EasyDarwin的RTP和RTSP会话的超时机制

今天是2016.08.05（这篇wiki写于公司内网的wiki平台上，现转载于此。），星期五，周末双休，又能回家了，但是在今天上午发生了一件事情，还是让我很惊奇，这件事情就是RTP会话被超时结束了，但是设备（拉流）还是能建立RTSP会话，只不过拉取不到任何数据，从抓包来看，设备如果拉取不到数据，就会重新建立RTSP会话，具体可以看抓包日志和流媒体服务器的日志。

当推流端开始推送RTP包后，RTSP会话会调用到RTSPSession::HandleIncomingDataPacket()，在这个函数里调用了fRTPSession->RefreshTimeout()，于是我们可以看到fRTPSession里的fTimeoutTask任务，fTimeoutTask的超时时间是又配置文件里的<SERVER>部分的rtp_timeout字段的值，也就是120秒，如果120秒没有收到任何推送的RTP包，fTimeoutTask会触发超时（详情请见TimeoutTaskThread::Run()函数），也就是会给RTPSession这个任务发送一个Task::kTimeoutEvent事件。

<PREF NAME="rtsp_timeout" TYPE="UInt32" >0</PREF>
<PREF NAME="real_rtsp_timeout" TYPE="UInt32" >180</PREF>
<PREF NAME="rtp_timeout" TYPE="UInt32" >120</PREF>

SInt64 TimeoutTaskThread::Run()
{
    //ok, check for timeouts now. Go through the whole queue
    OSMutexLocker locker(&fMutex);
    SInt64 curTime = OS::Milliseconds();
    SInt64 intervalMilli = kIntervalSeconds * 1000;//always default to 60 seconds but adjust to smallest interval > 0
    SInt64 taskInterval = intervalMilli;
    for (OSQueueIter iter(&fQueue); !iter.IsDone(); iter.Next())
    {
        TimeoutTask* theTimeoutTask = (TimeoutTask*)iter.GetCurrent()->GetEnclosingObject();
        
        //if it's time to time this task out, signal it
        if ((theTimeoutTask->fTimeoutAtThisTime > 0) && (curTime >= theTimeoutTask->fTimeoutAtThisTime))
        {
#if TIMEOUT_DEBUGGING
            qtss_printf("TimeoutTask %"_S32BITARG_" timed out. Curtime = %"_64BITARG_"d, timeout time = %"_64BITARG_"d\n",(SInt32)theTimeoutTask, curTime, theTimeoutTask->fTimeoutAtThisTime);
#endif
            theTimeoutTask->fTask->Signal(Task::kTimeoutEvent);
        }
        else
        {
            taskInterval = theTimeoutTask->fTimeoutAtThisTime - curTime;
            if ( (taskInterval > 0) && (theTimeoutTask->fTimeoutInMilSecs > 0) && (intervalMilli > taskInterval) )
                intervalMilli = taskInterval + 1000; // set timeout to 1 second past this task's timeout
#if TIMEOUT_DEBUGGING
            qtss_printf("TimeoutTask %"_S32BITARG_" not being timed out. Curtime = %"_64BITARG_"d. timeout time = %"_64BITARG_"d\n", (SInt32)theTimeoutTask, curTime, theTimeoutTask->fTimeoutAtThisTime);
#endif
        }
    }
    (void)this->GetEvents();//we must clear the event mask!
    
    OSThread::ThreadYield();
    
#if TIMEOUT_DEBUGGING
    qtss_printf ("TimeoutTaskThread::Run interval seconds= %"_S32BITARG_"\n", (SInt32) intervalMilli/1000);
#endif
    
    return intervalMilli;//don't delete me!
}

RTPSession收到kTimeoutEvent事件后会向其它模块发送QTSS_ClientSessionClosing_Role角色的事件，至此RTPSession会话任务结束掉。

SInt64 RTPSession::Run()
{
    //if we have been instructed to go away, then let's delete ourselves
    if ((events & Task::kKillEvent) || (events & Task::kTimeoutEvent) || (fModuleDoingAsyncStuff))
    {
        if (!fModuleDoingAsyncStuff)
    {
        if (events & Task::kTimeoutEvent)
            fClosingReason = qtssCliSesCloseTimeout;
            
        //deletion is a bit complicated. For one thing, it must happen from within
        //the Run function to ensure that we aren't getting events when we are deleting
        //ourselves. We also need to make sure that we aren't getting RTSP requests
        //(or, more accurately, that the stream object isn't being used by any other
        //threads). We do this by first removing the session from the session map.
        
