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