//Compile with 
// dcc -pthread etc....
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <error.h>
#include <errno.h> 
#include <unistd.h>

#define NUM_THREADS 3

 
void *do_stuff(void *argument) {
   int *arg;
   arg = argument; 

   int *val = malloc(sizeof(int)); 
   *val = *arg *2;

   printf("Thread processing with arg %d returning %d\n",*arg, *val);
   return val;
}
 
int main(int argc, char** argv) {   
   int args[NUM_THREADS];
   int res;
   
   pthread_t threads[NUM_THREADS];
   // create all threads one by one
   for (int i = 0; i < NUM_THREADS; ++i) {
      args[i] = i; 
      printf("In main: creating thread %d\n", i);
      res = pthread_create(&threads[i], NULL, do_stuff, &args[i]);
   }
  
   // wait for each thread to complete
   // otherwise the main thread will die and all threads will die
   for (int i = 0; i < NUM_THREADS; ++i) {
      void *retval; 
      
      // block until thread 'i' completes
      res = pthread_join(threads[i], &retval);
      if(res < 0){
          fprintf(stderr, "Error: Joining threads\n");
          return 1;
      }
      int *result;
      result = retval;
      printf("In main: thread %d has completed\n", i);
      printf("retval %d\n",*result);
      free(retval); 
   }
   
   printf("In main: All threads completed successfully\n");
   return 0;
}