mongodb源码分析(三)mongo的启动

菜蜂 · 发表于 2015-11-10 13:50:51

　　mongo是mongodb的一个C++写的javascript交互式的可执行客户端。为了分析mongod对于服务请求的响应，这里分析下mongo。先来看看mongo的启动,mongo的启动代码在mongo/shell/dbshell.cpp中。其支持两个javascript 引擎，因为用visual stdio2012调试时默认编译的是spidermonkey，那么就分析spidermonkey那边吧。
　　当我们使用mongodb时最简单的一个保存命令是db.coll.save({a:1}),我们知道db是javascript对象，也是数据库名，coll是数据集collection,这里将{a:1}保存到coll的集合中，但是这里有一个疑问，javascript对象对于未定义的属性的访问不是通过db[coll]访问的吗,coll这里本应该是undefined,但是为什么结果成功的保存了呢。当我在阅读源码时就有这么个疑问，还好终于从源码中找到了答案，好了废话不多说了，直接分析。
　　

po::options_description shell_options( "options" );//同样是一大堆启动命令，具体含义不说了，自己可以看相关的文档
po::options_description hidden_options( "Hidden options" );
po::options_description cmdline_options( "Command line options" );
po::positional_options_description positional_options;
shell_options.add_options()
( "shell", "run the shell after executing files" )
( "nodb", "don't connect to mongod on startup - no 'db address' arg expected" )
( "norc", "will not run the \".mongorc.js\" file on start up" )
( "quiet", "be less chatty" )
( "port", po::value<string>( &port ), "port to connect to" )
( "host", po::value<string>( &dbhost ), "server to connect to" )
( "eval", po::value<string>( &script ), "evaluate javascript" )
( "username,u", po::value<string>(&username), "username for authentication" )
( "password,p", new mongo::PasswordValue( &password ), "password for authentication" )
( "help,h", "show this usage information" )
( "version", "show version information" )
( "verbose", "increase verbosity" )
( "ipv6", "enable IPv6 support (disabled by default)" )
if ( !nodb ) { // connect to db
//if ( ! mongo::cmdLine.quiet ) cout << "url: " << url << endl;
//如果启动时没有指定nodb,那么这里将生成一串javascript代码,用来连接mongod
stringstream ss;
if ( mongo::cmdLine.quiet )
ss << "__quiet = true;";
ss << "db = connect( \"" << fixHost( url , dbhost , port ) << "\")";
mongo::shell_utils::_dbConnect = ss.str();
if ( params.count( "password" ) && password.empty() )
password = mongo::askPassword();
if ( username.size() && password.size()) {
stringstream ss;
ss << "if ( ! db.auth( \"" << username << "\" , \"" << password << "\" ) ){ throw 'login failed'; }";
mongo::shell_utils::_dbAuth = ss.str();
}
}
mongo::ScriptEngine::setConnectCallback( mongo::shell_utils::onConnect );//这个回调函数用来做连接成功后的记录工作
mongo::ScriptEngine::setup();
mongo::globalScriptEngine->setScopeInitCallback( mongo::shell_utils::initScope );
auto_ptr< mongo::Scope > scope( mongo::globalScriptEngine->newScope() );
shellMainScope = scope.get();

　　现在来看看mongo::globalScriptEngine->newScope(),在mongo::ScriptEngine::setup()函数中globalScriptEngine=new SMEngine()。
　　

      virtual Scope * newScope() {
Scope *s = createScope();
if ( s && _scopeInitCallback )//_scopeInitCallback对应上面的mongo::shell_utils::initScope
_scopeInitCallback( *s );
installGlobalUtils( *s );
return s;
}
createScope对应spideMonkey则为new SMScope()　　
　　

