/**
 * The original version of the program comes from Linux man page
 * man pthread_attr_init
 *
 * This is a revised, simplified version to show the basics of
 * thread attributes
 */

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

#define DEFAULT_STACK_SIZE 0x200000    /* 2 MB */

#define handle_error_en(en, msg)				\
  { errno = en; perror(msg); exit(EXIT_FAILURE); }


void get_show_sched(pthread_attr_t *attr, char * prefix) {

  int s, i;
  struct sched_param sp;

  printf("Demonstrate get and set of scheduling parameters.\n");
  printf("=== retrieval scheduling default policy ===\n");
  s = pthread_attr_getschedpolicy(attr, &i);
  if (s != 0)
    handle_error_en(s, "pthread_attr_getschedpolicy and priority");

  printf("%sScheduling policy   = %s\n", prefix,
	 (i == SCHED_OTHER) ? "SCHED_OTHER" :
	 (i == SCHED_FIFO)  ? "SCHED_FIFO" :
	 (i == SCHED_RR)    ? "SCHED_RR" :
	 "???");

  s = pthread_attr_getschedparam(attr, &sp);
  if (s != 0)
    handle_error_en(s, "pthread_attr_getschedpolicy");

  printf("%sScheduling priority = %d\n", prefix, sp.sched_priority);

  printf("=== change scheduling parameters ===\n");
  printf("a. set scheduling policy to be RR (round-robin) ...\n");
  printf("b. lower scheduling priority by 1 (less preferrable)...\n");

  i = SCHED_RR;
  s = pthread_attr_setschedpolicy(attr, i);
  if (s != 0) 
    handle_error_en(s, "pthread_attr_setschedpolicy");

  s = pthread_attr_getschedpolicy(attr, &i);
  if (s != 0)
    handle_error_en(s, "pthread_attr_getschedpolicy");

  sp.sched_priority ++;
  s = pthread_attr_setschedparam(attr, &sp);
  if (s != 0)
    handle_error_en(s, "pthread_attr_setschedpolicy");

  s = pthread_attr_getschedparam(attr, &sp);
  if (s != 0)
    handle_error_en(s, "pthread_attr_getschedpolicy");

  printf("%sScheduling policy   = %s\n", prefix,
	 (i == SCHED_OTHER) ? "SCHED_OTHER" :
	 (i == SCHED_FIFO)  ? "SCHED_FIFO" :
	 (i == SCHED_RR)    ? "SCHED_RR" :
	 "???");
  printf("%sScheduling priority = %d\n", prefix, sp.sched_priority);

}

void
get_show_stack(pthread_attr_t *attr, char *prefix) {

  int s;
  size_t v;
  void *stkaddr;

  printf("Demonstrate get and set of stack parameters.\n");
  printf("=== retrieval stack parameters ===\n");

  s = pthread_attr_getstack(attr, &stkaddr, &v);
  if (s != 0)
    handle_error_en(s, "pthread_attr_getschedpolicy");

  printf("%sStack address       = %p\n", prefix, stkaddr);
  printf("%sStack size          = 0x%x bytes\n", prefix, v);

  printf("=== reset stack size (double it) ===\n");
  v *= 2; // double the size
  s = pthread_attr_setstack(attr, stkaddr, v);
  s = pthread_attr_getstack(attr, &stkaddr, &v);
  if (s != 0)
    handle_error_en(s, "pthread_attr_getschedpolicy");

  printf("%sStack address       = %p\n", prefix, stkaddr);
  printf("%sStack size          = 0x%x bytes\n", prefix, v);
}

void
display_pthread_attr(pthread_attr_t *attr, char *prefix) {

  /* get, set, and show sheduling policy and parameters */
  get_show_sched(attr, prefix);

  /* get, set, and show stack parameters */
  get_show_stack(attr, prefix);

}

static void *
thread_start(void *arg)
{
  int s;
  pthread_attr_t gattr;

  /* pthread_getattr_np() is a non-standard GNU extension that
     retrieves the attributes of the thread specified in its
     first argument */

  s = pthread_getattr_np(pthread_self(), &gattr);
  if (s != 0)
    handle_error_en(s, "pthread_getattr_np");

  printf("Thread attributes for thread %u:\n", pthread_self());
  display_pthread_attr(&gattr, "\t");

  exit(EXIT_SUCCESS);         /* Terminate all threads */
}

int
main(int argc, char *argv[])
{
  pthread_t thr;
  pthread_attr_t attr;
  pthread_attr_t *attrp;      /* NULL or &attr */
  int s;
  void *sp;

  attrp = NULL;

  s = pthread_create(&thr, attrp, &thread_start, NULL);
  if (s != 0)
    handle_error_en(s, "pthread_create");

  pause();    /* Terminates when other thread calls exit() */
}