IceStorm synchronous call

[kexiongwang]

Hi ! Can IceStorm support synchronous calls and replies? I want to use the properties of IceStorm broadcasting, and at the same time, I want to add response and synchronous call functions.

[bernardnormier]

IceStorm as a whole is purely one-way: a publisher sends a message to a topic hosted by IceStorm, and the topic implementation forwards this message to its subscribers. You can't send back a reply via IceStorm. And the publisher does not wait for IceStorm to forward anything.

A separate question is how your publisher sends a message to IceStorm (the topic in IceStorm), and how IceStorm forwards this message to the subscribers. These are all Ice invocations, and they can be two-way, one-way, or even datagram (= UDP).

For example, your publisher can make a synchronous two-way invocation to send a message to IceStorm. This means your publisher waits for IceStorm to queue the message before replying "void". With a two-way invocation, the publisher knows the message was successfully queued; this also provides ordering benefits. But it's slower since you're waiting for the reply from IceStorm.

[kexiongwang]

thanks for your replay!
I know that IceStorm is unidirectional. Since I want to monitor both the actual messages being sent and any potential replies, I am wondering if it is possible to add a discovery service where publishers automatically discover subscribers and then perform targeted, point-to-point publishing？

[bernardnormier]

With IceStorm, the publishers and subscribers are decoupled - that's the whole point of IceStorm. A publisher publishes to a topic and a subscriber subscribes to a topic; they don't know about each other.

If you want point-to-point and replies, just use plain Ice. And you could use IceDiscovery to discover Ice servers.