Service and Periodic execution of ping

[a-martynovich]

Closes #35
The new Executor allows to schedule periodic or one-shot execution of a function in separate process. An arbitrary number of functions can be scheduled, but only MAX_WORKERS processes will be spawned, which is the max number of simultaneously executed functions while others are waiting.

If a function crashes it won't destroy the main process. All function's stdout/stderr is attached to the main process. If a function hangs longer than the specified timeout its process gets killed. All spawned processes are destroyed at main process exit.

A function can be scheduled at any time. It is also possible to stop periodic execution of a single function.

[a-martynovich]

@vpetersson This PR is ready for merge.
A note: if an older version of agent (< 0.1.4.9 ) was installed on the device the newer agent won't start automatically after installation. It will start either after a reboot or if you do apt purge wott-agent before installing 0.1.5.0.

[vpetersson]

@a-martynovich noted on the older versions - that's fine in this stage. How do we control the granularity of the periodic runs and how are they run right now?

[a-martynovich]

@vpetersson

agent/agent/__main__.py

Lines 51 to 59 in 61ccadf

	PING_INTERVAL = 60 * 60
	PING_TIMEOUT = 10 * 60
	def run_daemon(debug, dev):
	exe = executor.Executor(PING_INTERVAL, run, (True, debug, dev),
	timeout=PING_TIMEOUT, debug=debug)
	executor.schedule(exe)
	executor.spin()

Here’s how ping is run right now. Hopefully this code speaks for itself.

[vpetersson]

Got it - yep. So i guess what we need to do is to start breaking ping apart and classify how often various operations should run.

[rptrchv]

@a-martynovich is is possible to test your new code?

[a-martynovich]

@rptrchv Manually for now. Proper automated testing for this will take a lot of time to code.

[rptrchv]

lgtm