[GitHub] [logging-log4cxx] swebb2066 commented on a diff in pull request #148: Reduce std::ostream logging overhead

[GitBox <gi...@apache.org>]

swebb2066 commented on code in PR #148:
URL: https://github.com/apache/logging-log4cxx/pull/148#discussion_r1015945163


##########
src/main/cpp/messagebuffer.cpp:
##########
@@ -149,10 +118,14 @@ CharMessageBuffer& CharMessageBuffer::operator<<(const char msg)
 
 CharMessageBuffer::operator std::basic_ostream<char>& ()
 {
-	if (m_priv->stream == 0)
+	if (!m_priv->stream)
 	{
+#if LOG4CXX_HAS_THREAD_LOCAL
+		thread_local static std::basic_ostringstream<char> sStream;
+		m_priv->stream = &sStream;
+#else
 		m_priv->stream = new std::basic_ostringstream<char>();
-
+#endif

Review Comment:
   > would it make sense to simply make `m_priv->stream` a `thread_local `variable instead of holding a pointer
   
   The `m_priv->stream` must be zero when logging only `std::string` or `char* ` to implement the static string logging optimization.
   
   > looks like if two threads are logging at the same time they could both get the same ostringstream
   
   The `thread_local ` implementation should ensure the sSteam obtained by each thread will be different, and the `m_priv->stream` pointer life-time is the `MessageBuffer` lifetime. The only way two threads could share the same `ostringstream` is if the user provides a `MessageBuffer` object reference to the other thread. `MessageBuffer` is not intended to be used outside LOG4CXX_* macros.
   



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