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UDT协议相关初始化分析

钱卓君
2023-12-01

UDT本身提供了一些测试案例,位于UDT/app文件中,如appclient.cpp/appserver.cpp等。本节以appclient.cpp/appserver.cpp为例,介绍下UDT的操作以及client/server初始化流程。本节主要介绍了初始阶段UDT::startup、UDT::cleanup、UDT::socket、UDT::bind、UDT::listen这几个套接口。关于UDT::connect和UDT::accpet放到握手部分来讲解。

appclient.cpp源代码分析

代码如下:

#ifndef WIN32
   #include <unistd.h>
   #include <cstdlib>
   #include <cstring>
   #include <netdb.h>
#else
   #include <winsock2.h>
   #include <ws2tcpip.h>
   #include <wspiapi.h>
#endif
#include <iostream>
#include <udt.h>
#include "cc.h"
#include "test_util.h"

using namespace std;

#ifndef WIN32
void* monitor(void*);
#else
DWORD WINAPI monitor(LPVOID);
#endif

int main(int argc, char* argv[])
{
   if ((3 != argc) || (0 == atoi(argv[2])))
   {
      cout << "usage: appclient server_ip server_port" << endl;
      return 0;
   }

   // Automatically start up and clean up UDT module.
   UDTUpDown _udt_;//用RAII手法进行资源管理,其相关定义位于test_util.h中。

   struct addrinfo hints, *local, *peer;

   memset(&hints, 0, sizeof(struct addrinfo));

   hints.ai_flags = AI_PASSIVE;
   hints.ai_family = AF_INET;
   hints.ai_socktype = SOCK_STREAM;
   //hints.ai_socktype = SOCK_DGRAM;

   if (0 != getaddrinfo(NULL, "9000", &hints, &local))
   {
      cout << "incorrect network address.\n" << endl;
      return 0;
   }

   UDTSOCKET client = UDT::socket(local->ai_family, local->ai_socktype, local->ai_protocol);//建立UDT 套接口,和TCP的一样

   // UDT Options
   //UDT::setsockopt(client, 0, UDT_CC, new CCCFactory<CUDPBlast>, sizeof(CCCFactory<CUDPBlast>));
   //UDT::setsockopt(client, 0, UDT_MSS, new int(9000), sizeof(int));
   //UDT::setsockopt(client, 0, UDT_SNDBUF, new int(10000000), sizeof(int));
   //UDT::setsockopt(client, 0, UDP_SNDBUF, new int(10000000), sizeof(int));
   //UDT::setsockopt(client, 0, UDT_MAXBW, new int64_t(12500000), sizeof(int));

   // Windows UDP issue
   // For better performance, modify HKLM\System\CurrentControlSet\Services\Afd\Parameters\FastSendDatagramThreshold
   #ifdef WIN32
      UDT::setsockopt(client, 0, UDT_MSS, new int(1052), sizeof(int));
   #endif

   // for rendezvous connection, enable the code below//采用汇合连接时,需要进行的设置。汇合连接相关部分,详见UDT连接分析。
   /*
   UDT::setsockopt(client, 0, UDT_RENDEZVOUS, new bool(true), sizeof(bool));
   if (UDT::ERROR == UDT::bind(client, local->ai_addr, local->ai_addrlen))
   {
      cout << "bind: " << UDT::getlasterror().getErrorMessage() << endl;
      return 0;
   }
   */

   freeaddrinfo(local);

   if (0 != getaddrinfo(argv[1], argv[2], &hints, &peer))
   {
      cout << "incorrect server/peer address. " << argv[1] << ":" << argv[2] << endl;
      return 0;
   }

   // connect to the server, implict bind
   if (UDT::ERROR == UDT::connect(client, peer->ai_addr, peer->ai_addrlen))//建立连接,其相关协议和源码分析,详见UDT连接分析。
   {
      cout << "connect: " << UDT::getlasterror().getErrorMessage() << endl;
      return 0;
   }

   freeaddrinfo(peer);

