Re: [PATCH 2/3]: C++20 P0482R6 and C2X N2653: Implement mbrtoc8, c8rtomb, char8_t

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella via Libc-alpha:

> On 17/05/2022 15:12, Joseph Myers wrote:
>> On Tue, 17 May 2022, Adhemerval Zanella wrote:
>> 
>>>> +/* This is the private state used if PS is NULL.  */
>>>> +static mbstate_t state;
>>>
>>> Although it was done for other convertion interfaces, I wonder if we should
>>> keep supporting this mt-unsafe usage for newer ones.  It was not clear from 
>> 
>> In C23 it's implementation-defined whether the internal state for such 
>> functions has static or thread storage duration (see the general 
>> introduction to the uchar.h functions).
>> 
>
> Right, so glibc still need to support either mode.

No, I think we can and should switch.  Maybe with new symbol versions
(but the same implementation) if we want to play it conservative.

The intent in POSIX and C has been for a long time that thread-local
state is permitted for these functions, only the wording did not
technically allow it.  The phrase was “not required to avoid data
races”.  The problem is that it's possible to tell the difference
without data races (with external synchronization).  Many libcs already
use thread-local state for these functions, without any apparent ill
effects.

Thanks,
Florian