      SMScope() ://spideMonkey的初始化
_this( 0 ),
_reportError( true ),
_externalSetup( false ),
_localConnect( false ) {
smlock;
_context = JS_NewContext( globalSMEngine->_runtime , 8192 );
_convertor = new Convertor( _context );
massert( 10431 ,  "JS_NewContext failed" , _context );
JS_SetOptions( _context , JSOPTION_VAROBJFIX);
//JS_SetVersion( _context , JSVERSION_LATEST); TODO
JS_SetErrorReporter( _context , errorReporter );
_global = JS_NewObject( _context , &global_class, NULL, NULL);
massert( 10432 ,  "JS_NewObject failed for global" , _global );
JS_SetGlobalObject( _context , _global );
massert( 10433 ,  "js init failed" , JS_InitStandardClasses( _context , _global ) );
JS_SetOptions( _context , JS_GetOptions( _context ) | JSOPTION_VAROBJFIX );
JS_DefineFunctions( _context , _global , globalHelpers );//预先定义的几个函数
JS_DefineFunctions( _context , _convertor->getGlobalObject( "Object" ), objectHelpers );
//JS_SetGCCallback( _context , no_gc ); // this is useful for seeing if something is a gc problem
_postCreateHacks();
}
JSFunctionSpec globalHelpers[] = {//这里定义的几个函数映射,javascript中执行相应的函数则会调用这里的本地函数。
{ "print" , &native_print , 0 , 0 , 0 } ,
{ "nativeHelper" , &native_helper , 1 , 0 , 0 } ,
{ "load" , &native_load , 1 , 0 , 0 } ,
{ "gc" , &native_gc , 1 , 0 , 0 } ,
{ "UUID", &_UUID, 0, 0, 0 } ,
{ "MD5", &_MD5, 0, 0, 0 } ,
{ "HexData", &_HexData, 0, 0, 0 } ,
{ 0 , 0 , 0 , 0 , 0 }
};
继续到newScope函数，接下来调用了_scopeInitCallback()函数，其实就是之前设置的initScope回调函数

      void initScope( Scope &scope ) {
scope.externalSetup();
mongo::shell_utils::installShellUtils( scope );
scope.execSetup(JSFiles::servers);//执行相应的javascript文件，相当于初始化javascript环境，以后命令行中执行相应代码时
scope.execSetup(JSFiles::shardingtest);//就能正确的找到环境了。
scope.execSetup(JSFiles::servers_misc);
scope.execSetup(JSFiles::replsettest);
scope.execSetup(JSFiles::replsetbridge);
if ( !_dbConnect.empty() ) {//执行登录代码
uassert( 12513, "connect failed", scope.exec( _dbConnect , "(connect)" , false , true , false ) );
if ( !_dbAuth.empty() ) {//用户账号登陆认证
installGlobalUtils( scope );
uassert( 12514, "login failed", scope.exec( _dbAuth , "(auth)" , true , true , false ) );
}
}
}
initScope->externalSetup->initMongoJS

void initMongoJS( SMScope * scope , JSContext * cx , JSObject * global , bool local ) {
//JS Class的初始化过程，几乎所有的mongodb使用到的class都在这里创建，所有new XXX对象的构建都是下面这里的函数完成的,比如说db,collection,dbquery
verify( JS_InitClass( cx , global , 0 , &mongo_class , local ? mongo_local_constructor : mongo_external_constructor , 0 , 0 , mongo_functions , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &object_id_class , object_id_constructor , 0 , 0 , 0 , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &db_class , db_constructor , 2 , 0 , 0 , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &db_collection_class , db_collection_constructor , 4 , 0 , 0 , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &internal_cursor_class , internal_cursor_constructor , 0 , 0 , internal_cursor_functions , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &dbquery_class , dbquery_constructor , 0 , 0 , 0 , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &dbpointer_class , dbpointer_constructor , 0 , 0 , dbpointer_functions , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &bindata_class , bindata_constructor , 0 , 0 , bindata_functions , 0 , 0 ) );
//       verify( JS_InitClass( cx , global , 0 , &uuid_class , uuid_constructor , 0 , 0 , uuid_functions , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , ×tamp_class , timestamp_constructor , 0 , 0 , 0 , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &numberlong_class , numberlong_constructor , 0 , 0 , numberlong_functions , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &numberint_class , numberint_constructor , 0 , 0 , numberint_functions , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &minkey_class , 0 , 0 , 0 , 0 , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &maxkey_class , 0 , 0 , 0 , 0 , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &map_class , map_constructor , 0 , 0 , map_functions , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &bson_ro_class , bson_cons , 0 , 0 , bson_functions , 0 , 0 ) );
verify( JS_InitClass( cx , global , 0 , &bson_class , bson_cons , 0 , 0 , bson_functions , 0 , 0 ) );
static const char *dbrefName = "DBRef";
dbref_class.name = dbrefName;
verify( JS_InitClass( cx , global , 0 , &dbref_class , dbref_constructor , 2 , 0 , bson_functions , 0 , 0 ) );
scope->execCoreFiles();
}