   // using CC method
   //CUDPBlast* cchandle = NULL;
   //int temp;
   //UDT::getsockopt(client, 0, UDT_CC, &cchandle, &temp);
   //if (NULL != cchandle)
   //   cchandle->setRate(500);

   int size = 100000;
   char* data = new char[size];

   #ifndef WIN32
      pthread_create(new pthread_t, NULL, monitor, &client);
   #else
      CreateThread(NULL, 0, monitor, &client, 0, NULL);
   #endif

   for (int i = 0; i < 1000000; i ++)
   {
      int ssize = 0;
      int ss;
      while (ssize < size)
      {
         if (UDT::ERROR == (ss = UDT::send(client, data + ssize, size - ssize, 0)))//发送数据
         {
            cout << "send:" << UDT::getlasterror().getErrorMessage() << endl;
            break;
         }

         ssize += ss;
      }

      if (ssize < size)
         break;
   }

   UDT::close(client);//关闭UDT连接
   delete [] data;
   return 0;
}

#ifndef WIN32
void* monitor(void* s)//性能监视程序
#else
DWORD WINAPI monitor(LPVOID s)
#endif
{
   UDTSOCKET u = *(UDTSOCKET*)s;

   UDT::TRACEINFO perf;

   cout << "SendRate(Mb/s)\tRTT(ms)\tCWnd\tPktSndPeriod(us)\tRecvACK\tRecvNAK" << endl;

   while (true)
   {
      #ifndef WIN32
         sleep(1);
      #else
         Sleep(1000);
      #endif

      if (UDT::ERROR == UDT::perfmon(u, &perf))
      {
         cout << "perfmon: " << UDT::getlasterror().getErrorMessage() << endl;
         break;
      }

      cout << perf.mbpsSendRate << "\t\t" 
           << perf.msRTT << "\t" 
           << perf.pktCongestionWindow << "\t" 
           << perf.usPktSndPeriod << "\t\t\t" 
           << perf.pktRecvACK << "\t" 
           << perf.pktRecvNAK << endl;
   }

   #ifndef WIN32
      return NULL;
   #else
      return 0;
   #endif
}

appserver.cpp源码分析

代码如下:

#ifndef WIN32
   #include <unistd.h>
   #include <cstdlib>
   #include <cstring>
   #include <netdb.h>
#else
   #include <winsock2.h>
   #include <ws2tcpip.h>
   #include <wspiapi.h>
#endif
#include <iostream>
#include <udt.h>
#include "cc.h"
#include "test_util.h"

using namespace std;

#ifndef WIN32
void* recvdata(void*);
#else
DWORD WINAPI recvdata(LPVOID);
#endif

int main(int argc, char* argv[])
{
   if ((1 != argc) && ((2 != argc) || (0 == atoi(argv[1]))))
   {
      cout << "usage: appserver [server_port]" << endl;
      return 0;
   }

   // Automatically start up and clean up UDT module.
   UDTUpDown _udt_;//用RAII手法进行资源管理,其相关定义位于test_util.h中。


   addrinfo hints;
   addrinfo* res;

   memset(&hints, 0, sizeof(struct addrinfo));

   hints.ai_flags = AI_PASSIVE;
   hints.ai_family = AF_INET;
   hints.ai_socktype = SOCK_STREAM;
   //hints.ai_socktype = SOCK_DGRAM;

   string service("9000");
   if (2 == argc)
      service = argv[1];

   if (0 != getaddrinfo(NULL, service.c_str(), &hints, &res))
   {
      cout << "illegal port number or port is busy.\n" << endl;
      return 0;
   }

   UDTSOCKET serv = UDT::socket(res->ai_family, res->ai_socktype, res->ai_protocol);//建立UDT 套接口

