTTP('http://www.yahoo.com')
c = AsyncHTTP('http://www.com.com')
c = AsyncHTTP('http://www.bom.com')
#c = AsyncHTTP('http://www.no-such-host.ru') #!this line breaks execution!
asyncore.loop()

ps：我的系统是ubuntu 11.10 python 2.7.2

最佳答案

您执行self.connect((host,port))时调用阻止名称解析.结合您的本地DNS配置,这就是您的程序在启动时有很长时间延迟的原因.

作为asyncore的替代方案,并想知道如何自己进行非阻塞名称解析,您可能会考虑使用Twisted. Twisted的TCP连接设置API(主要是reactor.connectTCP或其上构建的API之一)不会阻止.所以天真地使用它将保持适当的异步.