Multithreading but first few threads are being skipped

Multithreading but first few threads are being skipped

Problem Description:

It’s been a few hours and i can’t seem to understand the issue. Build this program to count from 1 – 10. The goal of this program is to use multithreading and dynamically split the array depending on how many threads it requested. Problem is the first 2 threads are being skipped and the last thread is doing most of th e process. I suspect it’s the for loop that creates the threads.

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

typedef struct
{
    int *array;
    int batch;
    int start;
    int end;
} Parameter;

void *method(void *p)
{
    Parameter *param = (Parameter *)p;

    for (int i = param->start; i < param->end; i++)
    {
        printf("Start:%dtEnd:%dtIndex:%dtValue:%dn", param->start, param->end, i,param->array[i]);
        
    }
}

int main(int argc, char **argv)
{
    // Getting the user input
    int array_length = atoi(argv[1]);
    int batches = atoi(argv[2]);

    printf("User specified Array:%dtBatch:%dn", array_length, batches);

    // Creating an array
    int *array = (int *)calloc(array_length, sizeof(int));
    
    // Fill it up with some data
    for (int i = 0; i < array_length; i++)
    {
        array[i] = i;
    }

    // Determine the Batches
    int batch_size = array_length / batches;
    int remainder = array_length % batches;

    printf("%dn", batch_size);
    printf("%dn", remainder);

    int start = 0;
    int end = 0;
    int index =0;

    // List of parameters
    Parameter *param = (Parameter *)calloc(batches, sizeof(Parameter));
    pthread_t *threads = (pthread_t *)calloc(batches, sizeof(pthread_t));

    // Loop through each batch.
    for (int i = 0; i < batches; i++)
    {
        printf("nnBatch number -> %dn", i);
        end = start + batch_size;
        if (remainder > 0)
        {
            remainder --;
            end ++;
        }

        // Fill the parameters
        param[i].array = array;
        param[i].end = end;
        param[i].start = start;
        param[i].batch = i;

        // Call the thread.
        pthread_create(threads + index, NULL, method, (void *)&param[i]);
        index++;
        start = end;
    }

    for (int i = 0; i < batches; i++)
    {
        pthread_join(threads[i], NULL);
    }

    free(param);
    free(threads);
    free(array);

    return 0;
}

Been playing with the index of the for loop(line 57) as i’m certain it’s the cause of the issue. been getting some results but the main problem still persisted.

Solution – 1

Code Works as intended. I’m a dumbas who didn’t put the printf in the void function. like so:

void *method(void *p) {
Parameter *param = (Parameter *)p;
printf("nnBatch number -> %dn", param->batch); //<-- moved from main method
for (int i = param->start; i < param->end; i++)
{
    printf("Start:%dtEnd:%dtIndex:%dtValue:%dn", param->start, param->end, i,param->array[i]);
    
} }

Thanks for pointing it out that the program works