Threading.Condition problem

Gabriel Rossetti gabriel.rossetti at arimaz.com
Fri Jul 10 13:09:42 CEST 2009


Sorry if this appears twice, I sent it once with an attachment and it 
never arrived so maybe the attachment is posing problems. I inlined the 
code this time (at the bottom), thank you,

Gabriel

########################## Original message ############################

Hello everyone,

I wrote a small example that listens for xmpp msgs in a thread. The main
program calls a function that blocks (using Condition.wait) until a msg
has been received and then returns the msg. When a msg arrives, it is
put in a variable in the thread's object, it then calls the notify()
attr on the Condition object. For some reason, this doesn't work, the
thread gets the msg, tries to notify the Condition object, fails because
the lock has not been acquired yet and blocks. I tried ignoring the
failure, thinking that since it has not been acquired yet then when it
is, it will get the msg right away and never call Condition.wait, thus
not causing any problems, but this does not work either. Does someone
know what I am doing wrong? I attached the code to this msg.

Thank you,
Gabriel



############################ Example code ############################

from __future__ import with_statement
import xmpp, sys
from threading import Thread, Condition, Event


class Listener(Thread):
     def __init__(self, ws):
         Thread.__init__(self)
         self.interrupt = Event()
         self.message = None
         self._cv = ws._cv
         self.client = ws._client
         self.client.RegisterHandler('message', self.onMessage)

     def onMessage(self, conn, msg):
         self.message = msg
         try:
             self._cv.notify()
         except RuntimeError:
             print "self._cv has not acquired the lock yet"

     def getMsg(self):
         return self.message

     def run(self):
         try:
             while(not self.interrupt.isSet()):
                 self.client.Process(1)
         except KeyboardInterrupt:
             return 0

class WS(object):
     def __init__(self, username, password, res):
         self._jid = xmpp.protocol.JID(username)
         self._client = xmpp.Client(self._jid.getDomain())
         self._cv = Condition()

         if(self._client.connect(server=("localhost", 5222)) == ""):
             raise Exception("Error while connecting!")

         if(self._client.auth(self._jid.getNode(), password, res) is None):
             raise Exception("Authentication failed!")

         self._client.sendInitPresence()

         self._listener = Listener(self)
         self._listener.start()

     def getMsg(self, mid=None):
         """
         """
         with self._cv:
             res = self._listener.getMsg()
             while not res:
                 self._cv.wait()
                 res = self._listener.getMsg()
             return res

if(__name__ == "__main__"):
     ws = WS("test at localhost", "123", "test")
     res = ws.getMsg()
     print "I just received : %s" % str(res)
     sys.exit(0)





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