google glog分析2

分析logging.h，这个文件很重要，定义了各种宏，不同的宏开关定制不同的功能。

GOOGLE_STRIP_LOG是限制等级，低于这个等级的都不会被显示。这是在编译期完成的。从下面的代码就可以看出：

#if GOOGLE_STRIP_LOG == 0#define COMPACT_GOOGLE_LOG_INFO google::LogMessage( \      __FILE__, __LINE__)#define LOG_TO_STRING_INFO(message) google::LogMessage( \      __FILE__, __LINE__, google::GLOG_INFO, message)#else#define COMPACT_GOOGLE_LOG_INFO google::NullStream()#define LOG_TO_STRING_INFO(message) google::NullStream()#endif#if GOOGLE_STRIP_LOG <= 1#define COMPACT_GOOGLE_LOG_WARNING google::LogMessage( \      __FILE__, __LINE__, google::GLOG_WARNING)#define LOG_TO_STRING_WARNING(message) google::LogMessage( \      __FILE__, __LINE__, google::GLOG_WARNING, message)#else#define COMPACT_GOOGLE_LOG_WARNING google::NullStream()#define LOG_TO_STRING_WARNING(message) google::NullStream()#endif#if GOOGLE_STRIP_LOG <= 2#define COMPACT_GOOGLE_LOG_ERROR google::LogMessage( \      __FILE__, __LINE__, google::GLOG_ERROR)#define LOG_TO_STRING_ERROR(message) google::LogMessage( \      __FILE__, __LINE__, google::GLOG_ERROR, message)#else#define COMPACT_GOOGLE_LOG_ERROR google::NullStream()#define LOG_TO_STRING_ERROR(message) google::NullStream()#endif#if GOOGLE_STRIP_LOG <= 3#define COMPACT_GOOGLE_LOG_FATAL google::LogMessageFatal( \      __FILE__, __LINE__)#define LOG_TO_STRING_FATAL(message) google::LogMessage( \      __FILE__, __LINE__, google::GLOG_FATAL, message)#else#define COMPACT_GOOGLE_LOG_FATAL google::NullStreamFatal()#define LOG_TO_STRING_FATAL(message) google::NullStreamFatal()#endif

我们代码里使用的LOG(INFO)宏定义会经#define LOG(severity) COMPACT_GOOGLE_LOG_ ## severity.stream()转化为COMPACT_GOOGLE_LOG_INFO.stream()；而COMPACT_GOOGLE_LOG_INFO又会转化为#define LOG_TO_STRING_INFO(message) google::LogMessage( \
      __FILE__, __LINE__, google::GLOG_INFO, message).stream()

看下#define GOOGLE_LOG_INFO(counter) google::LogMessage(__FILE__, __LINE__, google::GLOG_INFO, counter, &google::LogMessage::SendToLog)

下面就着重分析下LogMessage这个类：

class  LogMessage {public:  enum {    // Passing kNoLogPrefix for the line number disables the    // log-message prefix. Useful for using the LogMessage    // infrastructure as a printing utility. See also the --log_prefix    // flag for controlling the log-message prefix on an    // application-wide basis.    kNoLogPrefix = -1  };  class  LogStream : public std::ostream {  public:    LogStream(char *buf, int len, int ctr)        : std::ostream(NULL),          streambuf_(buf, len),          ctr_(ctr),          self_(this) {      rdbuf(&streambuf_);    }    int ctr() const { return ctr_; }    void set_ctr(int ctr) { ctr_ = ctr; }    LogStream* self() const { return self_; }    // Legacy std::streambuf methods.    size_t pcount() const { return streambuf_.pcount(); }    char* pbase() const { return streambuf_.pbase(); }    char* str() const { return pbase(); }  private:    base_logging::LogStreamBuf streambuf_;    int ctr_;  // Counter hack (for the LOG_EVERY_X() macro)    LogStream *self_;  // Consistency check hack  };public:  // icc 8 requires this typedef to avoid an internal compiler error.  typedef void (LogMessage::*SendMethod)();  LogMessage(const char* file, int line, LogSeverity severity, int ctr,             SendMethod send_method);  LogMessage(const char* file, int line);  LogMessage(const char* file, int line, LogSeverity severity);  LogMessage(const char* file, int line, LogSeverity severity, LogSink* sink,             bool also_send_to_log);  LogMessage(const char* file, int line, LogSeverity severity,             std::vector<std::string>* outvec);  LogMessage(const char* file, int line, LogSeverity severity,             std::string* message);  LogMessage(const char* file, int line, const CheckOpString& result);  ~LogMessage();  void Flush();  static const size_t kMaxLogMessageLen;  void SendToLog();  // Actually dispatch to the logs  void SendToSyslogAndLog();  // Actually dispatch to syslog and the logs  // Call abort() or similar to perform LOG(FATAL) crash.  static void Fail() ;  std::ostream& stream();  int preserved_errno() const;  static int64 num_messages(int severity);  struct LogMessageData;private:  void SendToSinkAndLog();  // Send to sink if provided and dispatch to the logs  void SendToSink();  // Send to sink if provided, do nothing otherwise.  void WriteToStringAndLog();  void SaveOrSendToLog();  // Save to stringvec if provided, else to logs  void Init(const char* file, int line, LogSeverity severity,            void (LogMessage::*send_method)());  void RecordCrashReason(glog_internal_namespace_::CrashReason* reason);  static int64 num_messages_[NUM_SEVERITIES];  // under log_mutex  LogMessageData* allocated_;  LogMessageData* data_;  friend class LogDestination;  LogMessage(const LogMessage&);  void operator=(const LogMessage&);};

logmsg里嵌套了一个LogStream；LogStream继承自ostream 代码都很好看懂，时间晚了，也累了，明天继续看，不过看到下面留有扩展接口，很兴奋：

// A Logger is the interface used by logging modules to emit entries
// to a log.  A typical implementation will dump formatted data to a
// sequence of files.  We also provide interfaces that will forward
// the data to another thread so that the invoker never blocks.
// Implementations should be thread-safe since the logging system
// will write to them from multiple threads.