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ticker.go
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ticker.go
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package backoff
import (
"context"
"sync"
"time"
)
// Ticker holds a channel that delivers `ticks' of a clock at times reported by a BackOff.
//
// Ticks will continue to arrive when the previous operation is still running,
// so operations that take a while to fail could run in quick succession.
type Ticker struct {
C <-chan time.Time
c chan time.Time
b BackOff
ctx context.Context
timer Timer
stop chan struct{}
stopOnce sync.Once
}
// NewTicker returns a new Ticker containing a channel that will send
// the time at times specified by the BackOff argument. Ticker is
// guaranteed to tick at least once. The channel is closed when Stop
// method is called or BackOff stops. It is not safe to manipulate the
// provided backoff policy (notably calling NextBackOff or Reset)
// while the ticker is running.
func NewTicker(b BackOff) *Ticker {
return NewTickerWithTimer(b, &defaultTimer{})
}
// NewTickerWithTimer returns a new Ticker with a custom timer.
// A default timer that uses system timer is used when nil is passed.
func NewTickerWithTimer(b BackOff, timer Timer) *Ticker {
if timer == nil {
timer = &defaultTimer{}
}
c := make(chan time.Time)
t := &Ticker{
C: c,
c: c,
b: b,
ctx: getContext(b),
timer: timer,
stop: make(chan struct{}),
}
t.b.Reset()
go t.run()
return t
}
// Stop turns off a ticker. After Stop, no more ticks will be sent.
func (t *Ticker) Stop() {
t.stopOnce.Do(func() { close(t.stop) })
}
func (t *Ticker) run() {
c := t.c
defer close(c)
// Ticker is guaranteed to tick at least once.
afterC := t.send(time.Now())
for {
if afterC == nil {
return
}
select {
case tick := <-afterC:
afterC = t.send(tick)
case <-t.stop:
t.c = nil // Prevent future ticks from being sent to the channel.
return
case <-t.ctx.Done():
return
}
}
}
func (t *Ticker) send(tick time.Time) <-chan time.Time {
select {
case t.c <- tick:
case <-t.stop:
return nil
}
next := t.b.NextBackOff()
if next == Stop {
t.Stop()
return nil
}
t.timer.Start(next)
return t.timer.C()
}