【live555】UsageEnvrionment分析

UsageEnvrionment类中声明了两个指针，

void * liveMediaPriv和void * groupsockPriv

他们是public的，即

  // a pointer to additional, optional, client-specific state  void* liveMediaPriv;  void* groupsockPriv;

我感觉他们俩是指向另外俩类库用的指针。

再加上

  // task scheduler:  TaskScheduler& taskScheduler() const {return fScheduler;}

和

private:  TaskScheduler& fScheduler;

UsageEnvrionment就把其他三个类都囊括在了自己手中了。

因此，对于UsageEnvrionment的定位为“// An abstract base class, subclassed for each use of the library”

看来，实际使用中，可能这个类的重要性是作为每次使用的时候代表一次环境的类使用，这个环境里有live555全部类库的所有对象。

UsageEnvrionment.hh的重要性，是不是有点类似于common.h啥的，所以连strdup都被挪到这里，让大家都可以使用了：

#ifndef _STRDUP_HH
// "strDup()" is used often, so include this here, so everyone gets it:
#include "strDup.hh"
#endif

=====

在Media.hh中，有一个--Table类，

UsageEnvironment 的liveMediaPriv，实际上，是指向这样类的一个对象的：

// The structure pointed to by the "liveMediaPriv" UsageEnvironment field:class _Tables {public:  static _Tables* getOurTables(UsageEnvironment& env, Boolean createIfNotPresent = True);      // returns a pointer to an "ourTables" structure (creating it if necessary)  void reclaimIfPossible();      // used to delete ourselves when we're no longer used  MediaLookupTable* mediaTable;  void* socketTable;protected:  _Tables(UsageEnvironment& env);  virtual ~_Tables();private:  UsageEnvironment& fEnv;};

这个类，还有一个私有的指针，指向一个Envrionment对象：

UsageEnvironment& fEnv;