　　这里local为false，使用的是mongo_external_constructor函数。先看看mongo_class：
　　

JSClass mongo_class = {//为映射javascript对象而设置的函数，当javascript中new Mongo对象时会调用mongo_external_constructor来构造一个对象
"Mongo",                                     // class name
JSCLASS_HAS_PRIVATE | JSCLASS_NEW_RESOLVE,    // flags
JS_PropertyStub,                               // addProperty
JS_PropertyStub,                               // delProperty
JS_PropertyStub,                               // getProperty
JS_PropertyStub,                               // setProperty
JS_EnumerateStub,                            // enumerate
JS_ResolveStub,                               // resolve
JS_ConvertStub,                               // convert
mongo_finalize,                               // finalize
JSCLASS_NO_OPTIONAL_MEMBERS                   // optional members
};
再看看  mongo_functions:　　
　　

JSFunctionSpec mongo_functions[] = {//当在javascript中调用相应的函数时，这里对应的native函数将会被调用到，
{ "auth" , mongo_auth , 0 , JSPROP_READONLY | JSPROP_PERMANENT, 0 } ,
{ "logout", mongo_logout, 0, JSPROP_READONLY | JSPROP_PERMANENT, 0 },
{ "find" , mongo_find , 0 , JSPROP_READONLY | JSPROP_PERMANENT, 0 } ,
{ "update" , mongo_update , 0 , JSPROP_READONLY | JSPROP_PERMANENT, 0 } ,
{ "insert" , mongo_insert , 0 , JSPROP_READONLY | JSPROP_PERMANENT, 0 } ,
{ "remove" , mongo_remove , 0 , JSPROP_READONLY | JSPROP_PERMANENT, 0 } ,
{ 0 }
};
我们继续看，现在是出来上面的问题了db.coll.save({a:1})为什么没有问题。　　
　　

JSClass db_collection_class = {
"DBCollection",                               // class name
JSCLASS_HAS_PRIVATE | JSCLASS_NEW_RESOLVE,    // flags
JS_PropertyStub,                               // addProperty
JS_PropertyStub,                               // delProperty
JS_PropertyStub,                               // getProperty
JS_PropertyStub,                               // setProperty
JS_EnumerateStub,                            // enumerate
(JSResolveOp)db_collection_resolve,          // 注意这里，这是关键
JS_ConvertStub,                               // convert
JS_FinalizeStub,                               // finalize
JSCLASS_NO_OPTIONAL_MEMBERS                   // optional members
};
JSBool db_collection_resolve( JSContext *cx, JSObject *obj, jsval id, uintN flags, JSObject **objp ) {
try {
if ( flags & JSRESOLVE_ASSIGNING )
return JS_TRUE;
Convertor c( cx );
string collname = c.toString( id );
if ( isSpecialName( collname ) )
return JS_TRUE;
if ( obj == c.getGlobalPrototype( "DBCollection" ) )
return JS_TRUE;
JSObject * proto = JS_GetPrototype( cx , obj );
if ( c.hasProperty( obj , collname.c_str() ) || ( proto && c.hasProperty( proto , collname.c_str() )  ) )
return JS_TRUE;
string name = c.toString( c.getProperty( obj , "_shortName" ) );
name += ".";
name += collname;
jsval db = c.getProperty( obj , "_db" );
if ( ! JSVAL_IS_OBJECT( db ) )
return JS_TRUE;
JSObject * coll = doCreateCollection( cx , JSVAL_TO_OBJECT( db ) , name );//这个地方创建了个集合，当调用db.coll.save()时,javascript调用
if ( ! coll )    //resolve函数时在这里将coll集合创建了出来,所以coll不为undefined
return JS_FALSE;                                                    //原来如此,spidermonkey的具体流程就不清楚了，有感兴趣的自己去看吧
c.setProperty( obj , collname.c_str() , OBJECT_TO_JSVAL( coll ) );
*objp = obj;
}
catch ( const AssertionException& e ) {
if ( ! JS_IsExceptionPending( cx ) ) {
JS_ReportError( cx, e.what() );
}
return JS_FALSE;
}
catch ( const std::exception& e ) {
log() << "unhandled exception: " << e.what() << ", throwing Fatal Assertion" << endl;
fassertFailed( 16303 );
}
return JS_TRUE;
}
继续回到上面initMongoJS最后一行:       scope->execCoreFiles();　　
　　

void Scope::execCoreFiles() {//在javascript环境中执行一遍上面文件，然后javascript环境中就会留下那些文件的代码与数据，以后
// keeping same order as in SConstruct//在命令行中执行命令时就能正确执行相应代码了。
execSetup(JSFiles::utils);
execSetup(JSFiles::utils_sh);
execSetup(JSFiles::db);
execSetup(JSFiles::mongo);
execSetup(JSFiles::mr);
execSetup(JSFiles::query);
execSetup(JSFiles::collection);
}回到initScope：　　
　　

         if ( !_dbConnect.empty() ) {//执行登录代码
uassert( 12513, "connect failed", scope.exec( _dbConnect , "(connect)" , false , true , false ) );
if ( !_dbAuth.empty() ) {//用户账号登陆认证
installGlobalUtils( scope );
uassert( 12514, "login failed", scope.exec( _dbAuth , "(auth)" , true , true , false ) );
}
}

