Mastering Concurrency in Go/

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Fan-In, Fan-Out

Fan-In, Fan-Out

In this lesson, we will get familiar with Fan-In, Fan-Out techniques which are used to multiplex and demultiplex data in Go.

We'll cover the following...

Fan-In refers to a technique in which you join data from multiple inputs into a single entity. On the other hand, Fan-Out means to divide the data from a single source into multiple smaller chunks. In this lesson, we’ll learn how to make use of both these techniques.

The code below is from the previous lesson where two receiving operations were blocking each other.

	fmt.Println(<-positionChannel1)
	fmt.Println(<-positionChannel2)

These operations were taking turns not only in printing value on to the console but also in proceeding to the next computation.

Check it out below:

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package main
import ( "fmt"
		"math/rand"
		"time")
func updatePosition(name string) <-chan string { 
	positionChannel := make(chan string)
	go func() {
		for i := 0; ; i++ {
			positionChannel <- fmt.Sprintf("%s %d", name , i)
			time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
		}
	}()
	return positionChannel
}
func main() {
	positionChannel1 := updatePosition("Legolas :") 
	positionChannel2 := updatePosition("Gandalf :")
	
	for i := 0; i < 5; i++ {
		fmt.Println(<-positionChannel1)
		fmt.Println(<-positionChannel2)
	}
	fmt.Println("Done with getting updates on positions.")
}

But what if you want to get position updates as soon as they are updated? This is where the fan-in technique comes into play. By using this technique, we’ll combine the inputs from both channels and send them through a single channel. Look at the code below to see how it’s done:

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package main
import ( "fmt"
		  "math/rand"
		  "time")
func updatePosition(name string) <-chan string { 
	positionChannel := make(chan string)
	go func() {
		for i := 0; ; i++ {
			positionChannel <- fmt.Sprintf("%s %d", name , i)
			time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
		}
	}()
	return positionChannel
}
func fanIn(mychannel1, mychannel2 <-chan string) <-chan string {
	mychannel := make(chan string) 
	go func() { 
		for {
			mychannel <- <-mychannel1 
		}
	}()
	go func() { 
		for {
			mychannel <- <-mychannel2
		}
	}()
	return mychannel
}
func main() {
	positionsChannel := fanIn(updatePosition("Legolas :"), updatePosition("Gandalf :"))
	
	for i := 0; i < 10; i++ {
		fmt.Println(<-positionsChannel)
	}
	fmt.Println("Done with getting updates on positions.")
}
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