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// Copyright 2020 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
use std::convert::TryFrom;
use std::fmt::{self, Display};
use std::future::Future;
use std::os::unix::io::AsRawFd;
use std::pin::Pin;
use std::task::{Context, Poll};
use libc::{EWOULDBLOCK, O_NONBLOCK};
use cros_async::fd_executor::{self, add_read_waker, cancel_waker, WakerToken};
use sys_util::{self, add_fd_flags};
/// Errors generated while polling for events.
#[derive(Debug)]
pub enum Error {
/// An error occurred attempting to register a waker with the executor.
AddingWaker(fd_executor::Error),
/// Failure creating the event FD.
EventFdCreate(sys_util::Error),
/// An error occurred when reading the event FD.
EventFdRead(sys_util::Error),
/// An error occurred when setting the event FD non-blocking.
SettingNonBlocking(sys_util::Error),
}
pub type Result<T> = std::result::Result<T, Error>;
impl std::error::Error for Error {}
impl Display for Error {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
use self::Error::*;
match self {
AddingWaker(e) => write!(
f,
"An error occurred attempting to register a waker with the executor: {}.",
e
),
EventFdCreate(e) => write!(f, "An error occurred when creating the event FD: {}.", e),
EventFdRead(e) => write!(f, "An error occurred when reading the event FD: {}.", e),
SettingNonBlocking(e) => {
write!(f, "An error occurred setting the FD non-blocking: {}.", e)
}
}
}
}
/// Asynchronous version of `sys_util::EventFd`. Provides asynchronous values that complete when the
/// next event can be read from the eventfd.
///
/// # Example
///
/// ```
/// use std::convert::TryInto;
///
/// use async_core::{EventFd};
/// use sys_util::{self};
///
/// async fn process_events() -> std::result::Result<(), Box<dyn std::error::Error>> {
/// let mut async_events: EventFd = sys_util::EventFd::new()?.try_into()?;
/// while let Ok(e) = async_events.read_next().await {
/// // Handle event here.
/// }
/// Ok(())
/// }
/// ```
pub struct EventFd {
inner: sys_util::EventFd,
}
impl EventFd {
pub fn new() -> Result<EventFd> {
Self::try_from(sys_util::EventFd::new().map_err(Error::EventFdCreate)?)
}
/// Asynchronously read the next value from the eventfd.
/// Returns a Future that can be `awaited` for the next value.
///
/// # Example
///
/// ```
/// use async_core::EventFd;
/// async fn print_events(mut event_fd: EventFd) {
/// loop {
/// match event_fd.read_next().await {
/// Ok(e) => println!("Got event: {}", e),
/// Err(e) => break,
/// }
/// }
/// }
/// ```
pub fn read_next(&mut self) -> NextValFuture {
NextValFuture::new(self)
}
}
impl TryFrom<sys_util::EventFd> for EventFd {
type Error = crate::eventfd::Error;
fn try_from(eventfd: sys_util::EventFd) -> Result<EventFd> {
let fd = eventfd.as_raw_fd();
add_fd_flags(fd, O_NONBLOCK).map_err(Error::SettingNonBlocking)?;
Ok(EventFd { inner: eventfd })
}
}
/// A Future that yields the next value from the eventfd when it is ready.
pub struct NextValFuture<'a> {
eventfd: &'a mut EventFd,
waker_token: Option<WakerToken>,
}
impl<'a> NextValFuture<'a> {
fn new(eventfd: &'a mut EventFd) -> NextValFuture<'a> {
NextValFuture {
eventfd,
waker_token: None,
}
}
}
impl<'a> Future for NextValFuture<'a> {
type Output = Result<u64>;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
if let Some(token) = self.waker_token.take() {
let _ = cancel_waker(token);
}
match self.eventfd.inner.read() {
Ok(v) => Poll::Ready(Ok(v)),
Err(e) => {
if e.errno() == EWOULDBLOCK {
match add_read_waker(self.eventfd.inner.as_raw_fd(), cx.waker().clone()) {
Ok(token) => {
self.waker_token = Some(token);
Poll::Pending
}
Err(e) => Poll::Ready(Err(Error::AddingWaker(e))),
}
} else {
Poll::Ready(Err(Error::EventFdRead(e)))
}
}
}
}
}
impl<'a> Drop for NextValFuture<'a> {
fn drop(&mut self) {
if let Some(token) = self.waker_token.take() {
let _ = cancel_waker(token);
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use cros_async::{select2, SelectResult};
use futures::future::pending;
use futures::pin_mut;
#[test]
fn eventfd_write_read() {
let evt = EventFd::new().unwrap();
async fn read_one(mut evt: EventFd) -> u64 {
if let Ok(e) = evt.read_next().await {
e
} else {
66
}
}
async fn write_pend(evt: sys_util::EventFd) {
evt.write(55).unwrap();
let () = pending().await;
}
let write_evt = evt.inner.try_clone().unwrap();
let r = read_one(evt);
pin_mut!(r);
let w = write_pend(write_evt);
pin_mut!(w);
if let Ok((SelectResult::Finished(read_res), SelectResult::Pending(_pend_fut))) =
select2(r, w)
{
assert_eq!(read_res, 55);
} else {
panic!("wrong futures returned from select2");
}
}
}
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