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