Threads - Exercise 5

Write a multithreaded program that takes a matrix and multiplies each element in every row with a given scalar.

The program should create a separate thread to handle the multiplication of each row in the matrix by the scalar.

Once all threads complete their calculations, the program should return a new matrix with the updated values.

🕵️HINT

As you saw earlier, the routine takes only one argument, but in this case you may need to pass multiple values.

Consider using a struct to encapsulate multiple values into a single arg!

💡Solution

threads_7.c

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <errno.h>

#define ROWS 3
#define COLUMNS 4

typedef struct
{
    int *row;
    int columns;
    int scalar;
    int *result;
} Matrix;

void *multiply(void *args)
{
    Matrix *mArgs = (Matrix *)args;
    for(int i = 0; i < mArgs->columns; i++)
    {
        mArgs->result[i] = mArgs->row[i] * mArgs->scalar;
    }

    return NULL;
}

int main()
{
    int matrix[3][4] =
    {
        {1, 2, 3, 4},
        {5, 6, 7, 8},
        {9, 10, 11, 12}
    };

    int result[3][4];

    pthread_t threads[3];
    Matrix args[3];

    for(int i = 0; i < ROWS; i++)
    {
        args[i].row = matrix[i];
        args[i].columns = COLUMNS;
        args[i].scalar = 5;
        args[i].result = result[i];

        if(pthread_create(&threads[i], NULL, multiply, &args[i]))
        {
            perror(NULL);
            return errno;
        }
    }

    for(int i = 0; i < ROWS; i++)
    {
        if(pthread_join(threads[i], NULL))
        {
            perror(NULL);
            return errno;
        }
    }

    for(int i = 0; i < ROWS; i++)
    {
        for(int j = 0; j < COLUMNS; j++)
        {
            printf("%d ", result[i][j]);
        }
        printf("\n");
    }

    return 0;
}