RUSTSEC-2021-0124

If a `tokio::sync::oneshot` channel is closed (via the [`oneshot::Receiver::close`] method), a data race may occur if the `oneshot::Sender::send` method is called while the corresponding `oneshot::Receiver` is `await`ed or calling `try_recv`.

When these methods are called concurrently on a closed channel, the two halves of the channel can concurrently access a shared memory location, resulting in a data race. This has been observed to [cause memory corruption][corruption].

Note that the race only occurs when **both** halves of the channel are used after the `Receiver` half has called `close`. Code where `close` is not used, or where the `Receiver` is not `await`ed and `try_recv` is not called after calling `close`, is not affected.

See [tokio#4225][issue] for more details.

[corruption]: https://github.com/tokio-rs/tokio/issues/4225#issuecomment-967434847 [issue]: https://github.com/tokio-rs/tokio/issues/4225 [`oneshot::Receiver::close`]: https://docs.rs/tokio/1.14.0/tokio/sync/oneshot/struct.Receiver.html#method.close