Hi, I'm writing this in connection with MyRocks Storage Engine and https://github.com/facebook/mysql-5.6/issues/904 C++ 11 includes "thread_local" specifier : https://en.cppreference.com/w/cpp/keyword/thread_local GNU also has __thread, which was available before C++11. RocksDB (and so MyRocks) uses both __thread and thread_local. thread_local is part of the standard, so they might switch to thread_local. The question: will it cause any issues for us? In other words, do we have compilers/environments that - claim to support C++11 (so that we attempt to compile MyRocks) - but do not support "thread_local" ? For Windows, RocksDB does this in port/win/port_win.h: #ifndef __thread #define __thread __declspec(thread) #endif but this page page about Visual Studio 2015) https://msdn.microsoft.com/en-us/library/6yh4a9k1.aspx says that C++11: The thread_local storage class specifier is the recommended way to specify thread-local storage for objects and class members. I assume this means it's ok to use thread_local on Windows? RocksDB source code mentions one problematic case: // However, thread_local is not supported in all compilers that accept -std=c++11 // (e.g., eg Mac with XCode < 8. XCode 8+ supports thread_local). As far as I understand this is not relevant for us? Anyone aware of other such cases? BR Sergei -- Sergei Petrunia, Software Developer MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog