Proposal: Slow dynamic TLS for internal glibc use

[Joseph Myers]

On Tue, 23 Oct 2018, Florian Weimer wrote:

> I'm working to get clarification for C2X that this is a valid
> implementation for the functions where C11 wasn't updated accordingly
> when objects of thread storage duration were introduced.

I'd suggest that for C2X it might be appropriate to require these 
functions to use thread-local storage for their state (and likewise for 
the next major revision of POSIX, for POSIX functions), rather than 
leaving the possibility of them being unsafe with threads.

Note that for some of them (e.g. strerror, localtime), using TLS is 
unambiguously OK; it's only those storing an internal state to be used by 
subsequent calls, as opposed to storing output data in some internal 
location to which a pointer is returned, for which there is some ambiguity 
about whether using them with threads and separate synchronization between 
calls in different threads is meant to share state between the threads.

-- 
Joseph S. Myers
joseph@codesourcery.com