don't recalculate timestamp for each log message

Log.cpp

@@ -1,5 +1,5 @@
-#include "Log.h"
 #include <boost/date_time/posix_time/posix_time.hpp>
+#include "Log.h"
 
 Log * g_Log = nullptr;
 
@@ -13,11 +13,26 @@ static const char * g_LogLevelStr[eNumLogLevels] =
 
 void LogMsg::Process()
 {
-	output << boost::posix_time::second_clock::local_time().time_of_day () <<  
-		"/" << g_LogLevelStr[level] << " - ";
+	auto& output = (log && log->GetLogStream ()) ? *log->GetLogStream () : std::cout;	
+	if (log)	
+		output << log->GetTimestamp ();
+	else
+		output << boost::posix_time::second_clock::local_time().time_of_day ();
+	output << "/" << g_LogLevelStr[level] << " - ";
 	output << s.str();
 }
 
+const std::string& Log::GetTimestamp ()
+{
+	auto ts = std::chrono::steady_clock::now ();	
+	if (ts > m_LastTimestampUpdate + std::chrono::milliseconds (500)) // 0.5 second
+	{
+		m_LastTimestampUpdate = ts;
+		m_Timestamp = boost::posix_time::to_simple_string (boost::posix_time::second_clock::local_time().time_of_day ());
+	}		
+	return m_Timestamp;
+}
+
 void Log::Flush ()
 {
 	if (m_LogStream)

Log.h

@@ -6,6 +6,7 @@
 #include <sstream>
 #include <fstream>
 #include <functional>
+#include <chrono>
 #include "Queue.h"
 
 enum LogLevel
@@ -17,13 +18,14 @@ enum LogLevel
 	eNumLogLevels
 };
 
+class Log;
 struct LogMsg
 {
 	std::stringstream s;
-	std::ostream& output;	
+	Log * log;	
 	LogLevel level;
 
-	LogMsg (std::ostream& o = std::cout, LogLevel l = eLogInfo): output (o), level (l) {};
+	LogMsg (Log * l = nullptr, LogLevel lv = eLogInfo): log (l), level (lv) {};
 	
 	void Process();
 };
@@ -38,6 +40,7 @@ class Log: public i2p::util::MsgQueue<LogMsg>
 		void SetLogFile (const std::string& fullFilePath);
 		void SetLogStream (std::ostream * logStream);
 		std::ostream * GetLogStream () const { return m_LogStream; };	
+		const std::string& GetTimestamp ();
 
 	private:
 
@@ -46,6 +49,8 @@ class Log: public i2p::util::MsgQueue<LogMsg>
 	private:
 		
 		std::ostream * m_LogStream;
+		std::string m_Timestamp;
+		std::chrono::steady_clock::time_point m_LastTimestampUpdate;		
 };
 
 extern Log * g_Log;
@@ -95,8 +100,7 @@ void LogPrint (std::stringstream& s, TValue arg, TArgs... args)
 template<typename... TArgs>
 void LogPrint (LogLevel level, TArgs... args) 
 {
-	LogMsg * msg = (g_Log && g_Log->GetLogStream ()) ? new LogMsg (*g_Log->GetLogStream (), level) : 
-		new LogMsg (std::cout, level);
+	LogMsg * msg = new LogMsg (g_Log, level);
 	LogPrint (msg->s, args...);
 	msg->s << std::endl;
 	if (g_Log)