timer

[huenchao]

No description provided.

[huenchao]

参考文章：https://juejin.im/post/5d175dad518825554940226d

[huenchao]

1. timer其实分c++和js两个部分。具体比较的实现在c++和js层面都是一样的，用的链表+最小二叉堆。
2. js层面会有一个map，这个map根据传进来的timeout为key，组层N个列表。
3. js和c++怎么连在一起的呢？主要是通过scheduleTimer，其实最终就是调用 uv_timer_start(timer_handle(), RunTimers, duration_ms, 0);那RunTimers从哪里来？其实是internal/bootstrap/nodejs的时候，注册进来的：

// We initialize the tick callbacks and the timer callbacks last during
// bootstrap to make sure that any operation done before this are synchronous.
// If any ticks or timers are scheduled before this they are unlikely to work.
{
 const { nextTick, runNextTicks } = setupTaskQueue();
 process.nextTick = nextTick;
 // Used to emulate a tick manually in the JS land.
 // A better name for this function would be `runNextTicks` but
 // it has been exposed to the process object so we keep this legacy name
 // TODO(joyeecheung): either remove it or make it public
 process._tickCallback = runNextTicks;

 const { getTimerCallbacks } = require('internal/timers');
 const { setupTimers } = internalBinding('timers');
 const { processImmediate, processTimers } = getTimerCallbacks(runNextTicks);
 // Sets two per-Environment callbacks that will be run from libuv:
 // - processImmediate will be run in the callback of the per-Environment
 //   check handle.
 // - processTimers will be run in the callback of the per-Environment timer.
 setupTimers(processImmediate, processTimers);
 // Note: only after this point are the timers effective
}

[huenchao]

我自己总计起来就是，js层面宏观控制，libuv部分微观控制。因为通过scheduleTimer 的调用是有条件的。除了第一次必定会注册到libuv里，其他都必须过期时间，比预期的长，才会注册。