Darwin在转发流过程中对推送端断开的处理问题

      最近在做项目的过程中遇到一个问题，在用Darwin Streaming Server中的QTSSReflectorModule模块做为流转发和分发服务，用live555的DarwinInjector类做为模拟设备

进行流推送时，如果按照正常RTSP推送流程:Announce、Setup、Play…、Teardown，Darwin能较好地完成流的转发，但是假如设备在不正常工作，例如网络异常断开，设备断电等中断了数据流的推送，而缺少了<设备->服务器>的Teardown过程，这样与此路推送相关的RTSPSession、RTPSession以及ReflectorSession等都需要等到配置的“rtp_timeout”时间后、RTPSession超时才能析构所有相关转发对象。先分析下原因：

      RTSPSession在创建RTPSession时

                        // Set the current RTSP session for this RTP session.
                        // We do this here because we need to make sure the SessionMutex
                        // is grabbed while we do this. Only do this if the RTSP session
                        // is still alive, of course.
                        if (this->IsLiveSession())
                            fRTPSession->UpdateRTSPSession(this);

void RTPSessionInterface::UpdateRTSPSession(RTSPSessionInterface* inNewRTSPSession)
{   
    if (inNewRTSPSession != fRTSPSession)
    {
        // If there was an old session, let it know that we are done
        if (fRTSPSession != NULL)
            fRTSPSession->DecrementObjectHolderCount();
        
        // Increment this count to prevent the RTSP session from being deleted
        fRTSPSession = inNewRTSPSession;
        fRTSPSession->IncrementObjectHolderCount();
    }
}

IncrementObjectHolderCount()增加了fRTPSession对RTSPSession的引用，而对应的DecrementObjectHolderCount()在RTPSession::Teardown()中执行，由于RTSPSession拥有很好的对象保护机制，只有当对当前RTSPSession的引用数为0时

    // Only delete if it is ok to delete!
    if (fObjectHolders == 0)
        return -1;

RTSPSession自身才能调用Task::Run(){return -1;} delete，所以在RTSPSession注销之前，必须等待RTPSession注销，而且RTPSession没有等到Teardown命令，就只能等超时，而这个超时时间不能定，及时几秒钟对于转发实时流来说也是不合理的。

解决办法：

在RTSPSession:Run()函数中的

while(IsLiveSession())
{
      switch(){case:}
}

状态机外加入代码及时析构RTPSession

	// Make absolutely sure there are no resources being occupied by the session
	// at this point.
	this->CleanupRequest();


	//Kill与RTSPSession相关的RTPSession
	if(!IsLiveSession()){
	OSRefTable* theMap = QTSServerInterface::GetServer()->GetRTPSessionMap();
	OSRef* theRef = theMap->Resolve(&fLastRTPSessionIDPtr);
	if (theRef != NULL){
		fRTPSession = (RTPSession*)theRef->GetObject();
		if(fRTPSession) fRTPSession->Teardown();
		theMap->Release(fRTPSession->GetRef());
		fRTPSession = NULL;
		} 
	}	
	// Only delete if it is ok to delete!    
	if (fObjectHolders == 0)        return -1;   
	// If we are here because of a timeout, but we can't delete because someone    
	// is holding onto a reference to this session, just reschedule the timeout.   
	// At this point, however, the session is DEAD.   
	return 0;

注意 this->CleanupRequest();在前,

这样就能在RTSPSession判断fObjectHolders之前将附属的RTPSession析构，进而析构RTSPSession.
由于工作比较忙，写的可能在思路上不是很清楚，欢迎指正！

/--------------------------------------割了------------------------------------/

在上段代码中可以加入一个补充条件进行代码的优化，并且CleanupRequest()必须在此之后！

	//fObjectHolders--  
	if(!IsLiveSession()&& fObjectHolders > 0){  
	OSRefTable* theMap = QTSServerInterface::GetServer()->GetRTPSessionMap();  
	OSRef* theRef = theMap->Resolve(&fLastRTPSessionIDPtr);  
	if (theRef != NULL){  
		fRTPSession = (RTPSession*)theRef->GetObject();  
		if(fRTPSession) fRTPSession->Teardown();  
		theMap->Release(fRTPSession->GetRef());  
		fRTPSession = NULL;  
		}   
	}    

    // Make absolutely sure there are no resources being occupied by the session
    // at this point.
    this->CleanupRequest();

    // Only delete if it is ok to delete!
    if (fObjectHolders == 0)
        return -1;

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