[{"_1":2,"_3":-5,"_4":-5},"loaderData",{"_5":6,"_7":8},"actionData","errors","root",{"_11":-5,"_55":56,"_57":58,"_59":60},"routes/user.$name.collections",{"_9":10,"_11":12,"_13":14,"_15":16,"_17":18,"_19":16},"topics",[36],"user",{"_20":21,"_13":14,"_22":23,"_24":25,"_26":27,"_28":29,"_30":31,"_32":33,"_34":35},"loginname","xiongjia","page",1,"limit",20,"total","id","9753","avatar_url","http://www.gravatar.com/avatar/80c5c6faf4b7960addb40e84e35fd970?size=48","githubUsername","","create_at","2013-09-06T14:18:06.136Z","score",35,"topic_count",0,"reply_count",7,"is_star",false,{"_20":37,"_38":39,"_40":-5,"_41":42,"_43":44,"_45":46,"_47":35,"_48":35,"_32":31,"_49":50,"_26":46,"_51":52},"96","author_id","68","tab","content","粗略研究了一下node.js源码，它有8000行C++代码，2000行javascript代码，来看看js和C++间是怎么组织连接起来，以及各个模块是怎样互相调用的。\r\n
\r\n
本文使用的node.js版本是0.4.8，可以在https://github.com/joyent/node/tree/v0.4.8这里看到源码。\r\n

js2c.py

\r\n
node.js使用了V8附带的js2c.py工具把所有内置的js代码转换成C++里的数组，生成node_natives.h直接include到程序中，成了C++源码的一部分。这样做能提高内置js模块的编译效率。\r\n
\r\n
node.js里内置的javascript包括了主程序src/node.js和模块程序lib/*.js，通过js2c.py让每一个js文件都生成一个源码数组，存放在build/src/node_natives.h里，node_natives.h在node.js编译后才会生成(编译的脚本wscript中调用了js2c.py)，可以看到大致的结构如下：\r\n
\r\n

\r\n
namespace node {\r\n
const char node_native[] = {47, 47, 32, 67, 112 ......}\r\n
const char console_native[] = {47, 47, 32, 67, 112 ......}\r\n
const char buffer_native[] = {47, 47, 32, 67, 112 ......}\r\n
.....\r\n
}\r\n
struct _native {  const char* name;  const char* source;  size_t source_len;};\r\n
static const struct _native natives[] = {\r\n
{ \"node\", node_native, sizeof(node_native)-1 },\r\n
{ \"dgram\", dgram_native, sizeof(dgram_native)-1 },\r\n
{ \"console\", console_native, sizeof(console_native)-1 },\r\n
{ \"buffer\", buffer_native, sizeof(buffer_native)-1 },\r\n
....\r\n
}\r\n

\r\n
这个文件被包含在node_javascript.cc里，node_javascript.cc提供了两个接口：\r\n
MainSource() 处理node_native源码返回v8::Handle类型的数据可供编译。\r\n
DefineJavaScript(target) 把其他所有模块源码变成v8::Handle类型后加载到传入的target对象上。\r\n
\r\n
所有的js模块都被转换成了C数组，接下来看看它们怎么执行和互相调用。\r\n
\r\n

执行js主程序/传递process

\r\n
先看看node.js的底层C++传递给javascript的一个变量process，在一开始运行node.js时，程序会先配置好process\r\n

\r\n
Handleprocess = SetupProcessObject(argc, argv);\r\n

\r\n
然后把process作为参数去调用js主程序src/node.js返回的函数，这样process就传递到javascript里了。\r\n

\r\n
//node.cc\r\n
//通过MainSource()获取已转化的src/node.js源码，并执行它\r\n
Local f_value = ExecuteString(MainSource(), IMMUTABLE_STRING(\"node.js\"));

\r\n
\r\n

//执行src/node.js后获得的是一个函数，从node.js源码可以看出：\r\n
//node.js\r\n
//(function(process) {\r\n
//    global = this;\r\n
//    ....\r\n
//})\r\n
Local f = Local::Cast(f_value);\r\n
\r\n