   // UDT Options
   //UDT::setsockopt(serv, 0, UDT_CC, new CCCFactory<CUDPBlast>, sizeof(CCCFactory<CUDPBlast>));
   //UDT::setsockopt(serv, 0, UDT_MSS, new int(9000), sizeof(int));
   //UDT::setsockopt(serv, 0, UDT_RCVBUF, new int(10000000), sizeof(int));
   //UDT::setsockopt(serv, 0, UDP_RCVBUF, new int(10000000), sizeof(int));

   if (UDT::ERROR == UDT::bind(serv, res->ai_addr, res->ai_addrlen))//绑定套接口 和 IP
   {
      cout << "bind: " << UDT::getlasterror().getErrorMessage() << endl;
      return 0;
   }

   freeaddrinfo(res);

   cout << "server is ready at port: " << service << endl;

   if (UDT::ERROR == UDT::listen(serv, 10))
   {
      cout << "listen: " << UDT::getlasterror().getErrorMessage() << endl;
      return 0;
   }

   sockaddr_storage clientaddr;
   int addrlen = sizeof(clientaddr);

   UDTSOCKET recver;

   while (true)
   {
      if (UDT::INVALID_SOCK == (recver = UDT::accept(serv, (sockaddr*)&clientaddr, &addrlen)))//准备建立连接了
      {
         cout << "accept: " << UDT::getlasterror().getErrorMessage() << endl;
         return 0;
      }

      char clienthost[NI_MAXHOST];
      char clientservice[NI_MAXSERV];
      getnameinfo((sockaddr *)&clientaddr, addrlen, clienthost, sizeof(clienthost), clientservice, sizeof(clientservice), NI_NUMERICHOST|NI_NUMERICSERV);
      cout << "new connection: " << clienthost << ":" << clientservice << endl;

      #ifndef WIN32
         pthread_t rcvthread;
         pthread_create(&rcvthread, NULL, recvdata, new UDTSOCKET(recver));
         pthread_detach(rcvthread);
      #else
         CreateThread(NULL, 0, recvdata, new UDTSOCKET(recver), 0, NULL);
      #endif
   }

   UDT::close(serv);

   return 0;
}

#ifndef WIN32
void* recvdata(void* usocket)
#else
DWORD WINAPI recvdata(LPVOID usocket)
#endif
{
   UDTSOCKET recver = *(UDTSOCKET*)usocket;
   delete (UDTSOCKET*)usocket;

   char* data;
   int size = 100000;
   data = new char[size];

   while (true)
   {
      int rsize = 0;
      int rs;
      while (rsize < size)
      {
         if (UDT::ERROR == (rs = UDT::recv(recver, data + rsize, size - rsize, 0)))//接收数据
         {
            cout << "recv:" << UDT::getlasterror().getErrorMessage() << endl;
            break;
         }

         rsize += rs;
      }

      if (rsize < size)
         break;
   }

   delete [] data;

   UDT::close(recver);//断开连接

   #ifndef WIN32
      return NULL;
   #else
      return 0;
   #endif
}

初始化操作之UDTUpDown _udt_分析,它的声明位于test_util.h文件中:

#ifndef _UDT_TEST_UTIL_H_
#define _UDT_TEST_UTIL_H_

struct UDTUpDown{
   UDTUpDown()
   {
      // use this function to initialize the UDT library
      UDT::startup();//初始化UDT库
   }
   ~UDTUpDown()
   {
      // use this function to release the UDT library
      UDT::cleanup();//释放UDT库
   }
};

#endif

UDT::startup()和UDT::cleanup()源码分析:

