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github: stjepang

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name: Build and test
on:
push:
branches:
- master
pull_request:
jobs:
build_and_test:
runs-on: ${{ matrix.os }}
strategy:
fail-fast: false
matrix:
os: [ubuntu-latest]
rust: [nightly, beta, stable]
steps:
- uses: actions/checkout@v2
- name: Set current week of the year in environnement
if: startsWith(matrix.os, 'ubuntu') || startsWith(matrix.os, 'macOS')
run: echo "::set-env name=CURRENT_WEEK::$(date +%V)"
- name: Set current week of the year in environnement
if: startsWith(matrix.os, 'windows')
run: echo "::set-env name=CURRENT_WEEK::$(Get-Date -UFormat %V)"
- name: Install latest ${{ matrix.rust }}
uses: actions-rs/toolchain@v1
with:
toolchain: ${{ matrix.rust }}
profile: minimal
override: true
- name: Run cargo check
uses: actions-rs/cargo@v1
with:
command: check
args: --all --benches --bins --examples --tests --all-features
- name: Run cargo test
uses: actions-rs/cargo@v1
with:
command: test

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name: Lint
on:
push:
branches:
- master
pull_request:
jobs:
clippy:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v2
- name: Set current week of the year in environnement
run: echo "::set-env name=CURRENT_WEEK::$(date +%V)"
- uses: actions-rs/toolchain@v1
with:
toolchain: stable
profile: minimal
components: clippy
- uses: actions-rs/clippy-check@v1
with:
token: ${{ secrets.GITHUB_TOKEN }}
args: --all-features -- -W clippy::all

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name: Security audit
on:
push:
branches:
- master
pull_request:
jobs:
security_audit:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v2
- name: Set current week of the year in environnement
run: echo "::set-env name=CURRENT_WEEK::$(date +%V)"
- uses: actions-rs/audit-check@v1
with:
token: ${{ secrets.GITHUB_TOKEN }}

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/target

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# Version 0.3.2
- Make `Blocking` implement `Send` in more cases.
# Version 0.3.1
- Add `Blocking::with_mut()`.
# Version 0.3.0
- Remove `Blocking::spawn()`.
- Implement `Future` for `Blocking` only when the inner type is a `FnOnce`.
# Version 0.2.0
- Initial version
# Version 0.1.0
- Reserved crate name

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# This file is automatically @generated by Cargo.
# It is not intended for manual editing.
[[package]]
name = "event-listener"
version = "0.1.0"

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[package]
name = "event-listener"
version = "1.0.0"
authors = ["Stjepan Glavina <stjepang@gmail.com>"]
edition = "2018"
description = "Notify async tasks or threads"
license = "Apache-2.0 OR MIT"
repository = "https://github.com/stjepang/event-listener"
homepage = "https://github.com/stjepang/event-listener"
documentation = "https://docs.rs/event-listener"
keywords = ["condvar", "eventcount", "wake", "blocking", "park"]
categories = ["asynchronous", "concurrency"]
readme = "README.md"

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# event-listener
[![Build](https://github.com/stjepang/event-listener/workflows/Build%20and%20test/badge.svg)](
https://github.com/stjepang/event-listener/actions)
[![License](https://img.shields.io/badge/license-MIT%2FApache--2.0-blue.svg)](
https://github.com/stjepang/event-listener)
[![Cargo](https://img.shields.io/crates/v/event-listener.svg)](
https://crates.io/crates/event-listener)
[![Documentation](https://docs.rs/event-listener/badge.svg)](
https://docs.rs/event-listener)
Notify async tasks or threads.
This is a synchronization primitive similar to [eventcounts] invented by Dmitry Vyukov.
You can use this crate to turn non-blocking data structures into async or blocking data
structures. See a [simple mutex] implementation that exposes an async and a blocking interface
for acquiring locks.
[eventcounts]: http://www.1024cores.net/home/lock-free-algorithms/eventcounts
[simple mutex]: TODO
## Examples
Wait until another thread sets a boolean flag:
```rust
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::thread;
use std::time::Duration;
use event_listener::Event;
let flag = Arc::new(AtomicBool::new(false));
let event = Arc::new(Event::new());
// Spawn a thread that will set the flag after 1 second.
thread::spawn({
let flag = flag.clone();
let event = event.clone();
move || {
// Wait for a second.
thread::sleep(Duration::from_secs(1));
// Set the flag.
flag.store(true, Ordering::SeqCst);
// Notify all listeners that the flag has been set.
event.notify_all();
}
});
// Wait until the flag is set.
loop {
// Check the flag.
if flag.load(Ordering::SeqCst) {
break;
}
// Start listening for events.
let listener = event.listen();
// Check the flag again after creating the listener.
if flag.load(Ordering::SeqCst) {
break;
}
// Wait for a notification and continue the loop.
listener.wait();
}
```
## License
Licensed under either of
* Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
at your option.
#### Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
dual licensed as above, without any additional terms or conditions.

