作为这个系列的开篇,本人特此声明,因为本人技术功力有限,且对mongodb源码目前也在研究探索中,可能会对mongodb内部某些实现机制及原作者的意图领会不够精确,因此错误再所难免,希望大家批评指正。另外本文所使用的mongodb源码为1.8 rc1,同时如果有条件的话,大家可以安装vs2010,用C++来编译调试mongodb源码,以便通过运行过程中的数据和流程来验证自己的判断。
VS2010 C++下编译调试MongoDB源码
http://www.cnblogs.com/daizhj/archive/2011/03/07/1973764.html
好了,开始今天的正文吧。
为了理解mongodb整体的运行机制,首先我们需要对其主要运行流程有一个大概的理解,而主入口函数main无疑是最佳突破口。首先我们在VS2010中打开db.sln文件,并打开db.cpp文件,找到主入口函数(位于文件613行),如下:
intmain(intargc,charargv[]) {
staticStaticObserver staticObserver;
getcurns=ourgetns;
po::options_description general_options("General options");//常规选项
#ifdefined(_WIN32)
po::options_description windows_scm_options("Windows Service Control Manager options");//windows服务控制管理选项仅限windows平台
#endif
po::options_description replication_options("Replication options");//Replication选项
po::options_description ms_options("Master/slave options");//主从选项
po::options_description rs_options("Replica set options");//Replica设置选项
po::options_description sharding_options("Sharding options");//数据分片选项
po::options_description visible_options("Allowed options");//可见选项
po::options_description hidden_options("Hidden options");//隐藏选项
po::positional_options_description positional_options;
general_options.add_options()
("auth","run with security")
("cpu","periodically show cpu and iowait utilization")
("dbpath", po::value<string>() ,"directory for datafiles")
("diaglog", po::value<int>(),"0=off 1=W 2=R 3=both 7=W+some reads")
("directoryperdb","each database will be stored in a separate directory")
.....
该方法的开头代码(上面)主要是绑定一个配置操作选项的说明,包括命令行模式下的参数说明,因为内容较长,这里就不做过多描述了,需要说明options_description的是这些内容被放到了boost库(一个C++开源库)的options_description对象中,其类型结构可以理解为key/value模式,主要用于记录一系列的选项描述(符)信息,以便于通过名称查询相应选项信息。同时mongodb将选项大致归为8类,如上所述。
接下说看一下其初始化时命令行参数的操作,如下:
if( argc==1)
cout<<dbExecCommand<<"--help for help and startup options"<<endl;
{
po::variables_mapparams;
stringerror_message=arg_error_check(argc, argv);
if(error_message!="") {
cout<<error_message<<endl<<endl;
show_help_text(visible_options);
return0;
}
if(!CmdLine::store( argc , argv , visible_options , hidden_options , positional_options ,params) )
return0;
上面方法对main主函数参数argc,argv及上面的那些选项实例进行存储并以此绑定到params实例上,因为接下来会通过params来设置cmdLine对象(CmdLine类型),并最终以该对象做为最终在mongodb内部标记相应启动命令参数信息的对象。形如:
if(params.count("version")) {
cout<<mongodVersion()<<endl;
printGitVersion();
return0;
}
if(params.count("dbpath") ) {
dbpath=params["dbpath"].as<string>();
if(params.count("fork")&&dbpath[0]!='/') {
//we need to change dbpath if we fork since we change
//cwd to "/"
//fork only exists on nix
//so '/' is safe
dbpath=cmdLine.cwd+"/"+dbpath;
}
}
else{
dbpath="d:/data/db/";//我在此处改了源码
}
if(params.count("directoryperdb")) {
directoryperdb=true;
}
if(params.count("cpu")) {
cmdLine.cpu=true;
}
......