UDT::startup()主要用于开启垃圾回收线程,详见代码分析。另外,在垃圾回收线程中,有一个缺点: pthread_cond_timedwait()会导致CPU利用率增大。
UDT::clean()主要是用于signal UDT::startup中的pthread_cond_timedwait()函数和回收套接字以及复用器,详见代码分析。

namespace UDT//在udt.h中声明,api.cpp中定义
{

int startup()
{
   return CUDT::startup();//CUDT在core.h中定义;CUDT在core.cpp和api.cpp中实现
   //CUDT的非static成员函数(private)是在是在core.cpp中实现
   //CUDT的static成员函数(public)是在api.cpp中实现的,即同namespace UDT在同一文件中
}

int cleanup()
{
   return CUDT::cleanup();
}

......
}

int CUDT::startup()//core.h中定义,api.cpp中实现
{
   return s_UDTUnited.startup();//UDT global management base,s_UDTUnited为static成员变量
}

int CUDT::cleanup()
{
   return s_UDTUnited.cleanup();
}

s_UDTUnited.startup()函数主要功能是开启垃圾回收线程。另外,不论上层调用几次startup函数,程序中只有一个垃圾线程,代码如下:

int CUDTUnited::startup()
{
   CGuard gcinit(m_InitLock);

   if (m_iInstanceCount++ > 0)//m_iInstanceCount初始值为0,++在后等于++在前的值,则表达式的值为0,也就是第一次调用startup的时候,会跳过这个if语句中的return 0,但是,之后调用startup的时候,则会返回return 0。
      return 0;

   // Global initialization code
   #ifdef WIN32
      WORD wVersionRequested;
      WSADATA wsaData;
      wVersionRequested = MAKEWORD(2, 2);

      if (0 != WSAStartup(wVersionRequested, &wsaData))
         throw CUDTException(1, 0,  WSAGetLastError());
   #endif

   //init CTimer::EventLock

   if (m_bGCStatus)//默认为false,后面会赋值为true;不论startup被调用多少次,垃圾回收线程只会启动一次。
      return true;

   m_bClosing = false;
   #ifndef WIN32
      pthread_mutex_init(&m_GCStopLock, NULL);
      pthread_cond_init(&m_GCStopCond, NULL);
      pthread_create(&m_GCThread, NULL, garbageCollect, this);//用于垃圾回收
   #else
      m_GCStopLock = CreateMutex(NULL, false, NULL);
      m_GCStopCond = CreateEvent(NULL, false, false, NULL);
      DWORD ThreadID;
      m_GCThread = CreateThread(NULL, 0, garbageCollect, this, 0, &ThreadID);
   #endif

   m_bGCStatus = true;//设置垃圾回收线程的状态,防止垃圾回收线程被启动多次。

   return 0;
}

垃圾回收函数garbageCollect函数如下:

#ifndef WIN32
   void* CUDTUnited::garbageCollect(void* p)
#else
   DWORD WINAPI CUDTUnited::garbageCollect(LPVOID p)
#endif
{
   CUDTUnited* self = (CUDTUnited*)p;

   CGuard gcguard(self->m_GCStopLock);

   while (!self->m_bClosing)
   {
      self->checkBrokenSockets();

      #ifdef WIN32
         self->checkTLSValue();
      #endif

      #ifndef WIN32
         timeval now;
         timespec timeout;
         gettimeofday(&now, 0);
         timeout.tv_sec = now.tv_sec + 1;
         timeout.tv_nsec = now.tv_usec * 1000;

         pthread_cond_timedwait(&self->m_GCStopCond, &self->m_GCStopLock, &timeout);//<span style="color:#ff0000;">1s多循环一次这样做CPU利用率会很高的</span>
      #else
         WaitForSingleObject(self->m_GCStopCond, 1000);
      #endif
   }

   // remove all sockets and multiplexers//删除所有套接字和复用器
......
}
s_UDTUnited.cleanup()函数的主要功能是signal 垃圾回收线程,回收资源。在这里织的注意的是,如果m_iInstanceCount=1是不会促发signal的。代码如下:
int CUDTUnited::cleanup()
{
   CGuard gcinit(m_InitLock);

   if (--m_iInstanceCount > 0)//
      return 0;