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//! A simple mutex implementation.
//!
//! This mutex exposes both blocking and async methods for acquiring a lock.
#![allow(dead_code)]
use std::cell::UnsafeCell;
use std::ops::{Deref, DerefMut};
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{mpsc, Arc};
use std::thread;
use std::time::{Duration, Instant};
use event_listener::Event;
/// A simple mutex.
struct Mutex<T> {
/// Set to `true` when the mutex is locked.
locked: AtomicBool,
/// Blocked lock operations.
lock_ops: Event,
/// The inner protected data.
data: UnsafeCell<T>,
}
unsafe impl<T: Send> Send for Mutex<T> {}
unsafe impl<T: Send> Sync for Mutex<T> {}
impl<T> Mutex<T> {
/// Creates a mutex.
fn new(t: T) -> Mutex<T> {
Mutex {
locked: AtomicBool::new(false),
lock_ops: Event::new(),
data: UnsafeCell::new(t),
}
}
/// Attempts to acquire a lock.
fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
if self.locked.swap(true, Ordering::Acquire) {
Some(MutexGuard(self))
} else {
None
}
}
/// Blocks until a lock is acquired.
fn lock(&self) -> MutexGuard<'_, T> {
let mut listener = None;
loop {
// Attempt grabbing a lock.
if let Some(guard) = self.try_lock() {
return guard;
}
// Set up an event listener or wait for a notification.
match listener.take() {
None => {
// Start listening and then try locking again.
listener = Some(self.lock_ops.listen());
}
Some(l) => {
// Wait until a notification is received.
l.wait();
}
}
}
}
/// Blocks until a lock is acquired or the timeout is reached.
fn lock_timeout(&self, timeout: Duration) -> Option<MutexGuard<'_, T>> {
let deadline = Instant::now() + timeout;
let mut listener = None;
loop {
// Attempt grabbing a lock.
if let Some(guard) = self.try_lock() {
return Some(guard);
}
// Set up an event listener or wait for an event.
match listener.take() {
None => {
// Start listening and then try locking again.
listener = Some(self.lock_ops.listen());
}
Some(l) => {
// Wait until a notification is received.
if !l.wait_deadline(deadline) {
return None;
}
}
}
}
}
/// Acquires a lock asynchronously.
async fn lock_async(&self) -> MutexGuard<'_, T> {
let mut listener = None;
loop {
// Attempt grabbing a lock.
if let Some(guard) = self.try_lock() {
return guard;
}
// Set up an event listener or wait for an event.
match listener.take() {
None => {
// Start listening and then try locking again.
listener = Some(self.lock_ops.listen());
}
Some(l) => {
// Wait until a notification is received.
l.await;
}
}
}
}
}
/// A guard holding a lock.
struct MutexGuard<'a, T>(&'a Mutex<T>);
unsafe impl<T: Send> Send for MutexGuard<'_, T> {}
unsafe impl<T: Sync> Sync for MutexGuard<'_, T> {}
impl<T> Deref for MutexGuard<'_, T> {
type Target = T;
fn deref(&self) -> &T {
unsafe { &*self.0.data.get() }
}
}
impl<T> DerefMut for MutexGuard<'_, T> {
fn deref_mut(&mut self) -> &mut T {
unsafe { &mut *self.0.data.get() }
}
}
fn main() {
const N: usize = 10;
// A shared counter.
let counter = Arc::new(Mutex::new(0));
// A channel that signals when all threads are done.
let (tx, rx) = mpsc::channel();
// Spawn a bunch of threads incrementing the counter.
for _ in 0..N {
let counter = counter.clone();
let tx = tx.clone();
thread::spawn(move || {
let mut counter = counter.lock();
*counter += 1;
// If this is the last increment, signal that we're done.
if *counter == N {
tx.send(()).unwrap();
}
});
}
// Wait until the last thread increments the counter.
rx.recv().unwrap();
// The counter must equal the number of threads.
assert_eq!(*counter.lock(), N);
println!("Done!");
}

