openRTSP分析1

openrtsp是live555里面作为rtsp客户端的一个例子程序。默认是接收rtsp流并保存为文件，里面对多种格式进行了处理。网上也有很多对openrtsp的分析的文章，但是个人感觉都不是太详细，一般都只有个大概的流程。这里再给这个过程捋一捋。

主要是一些重要的线路，细节部分就不予讨论。

在playCommon.cpp中是从main开始执行的。

开始是

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

这个是不变的。

做一些初始化参数的工作。然后是

ourClient = createClient(*env, streamURL, verbosityLevel, progName);

createClient的初始化这里省略。

if (sendOptionsRequest) {    // Begin by sending an "OPTIONS" command:    getOptions(continueAfterOPTIONS);  } else {    continueAfterOPTIONS(NULL, 0, NULL);  }

这里主要是发送option的函数。

其实是调用openRtsp中定义的函数

void getOptions(RTSPClient::responseHandler* afterFunc) {   ourRTSPClient->sendOptionsCommand(afterFunc, ourAuthenticator);}

我们来看看这个sendOptionsCommand

unsigned RTSPClient::sendOptionsCommand(responseHandler* responseHandler, Authenticator* authenticator) {  if (authenticator != NULL) fCurrentAuthenticator = *authenticator;  return sendRequest(new RequestRecord(++fCSeq, "OPTIONS", responseHandler));}

我们来看看这个RequestRecord类的初始化

RTSPClient::RequestRecord::RequestRecord(unsigned cseq, char const* commandName, responseHandler* handler, MediaSession* session, MediaSubsession* subsession, u_int32_t booleanFlags, double start, double end, float scale, char const* contentStr)  : fNext(NULL), fCSeq(cseq), fCommandName(commandName), fSession(session), fSubsession(subsession), fBooleanFlags(booleanFlags),    fStart(start), fEnd(end), fScale(scale), fContentStr(strDup(contentStr)), fHandler(handler) {}

