Executing threads in 'paralelism'

Question

I have a range of number (i.e 1~10000).
I need to create threads to search for a value X.
Each thread will have your own interval to search for it (i.e 10000/threadNumber).
I guess there is no meaning to make the threads run in sequence. I'm having problem to make they run concurrently...

My Code so far:

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#define limit 10000
#define n_threads 2


void* func1(void* arg)
{
    int i=0, *value = (int *)arg;
//How may I know which thread is running and make the thread search for the right range of values ?
    for(i=1; i<=limit/n_threads; i++)
    {
        if(*value == i){
           //Print the thread ID and the value found.
        }
        else
          //Print the thread ID and the value 0.
    }
    return NULL;
}

int main(int argc, char const *argv[])
{
    if(argc < 2)
        printf("Please, informe the value you want to search...\n");
    else{
        pthread_t t1, t2;
        int x = atoi(argv[1]);  //Value to search

        pthread_create(&t1, NULL, func1, (void *)(&x));
        pthread_create(&t2, NULL, func1, (void *)(&x));
        pthread_join(t1, NULL);
        pthread_join(t2, NULL);
    }

    return 0;
}

Problems so far:

I don't know how to find thread ID. (tried with pthread_self() but I always get a giant negaative number so I think something is wrong.
I know that pthread_create() creates and initialize the thread, also the pthread_join will make my main program to wait for the thread. But Looking into my code it doesn't seems to be runing concurrently.
How my threadX will know from what range of values it's suppose to start searching ? (i.e: If I have 10 threads, I don't think I'll have to create 10 functions o.O ).
is it possible to make them run concurrently without something like Mutex ?

perhaps this [SO post](http://stackoverflow.com/questions/21091000/how-to-get-thread-id-of-a-pthread-in-linux-c-program) can give additional info. — user3078414, May 08 '16 at 16:20
If you want to pass more than one value (eg. X and the range to search in) to your thread function, you can put them in a structure and pass a pointer to it. — Dmitri, May 08 '16 at 16:23

score 1 · Accepted Answer · edited May 23 '17 at 10:28

Getting the thread id varies according to your operating system.

See how to get thread id of a pthread in linux c program? as @user3078414 mentioned, and why compiler says ‘pthread_getthreadid_np’ was not declared in this scope?.

Credits to @Dmitri, an example of passing multiple values to the thread function. The threads run concurrently. Mutexes is a whole other chapter that deals with shared data and how you access it.

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

#define limit 10000
#define n_threads 2

struct targs {
  int from;
  int to;
};

void *func1(void *arg) {
  struct targs *args = (struct targs *) arg;
  printf("%d => %d\n", args->from, args->to);
  // free(arg)
  return NULL;
}

int main(int argc, char const *argv[]) {
  struct targs *args;
  pthread_t t1;
  pthread_t t2;

  args = (struct targs *) malloc(sizeof(args));
  args->from = 0;
  args->to = 100;
  pthread_create(&t1, NULL, func1, (void *) args);

  args = (struct targs *) malloc(sizeof(args));
  args->from = 100;
  args->to = 200;
  pthread_create(&t2, NULL, func1, (void *) args);

  pthread_join(t1, NULL);
  pthread_join(t2, NULL);

  return 0;
}

Executing threads in 'paralelism'

1 Answers1