why asynchat's initiate_send() get called twice after reconnect ?

davy zhang davyzhang at gmail.com
Sat Oct 25 15:10:17 CEST 2008


Python3.0rc1  windowsxp

in the lib\asynchat.py

   def handle_write (self):
       self.initiate_send()

   def push (self, data):
       sabs = self.ac_out_buffer_size
       if len(data) > sabs:
           for i in range(0, len(data), sabs):
               self.producer_fifo.append(data[i:i+sabs])
       else:
           self.producer_fifo.append(data)
       self.initiate_send()

when there's only one time connection, the object works just fine. but
problems came out when the client disconnected and reconnected again
to the server, it seems there are two ways to call the initiate_send,
one is from push() which I called in my program, one is from
handle_write() which automatically called in asyncore.loop(). I just
can't get it why one time connection works fine but multi-time
connection went bad.

I printed the traceback. I found when one time connection made, the
handle_write() always get silent, but when the second time, it get
called and start to call initiate_send in the same time as push()  get
called. So confusing....



So I tried to remove the initiate_send from push() and the code
magically works fine for me.

the main program lists below:
since it's need a flash client, I attached a webpage to reproduce the problem
click on the connect button multiple times and clicked on the send
button will make an error

import asyncore, asynchat
import os, socket, string
from multiprocessing import Process,Manager
import pickle
import _thread
import threading

PORT = 80

policyRequest = b"<policy-file-request/>"
policyReturn = b"""<cross-domain-policy>
            <allow-access-from  domain="*"  to-ports="*"  />
            </cross-domain-policy> \x00"""

def handler(taskList,msgList):
   while 1:
       print('getting task')
       item = pickle.loads(taskList.get())
       print('item before handle ', item)
       #do something
       item['msg'] += b' hanlded done'
       msgList.put(pickle.dumps(item))

def findClient(id):
   for item in clients:
       if item.idx == id:
           return item

def pushData(ch,data):
   global pushLock
   pushLock.acquire()
   try:
       ch.push(data)
   finally:
       pushLock.release()


def sender():
   global msgList
   print('thread started')
   while 1:
       item = pickle.loads(msgList.get())
       #print time()
       c = findClient(item['cid'])
       #print time()
       #wrong here it's not thread safe, need some wrapper
       #c.push(item['msg'])
       pushData(c,item['msg'])
       print('msg sent ',item['msg'])
       #print time()

class HTTPChannel(asynchat.async_chat):

   def __init__(self, server, sock, addr):
       global cid;
       asynchat.async_chat.__init__(self, sock)
       self.set_terminator(b"\x00")
       self.data = b""
       cid += 1
       self.idx = cid
       if not self in clients:
           print('add to clients:',self)
           clients.append(self)

   def collect_incoming_data(self, data):
       self.data = self.data + data
       print(data)

   def found_terminator(self):
       global taskList
       print("found",self.data)
       if self.data == policyRequest:
           pushData(self,policyReturn)
           self.close_when_done()
       else:
           d = {'cid':self.idx,'msg':self.data}
           taskList.put(pickle.dumps(d))
       self.data = b""

   def handle_close(self):
       if self in clients:
           print('remove from clients:',self)
           clients.remove(self)

class HTTPServer(asyncore.dispatcher):

   def __init__(self, port):
       asyncore.dispatcher.__init__(self)
       self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
       self.bind(("", port))
       self.listen(5)

   def handle_accept(self):
       conn, addr = self.accept()
       print('a new customer!')
       HTTPChannel(self, conn, addr)


#
# try it out
if __name__ == "__main__":
   s = HTTPServer(PORT)
   print ("serving at port", PORT, "...")

   #push data lock
   pushLock = threading.Lock()


   clients=[]

   cid = 0

   manager = Manager()

   taskList = manager.Queue()

   msgList = manager.Queue()


   h = Process(target=handler,args=(taskList,msgList))
   h.start()


   _thread.start_new_thread(sender,())
   print('entering loop')
   asyncore.loop()



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