父协程结束时终止子协程

偷偷努力，悄无声息地变强，然后惊艳所有人！哈哈，小伙伴们又来学习啦~今天我将给大家介绍《父协程结束时终止子协程》，这篇文章主要会讲到等等知识点，不知道大家对其都有多少了解，下面我们就一起来看一吧！当然，非常希望大家能多多评论，给出合理的建议，我们一起学习，一起进步！

我们有一个主 go 例程，它生成一个父 goroutine，而父 goroutine 又生成一个子 go 例程。

即使父协程返回，子协程仍然运行。这会导致 goroutine 泄漏。

我们如何避免这种情况？

下面我添加了一个代码片段来模拟以下内容 这里的子协程可以是任何长时间运行的进程，例如数据库查询、api 调用等

program output: 

in main function -  1
starting parent function -  2
starting child function -  3
child timed out -  3
completed parent -  2  // implying that child goroutine is still running with main routine

package main

import (
    "fmt"
    "runtime"
    "sync"
    "time"
)

// WaitGroup used by main to wait for parent goroutine
var wg sync.WaitGroup

// Long duration process time
var duration = 100


func main() {
    fmt.Println("In main function - ", runtime.NumGoroutine())
    wg.Add(1)
    go parentRoutine()
    wg.Wait()
    fmt.Println("Completed parent - ", runtime.NumGoroutine())
}

func parentRoutine() {
    fmt.Println("Starting parent function - ", runtime.NumGoroutine())
    childRes := make(chan int)


        // Spawning child goroutine
    go func() {

               // Here the child is a simulation of a long running process which might take more time than expected timeout. It runs even after parent returns due to timeout


        fmt.Println("Starting child function - ", runtime.NumGoroutine())
        time.Sleep(time.Duration(duration)*time.Second)
        fmt.Println("Child ended - ", runtime.NumGoroutine())
        childRes <- 1
    }()

    select {
    case <-childRes:
        fmt.Println("Child completed - ", runtime.NumGoroutine())
    case <- time.After(time.Duration(3)*time.Second):
        fmt.Println("Child timed out - ", runtime.NumGoroutine())
    }
    wg.Done()
}

解决方案

这是带有上下文的代码片段：https://play.golang.org/p/0TXyt4vuGKJ。

package main

import (
    "context"
    "fmt"
    "runtime"
    "sync"
    "time"
)

// waitgroup used by main to wait for parent goroutine
var wg sync.waitgroup

// long duration process time
var duration = 100

func main() {
    fmt.println("in main function - ", runtime.numgoroutine())
    wg.add(1)
    ctx, cancel := context.withcancel(context.background())
    go parentroutine(ctx)
    wg.wait()
    cancel()
    time.sleep(time.second) //if main immediately exists the child goroutine does not
                            //have the time to terminate.
    fmt.println("completed parent - ", runtime.numgoroutine())
}

func parentroutine(ctx context.context) {
    fmt.println("starting parent function - ", runtime.numgoroutine())
    childres := make(chan int)

    // spawning child goroutine
    go func(ctx context.context) {

        // here the child is a simulation of a long running process which might take more time than expected timeout. it runs even after parent returns due to timeout

        fmt.println("starting child function - ", runtime.numgoroutine())
        select {
        case <-ctx.done():
            fmt.println("child's context expired - ", runtime.numgoroutine())
        case <-time.after(time.duration(duration) * time.second):
            //time consuming task
        }
        fmt.println("child ended - ", runtime.numgoroutine())
        childres <- 1
    }(ctx)

    select {
    case <-ctx.done():
        fmt.println("parent's context expired - ", runtime.numgoroutine())
    case <-childres:
        fmt.println("child completed - ", runtime.numgoroutine())
    case <-time.after(time.duration(3) * time.second):
        fmt.println("child timed out - ", runtime.numgoroutine())
    }
    wg.done()
}

现在的输出如下：

In main function -  1
Starting parent function -  2
Starting child function -  3
Child timed out -  3
Child's context expired -  2
Child ended -  2
Completed parent -  2

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