   //destroy CTimer::EventLock

   if (!m_bGCStatus)
      return 0;

   m_bClosing = true;
   #ifndef WIN32
      pthread_cond_signal(&m_GCStopCond);
      pthread_join(m_GCThread, NULL);
      pthread_mutex_destroy(&m_GCStopLock);
      pthread_cond_destroy(&m_GCStopCond);
   #else
      SetEvent(m_GCStopCond);
      WaitForSingleObject(m_GCThread, INFINITE);
      CloseHandle(m_GCThread);
      CloseHandle(m_GCStopLock);
      CloseHandle(m_GCStopCond);
   #endif

   m_bGCStatus = false;

   // Global destruction code
   #ifdef WIN32
      WSACleanup();
   #endif

   return 0;
}

UDT::socket介绍

UDT::socket主要完成以下几项任务:
1、检查是否开启垃圾回收线程;
2、创建一个UDT套接口和一个UDT传输控制块;
3、完成UDT套接口和UDT传输控制块部分参数的初始化;
4、将UDT套接口所创建的ID和UDT传输控制块关联起来。
UDTSOCKET socket(int af, int type, int protocol)//protocol传进去,没啥用
{
   return CUDT::socket(af, type, protocol);
}
UDTSOCKET CUDT::socket(int af, int type, int)
{
   if (!s_UDTUnited.m_bGCStatus)
      s_UDTUnited.startup();//防止前面的startup没有开启,

   try
   {
      return s_UDTUnited.newSocket(af, type);
   }
......
}
UDTSOCKET CUDTUnited::newSocket(int af, int type)
{
   if ((type != SOCK_STREAM) && (type != SOCK_DGRAM))
      throw CUDTException(5, 3, 0);

   CUDTSocket* ns = NULL;//声明并定义一个UDT 套接口(套接口)

   try//可以看出,在调用关系上,UDT-->CUDTUnited-->CUDTSocket--->CUDT
   {
      ns = new CUDTSocket;//每次上层调用一次UDT::socket,下层就会new一次,这里的ns是关键,创建一个新的套接口
      ns->m_pUDT = new CUDT;//创建一个新的 UDT 传输控制块
      if (AF_INET == af)
      {
         ns->m_pSelfAddr = (sockaddr*)(new sockaddr_in);//创建存储自身地址的空间
         ((sockaddr_in*)(ns->m_pSelfAddr))->sin_port = 0;
      }
      else
      {
         ns->m_pSelfAddr = (sockaddr*)(new sockaddr_in6);
         ((sockaddr_in6*)(ns->m_pSelfAddr))->sin6_port = 0;
      }
   }
   catch (...)
   {
      delete ns;
      throw CUDTException(3, 2, 0);
   }

   CGuard::enterCS(m_IDLock);//提供多种类型的锁,有以对象为管理资源的,有手动管理和释放资源的,根据情况减小锁的粒度
   ns->m_SocketID = -- m_SocketID;//创建ns对象时,在构造函数中已完成初始化
   CGuard::leaveCS(m_IDLock);
	//完成UDT套接口ns和传输控制块m_pUDT相关变量的初始化
   ns->m_Status = INIT;
   ns->m_ListenSocket = 0;
   ns->m_pUDT->m_SocketID = ns->m_SocketID;
   ns->m_pUDT->m_iSockType = (SOCK_STREAM == type) ? UDT_STREAM : UDT_DGRAM;
   ns->m_pUDT->m_iIPversion = ns->m_iIPversion = af;
   ns->m_pUDT->m_pCache = m_pCache;//在CUDT构造函数中,m_pCache为NULL