　　

下面来看看登录:
      ss << "db = connect( \"" << fixHost( url , dbhost , port ) << "\")";
这里就是产生的javascript连接代码:
string fixHost( string url , string host , string port ) {//url传进来初始化值为test,这里就可以看出为啥默认连接到了test数据库了。
//cout << "fixHost url: " << url << " host: " << host << " port: " << port << endl;//若什么都没设置也知道为什么连接到了
//127.0.0.1:27017
if ( host.size() == 0 && port.size() == 0 ) {
if ( url.find( "/" ) == string::npos ) {
// check for ips
if ( url.find( "." ) != string::npos )
return url + "/test";
if ( url.rfind( ":" ) != string::npos &&
isdigit( url[url.rfind(":")+1] ) )
return url + "/test";
}
return url;
}
if ( url.find( "/" ) != string::npos ) {
cerr << "url can't have host or port if you specify them individually" << endl;
::_exit(-1);
}
if ( host.size() == 0 )
host = "127.0.0.1";
string newurl = host;
if ( port.size() > 0 )
newurl += ":" + port;
else if ( host.find(':') == string::npos ) {
// need to add port with IPv6 addresses
newurl += ":27017";
}
newurl += "/" + url;
return newurl;
}
下面来看看javascript代码connectconnect = function( url , user , pass ){
chatty( "connecting to: " + url )
if ( user && ! pass )
throw "you specified a user and not a password.  either you need a password, or you're using the old connect api";
var idx = url.lastIndexOf( "/" );
var db;
if ( idx < 0 )
db = new Mongo().getDB( url );//这里创建了Mongo对象,上面代码分析时已经提到New Mongo()会调用本地函数:mongo_external_constructor
else
db = new Mongo( url.substring( 0 , idx ) ).getDB( url.substring( idx + 1 ) );
if ( user && pass ){
if ( ! db.auth( user , pass ) ){
throw "couldn't login";
}
}
return db;
}
我们回到C++函数:mongo_external_constructor
JSBool mongo_external_constructor( JSContext *cx, JSObject *obj, uintN argc, jsval *argv, jsval *rval ) {
try {
smuassert( cx ,  "0 or 1 args to Mongo" , argc <= 1 );
string host( "127.0.0.1" );
Convertor c( cx );
if ( argc > 0 )
host = c.toString( argv[0] );
string errmsg;//注意这里的ConnectionString,其形式可为:server server:port foo/server:port,server:port  server,server,server
ConnectionString cs = ConnectionString::parse( host , errmsg );//可同时配置多个IP,还记得在QQ群里有个人问，使用replset模式时如
if ( ! cs.isValid() ) {//果主服务器挂了，那么php中怎么配置呢，我不知道php怎么配置，
JS_ReportError( cx , errmsg.c_str() );                   //但是看到这里大家应该明白了，mongo的连接地址配置其实是可以是
return JS_FALSE;                                        //多地址的,其connection有几种模式具体参见:ConnectionString
}
shared_ptr< DBClientWithCommands > conn( cs.connect( errmsg ) );//这里通过了ConnectionString屏蔽了具体的连接过程
if ( ! conn ) {
JS_ReportError( cx , errmsg.c_str() );
return JS_FALSE;
}
try {
ScriptEngine::runConnectCallback( *conn );//连接成功调用上面说的函数mongo::shell_utils::onConnect记录连接
}
catch ( const AssertionException& e ){
// Can happen if connection goes down while we're starting up here
// Catch so that we don't get a hard-to-trace segfault from SM
JS_ReportError( cx, ((string)( str::stream() << "Error during mongo startup." << causedBy( e ) )).c_str() );
return JS_FALSE;
}
catch ( const std::exception& e ) {
log() << "unhandled exception: " << e.what() << ", throwing Fatal Assertion" << endl;
fassertFailed( 16294 );
}
verify( JS_SetPrivate( cx , obj , (void*)( new shared_ptr< DBClientWithCommands >( conn ) ) ) );
jsval host_val = c.toval( host.c_str() );
verify( JS_SetProperty( cx , obj , "host" , &host_val ) );
}
catch ( const AssertionException& e ) {
if ( ! JS_IsExceptionPending( cx ) ) {
JS_ReportError( cx, e.what() );
}
return JS_FALSE;
}
catch ( const std::exception& e ) {
log() << "unhandled exception: " << e.what() << ", throwing Fatal Assertion" << endl;
fassertFailed( 16295 );
}
return JS_TRUE;
}
继续回到initScope,来看看认证过程。

