[PATCH 1/5] std::latch: reduce internal implementation from ptrdiff_t to int

[Thomas Rodgers]

On 2021-02-28 13:31, Hans-Peter Nilsson wrote:

>> On Fri, 26 Feb 2021, Thiago Macieira via Gcc-patches wrote:
>> 
>> On Friday, 26 February 2021 11:31:00 PST Andreas Schwab wrote: On Feb 
>> 26 2021, Thiago Macieira wrote: On Friday, 26 February 2021 10:14:42 
>> PST Andreas Schwab wrote: On Feb 26 2021, Thiago Macieira via 
>> Gcc-patches wrote: -    alignas(__alignof__(ptrdiff_t)) ptrdiff_t 
>> _M_a;
>> +    alignas(__alignof__(int)) int _M_a;
>> Futexes must be aligned to 4 bytes.
>> 
>> Agreed, but doesn't this accomplish that?
> No.  It uses whatever alignment the type already has, and is an
> elaborate no-op.
> I thought so too when I read the original line. But I expected it was 
> written
> like that for a reason, especially since the same pattern appears in 
> other
> places.

> I can change to "alignas(4)" (which is a GCC extension, I believe). Is 
> that
> the correct solution?
> IMNSHO make use of the corresponding atomic type.  Then there'd
> be no need for separate what's-the-right-align-curse games.

There is no predicate wait on atomic<T>.

> brgds, H-P