在昨天的例子中,有使用到close()來關閉channel.
那怎樣來判斷channel是否已經關閉呢.

我們把昨天的程式改寫一下,為了方便對照起見,有保留原本的異動部份.

// hello71
// producer_consumer 2
package main

import (
	"fmt"
	"time"
)

// integer producer
func numGen(start, count int, out chan<- int) {
	for i := 0; i < count; i++ {
		out <- start
		start += count
	}
	close(out)
	fmt.Printf("Producer: 送完  -%v\n", time.Now())
}

// integer consumer
func numEchoRange(in <-chan int, done chan<- bool) {
	//for num := range in {
	//	time.Sleep(time.Second)
	//	fmt.Printf("consumer: 收到%2d-%v\n", num, time.Now())
	//}

	for {
		input, open := <-in
		if !open {
			break
		}
		time.Sleep(time.Second)
		fmt.Printf("consumer: 收到%2d-%v\n", input, time.Now())
	}

	done <- true
}

func main() {
	numChan := make(chan int, 100)
	done := make(chan bool)
	go numGen(0, 10, numChan)
	go numEchoRange(numChan, done)
	<-done
	fmt.Println("Main():所有的工作都已完成!")
}

執行結果:

./hello71 
Producer: 送完  -2014-10-18 00:30:20.62187013 +0800 CST
consumer: 收到 0-2014-10-18 00:30:21.622183431 +0800 CST
consumer: 收到10-2014-10-18 00:30:22.622331389 +0800 CST
consumer: 收到20-2014-10-18 00:30:23.622454017 +0800 CST
consumer: 收到30-2014-10-18 00:30:24.622602616 +0800 CST
consumer: 收到40-2014-10-18 00:30:25.622749231 +0800 CST
consumer: 收到50-2014-10-18 00:30:26.622897952 +0800 CST
consumer: 收到60-2014-10-18 00:30:27.623024673 +0800 CST
consumer: 收到70-2014-10-18 00:30:28.623156869 +0800 CST
consumer: 收到80-2014-10-18 00:30:29.623288408 +0800 CST
consumer: 收到90-2014-10-18 00:30:30.623407953 +0800 CST
Main():所有的工作都已完成!