From 2212079ecd94b1479b625b61c54e173f8421423f Mon Sep 17 00:00:00 2001
From: Edward <chenlulei@gmail.com>
Date: Thu, 7 May 2020 12:03:03 +0800
Subject: [PATCH] add a fan in and out

---
 concurrency/fan/fan_in_out_test.go | 81 ++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 concurrency/fan/fan_in_out_test.go

diff --git a/concurrency/fan/fan_in_out_test.go b/concurrency/fan/fan_in_out_test.go
new file mode 100644
index 0000000..da16a32
--- /dev/null
+++ b/concurrency/fan/fan_in_out_test.go
@@ -0,0 +1,81 @@
+package main
+
+import (
+	"fmt"
+	"sync"
+	"testing"
+)
+
+func TestMergeNumbersSeq(T *testing.T) {
+	randomNumbers := []int{13, 44, 56, 99, 9, 45, 67, 90, 78, 23}
+	// generate the common channel with inputs
+	inputChan := generatePipeline(randomNumbers)
+
+	// Fan-out to 2 Go-routine
+	c1 := squareNumber(inputChan)
+	c2 := squareNumber(inputChan)
+
+	// Fan-in the resulting squared numbers
+	c := fanIn(c1, c2)
+	sum := 0
+
+	// Do the summation
+	for i := 0; i < len(randomNumbers); i++ {
+		sum += <-c
+	}
+	fmt.Printf("Total Sum of Squares: %d", sum)
+}
+
+func generatePipeline(numbers []int) <-chan int {
+	out := make(chan int)
+	go func() {
+		for _, n := range numbers {
+			out <- n
+		}
+		close(out)
+	}()
+	return out
+}
+
+func squareNumber(in <-chan int) <-chan int {
+	out := make(chan int)
+	go func() {
+		for n := range in {
+			out <- n * n
+		}
+		close(out)
+	}()
+	return out
+}
+
+// fanIn compose different channels into one
+func fanIn(cs ...<-chan int) <-chan int {
+	var wg sync.WaitGroup
+
+	out := make(chan int, 3)
+
+	wg.Add(len(cs))
+
+	// Start an send goroutine for each input channel in cs. send
+	// copies values from c to out until c is closed, then calls wg.Done.
+	send := func(c <-chan int) {
+		for n := range c {
+			out <- n
+		}
+		wg.Done()
+	}
+
+	//启动多个 go routine 开始工作
+	for _, c := range cs {
+		go send(c)
+	}
+	// Start a goroutine to close out once all the send goroutines are
+	// done.  This must start after the wg.Add call.
+	//关闭动作,放在发送一方，会更好
+	go func() {
+		wg.Wait()
+		close(out)
+	}()
+
+	return out
+}