   // protect the m_Sockets structure.
   CGuard::enterCS(m_ControlLock);
   try
   {
      m_Sockets[ns->m_SocketID] = ns;//std::map<UDTSOCKET, CUDTSocket*> m_Sockets;UDT套接口ID和 UDT套接口相关联
   }
   catch (...)
   {
      //failure and rollback
      CGuard::leaveCS(m_ControlLock);
      delete ns;
      ns = NULL;//删除后一定要赋值为NULL
   }
   CGuard::leaveCS(m_ControlLock);

   if (NULL == ns)
      throw CUDTException(3, 2, 0);

   return ns->m_SocketID;
}

UDT::bind分析

UDT::bind主要完成以下几项任务:
1、通过locate函数,根据传递进去的UDTSOCKET参数找到对应的UDT套接口;
2、通过套接口中的传输控制块指针,调用传输控制块中的open()函数;
3、调用updateMux函数。
namespace UDT
{
......
int bind(UDTSOCKET u, const struct sockaddr* name, int namelen)
{
   return CUDT::bind(u, name, namelen);
}
......
}
int CUDT::bind(UDTSOCKET u, const sockaddr* name, int namelen)
{
   try
   {
      return s_UDTUnited.bind(u, name, namelen);
   }
  ......
}
int CUDTUnited::bind(const UDTSOCKET u, const sockaddr* name, int namelen)
{
   CUDTSocket* s = locate(u);//查找套接口ID所对应的UDT套接口
   if (NULL == s)
      throw CUDTException(5, 4, 0);

   CGuard cg(s->m_ControlLock);//以对象的方式管理资源

   // cannot bind a socket more than once
   if (INIT != s->m_Status)//套接口状态在CUDTSocket构造函数中初始为INIT
      throw CUDTException(5, 0, 0);

   // check the size of SOCKADDR structure
   if (AF_INET == s->m_iIPversion)
   {
      if (namelen != sizeof(sockaddr_in))
         throw CUDTException(5, 3, 0);
   }
   else
   {
      if (namelen != sizeof(sockaddr_in6))
         throw CUDTException(5, 3, 0);
   }

   s->m_pUDT->open();//CUDTUnited和CUDT友元关系,所以可以访问private成员函数,在open()完成传输控制块相关参数的初始化,相关定时器初始化
   updateMux(s, name);
   s->m_Status = OPENED;

   // copy address information of local node
   s->m_pUDT->m_pSndQueue->m_pChannel->getSockAddr(s->m_pSelfAddr);

   return 0;
}

open()函数分析

open()函数主要完成以下几项任务:
1、初始化传输控制块的相关参数,如拥塞控制算法、定时器等;
2、新建CSNode和CRNode
3、改变传输控制块的状态,m_bOpen为true。
void CUDT::open()//core.cpp
{
   CGuard cg(m_ConnectionLock);//嵌套锁哟

   // Initial sequence number, loss, acknowledgement, etc.
   m_iPktSize = m_iMSS - 28;//1500-28(20+8)=1472
   m_iPayloadSize = m_iPktSize - CPacket::m_iPktHdrSize;//1472-16(packet.cpp)=1456

   m_iEXPCount = 1;
   m_iBandwidth = 1;
   m_iDeliveryRate = 16;//包在接收端到达的速率
   m_iAckSeqNo = 0;
   m_ullLastAckTime = 0;

   // trace information
   m_StartTime = CTimer::getTime();
   m_llSentTotal = m_llRecvTotal = m_iSndLossTotal = m_iRcvLossTotal = m_iRetransTotal = m_iSentACKTotal = m_iRecvACKTotal = m_iSentNAKTotal = m_iRecvNAKTotal = 0;
   m_LastSampleTime = CTimer::getTime();
   m_llTraceSent = m_llTraceRecv = m_iTraceSndLoss = m_iTraceRcvLoss = m_iTraceRetrans = m_iSentACK = m_iRecvACK = m_iSentNAK = m_iRecvNAK = 0;
   m_llSndDuration = m_llSndDurationTotal = 0;

   // structures for queue 接收队列 发送队列的初始化
   if (NULL == m_pSNode)
      m_pSNode = new CSNode;
   m_pSNode->m_pUDT = this;
   m_pSNode->m_llTimeStamp = 1;
   m_pSNode->m_iHeapLoc = -1;

   if (NULL == m_pRNode)
      m_pRNode = new CRNode;
   m_pRNode->m_pUDT = this;
   m_pRNode->m_llTimeStamp = 1;
   m_pRNode->m_pPrev = m_pRNode->m_pNext = NULL;
   m_pRNode->m_bOnList = false;

   m_iRTT = 10 * m_iSYNInterval;//10*10000=100000(100ms)
   m_iRTTVar = m_iRTT >> 1;
   m_ullCPUFrequency = CTimer::getCPUFrequency();

