在easylogging++的哪些事(三)总体设计我们介绍了easylogging++的总体设计，从今天开始正式进入源码分析部分，首先我们来看看easylogging++的主流程。

一、easylogging++的初始化

    easylogging++的那些事(一):功能介绍快速上手部分提到了接入easylogging++的方式是通过INITIALIZE_EASYLOGGINGPP宏完成初始化开始的，现在我们来看看这个宏:
    话不多说，直接上源码:

    #if ELPP_ASYNC_LOGGING
    #  define INITIALIZE_EASYLOGGINGPP ELPP_INIT_EASYLOGGINGPP(new el::base::Storage(el::LogBuilderPtr(new > el::base::DefaultLogBuilder()),\
    new el::base::AsyncDispatchWorker()))
    #else
    #  define INITIALIZE_EASYLOGGINGPP ELPP_INIT_EASYLOGGINGPP(new el::base::Storage(el::LogBuilderPtr(new > el::base::DefaultLogBuilder())))
    #endif  // ELPP_ASYNC_LOGGING

    其中ELPP_ASYNC_LOGGING宏是用于开启异步日志的，不管是否开启异步日志，INITIALIZE_EASYLOGGINGPP实际上就是创建了一个el::base::Storage对象。

    在easylogging++的哪些事(三)总体设计中，我们介绍过el::base::Storage类是日志库的入口类或者总的管理类，easylogging++的所有与日志输出相关的信息都保存在el::base::Storage类中，现在我们来看看el::base::Storage类的初始化做了哪些事情，下面是源码(源码的解释已经在注释中了):
    el::base::Storage类构造函数的声明:

    #if ELPP_ASYNC_LOGGING
        Storage(const LogBuilderPtr& defaultLogBuilder, base::IWorker* asyncDispatchWorker);
    #else
        explicit Storage(const LogBuilderPtr& defaultLogBuilder);
    #endif  // ELPP_ASYNC_LOGGING

    el::base::Storage类构造函数的定义:

  #if ELPP_ASYNC_LOGGING
  Storage::Storage(const LogBuilderPtr& defaultLogBuilder, base::IWorker* asyncDispatchWorker) :
  #else
  Storage::Storage(const LogBuilderPtr& defaultLogBuilder) :
  #endif  // ELPP_ASYNC_LOGGING
  //初始化指定文件指定行的用于是否记录日志的计数器
  m_registeredHitCounters(new base::RegisteredHitCounters()),
  //初始化注册的日志记录器的管理类 
  m_registeredLoggers(new base::RegisteredLoggers(defaultLogBuilder)),
  //初始化写日志时会用到的一些标志
  m_flags(ELPP_DEFAULT_LOGGING_FLAGS),
  //初始化Verbose日志相关信息的管理类(保存Verbose日志级别以及vModule相关信息)
  m_vRegistry(new base::VRegistry(0, &m_flags)),

  #if ELPP_ASYNC_LOGGING
  //启用异步日志时，异步日志队列(暂时保存日志)
  m_asyncLogQueue(new base::AsyncLogQueue()),
  //启用异步日志时，异步日志调度器(处理AsyncLogQueue中的日志)
  m_asyncDispatchWorker(asyncDispatchWorker),
  #endif  // ELPP_ASYNC_LOGGING
  //使用默认的日志回旋回调函数来初始化
  m_preRollOutCallback(base::defaultPreRollOutCallback) {
     // Register default logger 注册默认的日志记录器
     m_registeredLoggers->get(std::string(base::consts::kDefaultLoggerId));
     // We register default logger anyway (worse case it's not going to register) just in case 
     //再获取一次，以防未注册默认的日志记录器
     m_registeredLoggers->get("default");

     //注册性能跟踪日志记录器，并配置其日志格式
     #if defined(ELPP_FEATURE_ALL) || defined(ELPP_FEATURE_PERFORMANCE_TRACKING)
     // Register performance logger and reconfigure format
     Logger* performanceLogger = m_registeredLoggers->get(std::string(base::consts::kPerformanceLoggerId));
     m_registeredLoggers->get("performance");
     performanceLogger->configurations()->setGlobally(ConfigurationType::Format, std::string("%datetime %level %msg"));
     performanceLogger->reconfigure();
     #endif // defined(ELPP_FEATURE_ALL) || defined(ELPP_FEATURE_PERFORMANCE_TRACKING)

