Blocking Thrift calls with Twisted

Question

I have a Twisted/Thrift server that uses the TTwisted protocol. I want to keep connections from clients open until a given event happens (I am notified of this event by the Twisted reactor via a callback).

class ServiceHandler(object):
    interface.implements(Service.Iface)

    def listenForEvent(self):
        """
        A method defined in my Thrift interface that should block the Thrift
        response until my event of interest occurs.
        """
        # I need to somehow return immediately to free up the reactor thread,
        # but I don't want the Thrift call to be considered completed. The current
        # request needs to be marked as "waiting" somehow.

    def handleEvent(self):
        """
        A method called when the event of interest occurs. It is a callback method
        registered with the Twisted reactor.
        """
        # Find all the "waiting" requests and notify them that the event occurred.
        # This will cause all of the Thrift requests to complete.

How can I quickly return from a method of my handler object while maintaining the illusion of a blocking Thrift call?

---

I initialize the Thrift handler from the Twisted startup trigger:

def on_startup():
    handler = ServiceHandler()                      
    processor = Service.Processor(handler)                                   
    server = TTwisted.ThriftServerFactory(processor=processor,                  
        iprot_factory=TBinaryProtocol.TBinaryProtocolFactory())                 
    reactor.listenTCP(9160, server)

My client in PHP connects with:

  $socket = new TSocket('localhost', 9160);
  $transport = new TFramedTransport($socket);
  $protocol = new TBinaryProtocol($transport);
  $client = new ServiceClient($protocol);
  $transport->open();
  $client->listenForEvent();

That last call ($client->listenForEvent()) successfully makes it over to the server and runs ServiceHandler.listenForEvent, but even when that server method returns a twisted.internet.defer.Deferred() instance, the client immediately receives an empty array and I get the exception:

exception 'TTransportException' with message 'TSocket: timed out reading 4 bytes from localhost:9160 to local port 38395'

Answer 1

You should be able to return a Deferred from listenForEvent. Later handleEvent should fire that returned Deferred (or those returned Deferreds) to actually generate the response.