            if ( !_dbAuth.empty() ) {//用户账号登陆认证
installGlobalUtils( scope );
uassert( 12514, "login failed", scope.exec( _dbAuth , "(auth)" , true , true , false ) );
}
         ss << "if ( ! db.auth( \"" << username << "\" , \"" << password << "\" ) ){ throw 'login failed'; }";
通过上面的分析可知这里直接调用了函数mongo_auth。这个函数调用DBClientWithCommands::auth函数执行具体的认证动作。
bool DBClientWithCommands::auth(const string &dbname, const string &username, const string &password_text, string& errmsg, bool digestPassword, Auth::Level * level) {
string password = password_text;
if( digestPassword )
password = createPasswordDigest( username , password_text );//将用户名密码按照user:mongo:passwd做md5
if ( level != NULL )
*level = Auth::NONE;
BSONObj info;
string nonce;
if( !runCommand(dbname, getnoncecmdobj, info) ) {//执行命令{getnonce:1}从服务端得到一个nonce的值
errmsg = "getnonce fails - connection problem?";
return false;
}
{
BSONElement e = info.getField("nonce");
verify( e.type() == String );
nonce = e.valuestr();
}
BSONObj authCmd;
BSONObjBuilder b;
{
b << "authenticate" << 1 << "nonce" << nonce << "user" << username;
md5digest d;
{
md5_state_t st;
md5_init(&st);
md5_append(&st, (const md5_byte_t *) nonce.c_str(), nonce.size() );
md5_append(&st, (const md5_byte_t *) username.data(), username.length());
md5_append(&st, (const md5_byte_t *) password.c_str(), password.size() );
md5_finish(&st, d);
}
b << "key" << digestToString( d );
authCmd = b.done();
}
if( runCommand(dbname, authCmd, info) ) {//执行命令authenticate验证用户,数据发送到服务端后服务端验证用户通过后会将其加入到
if ( level != NULL ) {//一个map中，其保存了认证的数据库,用户名,以及权限，权限只有读或者写
if ( info.getField("readOnly").trueValue() )
*level = Auth::READ;
else
*level = Auth::WRITE;
}
return true;
}
errmsg = info.toString();
return false;
}
到这里initscope执行完毕，javascript初始化完毕。进入读取用户输入执行用户输入的javascript代码的流程中,部分代码如下:
         bool wascmd = false;
{
string cmd = linePtr;
if ( cmd.find( " " ) > 0 )
cmd = cmd.substr( 0 , cmd.find( " " ) );
if ( cmd.find( "\"" ) == string::npos ) {
try {//这里判断用户的输入是否是命令比如说use database,it这种命令
scope->exec( (string)"__iscmd__ = shellHelper[\"" + cmd + "\"];" , "(shellhelp1)" , false , true , true );
if ( scope->getBoolean( "__iscmd__" )  ) {//这里确实是命令，那么就去执行这些命令
scope->exec( (string)"shellHelper( \"" + cmd + "\" , \"" + code.substr( cmd.size() ) + "\");" , "(shellhelp2)" , false , true , false );
wascmd = true;
}
}
catch ( std::exception& e ) {
cout << "error2:" << e.what() << endl;
wascmd = true;
}
}
}
if ( ! wascmd ) {
try {//不是确切的命令，按照一般javascript的代码规则执行
if ( scope->exec( code.c_str() , "(shell)" , false , true , false ) )
scope->exec( "shellPrintHelper( __lastres__ );" , "(shell2)" , true , true , false );//打印结果,比如说用户查询
}                                                                                           //结果就是这里打印出来的
catch ( std::exception& e ) {
cout << "error:" << e.what() << endl;
}
}
shellHistoryAdd( code.c_str() );//记录这个代码，下次可以使用，用户可以按上下键调出就像linux shell一样。
free( line );
}
shellHistoryDone();
}

至此mongo的启动流程就分析完了，具体来说可以分为:
1. javascript环境的初始化(包括了一些辅助函数的注入如native_print和mongodb对象的注入如collection,db,dbquery)。
2. 客户端的登录流程(需要注意的是配置服务端地址时可设置多服务端地址，具体可参考ConnectionString这个类的实现)。

原文链接:http://blog.iyunv.com/yhjj0108/article/details/8252958
作者:yhjj0108,杨浩

　　

版权声明：本文为博主原创文章，未经博主允许不得转载。

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