当搜集到足够的启动信息(参数)后,mongodb开启执行下面两行代码:
Module::configAll(params);
上面用params来配置加载的模块信息,而就目前而言,mongodb中的模块有两个:其类模式和MMS模块,后者是当mongodb监视服务有效情况下,以后台线程方式(BackgroundJob)运行的程序,类定义如下:
/ Mongo Monitoring Service
if enabled, this runs in the background ands pings mss
/
classMMS :publicBackgroundJob , Module {
....
}
因为相关代码比较简单,这里就不多作说明了,如果大家感兴趣的话,以后会专门写一篇介绍Module,BackgroundJob的文章 。
回到正文,模块实始化完成了,就会运行如下代码:
dataFileSync.go();
这里要说明的是dataFileSync类也派生自BackgroundJob类,而BackgroundJob的功能就是生成一个后台线程并执行相应任务。而当前dataFileSync的任务就是在一段时间后(cmdLine.syncdelay)将内存中的数据flash到磁盘上(因为mongodb使用mmap方式将数据先放入内存中),代码如下:
classDataFileSync :publicBackgroundJob {
......
voidrun() {
if( cmdLine.syncdelay==0)
log()<<"warning: --syncdelay 0 is not recommended and can have strange performance"<<endl;
elseif( cmdLine.syncdelay==1)
log()<<"--syncdelay 1"<<endl;
elseif( cmdLine.syncdelay!=60)
log(1)<<"--syncdelay"<<cmdLine.syncdelay<<endl;
inttime_flushing=0;
while(!inShutdown() ) {
flushDiagLog();
if( cmdLine.syncdelay==0) {
//in case at some point we add an option to change at runtime
sleepsecs(5);
continue;
}
sleepmillis( (longlong) std::max(0.0, (cmdLine.syncdelay1000)-time_flushing) );
if( inShutdown() ) {
//occasional issue trying to flush during shutdown when sleep interrupted
break;
}
Date_t start=jsTime();
intnumFiles=MemoryMappedFile::flushAll(true);//使用系统提供的内存映射文件方法
time_flushing=(int) (jsTime()-start);
globalFlushCounters.flushed(time_flushing);
log(1)<<"flushing mmap took"<<time_flushing<<"ms"<<"for"<<numFiles<<"files"<<endl;
}
}
......
main主函数完成上面方法后,就会启动侦听方法,开始侦听客户端的链接请求,如下:
initAndListen(cmdLine.port, appsrvPath);
该侦听方法会最终调用db.cpp (467行)的如下方法,我们来看一下该方法做了些什么:
void_initAndListen(intlistenPort,constcharappserverLoc=NULL) {
首先是初始化一个名称“initandlisten”线程用于侦听客户端传来的操作信息(可能有误):
Client::initThread("initandlisten");
接着判断当前系统是32或64位系统?并获取当前进程ID并输出进程ID及数据库路径,端口信息以及当前mongodb及系统信息(这些信息也就是我们在命令行下经常看到的启动mongodb信息)
boolis32bit=sizeof(int)==4;
{
#if!defined(_WIN32)
pid_t pid=getpid();
#else
DWORD pid=GetCurrentProcessId();
#endif
Nullstream&l=log();
l<<"MongoDB starting : pid="<<pid<<"port="<<cmdLine.port<<"dbpath="<<dbpath;
if( replSettings.master ) l<<"master="<<replSettings.master;
if( replSettings.slave ) l<<"slave="<<(int) replSettings.slave;
l<<( is32bit?"32":"64")<<"-bit"<<endl;
}
DEV log()<<"_DEBUG build (which is slower)"<<endl;
show_warnings();
log()<<mongodVersion()<<endl;
printGitVersion();
printSysInfo();
完成这一步之后,接下来mongodb就会对相应路径下的数据文件进行检查,如出现文件错误(文件不存在等):
stringstream ss;
ss<<"dbpath ("<<dbpath<<") does not exist";
