c - progress for each thread - c

Question

I've got a program that takes n numbers that generates a sum of each number from 0 to N. A new thread is created for each number given:
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
struct sum_runner_struct {
long long limit;
long long answer;
};
// Thread function to generate sum of 0 to N
void* sum_runner(void* arg)
{
struct sum_runner_struct *arg_struct = (struct sum_runner_struct*) arg;
long long sum = 0;
for (long long i = 0; i <= arg_struct->limit; i++)
{
sum += i;
}
arg_struct->answer = sum;
pthread_exit(0);
}
int main(int argc, char **argv)
{
if (argc < 2)
{
printf("Usage: %s <num 1> <num 2> ... <num-n>\n", argv[0]);
exit(-1);
}
int num_args = argc - 1;
struct sum_runner_struct args[num_args];
// Launch thread
pthread_t tids[num_args];
for (int i = 0; i < num_args; i++)
{
args[i].limit = atoll(argv[i + 1]);
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_create(&tids[i], &attr, sum_runner, &args[i]);
}
// Wait until thread is done its work
for (int i = 0; i < num_args; i++)
{
pthread_join(tids[i], NULL);
printf("Sum for thread %d is %lld\n", i, args[i].answer);
}
}
I want to display the progress of each thread (maybe in a percentage?) and from there I can calculate overall progress given each thread progress. I don't know how I can implement the progress for each thread though, how could I go about doing this?

Answer 1

One way to do it would be to add a global mutex, plus add a new member variable like long long current_index to your sum_runner_struct.
Every so often (e.g. maybe once every 1 million iterations of the for-loop?), each thread would then lock the mutex, set arg_struct->current_index=i;, and then unlock the mutex.
Then the main thread could then occasionally lock the mutex, iterate over the array sum_runner_structs to print out each thread's current_index value, and also tally up the sum of all of the values for the global-progress calculation, then unlock the mutex.