go - Goroutines 的运行顺序

Question

我现在正在学习 Golang，并且在网上看到了一些有趣的教程。例如这个:https://golangbot.com/channels/

在这部分关于goroutines，有一个例子如下:

package main

import (
    "fmt"
)

func producer(chnl chan int) {
    for i := 0; i < 10; i++ {
        fmt.Println("debugging send...", i)
        chnl <- i
    }
    close(chnl)
}
func main() {
    ch := make(chan int)
    go producer(ch)
    for {
        v, ok := <-ch
        if ok == false {
            break
        }
        fmt.Println("Received ", v, ok)
    }
}

fmt.Println("debugging send...", i) 行是我为调试目的添加的。输出是:

debugging send... 0
debugging send... 1
Received  0 true
Received  1 true
debugging send... 2
debugging send... 3
Received  2 true
Received  3 true
debugging send... 4
debugging send... 5
Received  4 true
Received  5 true
debugging send... 6
debugging send... 7
Received  6 true
Received  7 true
debugging send... 8
debugging send... 9
Received  8 true
Received  9 true

输出顺序对我来说似乎很有趣，但不能完全理解幕后发生的事情。

Answer 1

唯一同步的地方是 channel 操作。在这些语句之外，goroutine 中的操作顺序之间不需要相关性。

多次运行你的程序，我得到了你大部分时间的输出，但有时我也会看到这样的东西:

debugging send... 0
debugging send... 1
Received  0 true
Received  1 true
debugging send... 2
debugging send... 3
Received  2 true
Received  3 true
debugging send... 4
debugging send... 5
Received  4 true
Received  5 true
debugging send... 6
debugging send... 7
Received  6 true
debugging send... 8
Received  7 true
Received  8 true
debugging send... 9
Received  9 true

尝试运行这个 Bash shell 脚本多次运行该程序并比较其输出:

#!/bin/bash

# c.go has your Go program
go run c.go > first.txt
cat first.txt

echo "======"
while :; do
    go run c.go > run.txt
    if ! diff -q run.txt first.txt; then
        break
    fi
done

cat run.txt

编辑:您可能会发现 https://golang.org/ref/mem阅读 Go 中的同步很有趣。