uassert(10296, ss.str().c_str(), boost::filesystem::exists( dbpath ) );
stringstream ss;
ss<<"repairpath ("<<repairpath<<") does not exist";
uassert(12590, ss.str().c_str(), boost::filesystem::exists( repairpath ) );
同时使用"路径锁"方式来移除指定路径下的临时文件夹信息,如下:
acquirePathLock();
remove_all( dbpath+"/_tmp/");
接着,mongodb还会启动持久化功能,该功能貌似是1.7版本后引入到系统中的,主要用于解决因系统宕机时,内存中的数据未写入磁盘而造成的数据丢失。其机制主要是通过log方式定时将操作日志(如cud操作等)记录到db的journal文件夹下,这样当系统再次重启时从该文件夹下恢复丢失的(内存)数据。有关这部分内容我会专门写文章加以介绍。
dur::startup();
if( cmdLine.durOptions&CmdLine::DurRecoverOnly )
return;
注:其命令行枚举定义如下
enum{//bits to be ORed
DurDumpJournal=1,//dump diagnostics on the journal during recovery
DurScanOnly=2,//don't do any real work, just scan and dump if dump specified
DurRecoverOnly=4,//terminate after recovery step
DurParanoid=8,//paranoid mode enables extra checks
DurAlwaysCommit=16//do a group commit every time the writelock is released
};
intdurOptions;//--durOptions
完成这一步之后,系统还会初始化脚本引擎,因为mongodb支持脚本语法做为其操作数据库的语言,如下:
if( scriptingEnabled ) {
ScriptEngine::setup();
globalScriptEngine->setCheckInterruptCallback( jsInterruptCallback );
globalScriptEngine->setGetInterruptSpecCallback( jsGetInterruptSpecCallback );
}
当这些主要工作做完之后,最后系统会调用下面方法正式启动侦听操作:
voidlisten(intport) {
log()<<"waiting for connections on port"<<port<<endl;
OurListener l(cmdLine.bind_ip, port);
l.setAsTimeTracker();
startReplication();
if(!noHttpInterface )
boost::thread web( boost::bind(&webServerThread,newRestAdminAccess()/takes ownership/));
#if(TESTEXHAUST)
boost::thread thr(testExhaust);
#endif
l.initAndListen();
}
注意上面的OurListener类其initAndListen()方法位于message.cpp中,因为mongodb采用message相关类来封装c/s双在的数据和操作:
voidListener::initAndListen() {
checkTicketNumbers();
vector<SockAddr>mine=ipToAddrs(_ip.c_str(), _port);
vector<int>socks;
SOCKET maxfd=0;//needed for select()
for(vector<SockAddr>::iterator it=mine.begin(), end=mine.end(); it!=end;++it) {
SockAddr&me=it;
SOCKET sock=::socket(me.getType(), SOCK_STREAM,0);
if( sock==INVALID_SOCKET ) {
log()<<"ERROR: listen(): invalid socket?"<<errnoWithDescription()<<endl;
}
if(me.getType()==AF_UNIX) {
#if!defined(_WIN32)
if(unlink(me.getAddr().c_str())==-1) {
intx=errno;
if(x!=ENOENT) {
log()<<"couldn't unlink socket file"<<me<<errnoWithDescription(x)<<"skipping"<<endl;
continue;
}
}
#endif
}
elseif(me.getType()==AF_INET6) {
//IPv6 can also accept IPv4 connections as mapped addresses (::ffff:127.0.0.1)
//That causes a conflict if we don't do set it to IPV6_ONLY
constintone=1;
setsockopt(sock, IPPROTO_IPV6, IPV6_V6ONLY, (constchar)&one,sizeof(one));
}
prebindOptions( sock );
if( ::bind(sock, me.raw(), me.addressSize)!=0) {
