有时 goroutine 不会从通道中获取事件数据

如何解决有时 goroutine 不会从通道中获取事件数据

我的问题有时是 goroutine NOT 从 reg.eventCh 获取事件数据

没有退出日志打印，这个goroutine没有退出，正在运行。

reg.eventCh 通道未关闭，日志可以打印长度增量。

日志显示：

reg.eventCh <- event,count: 1
event is coming

reg.eventCh <- event,count: 0  (why count is 0? log print after data in channel)
event is coming

reg.eventCh <- event,count: 1

reg.eventCh <- event,count: 2
.
.
.
reg.eventCh <- event,count: 999

reg.eventCh <- event,count: 1000

日志显示不要从 reg.eventCh 获取事件数据， 下面是我的代码：

reg := &Reg{}
reg.exitCh = make(chan *demo.Exit)
reg.eventCh = make(chan *demo.Event,1000)

go reader(reg)

// other goroutine will writer event to reg.eventCh like:

reg.eventCh <- event
log.Println("reg.eventCh <- event,count:",len(reg.eventCh))


func reader(reg *Reg) {
    for {
        select {
            case event := <-reg.eventCh:
                log.Println("event is coming")
                handler(event)
            case exit := reg.exitCh:
                log.Println("exit")
                return
        }
    }
}

我的代码有问题吗？

任何帮助将不胜感激，

谢谢，

吉米

演示代码：

package main

import (
    "log"
    "math/rand"
    "time"
)

type Event struct {
    testStr string
}

type Exit struct {
    testStr string
}

type Reg struct {
    des     string
    eventCh chan *Event
    exitCh  chan *Exit
}

// this demo code like my issue
// this issue is sometimes case event := <-reg.eventCh NOT work in go reader()
func main() {
    reg := &Reg{}
    reg.des = "sometime not read from reg.eventCh"
    reg.eventCh = make(chan *Event,1000)
    reg.exitCh = make(chan *Exit)

    // read data from channel
    go reader(reg)

    // simulate data: write in channel
    for i := 0; i < 10; i++ {
        go writer(reg)
    }

    select {}
}

func writer(reg *Reg) {
    for {
        time.Sleep(time.Duration(rand.Intn(500)) * time.Millisecond)
        event := new(Event)
        event.testStr = "1"
        reg.eventCh <- event
        log.Println("reg.eventCh <- event,channel count:",len(reg.eventCh))
    }
}

func reader(reg *Reg) {
    for {
        select {
        case event := <-reg.eventCh:
            log.Println("event is coming,len(reg.eventCh))
            handler(event)
        case exit := <-reg.exitCh:
            log.Println("goroutine exit: ",exit)
            return
        }
    }
}

func handler(e *Event) {
    // logic codes
}

需要时间来重现这个问题。

解决方法

您的代码有一些错误！它不向 exitCh 发送数据，它没有停止条件和死锁块。我将通过回答我提出的 3 个问题来分享我的答案。

问题#1： why count is 0? log print after data in channel

len(channel) 仅用于了解当前可用的数据量。如果接收方已经收到数据，则始终为0。

问题#2：为什么要使用 select 之类的退出控件？

您可以使用 <-context.Done() 或其他更惯用的代码。

问题#3：为什么没有 exitCh 的数据？

显然你创建了一个退出循环，但它不起作用

代码接收：

package main

import (
    "context"
    "fmt"
    "log"
)

var (
    ctx,cancel = context.WithCancel(context.Background())
)

type Event struct {
    testStr string
}

type Exit struct {
    testStr string
}

type Reg struct {
    des     string
    eventCh chan *Event
    exitCh  chan *Exit
}

// this demo code like my issue
// this issue is sometimes case event := <-reg.eventCh NOT work in go reader()
func main() {
    //
    reg := &Reg{}
    reg.des = "sometime not read from reg.eventCh"
    reg.eventCh = make(chan *Event,1000)
    reg.exitCh = make(chan *Exit)

    // read data from channel
    go reader(reg)

    // simulate data: write in channel
    for i := 0; i < 10; i++ {
        go writer(reg,fmt.Sprintf("gorouinte-%d",i))
    }
    // notify exit
    <-ctx.Done()
}

func writer(reg *Reg,tname string) {
    for /* infinity loop */ {
        // time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
        event := new(Event)
        event.testStr = "1"
        reg.eventCh <- event
        log.Println("reg.eventCh <- event,channel count:",len(reg.eventCh))
        // simulates stop condition
        if len(reg.eventCh) == 1000 {
            reg.exitCh <- &Exit{"exit now!"}
            log.Printf("stop write loop in routine %s\n",tname)
            return
        }
    }
}

func reader(reg *Reg) {
    for {
        select {
        case event := <-reg.eventCh:
            log.Println("event is comming,len(reg.eventCh))
            handler(event)
        case exit := <-reg.exitCh:
            log.Println("goroutine exit: ",exit)
            cancel() // used to exit this program
            return
        }
    }
}

func handler(e *Event) {
    // logic codes
}

Playground demo