jrtplib example4源程序问题

还是跟example3同样的问题，继承类中的两个函数在main函数中明明没有调用，为什么就可以在后台线程中接收数据呢，测试过了是可以接受数据的

希望看到的博友给予解释一下，谢谢！

/*

   This IPv4 example uses the background thread itself to process all packets.
   You can use example one to send data to the session that's created in this
   example.
*/


#include "rtpsession.h"
#include "rtppacket.h"
#include "rtpudpv4transmitter.h"
#include "rtpipv4address.h"
#include "rtpsessionparams.h"
#include "rtperrors.h"
#ifndef WIN32
#include <netinet/in.h>
#include <arpa/inet.h>
#else
#include <winsock2.h>
#endif // WIN32
#include "rtpsourcedata.h"
#include <stdlib.h>
#include <stdio.h>
#include <iostream>
#include <string>


using namespace jrtplib;


#ifdef RTP_SUPPORT_THREAD


//
// This function checks if there was a RTP error. If so, it displays an error
// message and exists.
//


void checkerror(int rtperr)
{
if (rtperr < 0)
{
std::cout << "ERROR: " << RTPGetErrorString(rtperr) << std::endl;
exit(-1);
}
}


//
// The new class routine
//


class MyRTPSession : public RTPSession
{
protected:
void OnPollThreadStep();
void ProcessRTPPacket(const RTPSourceData &srcdat,const RTPPacket &rtppack);
};


void MyRTPSession::OnPollThreadStep()
{
BeginDataAccess();

// check incoming packets
if (GotoFirstSourceWithData())
{
do
{
RTPPacket *pack;
RTPSourceData *srcdat;

srcdat = GetCurrentSourceInfo();

while ((pack = GetNextPacket()) != NULL)
{
ProcessRTPPacket(*srcdat,*pack);
DeletePacket(pack);
}
} while (GotoNextSourceWithData());
}

EndDataAccess();
}


void MyRTPSession::ProcessRTPPacket(const RTPSourceData &srcdat,const RTPPacket &rtppack)
{
// You can inspect the packet and the source's info here
std::cout << "Got packet " << rtppack.GetExtendedSequenceNumber() << " from SSRC " << srcdat.GetSSRC() << std::endl;
}


//
// The main routine
// 


int main(void)
{
#ifdef WIN32
WSADATA dat;
WSAStartup(MAKEWORD(2,2),&dat);
#endif // WIN32

MyRTPSession sess;
uint16_t portbase;
std::string ipstr;
int status,num;


        // First, we'll ask for the necessary information

std::cout << "Enter local portbase:" << std::endl;
std::cin >> portbase;
std::cout << std::endl;

std::cout << std::endl;
std::cout << "Number of seconds you wish to wait:" << std::endl;
std::cin >> num;

// Now, we'll create a RTP session, set the destination
// and poll for incoming data.

RTPUDPv4TransmissionParams transparams;
RTPSessionParams sessparams;

// IMPORTANT: The local timestamp unit MUST be set, otherwise
//            RTCP Sender Report info will be calculated wrong
// In this case, we'll be just use 8000 samples per second.
sessparams.SetOwnTimestampUnit(1.0/8000.0);

transparams.SetPortbase(portbase);
status = sess.Create(sessparams,&transparams);
checkerror(status);

// Wait a number of seconds
RTPTime::Wait(RTPTime(num,0));

sess.BYEDestroy(RTPTime(10,0),0,0);


#ifdef WIN32
WSACleanup();
#endif // WIN32
return 0;
}


#else


int main(void)
{
std::cerr << "Thread support is required for this example" << std::endl;
return 0;
}


#endif // RTP_SUPPORT_THREAD