intx=errno;
log()<<"listen(): bind() failed"<<errnoWithDescription(x)<<"for socket:"<<me.toString()<<endl;
if( x==EADDRINUSE )
log()<<"addr already in use"<<endl;
closesocket(sock);
return;
}
#if!defined(_WIN32)
if(me.getType()==AF_UNIX) {
if(chmod(me.getAddr().c_str(),0777)==-1) {
log()<<"couldn't chmod socket file"<<me<<errnoWithDescription()<<endl;
}
ListeningSockets::get()->addPath( me.getAddr() );
}
#endif
if( ::listen(sock,128)!=0) {
log()<<"listen(): listen() failed"<<errnoWithDescription()<<endl;
closesocket(sock);
return;
}
ListeningSockets::get()->add( sock );
socks.push_back(sock);
if(sock>maxfd)
maxfd=sock;
}
staticlongconnNumber=0;
structtimeval maxSelectTime;
while(!inShutdown() ) {
fd_set fds[1];
FD_ZERO(fds);
for(vector<int>::iterator it=socks.begin(), end=socks.end(); it!=end;++it) {
FD_SET(it, fds);
}
maxSelectTime.tv_sec=0;
maxSelectTime.tv_usec=10000;
constintret=select(maxfd+1, fds, NULL, NULL,&maxSelectTime);
if(ret==0) {
#ifdefined(linux)
_elapsedTime+=(10000-maxSelectTime.tv_usec )/1000;
#else
_elapsedTime+=10;
#endif
continue;
}
_elapsedTime+=ret;//assume 1ms to grab connection. very rough
if(ret<0) {
intx=errno;
#ifdef EINTR
if( x==EINTR ) {
log()<<"select() signal caught, continuing"<<endl;
continue;
}
#endif
if(!inShutdown() )
log()<<"select() failure: ret="<<ret<<""<<errnoWithDescription(x)<<endl;
return;
}
for(vector<int>::iterator it=socks.begin(), end=socks.end(); it!=end;++it) {
if(!(FD_ISSET(it, fds)))
continue;
SockAddr from;
ints=accept(it, from.raw(),&from.addressSize);
if( s<0) {
intx=errno;//so no global issues
if( x==ECONNABORTED||x==EBADF ) {
log()<<"Listener on port"<<_port<<"aborted"<<endl;
return;
}
if( x==0&&inShutdown() ) {
return;//socket closed
}
if(!inShutdown() )
log()<<"Listener: accept() returns"<<s<<""<<errnoWithDescription(x)<<endl;
continue;
}
if(from.getType()!=AF_UNIX)
disableNagle(s);
if( _logConnect&&!cmdLine.quiet )
log()<<"connection accepted from"<<from.toString()<<"#"<<++connNumber<<endl;
accepted(s, from);
}
}
}
上面方法基本上就是一个无限循环( while ( ! inShutdown() ) )的侦听服务端,它调用操作系统的底层socket api接口,并将侦听到的结果使用accepted()方法进行接收。这里要注意的是因为最终我们使用的是OurListener进行的侦听,所以最终系统会调用OurListener所实现的虚(virtual)方法,如下:
classOurListener :publicListener {
public:
OurListener(conststring&ip,intp) : Listener(ip, p) { }
virtualvoidaccepted(MessagingPortmp) {
if(!connTicketHolder.tryAcquire() ) {
log()<<"connection refused because too many open connections:"<<connTicketHolder.used()<<"of"<<connTicketHolder.outof()<<endl;
//TODO: would be nice if we notified them...
