Maximum element in a very large array using pthreads

Given a very large array of integers, find maximum within the array using multithreading. 

Examples:

Input :  1, 5, 7, 10, 12, 14, 15, 18, 20, 
         22, 25, 27, 30, 64, 110, 220
Output :Maximum Element is : 220
Input :  10, 50, 70, 100, 120, 140, 150, 180, 
         200, 220, 250, 270, 300, 640, 110, 220
Output : Maximum Element is : 640

Prerequisite : Multithreading Note : Useful in large files of size MB/GB. 

How to run : It can only be run on linux envirenment. command :

>> gcc -pthread maximum.c 
>> ./a.out

C++

// C++ code to find maximum of an array using Multithreading
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

// Size of array
#define max 16

// Max number of threads
#define Th_max 4

// Array
int a[max] = { 1, 5, 7, 10, 12, 14, 15, 18, 20,
            22, 25, 27, 300, 64, 110, 220 };

// Array to store max of threads
int max_num[Th_max] = { 0 };
int thread_no = 0;

// Function to find maximum
void* maximum(void* arg)
{
    int i, num = thread_no++;
    int maxs = 0;

    for (i = num * (max / 4); i < (num + 1) * (max / 4); i++) {
        if (a[i] > maxs)
            maxs = a[i];
    }

    max_num[num] = maxs;
}

// Driver code
int main()
{
    int maxs = 0;
    int i;
    pthread_t threads[Th_max];

    // creating 4 threads
    for (i = 0; i < Th_max; i++)
        pthread_create(&threads[i], NULL, maximum, (void*)NULL);

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

    // Finding max element in an array
    // by individual threads
    for (i = 0; i < Th_max; i++) {
        if (max_num[i] > maxs)
            maxs = max_num[i];
    }

    printf("Maximum Element is : %d", maxs);

    return 0;
}


// This code is contributed by Shivhack999

C

// C++ code to find maximum of an array using Multithreading
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

// Size of array
#define max 16

// Max number of thread
#define Th_max 4

// Array
int a[max] = { 1, 5, 7, 10, 12, 14, 15, 18, 20,
               22, 25, 27, 300, 64, 110, 220 };

// Array to store max of threads
int max_num[Th_max] = { 0 };
int thread_no = 0;

// Function to find maximum
void maximum(void* arg)
{
    int i, num = thread_no++;
    int maxs = 0;

    for (i = num * (max / 4); i < (num + 1) * (max / 4); i++) {
        if (a[i] > maxs)
            maxs = a[i];
    }

    max_num[num] = maxs;
}

// Driver code
int main()
{
    int maxs = 0;
    int i;
    pthread_t threads[Th_max];

    // creating 4 threads
    for (i = 0; i < Th_max; i++)
        pthread_create(&threads[i], NULL,
                       maximum, (void*)NULL);

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

    // Finding max element in an array
    // by individual threads
    for (i = 0; i < Th_max; i++) {
        if (max_num[i] > maxs)
            maxs = max_num[i];
    }

    printf("Maximum Element is : %d", maxs);

    return 0;
}

Java

import java.util.Arrays;

public class MaxElementThread extends Thread {
    int lo, hi;
    int[] arr;
    int max;

    public MaxElementThread(int[] arr, int lo, int hi) {
        this.arr = arr;
        this.lo = lo;
        this.hi = hi;
        this.max = Integer.MIN_VALUE;
    }

    public void run() {
        for (int i = lo; i < hi; i++) {
            if (arr[i] > max) {
                max = arr[i];
            }
        }
    }

    public static void main(String[] args) {
        int[] arr = { 1, 5, 7, 10, 12, 14, 15, 18, 20, 22, 25, 27, 300, 64, 110, 220 };
        int n = arr.length;
        int numThreads = 4;
        MaxElementThread[] threads = new MaxElementThread[numThreads];
        int blockSize = n / numThreads;

        for (int i = 0; i < numThreads; i++) {
            int lo = i * blockSize;
            int hi = (i == numThreads - 1) ? n : (i + 1) * blockSize;
            threads[i] = new MaxElementThread(arr, lo, hi);
            threads[i].start();
        }

        int max = Integer.MIN_VALUE;
        for (int i = 0; i < numThreads; i++) {
            try {
                threads[i].join();
                if (threads[i].max > max) {
                    max = threads[i].max;
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        System.out.println("Maximum Element is : " + max);
    }
}

Python3

# C++ code to find maximum of an array using Multithreading
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, 300, 64, 110, 220]

# Max array for storing max of each part computed
max_num = [0 for _ in range(MAX_THREAD)]
thread_no = 0

# Function to calculate maximum


def maximum():
    global thread_no
    index = thread_no
    thread_no += 1
    # Each thread computes max of 1/4th of array
    start, end = int(index*(MAX/4)), int((index+1)*(MAX/4))
    for i in range(start, end, 1):
        max_num[index] = max(max_num[index], 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=maximum)
        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_max = 0
    for x in max_num:
        actual_max = max(actual_max, x)
    print("Maximum element is : %d" % actual_max)

C#

using System;
using System.Threading;

public class MaxArrayThread
{
    // 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, 300, 64, 110, 220 };

    // Max array for storing max of each part computed
    static int[] max_num = new int[MAX_THREAD];
    static int thread_no = 0;

    // Function to calculate maximum
    static void Maximum()
    {
        int index = Interlocked.Increment(ref thread_no) - 1;
        // Each thread computes max of 1/4th of array
        int start = (int)(index * (MAX / 4));
        int end = (int)((index + 1) * (MAX / 4));
        for (int i = start; i < end; i++)
        {
            max_num[index] = Math.Max(max_num[index], arr[i]);
        }
    }

    public static void Main()
    {
        // Creating array of size MAX_THREAD
        Thread[] thread = new Thread[MAX_THREAD];
        // Creating MAX_THREAD number of threads
        for (int i = 0; i < MAX_THREAD; i++)
        {
            thread[i] = new Thread(Maximum);
            thread[i].Start();
        }

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

        // Adding sum of all 4 parts
        int actual_max = 0;
        for (int i = 0; i < MAX_THREAD; i++)
        {
            actual_max = Math.Max(actual_max, max_num[i]);
        }
        Console.WriteLine("Maximum element is : {0}", actual_max);
    }
}
// This code is contributed by shivregkec

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, 300, 64, 110, 220];
// Max array for storing max of each part computed
const maxNum = new Array(MAX_THREAD).fill(0);
let threadNo = 0;

// Function to calculate maximum
function maximum() {
    const index = threadNo;
    threadNo += 1;

    // Each thread computes max of 1/4th of array
    const start = Math.floor(index * (MAX / 4));
    const end = Math.floor((index + 1) * (MAX / 4));
    for (let i = start; i < end; i++) {
        maxNum[index] = Math.max(maxNum[index], arr[i]);
    }
}

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

// Waiting for all threads to finish
Promise.all(threads).then(() => {
    // Adding max of all 4 parts
    const actualMax = maxNum.reduce((max, x) => Math.max(max, x), 0);
    console.log(`Maximum element is: ${actualMax}`);
});

Output

Maximum element is : 300

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