ACP: JoinHandle extensions for ScopedJoinHandle

[Rosdf]

Proposal

Problem statement

JoinHandleExt, AsRawHandle and IntoRawHandle are not implemented for ScopedJoinHandle.

Motivating examples or use cases

In my use case i need to set affinity for scoped thread.

Solution sketch

impl<T> JoinHandleExt for ScopedJoinHandle<'_, T> {
    fn as_pthread_t(&self) -> RawPthread {
        self.as_inner().id() as RawPthread
    }

    fn into_pthread_t(self) -> RawPthread {
        self.into_inner().into_id() as RawPthread
    }
}

impl<T> AsRawHandle for thread::ScopedJoinHandle<'_, T> {
    #[inline]
    fn as_raw_handle(&self) -> RawHandle {
        self.as_inner().handle().as_raw_handle() as *mut _
    }
}

impl<T> IntoRawHandle for thread::ScopedJoinHandle<'_, T> {
    #[inline]
    fn into_raw_handle(self) -> RawHandle {
        self.into_inner().into_handle().into_raw_handle() as *mut _
    }
}

Alternatives

I do not see any good alternative, looks like this feature was forgotten, when scoped threads were implemented.

Links and related work

rust-lang/rust#29791
rust-lang/rust#93203

What happens now?

This issue contains an API change proposal (or ACP) and is part of the libs-api team feature lifecycle. Once this issue is filed, the libs-api team will review open proposals as capability becomes available. Current response times do not have a clear estimate, but may be up to several months.

Possible responses

The libs team may respond in various different ways. First, the team will consider the problem (this doesn't require any concrete solution or alternatives to have been proposed):

• We think this problem seems worth solving, and the standard library might be the right place to solve it.
• We think that this probably doesn't belong in the standard library.

Second, if there's a concrete solution:

• We think this specific solution looks roughly right, approved, you or someone else should implement this. (Further review will still happen on the subsequent implementation PR.)
• We're not sure this is the right solution, and the alternatives or other materials don't give us enough information to be sure about that. Here are some questions we have that aren't answered, or rough ideas about alternatives we'd want to see discussed.

[Amanieu]

We discussed this in the libs-api team and are happy to accept this with some small changes. ScopedJoinHandle should also implement AsHandle and From<JoinHandle<T>> just like JoinHandle.