[Development] Why can't QString use UTF-8 internally?

Matthew Woehlke mw_triad at users.sourceforge.net
Wed Feb 11 01:10:29 CET 2015

On 2015-02-10 18:40, Marc Mutz wrote:
> On Tuesday 10 February 2015 22:26:50 Thiago Macieira wrote:
>> It's not insurmountable. I can think of two solutions:
>>  1) pre-allocate enough space for the UTF-16 data (strlen(utf8) * 2), so
>> that  the const functions can implicitly write to the UTF-16 block when
>> needed. Since the original UTF-8 data is constant and if there are no
>> out-of-thin-air values, multiple threads could do this operation
>> simultaneously safely.
> No, they can't. The writes conflict and neither happens-before the other -> 
> data race -> UB.

If I spin up a bunch of threads that do a memcpy into a common output
buffer from a common input buffer, where the latter (input) is immutable
(at least until all threads are done executing), do you mean that the
contents of the output buffer after any memcpy completes are
unpredictable? ...because that would surprise me. (Assume that all
writes that occur in the memcpy are atomic.)


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