Currently when `RwLockWriteGuard::downgrade` the `MAX_READS - 1`
permits are added to the semaphore. When `RwLockWriteGuard::drop`
gets invoked however another `MAX_READS` permits are added. This
results in releasing more permits that were actually aquired when
downgrading a write to a read lock. This is why we need to call
`mem::forget` on the `RwLockWriteGuard` in order to avoid
invoking the destructor.
Fixes: #2941
* io: Add AsyncFd
This adds AsyncFd, a unix-only structure to allow for read/writability states
to be monitored for arbitrary file descriptors.
Issue: #2728
* driver: fix shutdown notification unreliability
Previously, there was a race window in which an IO driver shutting down could
fail to notify ScheduledIo instances of this state; in particular, notification
of outstanding ScheduledIo registrations was driven by `Driver::drop`, but
registrations bypass `Driver` and go directly to a `Weak<Inner>`. The `Driver`
holds the `Arc<Inner>` keeping `Inner` alive, but it's possible that a new
handle could be registered (or a new readiness future created for an existing
handle) after the `Driver::drop` handler runs and prior to `Inner` being
dropped.
This change fixes this in two parts: First, notification of outstanding
ScheduledIo handles is pushed down into the drop method of `Inner` instead,
and, second, we add state to ScheduledIo to ensure that we remember that the IO
driver we're bound to has shut down after the initial shutdown notification, so
that subsequent readiness future registrations can immediately return (instead
of potentially blocking indefinitely).
Fixes: #2924
The `Receiver` handle maintains a position in the broadcast channel for
itself. Cloning implies copying the state of the value. Intuitively,
cloning a `broadcast::Receiver` would return a new receiver with an
identical position. However, the current implementation returns a new
`Receiver` positioned at the tail of the channel.
This behavior subtlety is why `new_subscriber()` is used to create
`Receiver` handles. An alternate API should consider the position issue.
Refs: #2933
This allows writing
rt.spawn_blocking(f);
instead of
let _enter = rt.enter();
tokio::task::spawn_blocking(f);
Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
This combines the `dns` and `net` feature flags. Previously, `dns` was
included as part of `net`. Given that is is rare that one would want
`dns` without `net`, DNS is now entirely gated w/ `net`.
The `parking_lot` feature is included as part of `full`.
Some misc docs are tweaked to reflect feature flag changes.
Changes inherent methods to take `&self` instead of `&mut self`. This
brings the API in line with `std`.
This patch is implemented by using a `tokio::sync::Mutex` to guard the
internal `File` state. This is not an ideal implementation strategy
doesn't make a big impact compared to having to dispatch operations to a
background thread followed by a blocking syscall.
In the future, the implementation can be improved as we explore async
file-system APIs provided by the operating-system (iocp / io_uring).
Closes#2927
