live555学习笔记15－RTCPInstance类小结

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十五：RTCPInstance类小结

RTCPInstance是对rtcp通信的封装．RTCP主要是功能是统计包的收发为流量控制提供依据．RTCPInstance统计数据的取得仅依赖于RTPSink的一些函数（因为RTPSink发送RTP包），所以RTCPInstance与其它类（GroupSock,RTPInterface等基础类除外）基本关系不大，封装的比较完整．

RTCPInstance靠RTPInterface提供网络通讯支持，所以它既支持rtcp over udp,又支持rtcp over tcp．
RTCPInstance接收到的包在函数static void incomingReportHandler(RTCPInstance* instance, int /*mask*/)中处理．
最值得关注的是这个成员函数：void setSpecificRRHandler(netAddressBits fromAddress, Port fromPort,TaskFunc* handlerTask, void* clientData)．它的作用是让调用者可以设置回调函数，调用者就可以在收到RR包时做出一定的动作．参数fromAddress和fromPort指明要对哪个客户端的RR包做出响应．
利用这个机制的例子是RTSPServer::RTSPClientSession．它会把自己的RRHandler函数经过层层传递，最终传给RTCPInstance．于是RTSPServer::RTSPClientSession就可以在每次收到对应的客户端的RR包时调用它传入的函数，这个函数是void RTSPServer::RTSPClientSession::noteClientLiveness(RTSPClientSession* clientSession).此函数只是以下函数的过渡：

[cpp] view plaincopyprint?

void RTSPServer::RTSPClientSession::noteLiveness()
{
#ifdef DEBUG
fprintf(stderr, "Liveness indication from client at %s\n", our_inet_ntoa(fClientAddr.sin_addr));
#endif
if (fOurServer.fReclamationTestSeconds > 0) {
envir().taskScheduler().rescheduleDelayedTask(fLivenessCheckTask,
fOurServer.fReclamationTestSeconds * 1000000,
(TaskFunc*) livenessTimeoutTask, this);
}
}

void RTSPServer::RTSPClientSession::noteLiveness(){#ifdef DEBUGfprintf(stderr, "Liveness indication from client at %s\n", our_inet_ntoa(fClientAddr.sin_addr));#endifif (fOurServer.fReclamationTestSeconds > 0) {envir().taskScheduler().rescheduleDelayedTask(fLivenessCheckTask,fOurServer.fReclamationTestSeconds * 1000000,(TaskFunc*) livenessTimeoutTask, this);}}

可以看到，每收到一次指定客户端的RR包，就重置一下livenessTimeoutTask()的运行时间，如果livenessTimeoutTask()一旦运行，看一下livenessTimeoutTask():

[cpp] view plaincopyprint?

void RTSPServer::RTSPClientSession::livenessTimeoutTask(RTSPClientSession* clientSession)
{
// If this gets called, the client session is assumed to have timed out,
// so delete it:
#ifdef DEBUG
fprintf(stderr, "RTSP client session from %s has timed out (due to inactivity)\n", our_inet_ntoa(clientSession->fClientAddr.sin_addr));
#endif
delete clientSession;
}

void RTSPServer::RTSPClientSession::livenessTimeoutTask(RTSPClientSession* clientSession){// If this gets called, the client session is assumed to have timed out,// so delete it:#ifdef DEBUGfprintf(stderr, "RTSP client session from %s has timed out (due to inactivity)\n", our_inet_ntoa(clientSession->fClientAddr.sin_addr));#endifdelete clientSession;}

那么RTSPServer::RTSPClientSession就会自杀（真是想不开啊）．也就是说fOurServer.fReclamationTestSeconds * 1000000是超时时间（默认好像是60秒）．

如果你想监视一个客户端，最好的方式就是向RTCPInstance注册RRHandle．