如何正确停止定时器？

Question

var timer *time.Timer

func A() {
    timer.Stop() // cancel old timer
    go B() // new timer
}

func B() {
    timer = time.NewTimer(100 * time.Millisecond)
    select {
    case <- timer.C:
    // do something for timeout, like change state
    }
}

函数A和B都在不同的goroutines中。

假设 A 在 RPC goroutine 中。当应用程序收到 RPC 请求时，它会取消 B 中的旧计时器，并在另一个 goroutine 中启动一个新计时器。

医生说：

Stop does not close the channel, to prevent a read from the channel succeeding incorrectly.

那么如何打破B中的select来避免goroutine泄漏？

Answer 1

使用额外的独立抵消信号。由于您已经有一个 select 语句，另一个渠道是显而易见的选择：

import "time"

var timer *time.Timer
var canceled = make(chan struct{})

func A() {
    // cancel all current Bs
    select {
    case canceled <- struct{}{}:
    default:
    }   

    timer.Stop()

    go B()       // new timer
}

func B() {
    timer = time.NewTimer(100 * time.Millisecond)
    select {
    case <-timer.C:
        // do something for timeout, like change state
    case <-canceled:
        // timer aborted
    }
}

请注意，所有 A 和 B 都在为计时器值相互竞争。使用上面的代码，没有必要让 A 停止计时器，因此您不需要全局计时器，从而消除了竞争：

import "time"

var canceled = make(chan struct{})

func A() {
    // cancel all current Bs
    select {
    case canceled <- struct{}{}:
    default:
    }

    go B()
}

func B() {
    select {
    case <-time.After(100 * time.Millisecond):
        // do something for timeout, like change state
    case <-canceled:
        // aborted
    }
}

Answer 2

添加到上面的答案，如果你想一次取消所有服务员，你可以使用你自己的计时器机制封装行为，可以取消，在 After 通道中发送 true 或 false 到对于所有服务员，告诉您您是从取消中醒来还是超时。

package main

import (
    "fmt"
    "time"
)

type CancellableTimer struct {
    cancel chan bool
}

func NewCancellableTimer() *CancellableTimer {
    return &CancellableTimer{
        cancel: make(chan bool),
    }
}

// internal wait goroutine wrapping time.After
func (c *CancellableTimer) wait(d time.Duration, ch chan bool) {
    select {
    case <-time.After(d):
        ch <- true
    case <-c.cancel:
        ch <- false
    }
}

// After mimics time.After but returns bool to signify whether we timed out or cancelled
func (c *CancellableTimer) After(d time.Duration) chan bool {
    ch := make(chan bool)
    go c.wait(d, ch)
    return ch
}

// Cancel makes all the waiters receive false
func (c *CancellableTimer) Cancel() {
    close(c.cancel)

}

// a goroutine waiting for cancellation
func B(t *CancellableTimer) {
    select {
    // timedOut will signify a timeout or cancellation
    case timedOut := <-t.After(time.Second):
        if timedOut {
            fmt.Println("Time out!")
        } else {
            fmt.Println("Cancelled!")
        }
    }
}

func main() {
    t := NewCancellableTimer()
    // Start 3 goroutines that wait for different timeouts on the same timer
    go B(t)
    go B(t)
    go B(t)

    // sleep a bit before cancelling
    time.Sleep(100 * time.Millisecond)

    // cancel the timer and all its waiters
    t.Cancel()

    // this is just to collect the output
    time.Sleep(time.Second)

}

输出：

Cancelled!
Cancelled!
Cancelled!

操场link：

https://play.golang.org/p/z8OscJCXTvD

如何正确停止定时器？

How to stop a timer correctly?

go

goroutine