这里主要数初始化了fCommondName和fHandler其他参数都是初始化了的。

unsigned RTSPClient::sendRequest(RequestRecord* request) {  char* cmd = NULL;  do {    Boolean connectionIsPending = False;    if (!fRequestsAwaitingConnection.isEmpty()) {      // A connection is currently pending (with at least one enqueued request).  Enqueue this request also:      connectionIsPending = True;    } else if (fInputSocketNum < 0) { // we need to open a connection      int connectResult = openConnection();      if (connectResult < 0) break; // an error occurred      else if (connectResult == 0) {// A connection is pending        connectionIsPending = True;      } // else the connection succeeded.  Continue sending the command.u    }    if (connectionIsPending) {      fRequestsAwaitingConnection.enqueue(request);      return request->cseq();    }    // If requested (and we're not already doing it, or have done it), set up the special protocol for tunneling RTSP-over-HTTP:    if (fTunnelOverHTTPPortNum != 0 && strcmp(request->commandName(), "GET") != 0 && fOutputSocketNum == fInputSocketNum) {      if (!setupHTTPTunneling1()) break;      fRequestsAwaitingHTTPTunneling.enqueue(request);      return request->cseq();    }    // Construct and send the command:    // First, construct command-specific headers that we need:    char* cmdURL = fBaseURL; // by default    Boolean cmdURLWasAllocated = False;    char const* protocolStr = "RTSP/1.0"; // by default    char* extraHeaders = (char*)""; // by default    Boolean extraHeadersWereAllocated = False;     char* contentLengthHeader = (char*)""; // by default    Boolean contentLengthHeaderWasAllocated = False;    char const* contentStr = request->contentStr(); // by default    if (contentStr == NULL) contentStr = "";    unsigned contentStrLen = strlen(contentStr);    if (contentStrLen > 0) {      char const* contentLengthHeaderFmt ="Content-Length: %d\r\n";      unsigned contentLengthHeaderSize = strlen(contentLengthHeaderFmt)+ 20 /* max int len */;      contentLengthHeader = new char[contentLengthHeaderSize];      sprintf(contentLengthHeader, contentLengthHeaderFmt, contentStrLen);      contentLengthHeaderWasAllocated = True;    }//根据commandName不同执行不同的程序段。    if (strcmp(request->commandName(), "DESCRIBE") == 0) {      extraHeaders = (char*)"Accept: application/sdp\r\n";    } else if (strcmp(request->commandName(), "OPTIONS") == 0) {    } else if (strcmp(request->commandName(), "ANNOUNCE") == 0) {      extraHeaders = (char*)"Content-Type: application/sdp\r\n";    } else if (strcmp(request->commandName(), "SETUP") == 0) {      MediaSubsession& subsession = *request->subsession();      Boolean streamUsingTCP = (request->booleanFlags()&0x1) != 0;      Boolean streamOutgoing = (request->booleanFlags()&0x2) != 0;      Boolean forceMulticastOnUnspecified = (request->booleanFlags()&0x4) != 0;      char const *prefix, *separator, *suffix;      constructSubsessionURL(subsession, prefix, separator, suffix);      char const* transportFmt;      if (strcmp(subsession.protocolName(), "UDP") == 0) {suffix = "";transportFmt = "Transport: RAW/RAW/UDP%s%s%s=%d-%d\r\n";      } else {transportFmt = "Transport: RTP/AVP%s%s%s=%d-%d\r\n";      }      cmdURL = new char[strlen(prefix) + strlen(separator) + strlen(suffix) + 1];      cmdURLWasAllocated = True;      sprintf(cmdURL, "%s%s%s", prefix, separator, suffix);      // Construct a "Transport:" header.      char const* transportTypeStr;      char const* modeStr = streamOutgoing ? ";mode=receive" : "";          // Note: I think the above is nonstandard, but DSS wants it this way      char const* portTypeStr;      portNumBits rtpNumber, rtcpNumber;      if (streamUsingTCP) { // streaming over the RTSP connectiontransportTypeStr = "/TCP;unicast";portTypeStr = ";interleaved";rtpNumber = fTCPStreamIdCount++;rtcpNumber = fTCPStreamIdCount++;      } else { // normal RTP streamingunsigned connectionAddress = subsession.connectionEndpointAddress();        Boolean requestMulticastStreaming  = IsMulticastAddress(connectionAddress) || (connectionAddress == 0 && forceMulticastOnUnspecified);transportTypeStr = requestMulticastStreaming ? ";multicast" : ";unicast";portTypeStr = ";client_port";rtpNumber = subsession.clientPortNum();if (rtpNumber == 0) {  envir().setResultMsg("Client port number unknown\n");  delete[] cmdURL;  break;}rtcpNumber = rtpNumber + 1;      }      unsigned transportSize = strlen(transportFmt)+ strlen(transportTypeStr) + strlen(modeStr) + strlen(portTypeStr) + 2*5 /* max port len */;      char* transportStr = new char[transportSize];      sprintf(transportStr, transportFmt,      transportTypeStr, modeStr, portTypeStr, rtpNumber, rtcpNumber);      // When sending more than one "SETUP" request, include a "Session:" header in the 2nd and later commands:      char* sessionStr = createSessionString(fLastSessionId);      // The "Transport:" and "Session:" (if present) headers make up the 'extra headers':      extraHeaders = new char[transportSize + strlen(sessionStr)];      extraHeadersWereAllocated = True;      sprintf(extraHeaders, "%s%s", transportStr, sessionStr);      delete[] transportStr; delete[] sessionStr;    } else if (strcmp(request->commandName(), "GET") == 0 || strcmp(request->commandName(), "POST") == 0) {      // We will be sending a HTTP (not a RTSP) request.      // Begin by re-parsing our RTSP URL, just to get the stream name, which we'll use as our 'cmdURL' in the subsequent request:      char* username;      char* password;      NetAddress destAddress;      portNumBits urlPortNum;      if (!parseRTSPURL(envir(), fBaseURL, username, password, destAddress, urlPortNum, (char const**)&cmdURL)) break;      if (cmdURL[0] == '\0') cmdURL = (char*)"/";      delete[] username;      delete[] password;      protocolStr = "HTTP/1.0";      if (strcmp(request->commandName(), "GET") == 0) {// Create a 'session cookie' string, using MD5:struct {  struct timeval timestamp;  unsigned counter;} seedData;gettimeofday(&seedData.timestamp, NULL);seedData.counter = ++fSessionCookieCounter;our_MD5Data((unsigned char*)(&seedData), sizeof seedData, fSessionCookie);// DSS seems to require that the 'session cookie' string be 22 bytes long:fSessionCookie[23] = '\0';char const* const extraHeadersFmt =  "x-sessioncookie: %s\r\n"  "Accept: application/x-rtsp-tunnelled\r\n"  "Pragma: no-cache\r\n"  "Cache-Control: no-cache\r\n";unsigned extraHeadersSize = strlen(extraHeadersFmt)  + strlen(fSessionCookie);extraHeaders = new char[extraHeadersSize];extraHeadersWereAllocated = True;sprintf(extraHeaders, extraHeadersFmt,fSessionCookie);      } else { // "POST"char const* const extraHeadersFmt =  "x-sessioncookie: %s\r\n"  "Content-Type: application/x-rtsp-tunnelled\r\n"  "Pragma: no-cache\r\n"  "Cache-Control: no-cache\r\n"  "Content-Length: 32767\r\n"  "Expires: Sun, 9 Jan 1972 00:00:00 GMT\r\n";unsigned extraHeadersSize = strlen(extraHeadersFmt)  + strlen(fSessionCookie);extraHeaders = new char[extraHeadersSize];extraHeadersWereAllocated = True;sprintf(extraHeaders, extraHeadersFmt,fSessionCookie);      }    } else { // "PLAY", "PAUSE", "TEARDOWN", "RECORD", "SET_PARAMETER", "GET_PARAMETER"      // First, make sure that we have a RTSP session in progress      if (fLastSessionId == NULL) {envir().setResultMsg("No RTSP session is currently in progress\n");break;      }      char const* sessionId;      float originalScale;      if (request->session() != NULL) {// Session-level operationcmdURL = (char*)sessionURL(*request->session());sessionId = fLastSessionId;originalScale = request->session()->scale();      } else {// Media-level operationchar const *prefix, *separator, *suffix;constructSubsessionURL(*request->subsession(), prefix, separator, suffix);cmdURL = new char[strlen(prefix) + strlen(separator) + strlen(suffix) + 1];cmdURLWasAllocated = True;sprintf(cmdURL, "%s%s%s", prefix, separator, suffix);sessionId = request->subsession()->sessionId();originalScale = request->subsession()->scale();      }      if (strcmp(request->commandName(), "PLAY") == 0) {// Create "Session:", "Scale:", and "Range:" headers; these make up the 'extra headers':char* sessionStr = createSessionString(sessionId);char* scaleStr = createScaleString(request->scale(), originalScale);char* rangeStr = createRangeString(request->start(), request->end());extraHeaders = new char[strlen(sessionStr) + strlen(scaleStr) + strlen(rangeStr) + 1];extraHeadersWereAllocated = True;sprintf(extraHeaders, "%s%s%s", sessionStr, scaleStr, rangeStr);delete[] sessionStr; delete[] scaleStr; delete[] rangeStr;      } else {// Create a "Session:" header; this makes up our 'extra headers':extraHeaders = createSessionString(sessionId);extraHeadersWereAllocated = True;      }    }    char* authenticatorStr = createAuthenticatorString(request->commandName(), fBaseURL);    char const* const cmdFmt =      "%s %s %s\r\n"      "CSeq: %d\r\n"      "%s"      "%s"      "%s"      "%s"      "\r\n"      "%s";    unsigned cmdSize = strlen(cmdFmt)      + strlen(request->commandName()) + strlen(cmdURL) + strlen(protocolStr)      + 20 /* max int len */      + strlen(authenticatorStr)      + fUserAgentHeaderStrLen      + strlen(extraHeaders)      + strlen(contentLengthHeader)      + contentStrLen;    cmd = new char[cmdSize];    sprintf(cmd, cmdFmt,    request->commandName(), cmdURL, protocolStr,    request->cseq(),    authenticatorStr,    fUserAgentHeaderStr,            extraHeaders,    contentLengthHeader,    contentStr);    delete[] authenticatorStr;    if (cmdURLWasAllocated) delete[] cmdURL;    if (extraHeadersWereAllocated) delete[] extraHeaders;    if (contentLengthHeaderWasAllocated) delete[] contentLengthHeader;    if (fVerbosityLevel >= 1) envir() << "Sending request: " << cmd << "\n";    if (fTunnelOverHTTPPortNum != 0 && strcmp(request->commandName(), "GET") != 0 && strcmp(request->commandName(), "POST") != 0) {      // When we're tunneling RTSP-over-HTTP, we Base-64-encode the request before we send it.      // (However, we don't do this for the HTTP "GET" and "POST" commands that we use to set up the tunnel.)      char* origCmd = cmd;      cmd = base64Encode(origCmd, strlen(cmd));      if (fVerbosityLevel >= 1) envir() << "\tThe request was base-64 encoded to: " << cmd << "\n\n";      delete[] origCmd;    }//将命令发送出去，上面是对发送命令做一个拼接    if (send(fOutputSocketNum, cmd, strlen(cmd), 0) < 0) {      char const* errFmt = "%s send() failed: ";      unsigned const errLength = strlen(errFmt) + strlen(request->commandName());      char* err = new char[errLength];      sprintf(err, errFmt, request->commandName());      envir().setResultErrMsg(err);      delete[] err;      break;    }    // The command send succeeded, so enqueue the request record, so that its response (when it comes) can be handled:    fRequestsAwaitingResponse.enqueue(request);    delete[] cmd;    return request->cseq();  } while (0);  // An error occurred, so call the response handler immediately (indicating the error):  delete[] cmd;  handleRequestError(request);  delete request;  return 0;}

上面这段代码主要是针对不同的命令做一些拼接，然后send出去。但是我们看看这个send使用的socket是fOutputSocketNum是什么时候建立的呢。

在sendReques中先判断fRequestsAwaitingConnection是否为isEmpty，如果不是就会openConnection()

在我们再来看看这个openConnection

int RTSPClient::openConnection() {  do {    // Set up a connection to the server.  Begin by parsing the URL:    char* username;    char* password;    NetAddress destAddress;    portNumBits urlPortNum;    char const* urlSuffix;    if (!parseRTSPURL(envir(), fBaseURL, username, password, destAddress, urlPortNum, &urlSuffix)) break;    portNumBits destPortNum = fTunnelOverHTTPPortNum == 0 ? urlPortNum : fTunnelOverHTTPPortNum;    if (username != NULL || password != NULL) {      fCurrentAuthenticator.setUsernameAndPassword(username, password);      delete[] username;      delete[] password;    }    // We don't yet have a TCP socket (or we used to have one, but it got closed).  Set it up now.    fInputSocketNum = fOutputSocketNum = setupStreamSocket(envir(), 0);    if (fInputSocketNum < 0) break;          // Connect to the remote endpoint:    fServerAddress = *(netAddressBits*)(destAddress.data());    int connectResult = connectToServer(fInputSocketNum, destPortNum);    if (connectResult < 0) break;    else if (connectResult > 0) {      // The connection succeeded.  Arrange to handle responses to requests sent on it:      envir().taskScheduler().setBackgroundHandling(fInputSocketNum, SOCKET_READABLE,    (TaskScheduler::BackgroundHandlerProc*)&incomingDataHandler, this);    }    return connectResult;  } while (0);    resetTCPSockets();  return -1;}

我们看到这里fInputSocketNum = fOutputSocketNum = setupStreamSocket(envir(), 0);了

这里面主要是

int setupStreamSocket(UsageEnvironment& env,                      Port port, Boolean makeNonBlocking) {  if (!initializeWinsockIfNecessary()) {    socketErr(env, "Failed to initialize 'winsock': ");    return -1;  }  int newSocket = createSocket(SOCK_STREAM);  if (newSocket < 0) {    socketErr(env, "unable to create stream socket: ");    return newSocket;  }  int reuseFlag = groupsockPriv(env)->reuseFlag;  reclaimGroupsockPriv(env);  if (setsockopt(newSocket, SOL_SOCKET, SO_REUSEADDR, (const char*)&reuseFlag, sizeof reuseFlag) < 0) {    socketErr(env, "setsockopt(SO_REUSEADDR) error: ");    closeSocket(newSocket);    return -1;  }  // SO_REUSEPORT doesn't really make sense for TCP sockets, so we  // normally don't set them.  However, if you really want to do this  // #define REUSE_FOR_TCP#ifdef REUSE_FOR_TCP#if defined(__WIN32__) || defined(_WIN32)  // Windoze doesn't properly handle SO_REUSEPORT#else#ifdef SO_REUSEPORT  if (setsockopt(newSocket, SOL_SOCKET, SO_REUSEPORT, (const char*)&reuseFlag, sizeof reuseFlag) < 0) {    socketErr(env, "setsockopt(SO_REUSEPORT) error: ");    closeSocket(newSocket);    return -1;  }#endif#endif#endif  // Note: Windoze requires binding, even if the port number is 0#if defined(__WIN32__) || defined(_WIN32)#else  if (port.num() != 0 || ReceivingInterfaceAddr != INADDR_ANY) {#endif    MAKE_SOCKADDR_IN(name, ReceivingInterfaceAddr, port.num());    if (bind(newSocket, (struct sockaddr*)&name, sizeof name) != 0) {      char tmpBuffer[100];      sprintf(tmpBuffer, "bind() error (port number: %d): ",      ntohs(port.num()));      socketErr(env, tmpBuffer);      closeSocket(newSocket);      return -1;    }#if defined(__WIN32__) || defined(_WIN32)#else  }#endif  if (makeNonBlocking) {    if (!makeSocketNonBlocking(newSocket)) {      socketErr(env, "failed to make non-blocking: ");      closeSocket(newSocket);      return -1;    }  }  return newSocket;}

