lnd.xprv/ticker/ticker.go
2019-02-12 16:05:24 -08:00

127 lines
3.6 KiB
Go

package ticker
import "time"
// Ticker defines a resumable ticker interface, whose activity can be toggled to
// free up resources during periods of inactivity.
//
// Example of resuming ticker:
//
// ticker.Resume() // can remove to keep inactive at first
// defer ticker.Stop()
// for {
// select {
// case <-ticker.Tick():
// if shouldGoInactive {
// ticker.Pause()
// continue
// }
// ...
//
// case <-otherEvent:
// ...
// if shouldGoActive {
// ticker.Resume()
// }
// }
//
// NOTE: ONE DOES NOT SIMPLY assume that Tickers are safe for concurrent access.
type Ticker interface {
// Ticks returns a read-only channel delivering ticks according to a
// prescribed interval. The value returned does not need to be the same
// channel, and may be nil.
//
// NOTE: Callers should assume that reads from Ticks() are stale after
// any invocations of Resume, Pause, or Stop.
Ticks() <-chan time.Time
// Resume starts or resumes the underlying ticker, such that Ticks()
// will fire at regular intervals. After calling Resume, Ticks() should
// minimally send ticks at the prescribed interval.
//
// NOTE: It MUST be safe to call Resume at any time, and more than once
// successively.
Resume()
// Pause suspends the underlying ticker, such that Ticks() stops
// signaling at regular intervals. After calling Pause, the ticker
// should not send any ticks scheduled with the chosen interval. Forced
// ticks are still permissible, as in the case of the Force Ticker.
//
// NOTE: It MUST be safe to call Pause at any time, and more than once
// successively.
Pause()
// Stop suspends the underlying ticker, such that Ticks() stops
// signaling at regular intervals, and permanently frees up any
// remaining resources.
//
// NOTE: The behavior of a Ticker is undefined after calling Stop.
Stop()
}
// T is the production implementation of the resumable Ticker interface. This
// allows various components to toggle their need for tick events, which may
// vary depending on system load.
type T struct {
// interval is the desired duration between ticks when active.
interval time.Duration
// ticker is the ephemeral, underlying time.Ticker. We keep a reference
// to this ticker so that it can be stopped and cleaned up on Pause or
// Stop.
ticker *time.Ticker
}
// A compile-time constraint to ensure T satisfies the Ticker interface.
var _ Ticker = (*T)(nil)
// New returns a new ticker that signals with the given interval when not
// paused. The ticker starts off inactive.
func New(interval time.Duration) *T {
return &T{
interval: interval,
}
}
// Ticks returns a receive-only channel that delivers times at the ticker's
// prescribed interval. This method returns nil when the ticker is paused.
//
// NOTE: Part of the Ticker interface.
func (t *T) Ticks() <-chan time.Time {
if t.ticker == nil {
return nil
}
return t.ticker.C
}
// Resume starts underlying time.Ticker and causes the ticker to begin
// delivering scheduled events.
//
// NOTE: Part of the Ticker interface.
func (t *T) Resume() {
if t.ticker == nil {
t.ticker = time.NewTicker(t.interval)
}
}
// Pause suspends the underlying ticker, such that Ticks() stops signaling at
// regular intervals.
//
// NOTE: Part of the Ticker interface.
func (t *T) Pause() {
if t.ticker != nil {
t.ticker.Stop()
t.ticker = nil
}
}
// Stop suspends the underlying ticker, such that Ticks() stops signaling at
// regular intervals, and permanently frees up any resources. For this
// implementation, this is equivalent to Pause.
//
// NOTE: Part of the Ticker interface.
func (t *T) Stop() {
t.Pause()
}