Atomic sample (gcc -std=gnu11 -pthread -o atomic atomic.c)

atomic.c

#include <stdio.h>
#include <string.h>
#include <stdatomic.h>
#include <pthread.h>
#include <stdint.h>
#define __STDC_FORMAT_MACROS
#include <inttypes.h>

struct object
{
  _Atomic uint64_t aval;
  uint64_t val;
} obj;

void *
cnt_add (void *arg)
{
  int i;

  for (i = 0; i < 10000; i++)
    {
      obj.aval++;
      obj.val++;
    }

  pthread_exit (NULL);
}

int
main (int argc, char **argv)
{
  int i;
  pthread_t tid[1000];

  memset (&obj, 0, sizeof (struct object));

  for (i = 0; i < 1000; i++)
    pthread_create (&tid[i], NULL, cnt_add, NULL);
  for (i = 0; i < 1000; i++)
    pthread_join (tid[i], NULL);

  printf ("obj.aval = %" PRIu64 "\n", obj.aval);
  printf ("obj.val = %" PRIu64 "\n", obj.val);

  return 0;
}