Automatically flush log if message level is above certain severity.

include/spdlog/details/line_logger_impl.h

@@ -46,6 +46,11 @@ inline spdlog::details::line_logger::~line_logger()
 #endif
         _callback_logger->_log_msg(_log_msg);
     }
+
+    if (_log_msg.level >= _callback_logger->_flush_level)
+    {
+        _callback_logger->flush();
+    }
 }
 
 //

include/spdlog/details/logger_impl.h

@@ -21,6 +21,7 @@ inline spdlog::logger::logger(const std::string& logger_name, const It& begin, c
 
     // no support under vs2013 for member initialization for std::atomic
     _level = level::info;
+    _flush_level = level::off;
 }
 
 // ctor with sinks as init list
@@ -266,6 +267,11 @@ inline void spdlog::logger::set_level(spdlog::level::level_enum log_level)
     _level.store(log_level);
 }
 
+inline void spdlog::logger::flush_on(level::level_enum log_level)
+{
+    _flush_level.store(log_level);
+}
+
 inline spdlog::level::level_enum spdlog::logger::level() const
 {
     return static_cast<spdlog::level::level_enum>(_level.load(std::memory_order_relaxed));

include/spdlog/logger.h

@@ -41,6 +41,9 @@ public:
     const std::string& name() const;
     bool should_log(level::level_enum) const;
 
+    // automatically call flush() after a message of level log_level or higher is emitted
+    void flush_on(level::level_enum log_level);
+
     // logger.info(cppformat_string, arg1, arg2, arg3, ...) call style
     template <typename... Args> details::line_logger trace(const char* fmt, const Args&... args);
     template <typename... Args> details::line_logger debug(const char* fmt, const Args&... args);
@@ -104,6 +107,7 @@ protected:
     std::vector<sink_ptr> _sinks;
     formatter_ptr _formatter;
     spdlog::level_t _level;
+    spdlog::level_t _flush_level;
 };
 }