[libcxx-dev] __libcpp_thread_id_equal issue (affecting FreeBSD)

[Marshall Clow via libcxx-dev]

On Wed, Jul 31, 2019 at 8:54 AM Ed Maste via libcxx-dev <
libcxx-dev at lists.llvm.org> wrote:

> We just had a FreeBSD bug submitted for a failure arising from
> libc++'s use of pthread_equal.
>
> FreeBSD's pthread_equal stub implementation (used in non-threaded
> programs) returns true unconditionally, since a non-threaded program
> cannot have two different threads. However, std::thread::id defines a
> special value that should not equal any real thread, and this is may
> be passed to pthread_equal. See FreeBSD PR 239550 for more details,
> and PR 239038 for the user-facing issue that prompted this.
>
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=239550
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=239038
>
> Now the most expedient fix is probably for us to make pthread_equal
> somewhat less of a stub, but for correctness it seems
> __libcpp_thread_id_equal would need to check for libc++'s special
> value before calling pthread_equal.
>

Written up as bug https://bugs.llvm.org/show_bug.cgi?id=42918

-- Marshall
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