uv_update_time(loop);
/* 检查计时器是否到期，并执行对应计时器回调 */
uv_process_timers(loop);
/* Call idle callbacks if nothing to do. */
if (loop->pending_reqs_tail == NULL &&
loop->endgame_handles == NULL) {
/* 防止event loop退出 */
uv_idle_invoke(loop);
}
uv_process_reqs(loop);
uv_process_endgames(loop);
uv_prepare_invoke(loop);
/* 收集 IO 事件 */
(*poll)(loop, loop->idle_handles == NULL &&
loop->pending_reqs_tail == NULL &&
loop->endgame_handles == NULL &&
!loop->stop_flag &&
(loop->active_handles > 0 ||
!ngx_queue_empty(&loop->active_reqs)) &&
!(mode & UV_RUN_NOWAIT));
/* setImmediate() 等 */
uv_check_invoke(loop);
r = uv__loop_alive(loop);
if (mode & (UV_RUN_ONCE | UV_RUN_NOWAIT))
break;
}
其中 uv_update_time 函数的源码如下：（https://github.com/joyent/libuv/blob/v0.10/src/win/timer.c））
void uv_update_time(uv_loop_t* loop) {
/* 获取当前系统时间 */
DWORD ticks = GetTickCount();
/* The assumption is made that LARGE_INTEGER.QuadPart has the same type */
/* loop->time, which happens to be. Is there any way to assert this? */
LARGE_INTEGER* time = (LARGE_INTEGER*) &loop->time;
/* If the timer has wrapped, add 1 to it’s high-order dword. */
/* uv_poll must make sure that the timer can never overflow more than */
/* once between two subsequent uv_update_time calls. */
