go - channel slice 和并发函数执行

Question

如何在 slice 迭代中创建 channel slice 并同时运行函数 double(i):

package main

import (
    "fmt"
    "time"
)

func double(i int) int {
    result := 2 * i
    fmt.Println(result)
    time.Sleep(500000000)
    return result
}

func notParallel(arr []int) (outArr []int) {
    for _, i := range arr {
        outArr = append(outArr, double(i))
    }
    return
}

// how to do the same as notParallel func in parallel way.
// For each element of array double func should evaluate concuruntly
// without waiting each next element to eval
func parallel(arr []int) (outArr []int) {

    var chans []chan int
    for i := 0; i < len(arr); i++ {
        chans[i] = make(chan int) // i = 0 : panic: runtime error: index out of range
    }

    for counter, number := range arr {
        go func() {
            chans[counter] <- double(number)
        }()
    }

    return
}

func main() {
    arr := []int{7, 8, 9}
    fmt.Printf("%d\n", notParallel(arr))
    fmt.Printf("%d\n", parallel(arr))
}

playground

作为函数 double(i) 休眠 500 毫秒函数 notParallel(arr []int) 为 arr []int 的 3 个元素工作 1500 毫秒 但函数 parallel(arr []int) 将工作大约 500 毫秒。

在我的实现中有错误...

panic: runtime error: index out of range

...在线...

chans[i] = make(chan int) // i = 0

Answer 1

在这种情况下，您不需要使用 chan。

package main

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

func double(i int) int {
    result := 2 * i
    fmt.Println(result)
    time.Sleep(500000000)
    return result
}

func notParallel(arr []int) (outArr []int) {
    for _, i := range arr {
        outArr = append(outArr, double(i))
    }
    return
}

// how to do the same as notParallel func in parallel way.
// For each element of array double func should evaluate concuruntly
// without waiting each next element to eval
func parallel(arr []int) (outArr []int) {
    outArr = make([]int, len(arr))
    var wg sync.WaitGroup
    for counter, number := range arr {
        wg.Add(1)
        go func(counter int, number int) {
            outArr[counter] = double(number)
            wg.Done()
        }(counter, number)
    }
    wg.Wait()

    return
}

func main() {
    arr := []int{7, 8, 9}
    fmt.Printf("%d\n", notParallel(arr))
    fmt.Printf("%d\n", parallel(arr))
}

因为并行必须等待所有 goroutine 完成。

我注意到您的代码不起作用，因为您在同一函数范围内引用了 counter、number。