sem-simple.c

#include <stdio.h>
#include <assert.h>

#include "uv.h"

#define ITER 1e6
#define ACCESS_ONCE(type, var)                                                \
  (*(volatile type*) &(var))

static uv_mutex_t mutex;
static uv_sem_t sem_main;
static uv_sem_t sem_thread;
static uv_thread_t thread;

static int cntr = ITER;


static void thread_cb(void* arg) {
  while (ACCESS_ONCE(int, cntr) > 0) {
    uv_sem_post(&sem_main);
    uv_sem_wait(&sem_thread);
  }
}


int main() {
  assert(0 == uv_sem_init(&sem_main, 0));
  assert(0 == uv_sem_init(&sem_thread, 0));
  assert(0 == uv_mutex_init(&mutex));
  assert(0 == uv_thread_create(&thread, thread_cb, NULL));

  uint64_t time = uv_hrtime();

  while (--ACCESS_ONCE(int, cntr) > 0) {
    uv_sem_wait(&sem_main);
    uv_sem_post(&sem_thread);
  }

  time = uv_hrtime() - time;

  printf("%f us/op\n", time / 1e3 / ITER);

  uv_thread_join(&thread);
  uv_mutex_destroy(&mutex);
  uv_sem_destroy(&sem_main);
  uv_sem_destroy(&sem_thread);

  return 0;
}