Note the practical affects of this change:
- Dependency count with --features full dropped from 65 to 55.
- Time to compile after a clean dropped from 48s to 35s (on a pretty underpowered VM).
Closes#2388
The current implementation of `drain` uses a `tokio::sync::watch`
channel to send the shutdown signal, and a `tokio::sync::mpsc` to signal
when all draining tasks have completed. No data is ever actually sent on
the MPSC; instead, it is simply used to notify the task that signalled
the drain when all draining tasks have been dropped.
Tokio 0.3's `watch::Sender` has a `closed` method that can be used to
await the dropping of all receivers. This can be used instead of the
MPSC channel. This commit updates `drain` to use `watch::Sender::closed`
instead. This has fewer moving parts, and may have slightly less
overhead (as it doesn't require additional allocation forthe MPSC which
is never actually used).
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
Until this commit, servers have required that `Service` and their
`Future` to be `Send`, since the server needs to spawn some internal
tasks to an executor, and by default, that is `tokio::spawn`, which
could be spawning to a threadpool. This was true even if the user were
certain there was no threadpool involved, and was instead using a
different single-threaded runtime, like
`tokio::runtime::current_thread`.
This changes makes all the server pieces generic over an `E`, which is
essentially `Executor<PrivateTypes<Server::Future>>`. There's a new set
of internal traits, `H2Exec` and `NewSvcExec`, which allow for the type
signature to only show the generics that the user is providing. The
traits cannot be implemented explicitly, but there are blanket
implementations for `E: Executor<SpecificType>`. If the user provides
their own executor, it simply needs to have a generic `impl<F>
Executor<F> for MyExec`. That impl can have bounds deciding whether to
require `F: Send`. If the executor does require `Send`, and the
`Service` futures are `!Send`, there will be compiler errors.
To prevent a breaking change, all the types that gained the `E` generic
have a default type set, which is the original `tokio::spawn` executor.
This adds a "combinator" method to `Server`, which accepts a user's
future to "select" on. All connections received by the `Server` will
be tracked, and if the user's future finishes, graceful shutdown will
begin.
- The listener will be closed immediately.
- The currently active connections will all be notified to start a
graceful shutdown. For HTTP/1, that means finishing the existing
response and using `connection: clone`. For HTTP/2, the graceful
`GOAWAY` process is started.
- Once all active connections have terminated, the graceful future
will return.
Closes#1575
