C++ Logo


Advanced search

Re: Unsynchronized placement-new

From: Edward Catmur <ecatmur_at_[hidden]>
Date: Tue, 20 Dec 2022 09:49:40 +0100
On Tue, 20 Dec 2022 at 06:43, Jason McKesson via Std-Discussion <
std-discussion_at_[hidden]> wrote:

> [new.delete.dataraces] states that calling "the library versions of
> operator new" is not a data race. It then goes on to talk about memory
> allocation and deallocation.
> But placement-new doesn't do allocation. And I cannot imagine how
> performing placement-new from different threads on the same storage
> isn't a data race.
> Now, if the new expression that invokes placement-new involves
> initialization, then yes, that does cause a data race with other
> initializing placement-new operations on that storage. This is because
> of the initialization operations conflicting by accessing the same
> memory.
> And while we're here, `start_lifetime_as` doesn't seem to have any
> language about data races. So like... what does that mean?

I think we're covered by [basic.life]/11. Placement new or
std::start_lifetime_as ends the life of the other object by storage reuse,
so if two threads use the same storage for objects potentially
concurrently, that's a data race.

> --
> Std-Discussion mailing list
> Std-Discussion_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-discussion

Received on 2022-12-20 08:49:52