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Fix Send and Sync implementations on Id and WeakId #8

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Fix Send and Sync implementations on Id and WeakId #8

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0d5eac6
Correct Send and Sync implementations on Id
madsmtm Jun 15, 2021
8833c22
Correct Send and Sync implementations on WeakId
madsmtm Jun 15, 2021
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31 changes: 26 additions & 5 deletions src/id.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -80,11 +80,30 @@ impl<T> Clone for Id<T, Shared> where T: Message {
}
}

unsafe impl<T, O> Sync for Id<T, O> where T: Sync { }
/// The `Send` implementation requires `T: Sync` because `Id<T, Shared>` give
/// access to `&T`.
///
/// Additiontally, it requires `T: Send` because if `T: !Send`, you could
/// clone a `Id<T, Shared>`, send it to another thread, and drop the clone
/// last, making `dealloc` get called on the other thread, and violate
/// `T: !Send`.
unsafe impl<T: Sync + Send> Send for Id<T, Shared> {}

/// The `Sync` implementation requires `T: Sync` because `&Id<T, Shared>` give
/// access to `&T`.
///
/// Additiontally, it requires `T: Send`, because if `T: !Send`, you could
/// clone a `&Id<T, Shared>` from another thread, and drop the clone last,
/// making `dealloc` get called on the other thread, and violate `T: !Send`.
unsafe impl<T: Sync + Send> Sync for Id<T, Shared> {}

unsafe impl<T> Send for Id<T, Owned> where T: Send { }
/// `Id<T, Owned>` are `Send` if `T` is `Send` because they give the same
/// access as having a T directly.
unsafe impl<T: Send> Send for Id<T, Owned> {}

unsafe impl<T> Send for Id<T, Shared> where T: Sync { }
/// `Id<T, Owned>` are `Sync` if `T` is `Sync` because they give the same
/// access as having a `T` directly.
unsafe impl<T: Sync> Sync for Id<T, Owned> {}

impl<T, O> Deref for Id<T, O> {
type Target = T;
Expand Down Expand Up @@ -161,9 +180,11 @@ impl<T> WeakId<T> where T: Message {
}
}

unsafe impl<T> Sync for WeakId<T> where T: Sync { }
/// This implementation follows the same reasoning as `Id<T, Shared>`.
unsafe impl<T: Sync + Send> Sync for WeakId<T> {}

unsafe impl<T> Send for WeakId<T> where T: Sync { }
/// This implementation follows the same reasoning as `Id<T, Shared>`.
unsafe impl<T: Sync + Send> Send for WeakId<T> {}

#[cfg(test)]
mod tests {
Expand Down