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use crate::io::driver::{Direction, Handle, Interest, ReadyEvent, ScheduledIo};
use crate::util::slab;
use mio::event::Source;
use std::io;
use std::task::{Context, Poll};
cfg_io_driver! {
/// Associates an I/O resource with the reactor instance that drives it.
///
/// A registration represents an I/O resource registered with a Reactor such
/// that it will receive task notifications on readiness. This is the lowest
/// level API for integrating with a reactor.
///
/// The association between an I/O resource is made by calling [`new`]. Once
/// the association is established, it remains established until the
/// registration instance is dropped.
///
/// A registration instance represents two separate readiness streams. One
/// for the read readiness and one for write readiness. These streams are
/// independent and can be consumed from separate tasks.
///
/// **Note**: while `Registration` is `Sync`, the caller must ensure that
/// there are at most two tasks that use a registration instance
/// concurrently. One task for [`poll_read_ready`] and one task for
/// [`poll_write_ready`]. While violating this requirement is "safe" from a
/// Rust memory safety point of view, it will result in unexpected behavior
/// in the form of lost notifications and tasks hanging.
///
/// ## Platform-specific events
///
/// `Registration` also allows receiving platform-specific `mio::Ready`
/// events. These events are included as part of the read readiness event
/// stream. The write readiness event stream is only for `Ready::writable()`
/// events.
///
/// [`new`]: method@Self::new
/// [`poll_read_ready`]: method@Self::poll_read_ready`
/// [`poll_write_ready`]: method@Self::poll_write_ready`
#[derive(Debug)]
pub(crate) struct Registration {
/// Handle to the associated driver.
handle: Handle,
/// Reference to state stored by the driver.
shared: slab::Ref<ScheduledIo>,
}
}
unsafe impl Send for Registration {}
unsafe impl Sync for Registration {}
// ===== impl Registration =====
impl Registration {
/// Registers the I/O resource with the default reactor, for a specific
/// `Interest`. `new_with_interest` should be used over `new` when you need
/// control over the readiness state, such as when a file descriptor only
/// allows reads. This does not add `hup` or `error` so if you are
/// interested in those states, you will need to add them to the readiness
/// state passed to this function.
///
/// # Return
///
/// - `Ok` if the registration happened successfully
/// - `Err` if an error was encountered during registration
pub(crate) fn new_with_interest_and_handle(
io: &mut impl Source,
interest: Interest,
handle: Handle,
) -> io::Result<Registration> {
let shared = if let Some(inner) = handle.inner() {
inner.add_source(io, interest)?
} else {
return Err(io::Error::new(
io::ErrorKind::Other,
"failed to find event loop",
));
};
Ok(Registration { handle, shared })
}
/// Deregisters the I/O resource from the reactor it is associated with.
///
/// This function must be called before the I/O resource associated with the
/// registration is dropped.
///
/// Note that deregistering does not guarantee that the I/O resource can be
/// registered with a different reactor. Some I/O resource types can only be
/// associated with a single reactor instance for their lifetime.
///
/// # Return
///
/// If the deregistration was successful, `Ok` is returned. Any calls to
/// `Reactor::turn` that happen after a successful call to `deregister` will
/// no longer result in notifications getting sent for this registration.
///
/// `Err` is returned if an error is encountered.
pub(crate) fn deregister(&mut self, io: &mut impl Source) -> io::Result<()> {
let inner = match self.handle.inner() {
Some(inner) => inner,
None => return Err(io::Error::new(io::ErrorKind::Other, "reactor gone")),
};
inner.deregister_source(io)
}
pub(crate) fn clear_readiness(&self, event: ReadyEvent) {
self.shared.clear_readiness(event);
}
// Uses the poll path, requiring the caller to ensure mutual exclusion for
// correctness. Only the last task to call this function is notified.
