同時実行数制限付きでループを並列処理する。

concurLoop.go

package main

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

func main() {
        log(-1, -1)

        indexes := []int{1, 2, 3, 4, 5, 6, 7}

        fmt.Println("sleepなし。順番不定。")
        concurLoop(indexes, 3, outputWithoutWait)
        fmt.Println("sleepあり。順番に出力。")
        concurLoop(indexes, 3, outputWithWait)

        waits := []int{3, 2, 5, 2, 8, 1}
        fmt.Println("sleepあり。Sleepの短い順番に出力。")
        concurLoop(waits, 3, outputWithWait)
}

func outputWithoutWait(index, item int) {
        log(index, item)
}

func outputWithWait(index, wait int) {
        time.Sleep(time.Duration(wait) * time.Second)
        log(index, wait)
}

func log(index, item int) {
        fmt.Printf("time:%v\tindex:%d\titem:%v\n", time.Now(), index, item)
}

func concurLoop(array []int, limit int, handler func(int, int)) {
        var wg sync.WaitGroup
        var semaphore = make(chan struct{}, limit)

        for index, item := range array {
                wg.Add(1)
                semaphore <- struct{}{}

                go func(index, item int) {
                        defer func() {
                                wg.Done()
                                <-semaphore
                        }()

                        handler(index, item)
                }(index, item)
        }

        wg.Wait()
}