通过channel控制并发数量

使用 go 关键字有时候需要控制一下并发的数量, 但不至于去修改 runtime.GOMAXPROCS 这个数值, 这里就用到了缓冲channel的特性

demo:

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package pool

import (
	"sync"
)

// WaitGroup 一个异步结构体
type WaitGroup struct {
	workChan chan int
	wg       sync.WaitGroup
}

// NewPool 生成一个工作池, coreNum 限制
func NewPool(coreNum int) *WaitGroup {
	ch := make(chan int, coreNum)
	return &WaitGroup{
		workChan: ch,
		wg:       sync.WaitGroup{},
	}
}

// Add 添加
func (ap *WaitGroup) Add(num int) {
	for i := 0; i < num; i++ {
		ap.workChan <- i
		ap.wg.Add(1)
	}
}

// Done 完结
func (ap *WaitGroup) Done() {
LOOP:
	for {
		select {
		case <-ap.workChan:
			break LOOP
		}
	}
	ap.wg.Done()
}

// Wait 等待
func (ap *WaitGroup) Wait() {
	ap.wg.Wait()
}

test:

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package pool

import (
	"fmt"
	"testing"
	"time"
)

func TestRun(t *testing.T) {
	work := NewPool(4)

	for i := 0; i < 50; i++ {
		work.Add(1)
		go testFunc(i, work)
	}

	fmt.Println("waiting...")
	work.Wait()
	t.Log("done")
}

func testFunc(i int, wg *WaitGroup) {
	defer wg.Done()
	fmt.Println(time.Now().Format("2006-01-02T15:04:05Z07:00"), "output: ", i)
	time.Sleep(time.Second * 1)
	fmt.Println(time.Now().Format("2006-01-02T15:04:05Z07:00"), "output: ", i, "done")
}

输出:

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2018-12-04T14:22:27+08:00 output:  3
2018-12-04T14:22:27+08:00 output:  1
2018-12-04T14:22:27+08:00 output:  0
2018-12-04T14:22:27+08:00 output:  2
2018-12-04T14:22:28+08:00 output:  3 done
2018-12-04T14:22:28+08:00 output:  0 done
2018-12-04T14:22:28+08:00 output:  1 done
2018-12-04T14:22:28+08:00 output:  5
2018-12-04T14:22:28+08:00 output:  6
2018-12-04T14:22:28+08:00 output:  2 done
2018-12-04T14:22:28+08:00 output:  7
2018-12-04T14:22:28+08:00 output:  4
2018-12-04T14:22:29+08:00 output:  4 done
2018-12-04T14:22:29+08:00 output:  8
2018-12-04T14:22:29+08:00 output:  7 done
2018-12-04T14:22:29+08:00 output:  6 done
.....

这里还是要带上 sync.WaitGroup, 保证最后一次循环时携程不会过早退出

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