Timing

godoc

import "barista.run/timing"

By default, barista handles the pause/resume from the bar using the USR1 and USR2 signals. This allows suspension of processing while the bar is hidden, saving resources all around.

The timing package provides scheduling abilities that are aware of the bar’s paused status, and wait for the bar to resume before firing. This makes them very useful for scheduled, repeating work that directly results in output, by suspending the work until the bar is visible again.

Scheduler

Schedulers are pause/resume-aware ticking channels that can be set to trigger at a specific time, after a specific delay, or repeatedly with a specific interval.

Create a scheduler linked to the bar using timing.NewScheduler().

• After(time.Duration): Tick after the given duration.
• At(time.Time): Tick at a specific time. If in the past, tick immediately.
• Every(time.Duration): Tick after the given duration, and repeat.

C holds a chan <-struct{} that will be notified for each tick of the scheduler, similar to time.Ticker. It is almost guaranteed that the bar is active when a value is received on this channel. (There’s a small chance that the bar has paused again in the time since the signal was sent, but this is unlikely).

Example

Typical usage of a scheduler would be in a for loop, especially combined with a select.

func (m *Module) Stream(sink bar.Sink) {
	sch := timing.NewScheduler().Every(3*time.Second)
	settings := m.settings.Get()
	data := process()
	for {
		sink.Output(settings.format(data))
		select {
			case <-m.settings.Next():
				settings = m.settings.Get()
			case <-sch.C:
				data = process()
		}
	}
}

This basically loops forever, waiting for a change in m.settings, or for a scheduler tick. The process() work only happens on scheduler tick, so while the bar is hidden, process will almost never be called.

Now

The timing package also provides Now(), with the same signature as time.Now(), but with a few barista-specific changes:

• When using timing.TestMode(), the value returned by timing.Now() will be frozen until advanced using NextTick() or Advance...(). The movement of test time is consistent with how schedulers are triggered. See the timing tests for examples.

• The returned time.Time will try to be in the machine’s local time zone, even if the zone has changed since startup. This differs from time.Now(), which is pinned to the zone set when the binary starts.