boost log库 使用八

在真正的项目中，我需要在不同的cpp或者cc文件中写日志，通常在不同的线程中也需要这样做。

在前面的文章中，写日志需要一个logger对象。在一个真正的应用中，我需要这个logger成为全局变量，并且是可以线程安全的访问的。

官方文档在这里：http://www.boost.org/doc/libs/1_55_0/libs/log/doc/html/log/detailed/sources.html#log.detailed.sources.global_storage

现在我修改我的代码。

1. 创建一个logger.h文件，只有一行：

BOOST_LOG_INLINE_GLOBAL_LOGGER_DEFAULT(my_logger, src::severity_logger_mt)

2. 在main.cc文件中，include必须的头文件，然后使用my_logger::get()方法获取logger对象的引用

#include 
#include 
#include 
#include 

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
namespace logging = boost::log;
namespace attrs = boost::log::attributes;
namespace src = boost::log::sources;
namespace sinks = boost::log::sinks;
namespace expr = boost::log::expressions;
namespace keywords = boost::log::keywords;
enum sign_severity_level {
  trace,
  debug,
  info,
  warning,
  error,
  fatal,
  report
};
void InitLog() {
  typedef sinks::synchronous_sink text_sink;
  boost::shared_ptr< text_sink > sink1 = boost::make_shared();
  sink1->locked_backend()->add_stream(
          boost::make_shared("sign.log"));
  sink1->set_formatter (
   expr::format("[%1%]<%2%>(%3%): %4%")
   % expr::format_date_time< boost::posix_time::ptime >("TimeStamp", "%Y-%m-%d %H:%M:%S")
   % expr::attr("Severity")
   % expr::attr("ThreadID")
   % expr::smessage
   );
  logging::core::get()->add_sink(sink1);
  sink1->set_filter(expr::attr("Severity") >= warning);
  boost::shared_ptr< text_sink > sink2 = boost::make_shared< text_sink >();
  sink2->locked_backend()->add_stream(
          boost::make_shared< std::ofstream >("sign.csv"));
  sink2->set_formatter (
   expr::format("%1%,%2%,%3%")
   % expr::format_date_time< boost::posix_time::ptime >("TimeStamp", "%Y-%m-%d %H:%M:%S")
   % expr::attr("Severity")
   % expr::smessage
   );
  logging::core::get()->add_sink(sink2);
  sink2->set_filter(expr::attr("Severity") == report);
  logging::add_common_attributes();
  logging::core::get()->add_global_attribute("ThreadID", attrs::current_thread_id());
}
#include "logger.h"
int main(int, char*[]) {
  InitLog();
  src::severity_logger_mt& lg = my_logger::get();
  BOOST_LOG_SEV(lg, trace) << "A trace severity message";
  BOOST_LOG_SEV(lg, debug) << "A debug severity message";
  BOOST_LOG_SEV(lg, info) << "An informational severity message";
  BOOST_LOG_SEV(lg, warning) << "A warning severity message";
  BOOST_LOG_SEV(lg, error) << "An error severity message";
  BOOST_LOG_SEV(lg, fatal) << "A fatal severity message";
  BOOST_LOG_SEV(lg, report) << "A report severity message";
  return 0;
}

这就完了。

宏为我们定义了一个struct类型，也实现了get方法。作为singleton的logger会在第一次调用get方法时被创建出来。

下面是宏的代码：

./sources/global_logger_storage.hpp:185
//! The macro declares a global logger that will be default-constructed
#define BOOST_LOG_INLINE_GLOBAL_LOGGER_DEFAULT(tag_name, logger)\
    BOOST_LOG_INLINE_GLOBAL_LOGGER_INIT(tag_name, logger)\
    {\
        return logger_type();\
    }

//! The macro declares a global logger with a custom initialization
#define BOOST_LOG_INLINE_GLOBAL_LOGGER_INIT(tag_name, logger)\
    BOOST_LOG_GLOBAL_LOGGER(tag_name, logger)\
    inline BOOST_LOG_GLOBAL_LOGGER_INIT(tag_name, logger)
//! The macro forward-declares a global logger with a custom initialization
#define BOOST_LOG_GLOBAL_LOGGER(tag_name, logger)\
    struct tag_name\
    {\
        typedef logger logger_type;\
        enum registration_line_t { registration_line = __LINE__ };\
        static const char* registration_file() { return __FILE__; }\
        static logger_type construct_logger();\
        static inline logger_type& get()\
        {\
            return ::boost::log::sources::aux::logger_singleton< tag_name >::get();\
        }\
    };
//! The macro defines a global logger initialization routine
#define BOOST_LOG_GLOBAL_LOGGER_INIT(tag_name, logger)\
    tag_name::logger_type tag_name::construct_logger()

它产生了下面真正的C++代码

struct my_logger
    {
        typedef src::logger_mt logger_type;
        enum registration_line_t { registration_line = __LINE__ };
        static const char* registration_file() { return __FILE__; }
        static logger_type construct_logger();
        static inline logger_type& get()
        {
            return ::boost::log::sources::aux::logger_singleton::get();
        }
    };
    inline my_logger::logger_type my_logger::construct_logger()