Golang解決fatal error: all goroutines are asleep - deadlock!

今天進行一個協程操作demo時總是報錯

//workerpool.go
package main

import (
	"fmt"
	"time"
)

//工作線程
func workerPool(jobs <-chan int, results chan<- int) {
	for j := range jobs {
		fmt.Println("start job", j)
		time.Sleep(time.Second) //模擬耗時工作
		fmt.Println("finish job", j)
		results <- j
	}
}

func main() {
	const numJobs = 5
	jobs := make(chan int, numJobs)    //
	results := make(chan int, numJobs) //

	go workerPool(jobs, results)

	for i := 1; i <= numJobs; i++ {
		jobs <- i
	}
        close(jobs)
        for r := range results {
		fmt.Println("results :", r)
	}
}

go run workerpool.go 報錯

start job 1
finish job 1
start job 2
results : 1
finish job 2
start job 3
results : 2
finish job 3
start job 4
results : 3
finish job 4
start job 5
results : 4
finish job 5
fatal error: all goroutines are asleep - deadlock!
results : 5

goroutine 1 [chan receive]:
main.main()
	workerpool.go:30 +0x19d

asleep就是說協程都在睡覺沒做事
問題應該出在遍歷jobs上, jobs遍歷完沒數據可操作了，引發 asleep - deadlock 報錯
改進方法：
1、是無限循環輸入數據到jobs
2、用waitGroup

方法1的無限循環輸入數據就不做介紹了，比較簡單
下面展示一下方法2使用waitGroup的方式

package main

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

var wg sync.WaitGroup

//工作線程
func workerPool(jobs <-chan int, results chan<- int) {
	for j := range jobs {
		fmt.Println("start job", j)
		time.Sleep(time.Second)
		fmt.Println("finish job", j)
		results <- j
	}
}

func init() {
	wg = sync.WaitGroup{}
}

func main() {
	const numJobs = 5
	jobs := make(chan int)    //
	results := make(chan int) //

	go workerPool(jobs, results)
	go func() {
		for r := range results {
			fmt.Println("results :", r)
			wg.Done()//接收到數據,表示完成了一份工作
		}
	}()

	for i := 1; i <= numJobs; i++ {
		wg.Add(1)//標記開始一份工作
		jobs <- i
	}

	wg.Wait()

}

正常運行結果如下：
start job 1
finish job 1
start job 2
results : 1
finish job 2
start job 3
results : 2
finish job 3
start job 4
results : 3
finish job 4
start job 5
results : 4
finish job 5
results : 5

Process finished with exit code 0