\r\n
\r\n

//创建函数执行环境，调用函数，把process传入\r\n
Localglobal = v8::Context::GetCurrent()->Global();\r\n
Local args[1] = { Local::New(process) };\r\n
f->Call(global, 1, args);\r\n

\r\n

C++模块

\r\n
node.js的模块除了lib/*.js里用js语言编写的以外，还有一些使用C++编写，像os/stdio/crypto/buffer等。这些模块都通过node.h提供的NODE_MODULE方法存储在变量_module里。node_extensions.cc提供了get_builtin_module(name)接口获取这些模块。\r\n

process.binding/C++模块加载

\r\n
process提供的一个获取模块的接口是binding，它的实现Binding()函数可以在node.cc找到。\r\n

\r\n
Persistent binding_cache;\r\n
static Handle Binding(const Arguments& args) {\r\n
HandleScope scope;\r\n
Local module = args[0]->ToString();\r\n
String::Utf8Value module_v(module);\r\n
node_module_struct* modp;

\r\n
\r\n

if (binding_cache.IsEmpty()) {\r\n
binding_cache = Persistent::New(Object::New());\r\n
}\r\n
Local exports;\r\n
if (binding_cache->Has(module)) {\r\n
exports = binding_cache->Get(module)->ToObject();\r\n
\r\n
} else if ((modp = get_builtin_module(*module_v)) != NULL) {\r\n
exports = Object::New();\r\n
modp->register_func(exports);\r\n
binding_cache->Set(module, exports);\r\n
\r\n
} else if (!strcmp(*module_v, \"constants\")) {\r\n
exports = Object::New();\r\n
DefineConstants(exports);\r\n
binding_cache->Set(module, exports);\r\n
\r\n
#ifdef __POSIX__\r\n
} else if (!strcmp(*module_v, \"io_watcher\")) {\r\n
exports = Object::New();\r\n
IOWatcher::Initialize(exports);\r\n
binding_cache->Set(module, exports);\r\n
#endif\r\n
\r\n
} else if (!strcmp(*module_v, \"natives\")) {\r\n
exports = Object::New();\r\n
DefineJavaScript(exports);\r\n
binding_cache->Set(module, exports);\r\n
\r\n

\r\n
\r\n

 } else {\r\n
return ThrowException(Exception::Error(String::New(\"No such module\")));\r\n
}\r\n
return scope.Close(exports);\r\n
}\r\n

\r\n
从源码可以看到，调用process.binding时，先看缓存里是否已经存在此模块，不存在再调用get_builtin_module查找C++内置模块，找到的话获取后绑定在exports上，在最后返回exports。\r\n
\r\n
此外还有针对其他模块的特殊处理，其中natives模块就是调用上文提到的DefineJavaScript(exports)接口获取到所有内置的js模块绑定在exports上。\r\n
\r\n
现在在js上需要调用C++提供的模块只需要调用process.binding就行了，例如\r\n

\r\n
var stdio = process.binding(\"stdio\")\r\n

\r\n

js模块加载

\r\n
src/node.js上实现了一个NativeModule对象用于管理js模块，它通过调用process.binding(\"natives\")把所有内置的js模块放在NativeModule._source上，并提供require接口供调用。在require里会给代码加一层包装，把一些变量传给这个模块。\r\n

\r\n
NativeModule.wrapper = [\r\n
'(function (exports, require, module, __filename, __dirname) { ',\r\n
'\\n});'\r\n
];\r\n

\r\n
再用process提供的其中一个js编译接口process.runInThisContext执行代码。\r\n

\r\n
var fn = runInThisContext(source, this.filename, true);\r\n
fn(this.exports, NativeModule.require, this, this.filename);\r\n

\r\n
于是在主程序src/node.js上可以调用NativeModule.require(\"net\")去加载net模块，在lib/*.js的各个js模块里能通过调用传进来的require()去加载其他内置js模块。\r\n

总结流程

\r\n
粗略总结一下加载模块的流程：\r\n
\r\n
加载C++模块（以stdio为例）：\r\n
process.binding(\"stdio\") -> get_builtin_module(\"stdio\") -> _module -> NODE_MODULE(node_stdio, node::Stdio::Initialize)(定义)\r\n
\r\n
加载js模块（以net为例）\r\n
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