Scheduler [first draft]

[masci]

Please refer to the README for the overall design, here follows random notes on the changes.

TL;DR

The Scheduler is responsible to send a set of Checks to the execution pipeline consumed by the Runner at certain intervals. We keep a set of timers, one for each interval needed, and we append every Check to the relevant timer.

API

The Scheduler API exposes plain functions but uses channels under the hood to keep things in sync, this should allow to write cleaner code in the callers - for example scheduler.Start() instead of scheduler.start <- true or stuff like that that assume a caller knows the internals.

Test

Some of the tests rely on the asynchronous design of the components, so I had to provide an helper function that polls (instead of sleeping) until a certain condition is met (e.g. the scheduler has fully started). These kind of tests can be very flaky so we might need to adjust timeouts at some point.

[remh]

should be 15

[remh]

That's a really good first draft. It seems like interval customization at the configuration level is not implemented though ?

[masci]

Customizing the interval is responsibility of the Configure method: the configuration payload may or may not contain that information, in the latter a default value, hardcoded (for now, but could be provided by datadog.conf) will be used. If an interval was passed, it's up to the Check to store it so it can be returned by the Interval method. As you have noticed, this strategy was not implemented yet in this PR, will update it with a working example for the python check.

this method should be called GetDefaultInterval i believe ?

If the Check receives the desired interval during the Configure, this would return the configured value, falling back to the default

Can we avoid implementing this method if we just want to use the default ?

That's the problem with this approach: if we have checks that don't expect an interval from configuration, still they need to implement this method like:

func (c *SomeCheck) Interval() int {
  return check.DefaultCheckInterval
}

[remh]

Just a tiny nitpick otherwise feel free to merge

[remh]

Let's define it as time duration from the get go