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 *)¶m[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