pub(crate) fn poll_read_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<ReadyEvent>> {
self.poll_ready(cx, Direction::Read)
}
// Uses the poll path, requiring the caller to ensure mutual exclusion for
// correctness. Only the last task to call this function is notified.
pub(crate) fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<ReadyEvent>> {
self.poll_ready(cx, Direction::Write)
}
// Uses the poll path, requiring the caller to ensure mutual exclusion for
// correctness. Only the last task to call this function is notified.
pub(crate) fn poll_read_io<R>(
&self,
cx: &mut Context<'_>,
f: impl FnMut() -> io::Result<R>,
) -> Poll<io::Result<R>> {
self.poll_io(cx, Direction::Read, f)
}
// Uses the poll path, requiring the caller to ensure mutual exclusion for
// correctness. Only the last task to call this function is notified.
pub(crate) fn poll_write_io<R>(
&self,
cx: &mut Context<'_>,
f: impl FnMut() -> io::Result<R>,
) -> Poll<io::Result<R>> {
self.poll_io(cx, Direction::Write, f)
}
/// Polls for events on the I/O resource's `direction` readiness stream.
///
/// If called with a task context, notify the task when a new event is
/// received.
fn poll_ready(
&self,
cx: &mut Context<'_>,
direction: Direction,
) -> Poll<io::Result<ReadyEvent>> {
// Keep track of task budget
let coop = ready!(crate::coop::poll_proceed(cx));
let ev = ready!(self.shared.poll_readiness(cx, direction));
if self.handle.inner().is_none() {
return Poll::Ready(Err(gone()));
}
coop.made_progress();
Poll::Ready(Ok(ev))
}
fn poll_io<R>(
&self,
cx: &mut Context<'_>,
direction: Direction,
mut f: impl FnMut() -> io::Result<R>,
) -> Poll<io::Result<R>> {
loop {
let ev = ready!(self.poll_ready(cx, direction))?;
match f() {
Ok(ret) => {
return Poll::Ready(Ok(ret));
}
Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
self.clear_readiness(ev);
}
Err(e) => return Poll::Ready(Err(e)),
}
}
}
pub(crate) fn try_io<R>(
&self,
interest: Interest,
f: impl FnOnce() -> io::Result<R>,
) -> io::Result<R> {
let ev = self.shared.ready_event(interest);
// Don't attempt the operation if the resource is not ready.
if ev.ready.is_empty() {
return Err(io::ErrorKind::WouldBlock.into());
}
match f() {
Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
self.clear_readiness(ev);
Err(io::ErrorKind::WouldBlock.into())
}
res => res,
}
}
}
impl Drop for Registration {
fn drop(&mut self) {
// It is possible for a cycle to be created between wakers stored in
// `ScheduledIo` instances and `Arc<driver::Inner>`. To break this
// cycle, wakers are cleared. This is an imperfect solution as it is
// possible to store a `Registration` in a waker. In this case, the
// cycle would remain.
//
// See tokio-rs/tokio#3481 for more details.
self.shared.clear_wakers();
}
}
fn gone() -> io::Error {
io::Error::new(io::ErrorKind::Other, "IO driver has terminated")
}
cfg_io_readiness! {
impl Registration {
pub(crate) async fn readiness(&self, interest: Interest) -> io::Result<ReadyEvent> {
use std::future::Future;
use std::pin::Pin;
let fut = self.shared.readiness(interest);
pin!(fut);
crate::future::poll_fn(|cx| {
if self.handle.inner().is_none() {
return Poll::Ready(Err(io::Error::new(io::ErrorKind::Other, "reactor gone")));
}
Pin::new(&mut fut).poll(cx).map(Ok)
}).await
}
pub(crate) async fn async_io<R>(&self, interest: Interest, mut f: impl FnMut() -> io::Result<R>) -> io::Result<R> {
loop {
let event = self.readiness(interest).await?;
match f() {
Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
self.clear_readiness(event);
}
x => return x,
}
}
}
}
}