feat: support boot hook and add boot hook doc

Refs: #2520

docs/lifecyle.puml

@@ -0,0 +1,131 @@
+@startuml
+start
+: start master;
+partition agent {
+  : fork agent worker;
+  : load plugin.js, config.js, extends;
+  : load agent.js;
+  note right
+    类模式
+    configDidLoad
+    async didLoad
+    async willReady
+    async didReady
+    async serverDidReady
+    ====
+    方法模式
+    beforeStart(deprecate)
+  end note  
+  fork
+  : configDidLoad;
+  note left
+    文件都已经加载完成,
+    可以执行一些同步逻辑
+  end note
+  : async didLoad;
+  note left
+    文件, 配置已经加载完毕,
+    可以执行一些异步任务,
+    比如异步拉取配置来加载client,
+    或者检查client状态是否正常
+  end note
+  fork again
+    : beforeStart(deprecate);
+    note right
+      beforeStart注册的任务
+      在此时同时并行执行
+    end note  
+  endfork
+  : async willReady;
+  note left
+    插件已经完全加载完毕,
+    所有的插件可以正常的使用,
+    执行一些流量进入前的任务,
+    比如拉取应用所需的一些配置
+  end note
+  : async didReady;
+  note right
+    agent进程已经准备完毕,
+    可以正常工作
+    ====
+    时间点与原来的ready相同,
+    原来的ready不支持AsyncFunction    
+  end note
+  : emit 'agent-start';
+}
+partition app {
+  : start app workers;
+  : load plugin.js, config.js, extends;
+  : load app.js;
+  note right
+    类模式
+    configDidLoad
+    async didLoad
+    async willReady
+    async didReady
+    async serverDidReady
+    ====
+    方法模式
+    beforeStart(deprecate)
+  end note
+  fork
+    : configDidLoad;
+    note left
+      文件都已经加载完成,
+      与 app.js 里的同步逻辑相同,
+      可以修改一些配置, 修改中间件的顺序
+    end note
+    : load app/service;
+    : load app/middleware;
+    : load app/controller;
+    : load app/router.js;
+    : async DidLoad;
+  note left
+    文件, 配置已经加载完毕,
+    可以执行一些异步任务,
+    比如异步拉取配置来加载client,
+    或者检查client状态是否正常
+  end note
+  fork again
+    : beforeStart(deprecate);
+    note right
+      beforeStart注册的任务
+      在此时同时并行执行
+    end note
+  end fork
+    : async WillReady;
+  note left
+    插件已经完全加载完毕,
+    所有的插件可以正常的使用,
+    执行一些流量进入前的任务,
+    比如拉取应用所需的一些配置
+  end note
+  : async DidReady;
+  note right
+    app进程已经准备完毕,
+    HTTP server开始监听端口,
+    ====
+    时间点与原来的ready相同,
+    原来的ready不支持AsyncFunction
+  end note
+  : emit 'app-start';
+}
+: emit 'egg-ready';
+: async serverDidReady;
+note right
+  agent进程和所有的app进程已经准备完毕,
+  可以放入流量,
+end note
+: master receive SIGTERM;
+fork
+: agent beforeClose;
+fork again
+: app beforeClose;
+note right
+  以插入顺序逆序同步执行,
+  生产环境中不建议使用,
+  可能在进程结束前没有执行完成
+end note
+endfork
+stop
+@enduml

