Live555分析2

RtspServer的分析！

RtspServer类：继承自Medium，主要用于构建一个Rtsp服务器，同时该类在内部构建了一个RTSPClientSession类，用于处理单独的客户会话。

下面是一个RtspServer整体的介绍

1.RtspClient和RtspServer都一样，首先创建任务调度器和交互环境

TaskScheduler* scheduler = BasicTaskScheduler::createNew();UsageEnvironment *env = BasicUsageEnvironment::createNew(*scheduler);

2.创建Rtsp Server

RTSPServer* rtspServer = RTSPServer::createNew(*env, 8554, NULL);//8554是端口号

3.创建Session，创建大部分的对话都是这一个结构。

{char const* streamName = "mpeg4ESVideoTest";？//流的名称 比如rtsp://1.1.1.1/streamNamechar const* inputFileName = "test.m4e";      //从文件里读取流//创建会话ServerMediaSession* sms= ServerMediaSession::createNew(*env, streamName, streamName,descriptionString);sms->addSubsession(MPEG4VideoFileServerMediaSubsession::createNew(*env, inputFileName, reuseFirstSource));rtspServer->addServerMediaSession(sms);announceStream(rtspServer, sms, streamName, inputFileName);}

static void announceStream(RTSPServer* rtspServer, ServerMediaSession* sms,char const* streamName, char const* inputFileName) {char* url = rtspServer->rtspURL(sms);UsageEnvironment& env = rtspServer->envir();env << "\n\"" << streamName << "\" stream, from the file \""<< inputFileName << "\"\n";env << "Play this stream using the URL \"" << url << "\"\n";delete[] url;}

4.

// Also, attempt to create a HTTP server for RTSP-over-HTTP tunneling.// Try first with the default HTTP port (80), and then with the alternative HTTP// port numbers (8000 and 8080).if (rtspServer->setUpTunnelingOverHTTP(80) || rtspServer->setUpTunnelingOverHTTP(8000) || rtspServer->setUpTunnelingOverHTTP(8080)) {*env << "\n(We use port " << rtspServer->httpServerPortNum() << " for optional RTSP-over-HTTP tunneling.)\n";}else {*env << "\n(RTSP-over-HTTP tunneling is not available.)\n";}

5.事件循环

env->taskScheduler().doEventLoop(); // does not return

下面分析doEventLoop实现的细节：

void BasicTaskScheduler0::doEventLoop(char* watchVariable) {  // Repeatedly loop, handling readble sockets and timed events:  while (1) {    if (watchVariable != NULL && *watchVariable != 0) break;    SingleStep();  }}

