Node.js源码解析-启动-js部分
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Node.js 版本 8.x
Node.js 进程启动时，首先执行 c / c++ 代码，然后 c / c++ 加载并执行 lib/internal/bootstrap_node.js 并给予一个 process 参数( 运行上下文 )
// lib/internal/bootstrap_node.js 概览
// Hello, and welcome to hacking node.js!
//
// This file is invoked by node::LoadEnvironment in src/node.cc, and is
// responsible for bootstrapping the node.js core. As special caution is given
// to the performance of the startup process, many dependencies are invoked
// lazily.
'use strict';
// 这里的 process 对象来自 c / c++，属于原始数据
(function(process) {
// ...
startup();
})加载 lib/internal/bootstrap_node.js 后，直接执行 startup() 函数
startup()
// lib/internal/bootstrap_node.js
function startup() {
// 下面几行代码使 process 具有 EventEmitter 的特性，比如说 on，emit
// BEGIN
const EventEmitter = NativeModule.require('events');
process._eventsCount = 0;
const origProcProto = Object.getPrototypeOf(process);
Object.setPrototypeOf(process, Object.create(EventEmitter.prototype, {
constructor: Object.getOwnPropertyDescriptor(origProcProto, 'constructor')
}));
// 相当于 new EventEmitter() ，不过上下文是 process
EventEmitter.call(process);
// END
// 一些初始化操作
// BEGIN
setupProcessObject();
// do this good and early, since it handles errors.
setupProcessFatal();
setupProcessICUVersions();
setupGlobalVariables();
if (!process._noBrowserGlobals) {
setupGlobalTimeouts();
setupGlobalConsole();
}
// END
// process 对象的初始化操作
// BEGIN
// 这里的 internal/process 模块用于初始化 process
const _process = NativeModule.require('internal/process');
_process.setup_hrtime();
_process.setup_cpuUsage();
_process.setupMemoryUsage();
_process.setupConfig(NativeModule._source);
NativeModule.require('internal/process/warning').setup();
NativeModule.require('internal/process/next_tick').setup();
NativeModule.require('internal/process/stdio').setup();
_process.setupKillAndExit();
_process.setupSignalHandlers();
if (global.__coverage__)
NativeModule.require('internal/process/write-coverage').setup();
if (process.argv[1] !== '--debug-agent')
_process.setupChannel();
_process.setupRawDebug();
NativeModule.require('internal/url');
Object.defineProperty(process, 'argv0', {
enumerable: true,
configurable: false,
value: process.argv[0]
});
process.argv[0] = process.execPath;
// ...
// END
// 下面的 if-else 用来判断 node 的运行模式，我们只关注 node xx.js 的运行模式
// if () {
// ...
} else {
// 执行用户代码
// cluster 模块的 hook
if (process.argv[1] && process.env.NODE_UNIQUE_ID) {
const cluster = NativeModule.require('cluster');
cluster._setupWorker();
// Make sure it's not accidentally inherited by child processes.
delete process.env.NODE_UNIQUE_ID;
}
if (process._eval != null && !process._forceRepl) {
// ...
} else if (process.argv[1] && process.argv[1] !== '-') {
// node app.js
// make process.argv[1] into a full path
const path = NativeModule.require('path');
// 变为绝对路径
process.argv[1] = path.resolve(process.argv[1]);
const Module = NativeModule.require('module');
// check if user passed `-c` or `--check` arguments to Node.
if (process._syntax_check_only != null) {
const fs = NativeModule.require('fs');
// read the source
const filename = Module._resolveFilename(process.argv[1]);
var source = fs.readFileSync(filename, 'utf-8');
checkScriptSyntax(source, filename);
process.exit(0);
}
preloadModules();
Module.runMain();
} else {
// REPL 或其他
}
}
}startup() 最后调用 Module.runMain() 函数来加载并执行用户代码。在执行 startup() 函数的过程中，多次用到了 NativeModule.require() 来加载模块
NativeModule
NativeModule.require() 是专门用来加载 Node.js 内置模块的
// lib/internal/bootstrap_node.js
function NativeModule(id) {
this.filename = `${id}.js`;
this.id = id;
this.exports = {};
this.loaded = false;
this.loading = false;
}
NativeModule._source = process.binding('natives');
NativeModule._cache = {};
NativeModule.require = function(id) {
if (id === 'native_module') {
return NativeModule;
}
const cached = NativeModule.getCached(id);
if (cached && (cached.loaded || cached.loading)) {
return cached.exports;
}
if (!NativeModule.exists(id)) {
// Model the error off the internal/errors.js model, but
// do not use that module given that it could actually be
// the one causing the error if there's a bug in Node.js
const err = new Error(`No such built-in module: ${id}`);
err.code = 'ERR_UNKNOWN_BUILTIN_MODULE';
err.name = 'Error [ERR_UNKNOWN_BUILTIN_MODULE]';
throw err;
}
process.moduleLoadList.push(`NativeModule ${id}`);
const nativeModule = new NativeModule(id);
nativeModule.cache();
nativeModule.compile();
return nativeModule.exports;
};
NativeModule.getCached = function(id) {
return NativeModule._cache[id];
};
NativeModule.exists = function(id) {
return NativeModule._source.hasOwnProperty(id);
};
// ...
NativeModule.wrap = function(script) {
return NativeModule.wrapper[0] + script + NativeModule.wrapper[1];
};
NativeModule.wrapper = [
'(function (exports, require, module, __filename, __dirname) { ',
'\n});'
];
NativeModule.prototype.compile = function() {
var source = NativeModule.getSource(this.id);
source = NativeModule.wrap(source);
this.loading = true;
try {
const fn = runInThisContext(source, {
filename: this.filename,
lineOffset: 0,
displayErrors: true
});
fn(this.exports, NativeModule.require, this, this.filename);
this.loaded = true;
} finally {
this.loading = false;
}
};
NativeModule.prototype.cache = function() {
NativeModule._cache[this.id] = this;
};NativeModule 有几个重要的属性和方法:
id:NativeModule的标识符，例如events，internal/processfilename:NativeModule对应源码文件exports: 默认值是{}loaded/loading:NativeModule状态_cache: 简单的模块缓存_source: 模块源码资源require(): 先查询缓存，缓存没有则新建NativeModule并编译，返回exportswrap()/wrapper:wrapper是对模块上下文的包裹，如下:(function (exports, require, module, __filename, __dirname) { xxx });compile(): 将模块源码用wrapper包裹后，使用runInThisContext()（类似eval()）生成js函数，再执行之
Module.runMain()
Node.js 启动完成后，调用 Module.runMain()，源码如下:
// bootstrap main module.
Module.runMain = function() {
// Load the main module--the command line argument.
Module._load(process.argv[1], null, true);
// Handle any nextTicks added in the first tick of the program
process._tickCallback();
};Module._load() 加载并执行用户代码。至此 启动-js部分 已经全部完成，后续模块加载部分，见 Node.js源码解析-require背后
End
启动只是 Node.js 源码的一小部分，除此之外还有大量的内置模块和 c / c++ 源码
参考:
