Golang golang-parallel (snippet)

Go programming example 'golang-parallel'

golang-parallel

Golang beginners example: golang-parallel

package main

import (
    "fmt"
    "os"
)

var (
    // list of nth prime numbers to find
    requests = []int{200000, 500000, 100000, 250000, 550000, 150000, 350000, 300000}
)

func main() {
    if len(os.Args) == 1 {
        fmt.Println("start this application with the argument true to compute primenumbers parallel or false for serial")
        fmt.Println("you can configure the maximum processes/threads amount with: \"export GOMAXPROCS=$number\"")
        os.Exit(1)
    }

    if os.Args[1] == "true" {
        runParallel()
    } else {
        runSequential()
    }
}

func runSequential() {
    for _, index := range requests {
        fmt.Printf("the %dth prime number is: %d\n", index, getPrime(index))
    }
}

func runParallel() {
    // data struct that goroutines will send information
    // back to main thread
    type WorkerResponse struct {
        Index int
        Prime int
    }

    workerChan := make(chan WorkerResponse)
    defer close(workerChan)

    // send requests to n goroutines
    for _, index := range requests {
        // start this goroutine with the index in the loop
        // we must give this param, because index would be shared memory
        go func(idx int) {
            workerChan <- WorkerResponse{Index: idx, Prime: getPrime(idx)}
        }(index)
    }

    for i := 0; i < len(requests); i++ {
        response := <-workerChan
        fmt.Printf("the %dth prime number is: %d\n", response.Index, response.Prime)
    }
}

func Sqrt(n int) int {
    var t uint
    var b uint
    var r uint
    t = uint(n)
    p := uint(1 << 30)
    for p > t {
        p >>= 2
    }
    for ; p != 0; p >>= 2 {
        b = r | p
        r >>= 1
        if t >= b {
            t -= b
            r |= p
        }
    }
    return int(r)
}

func getPrime(n int) int {
    var primeList = []int{2}
    var isPrime int = 1
    var num int = 3
    var sqrtNum int = 0
    for len(primeList) < n {
        sqrtNum = Sqrt(num)
        for i := 0; i < len(primeList); i++ {
            if num%primeList[i] == 0 {
                isPrime = 0
            }
            if primeList[i] > sqrtNum {
                i = len(primeList)
            }
        }
        if isPrime == 1 {
            primeList = append(primeList, num)
        } else {
            isPrime = 1
        }
        num = num + 2
    }
    return primeList[n-1]
}

Useful links

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