     //注册syslog日志记录器，并配置其日志格式
     #if defined(ELPP_SYSLOG)
     // Register syslog logger and reconfigure format
     Logger* sysLogLogger = m_registeredLoggers->get(std::string(base::consts::kSysLogLoggerId));
     sysLogLogger->configurations()->setGlobally(ConfigurationType::Format, std::string("%level: %msg"));
     sysLogLogger->reconfigure();
     #endif //  defined(ELPP_SYSLOG)
     //未配置VMODULE,也允许记录Verbose日志
     addFlag(LoggingFlag::AllowVerboseIfModuleNotSpecified);
     #if ELPP_ASYNC_LOGGING
     //启用异步日志时，默认的LogDispatchCallback注册为AsyncLogDispatchCallback
     installLogDispatchCallback<base::AsyncLogDispatchCallback>(std::string("AsyncLogDispatchCallback"));
     #else
     //未启用异步日志时，默认的LogDispatchCallback注册为DefaultLogDispatchCallback
     installLogDispatchCallback<base::DefaultLogDispatchCallback>(std::string("DefaultLogDispatchCallback"));
     #endif  // ELPP_ASYNC_LOGGING
     //注册性能跟踪默认回调DefaultPerformanceTrackingCallback
     #if defined(ELPP_FEATURE_ALL) || defined(ELPP_FEATURE_PERFORMANCE_TRACKING)
     installPerformanceTrackingCallback<base::DefaultPerformanceTrackingCallback>
     (std::string("DefaultPerformanceTrackingCallback"));
     #endif // defined(ELPP_FEATURE_ALL) || defined(ELPP_FEATURE_PERFORMANCE_TRACKING)
     ELPP_INTERNAL_INFO(1, "Easylogging++ has been initialized");
     #if ELPP_ASYNC_LOGGING
     //启用异步日志时，开启一个线程(线程处理函数run)处理异步日志队列m_asyncLogQueue中保存的日志
     m_asyncDispatchWorker->start();
     #endif  // ELPP_ASYNC_LOGGING
  }  

二、easylogging++的反初始化

    el::base::Storage析构函数的定义如下：

  Storage::~Storage(void) {
      ELPP_INTERNAL_INFO(4, "Destroying storage");
    #if ELPP_ASYNC_LOGGING
      ELPP_INTERNAL_INFO(5, "Replacing log dispatch callback to synchronous");
      uninstallLogDispatchCallback<base::AsyncLogDispatchCallback>(std::string("AsyncLogDispatchCallback"));
      installLogDispatchCallback<base::DefaultLogDispatchCallback>(std::string("DefaultLogDispatchCallback"));
      ELPP_INTERNAL_INFO(5, "Destroying asyncDispatchWorker");
      base::utils::safeDelete(m_asyncDispatchWorker);
      ELPP_INTERNAL_INFO(5, "Destroying asyncLogQueue");
      base::utils::safeDelete(m_asyncLogQueue);
    #endif  // ELPP_ASYNC_LOGGING
      ELPP_INTERNAL_INFO(5, "Destroying registeredHitCounters");
      base::utils::safeDelete(m_registeredHitCounters);
      ELPP_INTERNAL_INFO(5, "Destroying registeredLoggers");
      base::utils::safeDelete(m_registeredLoggers);
      ELPP_INTERNAL_INFO(5, "Destroying vRegistry");
      base::utils::safeDelete(m_vRegistry);
  }   

    这里的逻辑就很简单了，就是初始化时动态创建的一些对象的释放，这里对不多说了。

easylogging++的主流程就介绍到这里，下一篇开始源码分析日志记录宏。

原文地址：http://www.cnblogs.com/DesignLife/p/16922074.html