#if RTPSESSION_DEBUGGING
        qtss_printf("RTPSession %"_S32BITARG_": about to be killed. Eventmask = %"_S32BITARG_"\n",(SInt32)this, (SInt32)events);
#endif
        // We cannot block waiting to UnRegister, because we have to
        // give the RTSPSessionTask a chance to release the RTPSession.
        OSRefTable* sessionTable = QTSServerInterface::GetServer()->GetRTPSessionMap();
        Assert(sessionTable != NULL);
        if (!sessionTable->TryUnRegister(&fRTPMapElem))
        {
            this->Signal(Task::kKillEvent);// So that we get back to this place in the code
            return kCantGetMutexIdleTime;
        }
        
            // The ClientSessionClosing role is allowed to do async stuff
            fModuleState.curTask = this;
            fModuleDoingAsyncStuff = true;  // So that we know to jump back to the
            fCurrentModule = 0;             // right place in the code
        
            // Set the reason parameter 
            theParams.clientSessionClosingParams.inReason = fClosingReason;
            
            // If RTCP packets are being generated internally for this stream, 
            // Send a BYE now.
            RTPStream** theStream = NULL;
            UInt32 theLen = 0;
            
            if (this->GetPlayFlags() & qtssPlayFlagsSendRTCP)
            {
                SInt64 byePacketTime = OS::Milliseconds();
                for (int x = 0; this->GetValuePtr(qtssCliSesStreamObjects, x, (void**)&theStream, &theLen) == QTSS_NoErr; x++)
                    if (theStream && *theStream != NULL)
                        (*theStream)->SendRTCPSR(byePacketTime, true);
            }
        }
        
        //at this point, we know no one is using this session, so invoke the
        //session cleanup role. We don't need to grab the session mutex before
        //invoking modules here, because the session is unregistered and
        //therefore there's no way another thread could get involved anyway
        UInt32 numModules = QTSServerInterface::GetNumModulesInRole(QTSSModule::kClientSessionClosingRole);
        {
            for (; fCurrentModule < numModules; fCurrentModule++)
            {  
                fModuleState.eventRequested = false;
                fModuleState.idleTime = 0;
                QTSSModule* theModule = QTSServerInterface::GetModule(QTSSModule::kClientSessionClosingRole, fCurrentModule);
                (void)theModule->CallDispatch(QTSS_ClientSessionClosing_Role, &theParams);
                // If this module has requested an event, return and wait for the event to transpire
                if (fModuleState.eventRequested)
                    return fModuleState.idleTime; // If the module has requested idle time...
            }
        }
        
        return -1;//doing this will cause the destructor to get called.
    }
}

RTSPSession的超时机制和RTPSession类似，RTSPSession的超时时间是配置文件的real_rtsp_timeout字段值，在kFilteringRequest状态时会去刷新fTimeoutTask的时间，如果超时，也会结束整个状态机的处理部分，同时调用fRTPSession的Teardown函数，结束RTPSession会话。

SInt64 RTSPSession::Run()
{
    ...
        
    //check for a timeout or a kill. If so, just consider the session dead
    if ((events & Task::kTimeoutEvent) || (events & Task::kKillEvent))
    {
    fLiveSession = false;
    }
    ...// 状态机的部分
    //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;
    // 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;

于是从以上可知，RTP会话超时是在120秒内没有收到任何RTP包就结束这个会话，此时RTSP会话还是存在的，也就是拉流端还是能够来请求拉流，鉴权也能通过，当RTSP会话在超过180秒内没有收到任何数据包则会结束整个RTSPSession。

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