Golang golang-fanin (snippet)

Go programming example 'golang-fanin'

golang-fanin

Golang beginners example: golang-fanin

package main

import (
    "fmt"
    "sync"
)

// returns a read only channel
func generator(start, end int) <-chan int {
    c := make(chan int) // ubuffered channel

    // Fire a goroutine to send values on the channel
    go func() {
        for i := start; i < end; i++ {
            c <- i // This blocks untill there is a reader for the chan
        }
        // close the channel when done; otherwise it leaks resources
        close(c)
    }()

    return c
}

/* The fan in pattern is an important pattern which combines
mulitple channels, returns a single channel from those channels
*/

func fanIn(chans ...<-chan int) chan int {
    var wg sync.WaitGroup

    c := make(chan int)

    // Closure to send values from a channel
    output := func(ch <-chan int) {
        for n := range ch {
            c <- n
        }
        wg.Done()
    }

    wg.Add(len(chans))

    // send values on c via differnt goroutines
    for _, ch := range chans {
        go output(ch)
    }

    // wait for all goroutines to finish before closing the channel
    go func() {
        wg.Wait()
        close(c)
    }()

    return c
}

func main() {
    s1 := generator(1, 10)
    s2 := generator(20, 30)
    s3 := generator(40, 50)
    s4 := generator(60, 70)

    // merge all the channels into one
    mergerd := fanIn(s1, s2, s3, s4)

    for n := range mergerd { // range loop terminates once the chan is closed, otherwise it blocks if there is no value
        fmt.Println(n)
    }
}

Useful links

• Learn Go: https://golangr.com
• Download Go: https://golang.org