Multiple Threads with pthread

An illustration on how to establish a multi-threaded program on a UNIX system. Threads contrast with processes, which are establishing using a fork(), but are generally more expensive to establish and don't share memory, so are harder to administer than threads. However processes should be faster once established and running.

Threads are created with pthread_create(). Arguments are:

• pointer to a buffer to hold the thread handle
• pointer to a thread attribute object
• pointer to the routine for the thread to execute
• pointer to the parameter to be passed to the thread routine

/********************************************************
 * An example source module to accompany...
 *
 * "Using POSIX Threads: Programming with Pthreads"
 *     by Brad nichols, Dick Buttlar, Jackie Farrell
 *     O'Reilly & Associates, Inc.
 *
 ********************************************************
 * simple_threads.c
 *
 * Simple multi-threaded example.
 */
 
#include <pthread.h>
 
void do_one_thing(int *);
void do_another_thing(int *);
void do_wrap_up(int, int);
 
int r1 = 0, r2 = 0;
 
 
main()
{
  pthread_t       thread1, thread2;
 
  pthread_create(&thread1, 
		 NULL,
		 (void *) do_one_thing,
		 (void *) &r1); 
 
  pthread_create(&thread2, 
		 NULL, 
		 (void *) do_another_thing,
		 (void *) &r2); 
 
  pthread_join(thread1, NULL);
  pthread_join(thread2, NULL);
 
  do_wrap_up(r1, r2);
 
}
 
void do_one_thing(int *pnum_times)
{
  int i, j, x;
 
  for (i = 0;  i < 4; i++) {
    printf("doing one thing\n"); 
    for (j = 0; j < 10000; j++) x = x + i;
    (*pnum_times)++;
  }
 
}
 
void do_another_thing(int *pnum_times)
{
  int i, j, x;
 
  for (i = 0;  i < 4; i++) {
    printf("doing another \n"); 
    for (j = 0; j < 10000; j++) x = x + i;
    (*pnum_times)++;
  }
 
}
 
void do_wrap_up(int one_times, int another_times)
{
  int total;
 
  total = one_times + another_times;
  printf("All done, one thing %d, another %d for a total of %d\n",
	one_times, another_times, total);
}