Simon Pickles wrote:

Hi,

I've been using twisted in a low-level way for some time and am now interested in the higher level aspects.

Particularly I hope to be able to make deferred requests across a network. I'd like to have a hub server, with many small apps (modules) which are all clients of the hub server.

I'd like the modules to be able to request information from each other, via the hub, in a deferred way, so the callback will be triggered when the requested information arrives.

So I need a chain like this:

ModuleA.RequestName(id).addCallback(modACallback) -> Hub Hub.RequestName(id).addCallback(hubCallback)-> ModuleB ModuleB.SendNameToHub() -> Hub Hub.hubCallback triggered: SendNameToModA() -> ModuleA ModuleA.modACallback triggered - request is complete.

Perhaps one issue is that I have a client->server->client sequence.

Although it looks slow, I am designing my system to be as concurrent as possible. Also, the hub can make decisions about sharing requests with several modules on a round-robin, or sending requests (and events, particularly) to more than one module.

I know I can do this through TCP or similar, but hoped someone might suggest which elements of twisted (a very large framework) I should look at more closely.

Perspective broker (pb) would work, provided the values you are passing round are plain python types e.g. int, str, list, dict, tuple. You'd have something like: from twisted.spread import pb from twisted.internet import reactor class Module(pb.Referenceable): def __init__(self, name, server, port=1234): self.f = pb.PBClientFactory() reactor.connectTCP(server, port, f) self.f.getRootObject().addCallback(self.signon, name) def signon(self, root, name): self.root = root self.root.callRemote('signon', name, self) # methods for use by remote def remote_doThing(self): return aDeferredThing() # methods for use by local process def requestName(self, id): return self.root.addCallback(requestName2, id) def requestName2(self, root, id): return root.callRemote('requestName', id) ModuleA = Module('ModuleA', server) reactor.run() ...and on the server site: from twisted.spread import pb class Server(pb.Root): modules = {} # function a module registers with def remote_signon(self, name, module): if name in self.modules: self.modules[name].append(module) else: self.modules[name] = [module] # proxy to a copy of ModuleA, with load-balancing def remote_modulea_doThing(self, arg): modulea_list = self.modules['ModuleA'] mod = random.choice(modulea_list) return mod.callRemote('doThing', arg) # proxy wherever... def remote_requestName(self, id): mod = ... return mod.requestName(id) The above is very hacky - the class-global dict() is wrong, and there is no handling of PB disconnection errors and so forth, but the basic idea is sound.

Many thanks!

Simon