Sum of an array using pthreads

Sum of array is a small problem where we have to add each element in the array by traversing through the entire array. But when the number of elements are too large, it could take a lot of time. But this could solved by dividing the array into parts and finding sum of each part simultaneously i.e. by finding sum of each portion in parallel. This could be done by using multi-threading where each core of the processor is used. In our case, each core will evaluate sum of one portion and finally we will add the sum of all the portion to get the final sum. In this way we could improve the performance of a program as well as utilize the cores of processor. It is better to use one thread for each core. Although you can create as many thread as you want for better understanding of multi-threading. Examples:

Input :  1, 5, 7, 10, 12, 14, 15, 18, 20, 22, 25, 27, 30, 64, 110, 220
Output : sum is 600

Input :  10, 50, 70, 100, 120, 140, 150, 180, 200, 220, 250, 270, 300, 640, 110, 220
Output : sum is 3030

Note – It is advised to execute the program in Linux based system. Compile in linux using following code:

g++ -pthread program_name.cpp

Code – 

CPP

// CPP Program to find sum of array
#include <iostream>
#include <pthread.h>

// size of array
#define MAX 16

// maximum number of threads
#define MAX_THREAD 4

using namespace std;

int a[] = { 1, 5, 7, 10, 12, 14, 15, 18, 20, 22, 25, 27, 30, 64, 110, 220 };
int sum[4] = { 0 };
int part = 0;

void* sum_array(void* arg)
{

    // Each thread computes sum of 1/4th of array
    int thread_part = part++;

    for (int i = thread_part * (MAX / 4); i < (thread_part + 1) * (MAX / 4); i++)
        sum[thread_part] += a[i];
}

// Driver Code
int main()
{

    pthread_t threads[MAX_THREAD];

    // Creating 4 threads
    for (int i = 0; i < MAX_THREAD; i++)
        pthread_create(&threads[i], NULL, sum_array, (void*)NULL);

    // joining 4 threads i.e. waiting for all 4 threads to complete
    for (int i = 0; i < MAX_THREAD; i++)
        pthread_join(threads[i], NULL);

    // adding sum of all 4 parts
    int total_sum = 0;
    for (int i = 0; i < MAX_THREAD; i++)
        total_sum += sum[i];

    cout << "sum is " << total_sum << endl;

    return 0;
}

Java

import java.util.concurrent.*;

class Main {

    // Size of array
    private static final int MAX = 16;

    // Maximum number of threads
    private static final int MAX_THREAD = 4;

    private static int[] a = { 1, 5, 7, 10, 12, 14, 15, 18, 20, 22, 25, 27, 30, 64, 110, 220 };
    private static int[] sum = new int[MAX_THREAD];
    private static int part = 0;

    static class SumArray implements Runnable {

        @Override
        public void run() {

            // Each thread computes sum of 1/4th of array
            int thread_part = part++;

            for (int i = thread_part * (MAX / 4); i < (thread_part + 1) * (MAX / 4); i++) {
                sum[thread_part] += a[i];
            }
        }
    }

    // Driver Code
    public static void main(String[] args) throws InterruptedException {

        Thread[] threads = new Thread[MAX_THREAD];

        // Creating 4 threads
        for (int i = 0; i < MAX_THREAD; i++) {
            threads[i] = new Thread(new SumArray());
            threads[i].start();
        }

        // Joining 4 threads i.e. waiting for all 4 threads to complete
        for (int i = 0; i < MAX_THREAD; i++) {
            threads[i].join();
        }

        // Adding sum of all 4 parts
        int total_sum = 0;
        for (int i = 0; i < MAX_THREAD; i++) {
            total_sum += sum[i];
        }

