It’s funny how even early experiences change the way you think about a design. Two minor changes to SleepySketch have been suggested by early testing.

The first issue is obvious: milliseconds are a really inconvenient way to think about timing, especially when you’re planning on staying asleep for long periods. A single method in SleepySketch to convert from more programmer-friendly days/hours/minutes/seconds times makes a lot of difference.

The second issue concerns scheduling — or rather regular scheduling. Most sampling and communication tasks occur on predictable schedules, say every five hours. In an actor framework, that means the actor instance (or another one) has to be re-scheduled after the first has run. We can do this within the definition of the actor, for example using the post() action:

class PeriodicActor : public Actor {
   void post();
   void behaviour();
}

...

void PeriodicActor::post() {
   Sleepy.scheduleIn(this, Sleepy.expandTime(0, 5));
}

(This also demonstrates the expandTime() function to re-schedule after 0 days and 5 hours, incidentally.) Simple, but bad design: we can’t re-use PeriodicActor on a different schedule. If we add a variable to keep track of the repeating period, we’d be mixing up “real” behaviour with scheduling; more importantly, we’d have to do that for every actor that wants to run repeatedly.

A better way is to use an actor combinator that takes an actor and a period and creates an actor that runs first re-schedules the actor to run after the given period, and then runs the underlying actor. (We do it this way so that the period isn’t affected by the time the actor actually takes to run.)

   Actor *a = new RepeatingActor(new SomeActor(), Sleepy.expandTime(0, 5));
   Sleepy.scheduleIn(a, Sleepy.expandTime(0, 5))

The RepeatingActor runs the behaviour of SomeActor every 5 hours, and we initially schedule it to run in 5 hours. We can actually encapsulate all of this by adding a method to SleepySketch itself:

   Sleepy.scheduleEvery(new SomeActor(), Sleepy.expandTime(0, 5));

to perform the wrapping and initial scheduling automatically.

Simple sleepy sketches can now be created at set-up, by scheduling repeating actors, and we can define the various actors and re-use them in different scheduling situations without complicating their own code.

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