mp->shutdown();
delete mp;
return;
}
try{
boost::thread thr(boost::bind(&connThread,mp));
}
catch( boost::thread_resource_error&) {
log()<<"can't create new thread, closing connection"<<endl;
mp->shutdown();
delete mp;
}
catch( ... ) {
log()<<"unkonwn exception starting connThread"<<endl;
mp->shutdown();
delete mp;
}
}
};
上面方法中的try{}语句中包含的是boost库中的thread方法,其主要提供了跨操作系统的线程创建方式及相关并行操作(相关信息参数boost官方网站),我们这里只要知道,通过该语句,我们最终用一个线程来运行connThread方法及其所需参数mp即可。下面看一下connThread方法的代码:
voidconnThread( MessagingPortinPort ) {
TicketHolderReleaser connTicketReleaser(&connTicketHolder );
/todo: move to Client object/
LastErrorle=newLastError();
lastError.reset(le);
inPort->_logLevel=1;
auto_ptr<MessagingPort>dbMsgPort( inPort );
Client&c=Client::initThread("conn", inPort);
try{
c.getAuthenticationInfo()->isLocalHost=dbMsgPort->farEnd.isLocalHost();
Message m;
while(1) {
inPort->clearCounters();
if(!dbMsgPort->recv(m) ) {
if(!cmdLine.quiet )
log()<<"end connection"<<dbMsgPort->farEnd.toString()<<endl;
dbMsgPort->shutdown();
break;
}
sendmore:
if( inShutdown() ) {
log()<<"got request after shutdown()"<<endl;
break;
}
lastError.startRequest( m , le );
DbResponse dbresponse;
assembleResponse( m, dbresponse, dbMsgPort->farEnd );
if( dbresponse.response ) {
dbMsgPort->reply(m,dbresponse.response, dbresponse.responseTo);
if( dbresponse.exhaust ) {
...出现问题时
}
}
networkCounter.hit( inPort->getBytesIn() , inPort->getBytesOut() );
m.reset();
}
}
......
//thread ending...
{
Clientc=currentClient.get();
if( c ) c->shutdown();
}
globalScriptEngine->threadDone();
}
上面代码主要工作就是不断循环[while ( 1 )]获取当前客户端发来的信息(上面已封装成了message)并将其信息进行分析,并根据相应操作标志位确定当前操作是CRUD或构建索引等[assembleResponse()],如果一些正常,则向客户端发送应答信息:
voidconnThread( MessagingPortinPort ) {
TicketHolderReleaser connTicketReleaser(&connTicketHolder );
/todo: move to Client object/
LastErrorle=newLastError();
lastError.reset(le);
inPort->_logLevel=1;
auto_ptr<MessagingPort>dbMsgPort( inPort );
Client&c=Client::initThread("conn", inPort);
try{
c.getAuthenticationInfo()->isLocalHost=dbMsgPort->farEnd.isLocalHost();
Message m;
while(1) {
inPort->clearCounters();
if(!dbMsgPort->recv(m) ) {
if(!cmdLine.quiet )
log()<<"end connection"<<dbMsgPort->farEnd.toString()<<endl;
dbMsgPort->shutdown();
break;
}
sendmore:
if( inShutdown() ) {
log()<<"got request after shutdown()"<<endl;
break;
}
lastError.startRequest( m , le );
DbResponse dbresponse;
assembleResponse( m, dbresponse, dbMsgPort->farEnd );
if( dbresponse.response ) {
dbMsgPort->reply(m,dbresponse.response, dbresponse.responseTo);
if( dbresponse.exhaust ) {
...出现问题时
}
}
networkCounter.hit( inPort->getBytesIn() , inPort->getBytesOut() );
m.reset();
}
}
......
//thread ending...
{
Clientc=currentClient.get();
if( c ) c->shutdown();
}
globalScriptEngine->threadDone();
}
运行到这里,main函数的使命就完成了,本来想用一张时序图来大致回顾一下,只有等有时间再补充了。
好了,今天的内容到这里就告一段落了,在接下来的文章中,将会介绍客户端发起查询操作时,Mongodb的执行流程和运行机制。
原文链接:http://www.cnblogs.com/daizhj/archive/2011/03/17/1987311.html
作者: daizhj, 代震军
微博:http://t.sina.com.cn/daizhjTags: mongodb,c++,source codeTags: mongodb,c++,source code原文链接: https://www.cnblogs.com/daizhj/archive/2011/03/17/1987311.html
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