【Libevent】实战：负载均衡器 (Load Balancer)

struct backend {
  const char *ip;
  int port;
  int is_up;
};

struct backend pool[] = {
  {"10.0.0.1", 80, 1},
  {"10.0.0.2", 80, 1}
};

struct backend *select_backend() {
  static int idx = 0;
  for (int i = 0; i < 2; ++i) {
  int cur = (idx + i) % 2;
  if (pool[cur].is_up) {
  idx = cur + 1;
  return &pool[cur];
  }
  }
  return NULL;
}

void check_cb(evutil_socket_t fd, short events, void *arg) {
  struct backend *b = arg;
  // 尝试 connect
  // 如果成功 -> b->is_up = 1
  // 如果失败 -> b->is_up = 0
}

// 启动定时器
struct event *ev = event_new(base, -1, EV_PERSIST, check_cb, backend);
struct timeval tv = {2, 0};
event_add(ev, &tv);