maria-developers team mailing list archive

[Sergey Petrunia <sergey@xxxxxxxxxxx>]

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