我们看到这里主要是做了建立socket和bind的工作。

再看下面做做了connectToServer

int RTSPClient::connectToServer(int socketNum, portNumBits remotePortNum) {  MAKE_SOCKADDR_IN(remoteName, fServerAddress, htons(remotePortNum));  if (fVerbosityLevel >= 1) {    envir() << "Opening connection to " << AddressString(remoteName).val() << ", port " << remotePortNum << "...\n";  }  if (connect(socketNum, (struct sockaddr*) &remoteName, sizeof remoteName) != 0) {    int const err = envir().getErrno();    if (err == EINPROGRESS || err == EWOULDBLOCK) {      // The connection is pending; we'll need to handle it later.  Wait for our socket to be 'writable', or have an exception.      envir().taskScheduler().setBackgroundHandling(socketNum, SOCKET_WRITABLE|SOCKET_EXCEPTION,    (TaskScheduler::BackgroundHandlerProc*)&connectionHandler, this);      return 0;    }    envir().setResultErrMsg("connect() failed: ");    if (fVerbosityLevel >= 1) envir() << "..." << envir().getResultMsg() << "\n";    return -1;  }  if (fVerbosityLevel >= 1) envir() << "...local connection opened\n";  return 1;}

主要是tcp的connection操作。这里会执行if里面的，我们来看看这个setBackgroundHandling

void BasicTaskScheduler  ::setBackgroundHandling(int socketNum, int conditionSet, BackgroundHandlerProc* handlerProc, void* clientData) {  if (socketNum < 0) return;  FD_CLR((unsigned)socketNum, &fReadSet);  FD_CLR((unsigned)socketNum, &fWriteSet);  FD_CLR((unsigned)socketNum, &fExceptionSet);  if (conditionSet == 0) {    fHandlers->clearHandler(socketNum);    if (socketNum+1 == fMaxNumSockets) {      --fMaxNumSockets;    }  } else {    fHandlers->assignHandler(socketNum, conditionSet, handlerProc, clientData);    if (socketNum+1 > fMaxNumSockets) {      fMaxNumSockets = socketNum+1;    }    if (conditionSet&SOCKET_READABLE) FD_SET((unsigned)socketNum, &fReadSet);    if (conditionSet&SOCKET_WRITABLE) FD_SET((unsigned)socketNum, &fWriteSet);    if (conditionSet&SOCKET_EXCEPTION) FD_SET((unsigned)socketNum, &fExceptionSet);  }}

主要是将socket加入到set集中，这里设置的write和excetion

这里的assignHandler主要是将handlerProc加入到fHandlers中，并且将socketNum加入到这个节点中。

if (connectionIsPending) {      fRequestsAwaitingConnection.enqueue(request);      return request->cseq();    }

执行到上面的代码，即将request加入到fRequestsAwaitingConnection中，然后就返回。

回到main主程序，  env->taskScheduler().doEventLoop(); 

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

那让我们来分析一下这个SingleStep

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超时的时间  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");#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) {    while ((handler = iter.next()) != NULL) {      if (handler->socketNum == fLastHandledSocketNum) break;    }    if (handler == NULL) {      fLastHandledSocketNum = -1;      iter.reset(); // start from the beginning instead    }  }

//查找可执行的handler，执行  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;    }  }

如果任然没有找到可执行的handler，从头开始找  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;      }    }    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) {(*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) {  fTriggersAwaitingHandling &=~ mask;  if (fTriggeredEventHandlers[i] != NULL) {    (*fTriggeredEventHandlers[i])(fTriggeredEventClientDatas[i]);  }  fLastUsedTriggerMask = mask;  fLastUsedTriggerNum = i;  break;}      } while (i != fLastUsedTriggerNum);    }  }  // Also handle any delayed event that may have come due.  fDelayQueue.handleAlarm();}