/***********************************************************************
 * helloThreaded.c
 *
 * From https://computing.llnl.gov/tutorials/pthreads/.
 * Modified by Tom Kelliher
 *
 * This program demonstrates the pthreads library.  To compile under
 * Linux, a command similar to
 *
 *    gcc -o helloThreaded -lpthread helloThreaded.c
 *
 * should suffice.
 *
 * This program is a simple demonstration of the pthreads library.
 * The main thread creates NUM_THREADS child threads, each of which
 * prints a "Hello world" message.  By performing a join on each child
 * thread, the main thread hangs around until each child thread has
 * exited.
 ***********************************************************************/


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


#define NUM_THREADS 10


/* Function prototypes */

void *printHello(void *);


/***********************************************************************
 * main()
 ***********************************************************************/

int main (int argc, char *argv[])
{
   pthread_t threads[NUM_THREADS];   /* Array to store thread IDs. */
   long i;
   int rc;   /* Return code from function call. */

   for (i = 0; i < NUM_THREADS; i++)
   {
      printf("In main: creating thread %d.\n", i);

      /* Create a thread.  The first argument is a pointer to a variable
       * of type pthread_t and is used to store the newly-created
       * thread's ID.  The second argument is used to specify attributes
       * of the new thread.  Passing a NULL pointer will result in the
       * use of default attributes.  The third argument is a pointer
       * to the function that the thread will initially start in.  This
       * function must take a single argument of type pointer to void and
       * must return a value of type pointer to void.  The final argument
       * is the value to pass to the initial function.
       *
       * In this specific instance, each thread is passed its index
       * within the threads array; this value is used to identify the
       * various threads.
       */

      rc = pthread_create(&threads[i], NULL, printHello, (void *) i);

      if (rc)
      {
         printf("ERROR; return code from pthread_create() is %d.\n", rc);
         exit(-1);
      }
   }

   /* Wait for each of the child threads to exit.  The join call returns
    * immediately if the child has already exited.  In this example, we
    * we are not using the return value mechanism available to us.
    */

   for (i = 0; i < NUM_THREADS; i++)
      pthread_join(threads[i], NULL);

   printf("Main thread exiting.\n");
   return 0;
}


/***********************************************************************
 * printHello()
 ***********************************************************************/

void *printHello(void *threadid)
{
   long tid;   /* Thread ID */

   /* threadid was originally an int, cast to (void *).  Cast it back to
    * int.
    */

   tid = (long) threadid;
   printf("Hello World! It's me, thread #%d!\n", tid);
   pthread_exit(NULL);   /* Not returning a value. */
}