Golang Parallel

Issue

I am new to Golang and trying to understand Concurrency and Parallel. I read below mentioned article about Concurrency and Parallel. I have executed same program. But not getting the same ( mixed letter & character ) output. Getting first all letters then characters. it seems like concurrency is working not Parallel is not.

Article says add runtime.GOMAXPROCS(4) to make parallel.

Why I am not getting parallel out ?

I am using 4 core CPU system and GO version 1.8.2

https://www.goinggo.net/2014/01/concurrency-goroutines-and-gomaxprocs.html

I know that if we add Sleep then i can see parallel output, as per Concurrency concept . But Parallelism says if system has more than one CPU, then each thread will run in one CPU and it becomes Parallel process.
My question here is Why I am not getting parallel output though my system has 4 core and added runtime.GOMAXPROCS(4), .

Go Program

package main

import (
    "fmt"
    "runtime"
    "sync"
)

func main() {
    runtime.GOMAXPROCS(2)

    var wg sync.WaitGroup
    wg.Add(2)

    fmt.Println("Starting Go Routines")
    go func() {
        defer wg.Done()

        for char := ‘a’; char < ‘a’+26; char++ {
            fmt.Printf("%c ", char)
        }
    }()

    go func() {
        defer wg.Done()

        for number := 1; number < 27; number++ {
            fmt.Printf("%d ", number)
        }
    }()

    fmt.Println("Waiting To Finish")
    wg.Wait()

    fmt.Println("\nTerminating Program")
}

My Output

Starting Go Routines
Waiting To Finish
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 a
b c d e f g h i j k l m n o p q r s t u v w x y z
Terminating Program

Expected Output ( not the same , But Parallel output )

Starting Go Routines
Waiting To Finish
a b 1 2 3 4 c d e f 5 g h 6 i 7 j 8 k 9 10 11 12 l m n o p q 13 r s 14
t 15 u v 16 w 17 x y 18 z 19 20 21 22 23 24 25 26
Terminating Program

Solution

Since for loop has condition 27 in my above example, program execution was fast and not able to see parallelism. I have written different example and increased the condition then I could see the Parallel output.

package main

import (
    "fmt"
    "runtime"
    "sync"
)

var wg sync.WaitGroup

func init() {
    fmt.Println("!!!!!!!!!!!!!!!!!!!!!!!!!!!!", runtime.NumCPU())

}
func main() {
    fmt.Println(" Welcome to concurrency")
    wg.Add(2)
    go one()
    go two()
    fmt.Println("Waiting To Finish")
    wg.Wait()
    fmt.Println("\nTerminating Program")

}

func one() {
    for i := 0; i < 200; i++ {
        fmt.Println("one", i)
    }
    defer wg.Done()
}

func two() {
    for i := 0; i < 200; i++ {
        fmt.Println("Two:", i)
    }
    defer wg.Done()
}

UPDATE 8/28/2015: Go 1.5 is set to make the default value of GOMAXPROCS the same as the number of CPUs on your machine. I have removed the runtime.GOMAXPROCS(4)

Answered By – Gnana

Answer Checked By – Dawn Plyler (GoLangFix Volunteer)

Leave a Reply

Your email address will not be published.