tips

// 1. 对于事件循环的每个阶段（定时器队列，I/O 事件队列，immediates 队列，close 处理队列是 4 个主要阶段），
// 2. 事件循环在移动到某一阶段之前，Node 会检查 nextTick 队列中是否有可处理的事件。
// 3. 如果有，在前往下一个主要阶段之前，事件循环会先直接处理这个队列直至它为空（当然还有其他 microtask 队列）。

// 但 immediates 队列被确保会在事件循环的 I/O 阶段之后被立即执行
setImmediate(() => console.log('this is set immediate 1'));
setImmediate(() => console.log('this is set immediate 2'));
setImmediate(() => console.log('this is set immediate 3'));

// 当事件循环开始执行的时候，Node 首先会处理定时器队列。接着，在处理完 I/O 之后，会来到 immediates 队列
setTimeout(() => console.log('this is set timeout 1'), 0);
setTimeout(() => {
console.log('this is set timeout 2');
process.nextTick(() => console.log('this is process.nextTick added inside setTimeout'));
}, 0);
setTimeout(() => console.log('this is set timeout 3'), 0);
setTimeout(() => console.log('this is set timeout 4'), 0);
setTimeout(() => console.log('this is set timeout 5'), 0);

//
process.nextTick(() => console.log('this is process.nextTick 1'));
process.nextTick(() => {
// 第二次 循环 队头, 第一次 nextTick 队列 队尾
process.nextTick(console.log.bind(console, 'this is the inner next tick inside next tick'));
});
process.nextTick(() => console.log('this is process.nextTick 2'));
process.nextTick(() => console.log('this is process.nextTick 3'));
process.nextTick(() => console.log('this is process.nextTick 4'));

// 1. 不能确定的 setImmediate 与 setTimeout
// 设定一个 0 秒过期的定时器，永远不能保证在 0 秒后回调会被准时调用
setTimeout(function() {
console.log('setTimeout')
}, 0);
setImmediate(function() {
console.log('setImmediate')
});

// 2. 能 保证 setTimeout 执行后于 setImmediate
// due 在处理完 I/O 之后，会来到 immediates 队列
/**
const fs = require('fs');

fs.readFile(__filename, () => {
// 此 setTimeout 是被放到 下一轮 时间循环
setTimeout(() => {
console.log('timeout')
}, 0);
setImmediate(() => {
console.log('immediate')
})
});
*/