Calmm-way of doing async requests with interval?

Question

What's the most elegant way (in Calmm stack, Kefir, Karet Utils etc.) of doing repeated (infinite) async jobs with interval?

I want to get some json every 2000ms.

Example 1 (2000ms interval):

1. Fetch json (get takes 100ms)
2. Handle json
3. Wait the remaining time left on the interval, and start again from step 1

Example 2 (2000ms interval)

1. Fetch json (get takes 5000ms)
2. Handle json
3. Wait until steps 1 and 2 are finished before starting again at step 1

So in short, I want to to repeated gets (or any async work) and wait a minimum of 2000ms between requests.

I don't want the next request to fire until the previous one has finished in some way (success, fail, timeout).

Answer 1

This is how I would do that with Kefir without resorting to Kefir.stream. Note that job below would be the task you do at each tick. I stubbed a dummy task for the code to work.

let result = Kefir.repeat(() => {
    let job = Kefir.later(Math.random() * 5000);
    let wait = Kefir.later(2000).ignoreValues();
    return Kefir.merge([job, wait]);
});

Below is a visualization of the events using the style from the Kefir documentation:

spawned 1 - job:   ------1X
spawned 1 - wait:  -----------X
spawned 1 - merge: ------1----X
spawned 2 - job:               ------------------2X
spawned 2 - wait:              -----------X
spawned 2 - merge:             ------------------2X
spawned 3 - job:                                   ---3X
spawned 3 - wait:                                  -----------X
spawned 3 - merge:                                 ---3-------X
result:            ------1-----------------------2----3--------...