真是想不明白，为啥他们俩互相都记录着彼此的对象呢？？

===============================

/**********This library is free software; you can redistribute it and/or modify it underthe terms of the GNU Lesser General Public License as published by theFree Software Foundation; either version 2.1 of the License, or (at youroption) any later version. (See <http://www.gnu.org/copyleft/lesser.html>.)This library is distributed in the hope that it will be useful, but WITHOUTANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESSFOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License formore details.You should have received a copy of the GNU Lesser General Public Licensealong with this library; if not, write to the Free Software Foundation, Inc.,51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA**********/// Copyright (c) 1996-2013 Live Networks, Inc.  All rights reserved.// Usage Environment// C++ header#ifndef _USAGE_ENVIRONMENT_HH#define _USAGE_ENVIRONMENT_HH#ifndef _USAGEENVIRONMENT_VERSION_HH#include "UsageEnvironment_version.hh"#endif#ifndef _NETCOMMON_H#include "NetCommon.h"#endif#ifndef _BOOLEAN_HH#include "Boolean.hh"#endif#ifndef _STRDUP_HH// "strDup()" is used often, so include this here, so everyone gets it:#include "strDup.hh"#endif#ifndef NULL#define NULL 0#endif#ifdef __BORLANDC__#define _setmode setmode#define _O_BINARY O_BINARY#endifclass TaskScheduler; // forward// An abstract base class, subclassed for each use of the libraryclass UsageEnvironment {public:  void reclaim();  // task scheduler:  TaskScheduler& taskScheduler() const {return fScheduler;}  // result message handling:  typedef char const* MsgString;  virtual MsgString getResultMsg() const = 0;  virtual void setResultMsg(MsgString msg) = 0;  virtual void setResultMsg(MsgString msg1, MsgString msg2) = 0;  virtual void setResultMsg(MsgString msg1, MsgString msg2, MsgString msg3) = 0;  virtual void setResultErrMsg(MsgString msg, int err = 0) = 0;// like setResultMsg(), except that an 'errno' message is appended.  (If "err == 0", the "getErrno()" code is used instead.)  virtual void appendToResultMsg(MsgString msg) = 0;  virtual void reportBackgroundError() = 0;// used to report a (previously set) error message within// a background event  virtual void internalError(); // used to 'handle' a 'should not occur'-type error condition within the library.  // 'errno'  virtual int getErrno() const = 0;  // 'console' output:  virtual UsageEnvironment& operator<<(char const* str) = 0;  virtual UsageEnvironment& operator<<(int i) = 0;  virtual UsageEnvironment& operator<<(unsigned u) = 0;  virtual UsageEnvironment& operator<<(double d) = 0;  virtual UsageEnvironment& operator<<(void* p) = 0;  // a pointer to additional, optional, client-specific state  void* liveMediaPriv;  void* groupsockPriv;protected:  UsageEnvironment(TaskScheduler& scheduler); // abstract base class  virtual ~UsageEnvironment(); // we are deleted only by reclaim()private:  TaskScheduler& fScheduler;};typedef void TaskFunc(void* clientData);typedef void* TaskToken;typedef u_int32_t EventTriggerId;class TaskScheduler {public:  virtual ~TaskScheduler();  virtual TaskToken scheduleDelayedTask(int64_t microseconds, TaskFunc* proc,void* clientData) = 0;// Schedules a task to occur (after a delay) when we next// reach a scheduling point.// (Does not delay if "microseconds" <= 0)// Returns a token that can be used in a subsequent call to// unscheduleDelayedTask()  virtual void unscheduleDelayedTask(TaskToken& prevTask) = 0;// (Has no effect if "prevTask" == NULL)        // Sets "prevTask" to NULL afterwards.  virtual void rescheduleDelayedTask(TaskToken& task,     int64_t microseconds, TaskFunc* proc,     void* clientData);  // Combines "unscheduleDelayedTask()" with "scheduleDelayedTask()"  // (setting "task" to the new task token).  // For handling socket operations in the background (from the event loop):  typedef void BackgroundHandlerProc(void* clientData, int mask);    // Possible bits to set in "mask".  (These are deliberately defined    // the same as those in Tcl, to make a Tcl-based subclass easy.)    #define SOCKET_READABLE    (1<<1)    #define SOCKET_WRITABLE    (1<<2)    #define SOCKET_EXCEPTION   (1<<3)  virtual void setBackgroundHandling(int socketNum, int conditionSet, BackgroundHandlerProc* handlerProc, void* clientData) = 0;  void disableBackgroundHandling(int socketNum) { setBackgroundHandling(socketNum, 0, NULL, NULL); }  virtual void moveSocketHandling(int oldSocketNum, int newSocketNum) = 0;        // Changes any socket handling for "oldSocketNum" so that occurs with "newSocketNum" instead.  virtual void doEventLoop(char* watchVariable = NULL) = 0;      // Causes further execution to take place within the event loop.      // Delayed tasks, background I/O handling, and other events are handled, sequentially (as a single thread of control).      // (If "watchVariable" is not NULL, then we return from this routine when *watchVariable != 0)  virtual EventTriggerId createEventTrigger(TaskFunc* eventHandlerProc) = 0;      // Creates a 'trigger' for an event, which - if it occurs - will be handled (from the event loop) using "eventHandlerProc".      // (Returns 0 iff no such trigger can be created (e.g., because of implementation limits on the number of triggers).)  virtual void deleteEventTrigger(EventTriggerId eventTriggerId) = 0;  virtual void triggerEvent(EventTriggerId eventTriggerId, void* clientData = NULL) = 0;      // Causes the (previously-registered) handler function for the specified event to be handled (from the event loop).      // The handler function is called with "clientData" as parameter.      // Note: This function (unlike other library functions) may be called from an external thread - to signal an external event.  // The following two functions are deprecated, and are provided for backwards-compatibility only:  void turnOnBackgroundReadHandling(int socketNum, BackgroundHandlerProc* handlerProc, void* clientData) {    setBackgroundHandling(socketNum, SOCKET_READABLE, handlerProc, clientData);  }  void turnOffBackgroundReadHandling(int socketNum) { disableBackgroundHandling(socketNum); }  virtual void internalError(); // used to 'handle' a 'should not occur'-type error condition within the library.protected:  TaskScheduler(); // abstract base class};#endif