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repeat_timer.go
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repeat_timer.go
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package common
import (
"sync"
"time"
)
// Used by RepeatTimer the first time,
// and every time it's Reset() after Stop().
type TickerMaker func(dur time.Duration) Ticker
// Ticker is a basic ticker interface.
type Ticker interface {
// Never changes, never closes.
Chan() <-chan time.Time
// Stopping a stopped Ticker will panic.
Stop()
}
//----------------------------------------
// defaultTicker
var _ Ticker = (*defaultTicker)(nil)
type defaultTicker time.Ticker
func defaultTickerMaker(dur time.Duration) Ticker {
ticker := time.NewTicker(dur)
return (*defaultTicker)(ticker)
}
// Implements Ticker
func (t *defaultTicker) Chan() <-chan time.Time {
return t.C
}
// Implements Ticker
func (t *defaultTicker) Stop() {
((*time.Ticker)(t)).Stop()
}
//----------------------------------------
// LogicalTickerMaker
// Construct a TickerMaker that always uses `source`.
// It's useful for simulating a deterministic clock.
func NewLogicalTickerMaker(source chan time.Time) TickerMaker {
return func(dur time.Duration) Ticker {
return newLogicalTicker(source, dur)
}
}
type logicalTicker struct {
source <-chan time.Time
ch chan time.Time
quit chan struct{}
}
func newLogicalTicker(source <-chan time.Time, interval time.Duration) Ticker {
lt := &logicalTicker{
source: source,
ch: make(chan time.Time),
quit: make(chan struct{}),
}
go lt.fireRoutine(interval)
return lt
}
// We need a goroutine to read times from t.source
// and fire on t.Chan() when `interval` has passed.
func (t *logicalTicker) fireRoutine(interval time.Duration) {
source := t.source
// Init `lasttime`
lasttime := time.Time{}
select {
case lasttime = <-source:
case <-t.quit:
return
}
// Init `lasttime` end
for {
select {
case newtime := <-source:
elapsed := newtime.Sub(lasttime)
if interval <= elapsed {
// Block for determinism until the ticker is stopped.
select {
case t.ch <- newtime:
case <-t.quit:
return
}
// Reset timeleft.
// Don't try to "catch up" by sending more.
// "Ticker adjusts the intervals or drops ticks to make up for
// slow receivers" - https://golang.org/pkg/time/#Ticker
lasttime = newtime
}
case <-t.quit:
return // done
}
}
}
// Implements Ticker
func (t *logicalTicker) Chan() <-chan time.Time {
return t.ch // immutable
}
// Implements Ticker
func (t *logicalTicker) Stop() {
close(t.quit) // it *should* panic when stopped twice.
}
//---------------------------------------------------------------------
/*
RepeatTimer repeatedly sends a struct{}{} to `.Chan()` after each `dur`
period. (It's good for keeping connections alive.)
A RepeatTimer must be stopped, or it will keep a goroutine alive.
*/
type RepeatTimer struct {
name string
ch chan time.Time
tm TickerMaker
mtx sync.Mutex
dur time.Duration
ticker Ticker
quit chan struct{}
}
// NewRepeatTimer returns a RepeatTimer with a defaultTicker.
func NewRepeatTimer(name string, dur time.Duration) *RepeatTimer {
return NewRepeatTimerWithTickerMaker(name, dur, defaultTickerMaker)
}
// NewRepeatTimerWithTicker returns a RepeatTimer with the given ticker
// maker.
func NewRepeatTimerWithTickerMaker(name string, dur time.Duration, tm TickerMaker) *RepeatTimer {
var t = &RepeatTimer{
name: name,
ch: make(chan time.Time),
tm: tm,
dur: dur,
ticker: nil,
quit: nil,
}
t.reset()
return t
}
// receive ticks on ch, send out on t.ch
func (t *RepeatTimer) fireRoutine(ch <-chan time.Time, quit <-chan struct{}) {
for {
select {
case tick := <-ch:
select {
case t.ch <- tick:
case <-quit:
return
}
case <-quit: // NOTE: `t.quit` races.
return
}
}
}
func (t *RepeatTimer) Chan() <-chan time.Time {
return t.ch
}
func (t *RepeatTimer) Stop() {
t.mtx.Lock()
defer t.mtx.Unlock()
t.stop()
}
// Wait the duration again before firing.
func (t *RepeatTimer) Reset() {
t.mtx.Lock()
defer t.mtx.Unlock()
t.reset()
}
//----------------------------------------
// Misc.
// CONTRACT: (non-constructor) caller should hold t.mtx.
func (t *RepeatTimer) reset() {
if t.ticker != nil {
t.stop()
}
t.ticker = t.tm(t.dur)
t.quit = make(chan struct{})
go t.fireRoutine(t.ticker.Chan(), t.quit)
}
// CONTRACT: caller should hold t.mtx.
func (t *RepeatTimer) stop() {
if t.ticker == nil {
/*
Similar to the case of closing channels twice:
https://groups.google.com/forum/#!topic/golang-nuts/rhxMiNmRAPk
Stopping a RepeatTimer twice implies that you do
not know whether you are done or not.
If you're calling stop on a stopped RepeatTimer,
you probably have race conditions.
*/
panic("Tried to stop a stopped RepeatTimer")
}
t.ticker.Stop()
t.ticker = nil
/*
From https://golang.org/pkg/time/#Ticker:
"Stop the ticker to release associated resources"
"After Stop, no more ticks will be sent"
So we shouldn't have to do the below.
select {
case <-t.ch:
// read off channel if there's anything there
default:
}
*/
close(t.quit)
}