atomic_guard_side_effect.c

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

static atomic_bool lock = false;
static volatile int counter = 0;

void* thread_start(void *arg)
{
  for (int i = 0; i < 10000; i++)
    {
      bool expected_bool = false;
      while (!atomic_compare_exchange_weak_explicit(
        &lock, &expected_bool, true,
        memory_order_acquire,
        memory_order_relaxed))
        {
          expected_bool = false;
        }
      counter++;
      atomic_store_explicit(&lock, false, memory_order_release);
    }
  return NULL;
}

int main()
{
  pthread_t p1, p2;
  pthread_create(&p1, NULL, thread_start, NULL);
  pthread_create(&p2, NULL, thread_start, NULL);
  pthread_join(p1, NULL);
  pthread_join(p2, NULL);

  printf("counter: %d\n", counter);
  return 0;
}