docs/source/zh-cn/advanced/loader.md

@@ -190,6 +190,50 @@ plugin1 为 framework1 依赖的插件，配置合并后 object key 的顺序会
 
 ### 生命周期
 
+Egg提供了配置文件加载完成(`configDidLoad`), 文件加载完成(`didLoad`), 插件启动完毕(`willReady`), worker 准备就绪(`didReady`), 应用启动完成(`serverDidReady`), 应用即将关闭(`beforeClose`)这些生命周期函数。
+定义过程如下代码
+```js
+// app.js or agent.js
+class AppBootHook {
+  constructor(app) {
+  }
+
+  configDidLoad() {
+    // Config,plugin files have did load.
+  }
+
+  async didLoad() {
+    // All files have did load, start plugin here.
+  }
+
+  async willReady() {
+    // All plugins have started, can do some thing before app ready
+  }
+
+  async didReady() {
+    // Worker is ready, can do some things
+    // don't need to block the app boot.
+  }
+
+  async serverDidReady() {
+    // Server is listening.
+  }
+
+  async beforeClose() {
+    // Do some thing before app close.
+  }
+}
+```
+
+启动过程如图所示:
+
+![](https://user-images.githubusercontent.com/6897780/42219323-24cbd7a8-7efe-11e8-86b9-cf280846aa9f.png)
+
+使用 `beforeClose` 的时候需要注意，在 egg 的 进程关闭处理中是有超时时间的，如果 worker 进程在接收到进程退出信号之后，没有在所规定的时间内退出，将会被强制关闭。
+如果需要调整超时时间的话，查看[此处文档](https://github.com/eggjs/egg-cluster)。
+
+旧版的使用方法:
+
 Egg提供了应用启动(`beforeStart`), 启动完成(`ready`), 关闭(`beforeClose`)这三个生命周期方法。
 ```
    init master process

lib/egg.js

@@ -56,6 +56,12 @@ class EggApplication extends EggCore {
      */
     this.messenger = new Messenger();
 
+    // trigger serverDidReady hook when all app workers
+    // and agent worker is ready
+    this.messenger.on('egg-ready', () => {
+      this.lifecycle.triggerServerDidReady();
+    });
+
     // dump config after ready, ensure all the modifications during start will be recorded
     // make sure dumpConfig is the last ready callback
     this.ready(() => process.nextTick(() => {

lib/loader/agent_worker_loader.js

@@ -18,6 +18,7 @@ class AgentWorkerLoader extends EggLoader {
 
   load() {
     this.loadAgentExtend();
+    this.loadBootHook();
     this.loadCustomAgent();
   }
 }

lib/loader/app_worker_loader.js

@@ -30,6 +30,7 @@ class AppWorkerLoader extends EggLoader {
     this.loadHelperExtend();
 
     // app > plugin
+    this.loadBootHook();
     this.loadCustomApp();
     // app > plugin
     this.loadService();

test/fixtures/apps/boot-app/agent.js

@@ -0,0 +1,39 @@
+'use strict';
+
+const sleep = require('mz-modules/sleep');
+
+module.exports = class {
+  constructor(app) {
+    app.bootLog = [];
+    this.app = app;
+  }
+
+  configDidLoad() {
+    this.app.bootLog.push('configDidLoad');
+  }
+
+  async didLoad() {
+    await sleep(1);
+    this.app.bootLog.push('didLoad');
+  }
+
+  async willReady() {
+    await sleep(1);
+    this.app.bootLog.push('willReady');
+  }
+
+  async didReady() {
+    await sleep(1);
+    this.app.bootLog.push('didReady');
+  }
+
+  async beforeClose() {
+    await sleep(1);
+    this.app.bootLog.push('beforeClose');
+  }
+
+  async serverDidReady() {
+    await sleep(1);
+    this.app.bootLog.push('serverDidReady');
+  }
+};

test/fixtures/apps/boot-app/app.js

@@ -0,0 +1,39 @@
+'use strict';
+
+const sleep = require('mz-modules/sleep');
+
+module.exports = class {
+  constructor(app) {
+    app.bootLog = [];
+    this.app = app;
+  }
+
+  configDidLoad() {
+    this.app.bootLog.push('configDidLoad');
+  }
+
+  async didLoad() {
+    await sleep(1);
+    this.app.bootLog.push('didLoad');
+  }
+
+  async willReady() {
+    await sleep(1);
+    this.app.bootLog.push('willReady');
+  }
+
+  async didReady() {
+    await sleep(1);
+    this.app.bootLog.push('didReady');
+  }
+
+  async beforeClose() {
+    await sleep(1);
+    this.app.bootLog.push('beforeClose');
+  }
+
+  async serverDidReady() {
+    await sleep(1);
+    this.app.bootLog.push('serverDidReady');
+  }
+};

test/fixtures/apps/boot-app/package.json

@@ -0,0 +1,3 @@
+{
+  "name": "boot-app"
+}

test/lib/core/loader/load_boot.test.js

@@ -0,0 +1,30 @@
+'use strict';
+
+const assert = require('assert');
+const utils = require('../../../utils');
+
+describe('test/lib/core/loader/load_boot.test.js', () => {
+  let app;
+
+  before(() => {
+    app = utils.app('apps/boot-app');
+    return app.ready();
+  });
+
+  it('should load app.js', async () => {
+    await app.close();
+    assert.deepStrictEqual(app.bootLog, [ 'configDidLoad',
+      'didLoad',
+      'willReady',
+      'didReady',
+      'serverDidReady',
+      'beforeClose' ]);
+    assert.deepStrictEqual(app.agent.bootLog, [ 'configDidLoad',
+      'didLoad',
+      'willReady',
+      'didReady',
+      'serverDidReady',
+      'beforeClose' ]);
+  });
+
+});