下面看SingleStep()实现的细节：

void BasicTaskScheduler::SingleStep(unsigned maxDelayTime) {  fd_set readSet = fReadSet; // make a copy for this select() call  fd_set writeSet = fWriteSet; // ditto  fd_set exceptionSet = fExceptionSet; // ditto  //计算select socket们时的超时时间  DelayInterval const& timeToDelay = fDelayQueue.timeToNextAlarm();  struct timeval tv_timeToDelay;  tv_timeToDelay.tv_sec = timeToDelay.seconds();  tv_timeToDelay.tv_usec = timeToDelay.useconds();  // Very large "tv_sec" values cause select() to fail.  // Don't make it any larger than 1 million seconds (11.5 days)  const long MAX_TV_SEC = MILLION;  if (tv_timeToDelay.tv_sec > MAX_TV_SEC) {    tv_timeToDelay.tv_sec = MAX_TV_SEC;  }  // Also check our "maxDelayTime" parameter (if it's > 0):  if (maxDelayTime > 0 &&      (tv_timeToDelay.tv_sec > (long)maxDelayTime/MILLION ||       (tv_timeToDelay.tv_sec == (long)maxDelayTime/MILLION &&tv_timeToDelay.tv_usec > (long)maxDelayTime%MILLION))) {    tv_timeToDelay.tv_sec = maxDelayTime/MILLION;    tv_timeToDelay.tv_usec = maxDelayTime%MILLION;  }  int selectResult = select(fMaxNumSockets, &readSet, &writeSet, &exceptionSet, &tv_timeToDelay);  if (selectResult < 0) {#if defined(__WIN32__) || defined(_WIN32)    int err = WSAGetLastError();    // For some unknown reason, select() in Windoze sometimes fails with WSAEINVAL if    // it was called with no entries set in "readSet".  If this happens, ignore it:    if (err == WSAEINVAL && readSet.fd_count == 0) {      err = EINTR;      // To stop this from happening again, create a dummy socket:      int dummySocketNum = socket(AF_INET, SOCK_DGRAM, 0);      FD_SET((unsigned)dummySocketNum, &fReadSet);    }    if (err != EINTR) {#else    if (errno != EINTR && errno != EAGAIN) {#endif// Unexpected error - treat this as fatal:#if !defined(_WIN32_WCE)perror("BasicTaskScheduler::SingleStep(): select() fails");// Because this failure is often "Bad file descriptor" - which is caused by an invalid socket number (i.e., a socket number// that had already been closed) being used in "select()" - we print out the sockets that were being used in "select()",// to assist in debugging:fprintf(stderr, "socket numbers used in the select() call:");for (int i = 0; i < 10000; ++i) {  if (FD_ISSET(i, &fReadSet) || FD_ISSET(i, &fWriteSet) || FD_ISSET(i, &fExceptionSet)) {    fprintf(stderr, " %d(", i);    if (FD_ISSET(i, &fReadSet)) fprintf(stderr, "r");    if (FD_ISSET(i, &fWriteSet)) fprintf(stderr, "w");    if (FD_ISSET(i, &fExceptionSet)) fprintf(stderr, "e");    fprintf(stderr, ")");  }}fprintf(stderr, "\n");#endifinternalError();      }  }  // Call the handler function for one readable socket:  HandlerIterator iter(*fHandlers);  HandlerDescriptor* handler;  // To ensure forward progress through the handlers, begin past the last  // socket number that we handled:  if (fLastHandledSocketNum >= 0) {    //找到上次执行的socket handler的下一个    while ((handler = iter.next()) != NULL) {      if (handler->socketNum == fLastHandledSocketNum) break;    }    if (handler == NULL) {      fLastHandledSocketNum = -1;      iter.reset(); // start from the beginning instead    }  }  //从找到的handler开始，找一个可以执行的handler，不论其状态是可读，可写，还是出错，执行之  while ((handler = iter.next()) != NULL) {    int sock = handler->socketNum; // alias    int resultConditionSet = 0;    if (FD_ISSET(sock, &readSet) && FD_ISSET(sock, &fReadSet)/*sanity check*/) resultConditionSet |= SOCKET_READABLE;    if (FD_ISSET(sock, &writeSet) && FD_ISSET(sock, &fWriteSet)/*sanity check*/) resultConditionSet |= SOCKET_WRITABLE;    if (FD_ISSET(sock, &exceptionSet) && FD_ISSET(sock, &fExceptionSet)/*sanity check*/) resultConditionSet |= SOCKET_EXCEPTION;    if ((resultConditionSet&handler->conditionSet) != 0 && handler->handlerProc != NULL) {      fLastHandledSocketNum = sock;          // Note: we set "fLastHandledSocketNum" before calling the handler,          // in case the handler calls "doEventLoop()" reentrantly.      (*handler->handlerProc)(handler->clientData, resultConditionSet);      break;    }  }  //如果寻找完了依然没有执行任何handle，则从头再找  if (handler == NULL && fLastHandledSocketNum >= 0) {    // We didn't call a handler, but we didn't get to check all of them,    // so try again from the beginning:    iter.reset();    while ((handler = iter.next()) != NULL) {      int sock = handler->socketNum; // alias      int resultConditionSet = 0;      if (FD_ISSET(sock, &readSet) && FD_ISSET(sock, &fReadSet)/*sanity check*/) resultConditionSet |= SOCKET_READABLE;      if (FD_ISSET(sock, &writeSet) && FD_ISSET(sock, &fWriteSet)/*sanity check*/) resultConditionSet |= SOCKET_WRITABLE;      if (FD_ISSET(sock, &exceptionSet) && FD_ISSET(sock, &fExceptionSet)/*sanity check*/) resultConditionSet |= SOCKET_EXCEPTION;      if ((resultConditionSet&handler->conditionSet) != 0 && handler->handlerProc != NULL) {fLastHandledSocketNum = sock;    // Note: we set "fLastHandledSocketNum" before calling the handler,            // in case the handler calls "doEventLoop()" reentrantly.(*handler->handlerProc)(handler->clientData, resultConditionSet);break;      }    }    //依然没有找到可执行的handler    if (handler == NULL) fLastHandledSocketNum = -1;//because we didn't call a handler  }   //响应事件   // Also handle any newly-triggered event (Note that we do this *after* calling a socket handler,  // in case the triggered event handler modifies The set of readable sockets.)  if (fTriggersAwaitingHandling != 0) {    if (fTriggersAwaitingHandling == fLastUsedTriggerMask) {      // Common-case optimization for a single event trigger:      fTriggersAwaitingHandling = 0;      if (fTriggeredEventHandlers[fLastUsedTriggerNum] != NULL) {      //执行一个事件处理函数(*fTriggeredEventHandlers[fLastUsedTriggerNum])(fTriggeredEventClientDatas[fLastUsedTriggerNum]);      }    } else {      // Look for an event trigger that needs handling (making sure that we make forward progress through all possible triggers):      unsigned i = fLastUsedTriggerNum;      EventTriggerId mask = fLastUsedTriggerMask;      do {i = (i+1)%MAX_NUM_EVENT_TRIGGERS;mask >>= 1;if (mask == 0) mask = 0x80000000;if ((fTriggersAwaitingHandling&mask) != 0) {   //执行一个事件响应  fTriggersAwaitingHandling &=~ mask;  if (fTriggeredEventHandlers[i] != NULL) {    (*fTriggeredEventHandlers[i])(fTriggeredEventClientDatas[i]);  }  fLastUsedTriggerMask = mask;  fLastUsedTriggerNum = i;  break;}      } while (i != fLastUsedTriggerNum);    }  }   //执行一个最迫切的延迟任务  // Also handle any delayed event that may have come due.  fDelayQueue.handleAlarm();}

由上面代码可知，SingleStep()执行以下四步： 

１为所有需要操作的socket 执行select 。 
２找出第一个应执行的socket 任务(handler) 并执行之。 
３找到第一个应响应的事件，并执行之。 
４找到第一个应执行的延迟任务并执行之。