/* file: perthread.c
   author:  Ted Baker
   version: $Revision$
   last modified by: $Author: cop4610 $ on $Date: 2002/09/20 10:13:25 $
   purpose: 

   Demonstrate use of pthread_get/setspecific to keep per-thread data.

   The interesting feature is the procedure print_message(), which is
   able to print the id of the calling thread, by using pthread_getspecific()
   to look it up the per-thread data.

 */

#define _XOPEN_SOURCE 500
#define _REENTRANT
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define PCHECK(CALL){int result;\
 if ((result = (CALL)) != 0) {\
    fprintf (stderr, "FATAL: %s (%s)", strerror(result), #CALL);\
    exit (-1);}}

#define NTHREADS 10

typedef struct perthread_data {
  int id;
} * perthread_data_ptr;


pthread_key_t my_key;

/* ----------------
    my_key_destroy
   ----------------

This is called by the system whenever a thread dies, to clean up
its per-thread data.  We tell the system to use this for that
purpose when we create the attribute my_key, by passing it to
pthread_key_create(), in main().

*/

void
my_key_destroy (void * arg) {
  perthread_data_ptr mine = (perthread_data_ptr) arg;
  fprintf (stderr, "my_key_destroy called for thread %d\n", mine->id);
  free (mine);     
}

void
print_message () {
  perthread_data_ptr mine = pthread_getspecific (my_key);
  fprintf (stderr, "This is thread %d\n", mine->id);
}

void *
my_thread_body (void * arg) {
  int id = (int) arg;
  perthread_data_ptr mine =
    (perthread_data_ptr) malloc (sizeof (struct perthread_data));
  mine->id = id;
  PCHECK (pthread_setspecific (my_key, (void *) mine));
  print_message ();
  return NULL;
}

int
main (int argc, char **argv) {

  pthread_t thread_id[NTHREADS];
  int i;

  PCHECK (pthread_setconcurrency (2));

  PCHECK (pthread_key_create (&(my_key), my_key_destroy));

  /* The above creates a new per-thread attribute key, and
     associates it with the "destructor" function my_key_destroy() */

  for (i = 1; i < NTHREADS; i++) {
    PCHECK (pthread_create (
      &thread_id[i],   /* place to store the id of new thread */
      NULL,            /* use default thread creation attributes */
      my_thread_body,  /* function for thread to execute */
      (void *) i));    /* pass index of thread */
  }

  for (i = 1; i < NTHREADS; i++) {
    PCHECK (pthread_join (thread_id[i], NULL));
  }

  exit (0);
}