Question

My goal here is to make a simple server handling TCP message like “process My String” that send “My String” to be processed by a quite time taking operation called (here slowFunction). Here I’m calling this function through deferToThread but nothing seems to happened : the defered’s callback messages doesn’t show up anywhere (breakpoints show it’s never called) and the print in the function aren’t displayed (breakpoints show it’s never called)

from twisted import protocols
from twisted.protocols import basic
from twisted.internet import threads, protocol, reactor
from twisted.application import service, internet
import re
import time

def slowFunction(arg):
    print "starting process"
    time.sleep(1)
    print "processed "+arg

class MySimpleServer(basic.LineReceiver):

    PROCESS_COMMAND = "process (.*)" #re pattern
    processFunction = slowFunction
    clients = []

    def connectionMade(self):
        print "Client connected"
        MySimpleServer.clients.append(self)

    def connectionLost(self, reason):
        print "Client gone"
        MySimpleServer.clients.remove(self)

    def onProcessDone(self):
        self.message("Process done")

    def onError(self):
        self.message("Process fail with error")

    def lineReceived(self, line):
        processArgumentResult = re.search(MySimpleServer.PROCESS_COMMAND, line)
        if not processArgumentResult == None:
            processArgument = processArgumentResult.groups()[0] 
            deferred = threads.deferToThread(MySimpleServer.processFunction, processArgument)
            deferred.addCallback(self.onProcessDone)
            deferred.addErrback(self.onError)
            self.message("processing your request")
        else:
            print "Unknown message line: "+line

    def message(self, message):
        self.transport.write(message + '\n')

if __name__ == '__main__':
    factory = protocol.ServerFactory()
    factory.protocol = MySimpleServer
    factory.client = []

    reactor.listenTCP(8000, factory)
    reactor.run()

Answer 1

I’ve got some help by the guys of twisted irc

The points are : the callback (onProcessDone and onError) are supposed to take a result argument, and the function called by deferToThread will receive self as an argument (it should one of the MySimpleServer class’ method).

The final code is now :

from twisted import protocols
from twisted.protocols import basic
from twisted.internet import threads, protocol, reactor
from twisted.application import service, internet
import re
import time

def slowFunction(arg):
    print "starting process"
    time.sleep(20)
    print "processed "+arg

class MySimpleServer(basic.LineReceiver):

    PROCESS_COMMAND = "process (.*)" #re pattern
    clients = []

    def connectionMade(self):
        print "Client connected"
        MySimpleServer.clients.append(self)

    def connectionLost(self, reason):
        print "Client gone"
        MySimpleServer.clients.remove(self)

    def onProcessDone(self, result):
        self.message("Process done")

    def onError(self, result):
        self.message("Process fail with error")

    def processFunction(self, processArgument):
        slowFunction(processArgument)

    def lineReceived(self, line):
        processArgumentResult = re.search(MySimpleServer.PROCESS_COMMAND, line)
        if not processArgumentResult == None:
            processArgument = processArgumentResult.groups()[0] 
            deferred = threads.deferToThread(self.processFunction, processArgument)
            deferred.addCallback(self.onProcessDone)
            deferred.addErrback(self.onError)
            self.message("processing your request")
        else:
            print "Unknown message line: "+line

    def message(self, message):
        self.transport.write(message + '\n')

if __name__ == '__main__':
    factory = protocol.ServerFactory()
    factory.protocol = MySimpleServer
    factory.client = []

    reactor.listenTCP(8000, factory)
    reactor.run()