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time: fix tick accuracy when using multiple Tickers

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* correctly ignore obsolete ticks
* fix update of next alarm time
* tighten alarm channel buffers
Fixes #1379.

R=r, adg, r2
CC=golang-dev, soul9
https://golang.org/cl/3789045
This commit is contained in:
Eoghan Sherry 2011-01-08 21:24:44 -08:00 committed by Rob Pike
parent c6ed78a4c1
commit 0c02bd1801
1 changed files with 8 additions and 22 deletions
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30
src/pkg/time/tick.go
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@ -47,11 +47,12 @@ func (a *alarmer) set(ns int64) {
case a.wakeTime > ns:
// Next tick we expect is too late; shut down the late runner
// and (after fallthrough) start a new wakeLoop.
a.wakeMeAt <- -1
close(a.wakeMeAt)
fallthrough
case a.wakeMeAt == nil:
// There's no wakeLoop, start one.
a.wakeMeAt = make(chan int64, 10)
a.wakeMeAt = make(chan int64)
a.wakeUp = make(chan bool, 1)
go wakeLoop(a.wakeMeAt, a.wakeUp)
fallthrough
case a.wakeTime == 0:
@ -73,19 +74,10 @@ func startTickerLoop() {
// wakeLoop delivers ticks at scheduled times, sleeping until the right moment.
// If another, earlier Ticker is created while it sleeps, tickerLoop() will start a new
// wakeLoop but they will share the wakeUp channel and signal that this one
// is done by giving it a negative time request.
// wakeLoop and signal that this one is done by closing the wakeMeAt channel.
func wakeLoop(wakeMeAt chan int64, wakeUp chan bool) {
for {
wakeAt := <-wakeMeAt
if wakeAt < 0 { // tickerLoop has started another wakeLoop
return
}
now := Nanoseconds()
if wakeAt > now {
Sleep(wakeAt - now)
now = Nanoseconds()
}
for wakeAt := range wakeMeAt {
Sleep(wakeAt - Nanoseconds())
wakeUp <- true
}
}
@ -96,9 +88,7 @@ func wakeLoop(wakeMeAt chan int64, wakeUp chan bool) {
func tickerLoop() {
// Represents the next alarm to be delivered.
var alarm alarmer
// All wakeLoops deliver wakeups to this channel.
alarm.wakeUp = make(chan bool, 10)
var now, prevTime, wakeTime int64
var now, wakeTime int64
var tickers *Ticker
for {
select {
@ -110,10 +100,6 @@ func tickerLoop() {
alarm.set(t.nextTick)
case <-alarm.wakeUp:
now = Nanoseconds()
// Ignore an old time due to a dying wakeLoop
if now < prevTime {
continue
}
wakeTime = now + 1e15 // very long in the future
var prev *Ticker = nil
// Scan list of tickers, delivering updates to those
@ -151,12 +137,12 @@ func tickerLoop() {
if tickers != nil {
// Please send wakeup at earliest required time.
// If there are no tickers, don't bother.
alarm.wakeTime = wakeTime
alarm.wakeMeAt <- wakeTime
} else {
alarm.wakeTime = 0
}
}
prevTime = now
}
}