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Golang time.Ticker 阻塞一段時(shí)間后觸發(fā)兩次

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寶慕林4294392 2022-11-08 16:58:23

我正在使用time.Ticker一些阻塞代碼，發(fā)現(xiàn)一個(gè)奇怪的行為：func main() { ticker := time.NewTicker(1 * time.Second) i := 0 for { select { case <-ticker.C: log.Println(i) if i == 0 { time.Sleep(5 * time.Second) // simulate the blocking } i++ } }}示例輸出：2022/02/20 10:49:45 02022/02/20 10:49:50 1 <- shows at same time2022/02/20 10:49:50 2 <- shows at same time2022/02/20 10:49:51 32022/02/20 10:49:52 42022/02/20 10:49:53 5...“1”和“2”總是同時(shí)顯示，這是為什么呢？

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2 回答

動(dòng)漫人物

TA貢獻(xiàn)1815條經(jīng)驗(yàn) 獲得超10個(gè)贊

代碼創(chuàng)建一個(gè)容量為 1的緩沖通道。當(dāng)通道已滿時(shí)，自動(dòng)收?qǐng)?bào)機(jī)會(huì)丟棄時(shí)間值。

這是問(wèn)題中跟蹤的時(shí)間表。同一時(shí)間列出的事件按列出的順序依次發(fā)生一點(diǎn)點(diǎn)。

1s - ticker sends value

1s - main goroutine receives first value

1s - main goroutine starts sleep for 5s

2s - ticker sends value (channel has capacity 1).

3s - ticker fails to send value because channel is full

4s - ticker fails to send value because channel is full

5s - ticker fails to send value because channel is full

6s - main goroutine exits sleep and receives buffered value

6s - ticker sends value

6s - main goroutine receives buffered value

ticker 和 main goroutine 跑到 6s 標(biāo)記，因?yàn)?sleep 是 ticker 周期的倍數(shù)。在您的跟蹤中，主 goroutine 贏得了比賽。在我的機(jī)器上，自動(dòng)收?qǐng)?bào)機(jī)贏得了比賽，我得到了你期望的時(shí)間。這是我機(jī)器上的樣子。

...

5s - ticker fails to send value because channel is full

6s - ticker fails to send value because channel is full

6s - main goroutine receives buffered value

7s - ticker sends value

7s - main goroutine receives value

自動(dòng)收?qǐng)?bào)機(jī)在操場(chǎng)上以 6 秒的成績(jī)贏得比賽。在這里運(yùn)行它。當(dāng)睡眠時(shí)間減少 1μs 時(shí)，主 goroutine 贏得了比賽。在這里運(yùn)行它。

當(dāng)睡眠持續(xù)時(shí)間不是代碼周期的倍數(shù)時(shí)，這很容易看出。以下是睡眠持續(xù)時(shí)間為 2.5 秒時(shí)發(fā)生的情況：

1s - ticker sends value

1s - main goroutine receives first value

1s - main goroutine starts sleep for 2.5s

2s - ticker sends value

3s - ticker fails to send value because channel is full

3.5s - main goroutine exits sleep and receives buffered value

4s - ticker sends value

4s - main goroutine receives value

反對(duì) 回復(fù) 2022-11-08

慕的地8271018

TA貢獻(xiàn)1796條經(jīng)驗(yàn) 獲得超4個(gè)贊

在time.Ticker中，有一個(gè)chan Time. 在NewTicker(d Duration) *Ticker函數(shù)中，它創(chuàng)建tickers時(shí)間通道作為容量為1的緩沖通道。在函數(shù)中，如下所述。

// 給通道一個(gè) 1 元素的時(shí)間緩沖區(qū)。
// 如果客戶在閱讀時(shí)落后了，我們將滴答聲
// 放在地板上，直到客戶趕上。

在您的情況下，時(shí)間每秒都會(huì)滴答并寫入頻道。睡眠時(shí)，ticker 向通道寫入一次，循環(huán)繼續(xù)后立即被 select case 接收并打印。在另外 4 秒內(nèi)，通道被阻塞并且滴答聲被丟棄。立即循環(huán)繼續(xù)它被暢通并接受更多的通道滴答聲。

通過(guò)通道打印時(shí)間，您可以輕松了解行為。更新代碼如下。

func main() {

ticker := time.NewTicker(1 * time.Second)

i := 0

for {

select {

case t := <-ticker.C:

log.Println(i, t)

if i == 0 {

time.Sleep(5 * time.Second) // simulate the blocking

}

i++

}

輸出：

2022/02/20 08:47:58 0 2022-02-20 08:47:58.773375 +0530 +0530 m=+1.004241004

2022/02/20 08:48:03 1 2022-02-20 08:47:59.772787 +0530 +0530 m=+2.003666993

2022/02/20 08:48:03 2 2022-02-20 08:48:03.774272 +0530 +0530 m=+6.005207433 // printing time is same, but channel's received time has 4 sec difference.

2022/02/20 08:48:04 3 2022-02-20 08:48:04.774203 +0530 +0530 m=+7.005151715

反對(duì) 回復(fù) 2022-11-08