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exports-
wrap()/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
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: