Support simulations with callback vs. just return values

[eslick]

I have a web system that I want to load test and evaluate for its end to end performance where the request starts off a process, but the actual transaction is completed only when the system POSTs to a URL endpoint. We're interested in getting a sense of both latency and throughput for the GET -> POST response transaction. Is there a clean way to implement this, or do you have suggestions for a patch I could submit? We've been looking at doing something more ad-hoc on top of Riemann, but intrigued by your approach here.

[mhjort]

I think this is something that can be implemented with clj-gatling out-of-the box. In addition to returning the value directly you can return core.async channel which you can later on write to. Solution looks something like this:

Your clj-gatling request function.

(defn request []
  (let [return-channel (async/chan)
        identifier (do-get-request)]
    (register-identifier! identifier return-channel)
    return-channel)))

So in here I am assuming you have some kind of a way for identifying requests. Later on that can be used to connect them to correct POST responses. For registering you can use for example atom to store. Then you need a http server (e.g. http-kit or Jetty) running in same process. Your post handler should look like this:

(defn post-handler [identifier]
  (let [return-channel (get-from-register identifier)]
    (>!! return-channel true)))

So in here you get correct return-channel from registry and write the result to that channel.

Does this make sense?

[eslick]

Great suggestion, thank you. I was able to accomplish that without too much trouble.