   // set up the timers
   m_ullSYNInt = m_iSYNInterval * m_ullCPUFrequency;//10ms
  
   // set minimum NAK and EXP timeout to 100ms
   m_ullMinNakInt = 300000 * m_ullCPUFrequency;//300ms
   m_ullMinExpInt = 300000 * m_ullCPUFrequency;//300ms

   m_ullACKInt = m_ullSYNInt;//10ms
   m_ullNAKInt = m_ullMinNakInt;//300ms

   uint64_t currtime;
   CTimer::rdtsc(currtime);
   m_ullLastRspTime = currtime;
   m_ullNextACKTime = currtime + m_ullSYNInt;
   m_ullNextNAKTime = currtime + m_ullNAKInt;

   m_iPktCount = 0;
   m_iLightACKCount = 1;

   m_ullTargetTime = 0;
   m_ullTimeDiff = 0;

   // Now UDT is opened.
   m_bOpened = true;//改变传输控制块的状态
}

updateMux(s,name)函数分析

updateMux主要完成以下几项任务:
1、查找复用器multiplexer中是否有该port,若有则对该端口进行复用,即使用已有的发送/接收队列;
2、若复用器multiplexer中没有这个port,则创建一个channel对象,并通过该channel对象创建/绑定udp套接口,并对udp套接口的接收和发送缓存进行设置;
3、另外,还得新建定时器、发送和接收队列, 在发送和接收队列中完成了发送和接收线程的创建
void CUDTUnited::updateMux(CUDTSocket* s, const sockaddr* addr, const UDPSOCKET* udpsock)//后面两个参数默认为NULL
{
   CGuard cg(m_ControlLock);

   if ((s->m_pUDT->m_bReuseAddr) && (NULL != addr))//m_bReuseAddr初始值为true //reuse an exiting port or not, for udp multiplexer
   {
      int port = (AF_INET == s->m_pUDT->m_iIPversion) ? ntohs(((sockaddr_in*)addr)->sin_port) : ntohs(((sockaddr_in6*)addr)->sin6_port);

      // find a reusable address
      for (map<int, CMultiplexer>::iterator i = m_mMultiplexer.begin(); i != m_mMultiplexer.end(); ++ i)
      {
         if ((i->second.m_iIPversion == s->m_pUDT->m_iIPversion) && (i->second.m_iMSS == s->m_pUDT->m_iMSS) && i->second.m_bReusable)
         {
            if (i->second.m_iPort == port)//找到了就return结束了
            {
               // reuse the existing multiplexer
               ++ i->second.m_iRefCount;//与这个multiplexer关联的传输控制块的个数
               s->m_pUDT->m_pSndQueue = i->second.m_pSndQueue;//端口复用后,不用创建新的发送线程/接收线程
               s->m_pUDT->m_pRcvQueue = i->second.m_pRcvQueue;
               s->m_iMuxID = i->second.m_iID;
               return;
            }
         }
      }
   }

   // a new multiplexer is needed
   CMultiplexer m;//建立一个新的multiplexer
   m.m_iMSS = s->m_pUDT->m_iMSS;
   m.m_iIPversion = s->m_pUDT->m_iIPversion;
   m.m_iRefCount = 1;
   m.m_bReusable = s->m_pUDT->m_bReuseAddr;//bool 默认值是true
   m.m_iID = s->m_SocketID;

   m.m_pChannel = new CChannel(s->m_pUDT->m_iIPversion);//创建一个channel对象
   m.m_pChannel->setSndBufSize(s->m_pUDT->m_iUDPSndBufSize);
   m.m_pChannel->setRcvBufSize(s->m_pUDT->m_iUDPRcvBufSize);

