Go基础知识学习7并发

Golang原生支持并发。并发的最小单位是goroutine，相互之间的通信采用channel. 这里不涉及锁等复杂的内容，先简单的弄个例子了解一下Golang并发实现的简洁。

例子，实现slice的求和

具体步骤：创建两个goroutine 一个对slice的前一半数据求和，一个对slice后一半数据求和，最后综合两个结果完整的代码见： https://github.com/panyingyun/gostudy/blob/master/exp10.go 这里给出片段

        runtime.GOMAXPROCS(4)
	s := make([]int64, 100000000)
	for index, _ := range s {
		s[index] = int64(index * 2)
	}
	c1 := make(chan int64)
	c2 := make(chan int64)

	go sum(s[:len(s)/2], c1, "Google")
	go sum(s[len(s)/2:], c2, "Apple")
	
	sum1 := <-c1
	fmt.Println(sum1)
	sum2 := <-c2
	fmt.Println(sum2)
	fmt.Println(sum1 + sum2)

func sum(a []int64, c chan int64, flag string) {
	//fmt.Println("a = ", a)
	fmt.Println("time = ", time.Now(), flag)
	var sum int64 = 0
	//sum := 0
	for _, v := range a {
		sum += v
	}
	fmt.Println("sum = ", sum, flag)
	fmt.Println("time = ", time.Now(), flag)
	c <- sum // send sum to c
}

结果输出

runtime.GOMAXPROCS(1) 时结果：

Gorountine number =  2
Gorountine number =  4
time =  2014-08-13 18:19:22.8741904 +0800 CST Google
time =  2014-08-13 18:19:23.0051979 +0800 CST Apple
sum =  2499999950000000 Google
time =  2014-08-13 18:19:23.1372054 +0800 CST Google
sum =  7499999950000000 Apple
time =  2014-08-13 18:19:23.1372054 +0800 CST Apple
2499999950000000
7499999950000000
9999999900000000
total exec time =  498.0285ms

runtime.GOMAXPROCS(4) 时结果：

Gorountine number =  2
Gorountine number =  4
time =  2014-08-13 18:18:42.218865 +0800 CST Google
time =  2014-08-13 18:18:42.218865 +0800 CST Apple
sum =  2499999950000000 Google
time =  2014-08-13 18:18:42.3548728 +0800 CST Google
2499999950000000
sum =  7499999950000000 Apple
time =  2014-08-13 18:18:42.3568729 +0800 CST Apple
7499999950000000
9999999900000000
total exec time =  378.0216ms

从输出的flag（”Google”和”Apple”）看，无论CPU设置为1 or 4，在当前这个例子中，两个goroutine宏观上看是并发的，因为flag交叉打印输出了。另外，runtime.GOMAXPROCS(1) 设置运行CPU为1和4时，整个程序执行的时间略有差异，CPU=4时时间略省，当然这里不能说明CPU数量和性能的关系，毕竟例子太过简单了。