Darwin在转发流过程中对推送端断开的处理问题 ..docx

    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
[cpp] view plaincopyprint?
1. // Set the current RTSP session for this RTP session.   
2. // We do this here because we need to make sure the SessionMutex   
3. // is grabbed while we do this. Only do this if the RTSP session   
4. // is still alive, of course.   
5. if (this->IsLiveSession())  
6.     fRTPSession->UpdateRTSPSession(this);  
// 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);

[cpp] view plaincopyprint?
1. void RTPSessionInterface::UpdateRTSPSession(RTSPSessionInterface* inNewRTSPSession)  
2. {     
3.     if (inNewRTSPSession != fRTSPSession)  
4.     {  
5.         // If there was an old session, let it know that we are done   
6.         if (fRTSPSession != NULL)  
7.             fRTSPSession->DecrementObjectHolderCount();  
8.           
9.         // Increment this count to prevent the RTSP session from being deleted   
10.         fRTSPSession = inNewRTSPSession;  
11.         fRTSPSession->IncrementObjectHolderCount();  
12.     }  
13. }  
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
[cpp] view plaincopyprint?
1. // Only delete if it is ok to delete!   
2. if (fObjectHolders == 0)  
3.     return -1;  
// 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
[cpp] view plaincopyprint?
1. while(IsLiveSession())  
2. {  
3.       switch(){case:}  
4. }  
while(IsLiveSession())
{
switch(){case:}
}

状态机外加入代码及时析构RTPSession
[cpp] view plaincopyprint?
1. // Make absolutely sure there are no resources being occupied by the session   
2. // at this point.   
3. this->CleanupRequest();  
4.   
5.   
6. //Kill与RTSPSession相关的RTPSession   
7. if(!IsLiveSession()){  
8. OSRefTable* theMap = QTSServerInterface::GetServer()->GetRTPSessionMap();  
9. OSRef* theRef = theMap->Resolve(&fLastRTPSessionIDPtr);  
10. if (theRef != NULL){  
11.     fRTPSession = (RTPSession*)theRef->GetObject();  
12.     if(fRTPSession) fRTPSession->Teardown();  
13.     theMap->Release(fRTPSession->GetRef());  
14.     fRTPSession = NULL;  
15.     }   
16. }     
17. // Only delete if it is ok to delete!       
18. if (fObjectHolders == 0)        return -1;     
19. // If we are here because of a timeout, but we can't delete because someone       
20. // is holding onto a reference to this session, just reschedule the timeout.      
21. // At this point, however, the session is DEAD.      
22. return 0;  
// 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！
[cpp] view plaincopyprint?
1. //fObjectHolders--     
2. if(!IsLiveSession()&& fObjectHolders > 0){    
3. OSRefTable* theMap = QTSServerInterface::GetServer()->GetRTPSessionMap();    
4. OSRef* theRef = theMap->Resolve(&fLastRTPSessionIDPtr);    
5. if (theRef != NULL){    
6.     fRTPSession = (RTPSession*)theRef->GetObject();    
7.     if(fRTPSession) fRTPSession->Teardown();    
8.     theMap->Release(fRTPSession->GetRef());    
9.     fRTPSession = NULL;    
10.     }     
11. }      
12.   
13.    // Make absolutely sure there are no resources being occupied by the session   
14.    // at this point.   
15.    this->CleanupRequest();  
16.   
17.    // Only delete if it is ok to delete!   
18.    if (fObjectHolders == 0)  
19.        return -1;