async_io/os/windows.rs
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//! Functionality that is only available on Windows.
use crate::reactor::{Reactor, Readable, Registration};
use crate::Async;
use std::future::Future;
use std::io::{self, Result};
use std::os::windows::io::{AsHandle, AsRawHandle, BorrowedHandle, OwnedHandle, RawHandle};
use std::pin::Pin;
use std::task::{Context, Poll};
/// A waitable handle registered in the reactor.
///
/// Some handles in Windows are “waitable”, which means that they emit a “readiness” signal after some event occurs. This function can be used to wait for such events to occur on a handle. This function can be used in addition to regular socket polling.
///
/// Waitable objects include the following:
///
/// - Console inputs
/// - Waitable events
/// - Mutexes
/// - Processes
/// - Semaphores
/// - Threads
/// - Timer
///
/// This structure can be used to wait for any of these objects to become ready.
///
/// ## Implementation
///
/// The current implementation waits on the handle by registering it in the application-global
/// Win32 threadpool. However, in the future it may be possible to migrate to an implementation
/// on Windows 10 that uses a mechanism similar to [`MsgWaitForMultipleObjectsEx`].
///
/// [`MsgWaitForMultipleObjectsEx`]: https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-msgwaitformultipleobjectsex
///
/// ## Caveats
///
/// Read the documentation for the [`Async`](crate::Async) type for more information regarding the
/// abilities and caveats with using this type.
#[derive(Debug)]
pub struct Waitable<T>(Async<T>);
impl<T> AsRef<T> for Waitable<T> {
fn as_ref(&self) -> &T {
self.0.as_ref()
}
}
impl<T: AsHandle> Waitable<T> {
/// Create a new [`Waitable`] around a waitable handle.
///
/// # Examples
///
/// ```no_run
/// use std::process::Command;
/// use async_io::os::windows::Waitable;
///
/// // Create a new process to wait for.
/// let mut child = Command::new("sleep").arg("5").spawn().unwrap();
///
/// // Wrap the process in an `Async` object that waits for it to exit.
/// let process = Waitable::new(child).unwrap();
///
/// // Wait for the process to exit.
/// # async_io::block_on(async {
/// process.ready().await.unwrap();
/// # });
/// ```
pub fn new(handle: T) -> Result<Self> {
Ok(Self(Async {
source: Reactor::get()
.insert_io(unsafe { Registration::new_waitable(handle.as_handle()) })?,
io: Some(handle),
}))
}
}
impl<T: AsRawHandle> AsRawHandle for Waitable<T> {
fn as_raw_handle(&self) -> RawHandle {
self.get_ref().as_raw_handle()
}
}
impl<T: AsHandle> AsHandle for Waitable<T> {
fn as_handle(&self) -> BorrowedHandle<'_> {
self.get_ref().as_handle()
}
}
impl<T: AsHandle + From<OwnedHandle>> TryFrom<OwnedHandle> for Waitable<T> {
type Error = io::Error;
fn try_from(handle: OwnedHandle) -> Result<Self> {
Self::new(handle.into())
}
}
impl<T: Into<OwnedHandle>> TryFrom<Waitable<T>> for OwnedHandle {
type Error = io::Error;
fn try_from(value: Waitable<T>) -> std::result::Result<Self, Self::Error> {
value.into_inner().map(|handle| handle.into())
}
}
impl<T> Waitable<T> {
/// Get a reference to the inner handle.
pub fn get_ref(&self) -> &T {
self.0.get_ref()
}
/// Get a mutable reference to the inner handle.
///
/// # Safety
///
/// The underlying I/O source must not be dropped or moved out using this function.
pub unsafe fn get_mut(&mut self) -> &mut T {
self.0.get_mut()
}
/// Consumes the [`Waitable`], returning the inner handle.
pub fn into_inner(self) -> Result<T> {
self.0.into_inner()
}
/// Waits until the [`Waitable`] object is ready.
///
/// This method completes when the underlying [`Waitable`] object has completed. See the documentation
/// for the [`Waitable`] object for more information.
///
/// # Examples
///
/// ```no_run
/// use std::process::Command;
/// use async_io::os::windows::Waitable;
///
/// # futures_lite::future::block_on(async {
/// let child = Command::new("sleep").arg("5").spawn()?;
/// let process = Waitable::new(child)?;
///
/// // Wait for the process to exit.
/// process.ready().await?;
/// # std::io::Result::Ok(()) });
/// ```
pub fn ready(&self) -> Ready<'_, T> {
Ready(self.0.readable())
}
/// Polls the I/O handle for readiness.
///
/// When this method returns [`Poll::Ready`], that means that the OS has delivered a notification
/// that the underlying [`Waitable`] object is ready. See the documentation for the [`Waitable`]
/// object for more information.
///
/// # Caveats
///
/// Two different tasks should not call this method concurrently. Otherwise, conflicting tasks
/// will just keep waking each other in turn, thus wasting CPU time.
///
/// # Examples
///
/// ```no_run
/// use std::process::Command;
/// use async_io::os::windows::Waitable;
/// use futures_lite::future;
///
/// # futures_lite::future::block_on(async {
/// let child = Command::new("sleep").arg("5").spawn()?;
/// let process = Waitable::new(child)?;
///
/// // Wait for the process to exit.
/// future::poll_fn(|cx| process.poll_ready(cx)).await?;
/// # std::io::Result::Ok(()) });
/// ```
pub fn poll_ready(&self, cx: &mut Context<'_>) -> Poll<Result<()>> {
self.0.poll_readable(cx)
}
}
/// Future for [`Filter::ready`].
#[must_use = "futures do nothing unless you `.await` or poll them"]
#[derive(Debug)]
pub struct Ready<'a, T>(Readable<'a, T>);
impl<T> Future for Ready<'_, T> {
type Output = Result<()>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
Pin::new(&mut self.0).poll(cx)
}
}