        System.out.println("sum is " + total_sum);
    }
}

Python3

# Python3 Program to find sum of array
# using multi-threading
from threading import Thread

# Size of array
MAX = 16
# Maximum number of threads
MAX_THREAD = 4

# Initial array
arr = [1, 5, 7, 10, 12, 14, 15, 18, 20, 22, 25, 27, 30, 64, 110, 220]
# Sum array for storing sum of each part computed
sum_arr = [0 for _ in range(MAX_THREAD)]
part = 0


def sum_array():
    global part
    thread_part = part
    part = part + 1

    # Each thread computes sum of 1/4th of array
    thread_start = int(thread_part*(MAX/4))
    thread_end = int((thread_part+1)*(MAX/4))
    for i in range(thread_start, thread_end, 1):
        sum_arr[thread_part] = sum_arr[thread_part] + arr[i]


if __name__ == "__main__":
    # Creating list of size MAX_THREAD
    thread = list(range(MAX_THREAD))
    # Creating MAX_THEAD number of threads
    for i in range(MAX_THREAD):
        thread[i] = Thread(target=sum_array)
        thread[i].start()

    # Waiting for all threads to finish
    for i in range(MAX_THREAD):
        thread[i].join()

    # Adding sum of all 4 parts
    actual_sum = 0
    for x in sum_arr:
        actual_sum = actual_sum + x
    print("Sum is %d" % actual_sum)

C#

// C# Program to find sum of array
// using multi-threading
using System;
using System.Threading;

class Program
{
// Size of array
const int MAX = 16;

// Maximum number of threads
const int MAX_THREAD = 4;

// Initial array
static int[] arr = new int[] { 1, 5, 7, 10, 12, 14, 15, 18, 20, 22, 25, 27, 30, 64, 110, 220 };

// Sum array for storing sum of each part computed
static int[] sum_arr = new int[MAX_THREAD];
static int part = 0;

static void SumArray()
{
    // Each thread computes sum of 1/4th of array
    int thread_part = Interlocked.Increment(ref part) - 1;
    int thread_start = (int)(thread_part * (MAX / 4));
    int thread_end = (int)((thread_part + 1) * (MAX / 4));
    for (int i = thread_start; i < thread_end; i++)
    {
        Interlocked.Add(ref sum_arr[thread_part], arr[i]);
    }
}

static void Main(string[] args)
{
    // Creating list of size MAX_THREAD
    Thread[] threads = new Thread[MAX_THREAD];

    // Creating MAX_THEAD number of threads
    for (int i = 0; i < MAX_THREAD; i++)
    {
        threads[i] = new Thread(new ThreadStart(SumArray));
        threads[i].Start();
    }

    // Waiting for all threads to finish
    for (int i = 0; i < MAX_THREAD; i++)
    {
        threads[i].Join();
    }

    // Adding sum of all 4 parts
    int actual_sum = 0;
    for (int i = 0; i < MAX_THREAD; i++)
    {
        actual_sum += sum_arr[i];
    }
    Console.WriteLine("Sum is {0}", actual_sum);
}
}


//This code is contributed by shivhack999

Javascript

// Size of array
const MAX = 16;
// Maximum number of threads
const MAX_THREAD = 4;

// Initial array
const arr = [1, 5, 7, 10, 12, 14, 15, 18, 20, 22, 25, 27, 30, 64, 110, 220];
// Sum array for storing sum of each part computed
const sumArr = new Array(MAX_THREAD).fill(0);
let part = 0;

function sumArray() {
    const threadPart = part;
    part = part + 1;

    // Each thread computes sum of 1/4th of array
    const threadStart = Math.floor(threadPart * (MAX / 4));
    const threadEnd = Math.floor((threadPart + 1) * (MAX / 4));
    for (let i = threadStart; i < threadEnd; i++) {
        sumArr[threadPart] += arr[i];
    }
}

// Creating MAX_THREAD number of threads
const threads = new Array(MAX_THREAD).fill(null).map(() => {
    return new Promise(resolve => {
        sumArray();
        resolve();
    });
});

// Waiting for all threads to finish
Promise.all(threads).then(() => {
    // Adding sum of all 4 parts
    const actualSum = sumArr.reduce((sum, x) => sum + x, 0);
    console.log(`Sum is ${actualSum}`);
});

Output:

sum is 600

Time Complexity: O(MAX_THREAD)

Auxiliary Space: O(1)