mutexを使いつつchannelが空かそうでないかで処理を分ける

chanpool.go

package main

import (
	"log"
	"math/rand"
	"sync"
	"time"
)

type ChanPool struct {
	pool chan interface{}
	sync.Mutex
}

func NewChanPool(num int) *ChanPool {
	pool := make(chan interface{}, num)
	for i := 0; i < num; i++ {
		pool <- struct{}{}
	}
	return &ChanPool{pool: pool}
}

func (cp *ChanPool) get() (interface{}, bool) {
	cp.Lock()
	defer cp.Unlock()
	num := len(cp.pool)
	log.Printf("num: %d", num)
	if num == 0 {
		return struct{}{}, false
	}
	return <-cp.pool, true
}

func (cp *ChanPool) put(s interface{}) {
	cp.pool <- s
}

func (cp *ChanPool) Run(okfn, overfn func()) {
	s, ok := cp.get()
	defer func() {
		if ok {
			cp.put(s)
		}
	}()
	if ok {
		okfn()
	} else {
		overfn()
	}
}

var sleep = []time.Duration{
	time.Millisecond * 50,
	time.Millisecond * 100,
	time.Millisecond * 150,
}

func run(cp *ChanPool) {
	cp.Run(
		func() {
			time.Sleep(sleep[rand.Intn(len(sleep))])
			log.Print("ok")
		},
		func() {
			log.Print("over")
		},
	)
}

func main() {
	cp := NewChanPool(10)
	for {
		go run(cp)
		time.Sleep(time.Millisecond * 10)
	}
}