Eliza Weisman d456706528

util: implement JoinMap (#4640) ...

## Motivation

In many cases, it is desirable to spawn a set of tasks associated with
keys, with the ability to cancel them by key. As an example use case for
this sort of thing, see Tower's [`ReadyCache` type][1].

Now that PR #4530 adds a way of cancelling tasks in a
`tokio::task::JoinSet`, we can implement a map-like API based on the
same `IdleNotifiedSet` primitive.

## Solution

This PR adds an implementation of a `JoinMap` type to
`tokio_util::task`, using the `JoinSet` type from `tokio::task`, the
`AbortHandle` type added in #4530, and the new task IDs added in #4630.

Individual tasks can be aborted by key using the `JoinMap::abort`
method, and a set of tasks whose key match a given predicate can be
aborted using `JoinMap::abort_matching`.

When tasks complete, `JoinMap::join_one` returns their associated key
alongside the output from the spawned future, or the key and the
`JoinError` if the task did not complete successfully.

Overall, I think the way this works is pretty straightforward; much of
this PR is just API boilerplate to implement the union of applicable
APIs from `JoinSet` and `HashMap`. Unlike previous iterations on the
`JoinMap` API (e.g. #4538), this version is implemented entirely in
`tokio_util`, using only public APIs from the `tokio` crate. Currently,
the required `tokio` APIs are unstable, but implementing `JoinMap` in
`tokio-util` means we will never have to make stability commitments for
the `JoinMap` API itself.

[1]: https://github.com/tower-rs/tower/blob/master/tower/src/ready_cache/cache.rs

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

2022-04-26 17:25:48 +00:00

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audit.toml

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config

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