为什么所有的 goroutine 都睡着了——死锁。识别瓶颈

Question

package main

import (

    "fmt"

    "runtime"

    "sync"

    "time"

)

func main() {

    intInputChan := make(chan int, 50)

    var wg sync.WaitGroup

    for i := 0; i < 3; i++ {

        wg.Add(1)

        go worker(intInputChan, wg)

    }

    for i := 1; i < 51; i++ {

        fmt.Printf("Inputs. %d \n", i)

        intInputChan <- i

    }

    close(intInputChan)

    wg.Wait()

    fmt.Println("Existing Main App... ")

    panic("---------------")

}

func worker(input chan int, wg sync.WaitGroup) {

    defer func() {

        fmt.Println("Executing defer..")

        wg.Done()

    }()

    for {

        select {

        case intVal, ok := <-input:

            time.Sleep(100 * time.Millisecond)

            if !ok {

                input = nil

                return

            }

            fmt.Printf("%d  %v\n", intVal, ok)

        default:

            runtime.Gosched()

        }

    }

}

抛出的错误是。

致命错误：所有 goroutine 都处于睡眠状态 - 死锁！

goroutine 1 [semacquire]：sync.(*WaitGroup).Wait(0xc082004600) c:/go/src/sync/waitgroup.go:132 +0x170 main.main() E:/Go/go_projects/go/src/Test .go:22 +0x21a

Answer 1

我刚刚尝试过（操场）通过 awg *sync.WaitGroup并且它有效。传递sync.WaitGroup意味着传递sync.WaitGroup（按值传递）的副本：goroutine 提到Done()了不同的 sync.WaitGroup.var wg sync.WaitGroupfor i := 0; i < 3; i++ {&nbsp; &nbsp; wg.Add(1)&nbsp; &nbsp; go worker(intInputChan, &wg)}请注意&wg：您正在按值传递指向原始 的指针sync.WaitGroup，供 goroutine 使用。

Answer 2

如所提到的，不从同步绕包传值的类型，右靠近的顶部sync包文档：“含有在此包中定义的类型的值不应该被复制。&nbsp;”这也包括类型本身（sync.Mutex，sync.WaitGroup等）。但是，有几个注意事项：wg.Add如果您知道要添加多少个，您可以只使用一次调用（但如文档所示，请确保在任何调用之前都已完成Wait）。你不想那样打电话runtime.Gosched；它使工人忙循环。您可以使用range从通道读取以简化在关闭时停止的过程。对于小函数，您可以使用闭包，而根本不需要传递通道或等待组。这变成了这样：package mainimport (&nbsp; &nbsp; "fmt"&nbsp; &nbsp; "sync"&nbsp; &nbsp; "time")func main() {&nbsp; &nbsp; const numWorkers = 3&nbsp; &nbsp; c := make(chan int, 10)&nbsp; &nbsp; var wg sync.WaitGroup&nbsp; &nbsp; wg.Add(numWorkers)&nbsp; &nbsp; for i := 0; i < numWorkers; i++ {&nbsp; &nbsp; &nbsp; &nbsp; go func() {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; defer func() {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; fmt.Println("Executing defer…")&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; wg.Done()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; for v := range c {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; fmt.Println("recv:", v)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; time.Sleep(100 * time.Millisecond)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; }()&nbsp; &nbsp; }&nbsp; &nbsp; for i := 1; i < 51; i++ {&nbsp; &nbsp; &nbsp; &nbsp; fmt.Println("send:", i)&nbsp; &nbsp; &nbsp; &nbsp; c <- i&nbsp; &nbsp; }&nbsp; &nbsp; fmt.Println("closing…")&nbsp; &nbsp; close(c)&nbsp; &nbsp; fmt.Println("waiting…")&nbsp; &nbsp; wg.Wait()&nbsp; &nbsp; fmt.Println("Exiting Main App... ")}