   try
   {
      if (NULL != udpsock)
         m.m_pChannel->open(*udpsock);
      else
         m.m_pChannel->open(addr);//默认执行这个函数,在open函数中 建立UDP socket,bind socket,并对UDP的接收/发送缓存的大小进行设置
   }
   catch (CUDTException& e)
   {
      m.m_pChannel->close();//发生错误后,则关闭套接口
      delete m.m_pChannel;
      throw e;
   }

   sockaddr* sa = (AF_INET == s->m_pUDT->m_iIPversion) ? (sockaddr*) new sockaddr_in : (sockaddr*) new sockaddr_in6;
   m.m_pChannel->getSockAddr(sa);
   m.m_iPort = (AF_INET == s->m_pUDT->m_iIPversion) ? ntohs(((sockaddr_in*)sa)->sin_port) : ntohs(((sockaddr_in6*)sa)->sin6_port);将port存进来,如果下次有其它连接bind该端口时,可以在前面的if语句中进行port复用
   if (AF_INET == s->m_pUDT->m_iIPversion) delete (sockaddr_in*)sa; else delete (sockaddr_in6*)sa;

   m.m_pTimer = new CTimer;//新建定时器对象

   m.m_pSndQueue = new CSndQueue;//新建发送队列对象
   m.m_pSndQueue->init(m.m_pChannel, m.m_pTimer);//创建发送队列的工作线程
   m.m_pRcvQueue = new CRcvQueue;//新建接收队列对象
   m.m_pRcvQueue->init(32, s->m_pUDT->m_iPayloadSize, m.m_iIPversion, 1024, m.m_pChannel, m.m_pTimer);//创建接收队列的工作线程

   m_mMultiplexer[m.m_iID] = m;//将套接口ID和复用器绑定在一起

   s->m_pUDT->m_pSndQueue = m.m_pSndQueue;
   s->m_pUDT->m_pRcvQueue = m.m_pRcvQueue;
   s->m_iMuxID = m.m_iID;//套接口ID 和 复用器ID是一样的
}

UDT::listen函数分析

UDT::listen函数的主要任务是:
1、创建两个队列:一个是等待accept的队列;一个是已经accept的队列;
2、判断是否有其它传输控制块在监听这个端口。
namespace UDT
{
.....
int listen(UDTSOCKET u, int backlog)
{
   return CUDT::listen(u, backlog);
}
......
}
int CUDT::listen(UDTSOCKET u, int backlog)
{
   try
   {
      return s_UDTUnited.listen(u, backlog);
   }
  ......
}
int CUDTUnited::listen(const UDTSOCKET u, int backlog)
{
......
   s->m_uiBackLog = backlog;

   try
   {
      s->m_pQueuedSockets = new set<UDTSOCKET>;// set of connections waiting for accept()

      s->m_pAcceptSockets = new set<UDTSOCKET>; // set of accept()ed connections

   }
   catch (...)
   {
      delete s->m_pQueuedSockets;
      delete s->m_pAcceptSockets;
      throw CUDTException(3, 2, 0);
   }

   s->m_pUDT->listen();

   s->m_Status = LISTENING;

   return 0;
}
void CUDT::listen()
{
   CGuard cg(m_ConnectionLock);

   if (!m_bOpened)
      throw CUDTException(5, 0, 0);

   if (m_bConnecting || m_bConnected)
      throw CUDTException(5, 2, 0);

   // listen can be called more than once
   if (m_bListening)
      return;

   // if there is already another socket listening on the same port
   if (m_pRcvQueue->setListener(this) < 0)//判断是否有其它传输控制块在监此端口号
      throw CUDTException(5, 11, 0);

   m_bListening = true;
}

由于UDT::connect和UDT::accept这两个套接口涉及到UDT的握手连接,所以关于这两个套接口的解析,详见UDT握手连接部分的分析。
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