Hello!

Today I demonstrating concurrency design pattern FANin.

In this sample concurrency design pattern FANin is being demonstrated using GoRoutine, Channels, Range, Select

Imp points
- Range will keep iterating and fetching the value until channel will be closed

• Select is useful which we are dealing with multiple channels together and we need to fetch from the channel whichever is ready with value.

In this design pattern a single channel accepts inputs from multiple output channels.

Test the code

package main

import "fmt"

func main() {
    even := make(chan int)
    odd := make(chan int)
    fanin := make(chan int)

    // Send, this will alunch a go routine, which will execute saparatly from mai routine
    go sendChannel(even, odd)
    go receiveChannel(even, odd, fanin)

       // range on channel will iterate until channel will be closed
    for v := range fanin {
        fmt.Printf("FanIn Channel value %v \n", v)
    }
    fmt.Printf("About to Exit")
}

func sendChannel(e, o chan<- int) {
    defer close(e)
    defer close(o)
    for index := 0; index < 10; index++ {
        if index%2 == 0 {
            e <- index
        } else {
            o <- index
        }
    }
}

func receiveChannel(e, o <-chan int, f int) {
    var okay int
    for {
        select {
        case v, ok := <-e:     // v will capture the channel value and ok will capture the state of channel
            if !ok {                                // If channel is closed then increase okay
                fmt.Printf("Even channel closed: %v  \n", ok)
                okay++
            } else {
                fmt.Printf("Even channel Value received: %v  \n", v)
                f <- v                         // Assign the value to fanin channel 
            }
        case v, ok := <-o:
            if !ok {
                fmt.Printf("Odd channel closed: %v \n", ok)
                okay++
            } else {
                fmt.Printf("Odd channel Value received: %v  \n", v)
                f <- v
            }
        }

              // Loop exit condition 
        if okay == 2 {
            fmt.Printf("Loop ends: %v \n", okay)
                        close(f)
            return
        }
    }
}

Cheers
Dev

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