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//! Notify async tasks or threads.
//!
//! This is a synchronization primitive similar to [eventcounts] invented by Dmitry Vyukov.
//!
//! You can use this crate to turn non-blocking data structures into async or blocking data
//! structures. See a [simple mutex] implementation that exposes an async and a blocking interface
//! for acquiring locks.
//!
//! [eventcounts]: http://www.1024cores.net/home/lock-free-algorithms/eventcounts
//! [simple mutex]: TODO
//!
//! # Examples
//!
//! Wait until another thread sets a boolean flag:
//!
//! ```
//! use std::sync::atomic::{AtomicBool, Ordering};
//! use std::sync::Arc;
//! use std::thread;
//! use std::time::Duration;
//! use event_listener::Event;
//!
//! let flag = Arc::new(AtomicBool::new(false));
//! let event = Arc::new(Event::new());
//!
//! // Spawn a thread that will set the flag after 1 second.
//! thread::spawn({
//! let flag = flag.clone();
//! let event = event.clone();
//! move || {
//! // Wait for a second.
//! thread::sleep(Duration::from_secs(1));
//!
//! // Set the flag.
//! flag.store(true, Ordering::SeqCst);
//!
//! // Notify all listeners that the flag has been set.
//! event.notify_all();
//! }
//! });
//!
//! // Wait until the flag is set.
//! loop {
//! // Check the flag.
//! if flag.load(Ordering::SeqCst) {
//! break;
//! }
//!
//! // Start listening for events.
//! let listener = event.listen();
//!
//! // Check the flag again after creating the listener.
//! if flag.load(Ordering::SeqCst) {
//! break;
//! }
//!
//! // Wait for a notification and continue the loop.
//! listener.wait();
//! }
//! ```
#![warn(missing_docs, missing_debug_implementations, rust_2018_idioms)]
use std::cell::Cell;
use std::fmt;
use std::future::Future;
use std::mem::{self, ManuallyDrop};
use std::ops::{Deref, DerefMut};
use std::pin::Pin;
use std::ptr::NonNull;
use std::sync::atomic::{self, AtomicPtr, AtomicUsize, Ordering};
use std::sync::{Arc, Mutex, MutexGuard};
use std::task::{Context, Poll, Waker};
use std::thread::{self, Thread};
use std::time::{Duration, Instant};
/// A bit set inside [`Event`] when there is at least one listener that has already been notified.
const NOTIFIED: usize = 1 << 0;
/// A bit set inside [`Event`] when there is at least one notifiable listener.
const NOTIFIABLE: usize = 1 << 1;
/// Inner state of [`Event`].
struct Inner {
/// Holds bits [`NOTIFIED`] and [`NOTIFIABLE`].
flags: AtomicUsize,
/// A linked list holding registered listeners.
list: Mutex<List>,
}
impl Inner {
/// Locks the list.
fn lock(&self) -> ListGuard<'_> {
ListGuard {
inner: self,
guard: self.list.lock().unwrap(),
}
}
}
/// A synchronization primitive for notifying async tasks and threads.
///
/// Listeners can be registered using [`Event::listen()`]. There are two ways of notifying
/// listeners:
///
/// 1. [`Event::notify_one()`] notifies one listener.
/// 2. [`Event::notify_all()`] notifies all listeners.
///
/// If there are no active listeners at the time a notification is sent, it simply gets lost.
///
/// Note that [`Event::notify_one()`] does not notify one *additional* listener - it only makes
/// sure *at least* one listener among the active ones is notified.
///
/// There are two ways for a listener to wait for a notification:
///
/// 1. In an asynchronous manner using `.await`.
/// 2. In a blocking manner by calling [`EventListener::wait()`] on it.
///
/// If a notified listener is dropped without receiving a notification, dropping will notify
/// another active listener.
///
/// Listeners are registered and notified in the first-in first-out fashion, ensuring fairness.
pub struct Event {
/// A pointer to heap-allocated inner state.
///
/// This pointer is initially null and gets lazily initialized on first use. Semantically, it
/// is an `Arc<Inner>` so it's important to keep in mind that it contributes to the [`Arc`]'s
/// reference count.
inner: AtomicPtr<Inner>,
}
unsafe impl Send for Event {}
unsafe impl Sync for Event {}
impl Event {
/// Creates a new [`Event`].
///
/// # Examples
///
/// ```
/// use event_listener::Event;
///
/// let event = Event::new();
/// ```
#[inline]
pub fn new() -> Event {
Event {
inner: AtomicPtr::default(),
}
}
/// Returns a guard listening for a notification.
///
/// # Examples
///
/// ```
/// use event_listener::Event;
///
/// let event = Event::new();
/// let listener = event.listen();
/// ```
#[cold]
pub fn listen(&self) -> EventListener {
let inner = self.inner();
let listener = EventListener {
inner: unsafe { Arc::clone(&ManuallyDrop::new(Arc::from_raw(inner))) },
entry: Some(inner.lock().insert()),
};
// Make sure the listener is registered before whatever happens next.
full_fence();
listener
}
/// Notifies a single active listener.
///
/// Note that this does not notify one *additional* listener - it only makes sure *at least*
/// one listener among the active ones is notified.
///
/// # Examples
///
/// ```
/// use event_listener::Event;
///
/// let event = Event::new();
///
/// // This notification gets lost because there are no listeners.
/// event.notify_one();
///
/// let listener1 = event.listen();
/// let listener2 = event.listen();
///
/// // Notifies just one of `listener1` and `listener2`.
/// //
/// // Listener queueing is fair, which means `listener1` gets notified
/// // here since it was the first to start listening.
/// event.notify_one();
/// ```
#[inline]
pub fn notify_one(&self) {
let inner = self.inner();
// Make sure the notification comes after whatever triggered it.
full_fence();
// Notify if no active listeners have been notified and there is at least one listener.
let flags = inner.flags.load(Ordering::Relaxed);
if flags & NOTIFIED == 0 && flags & NOTIFIABLE != 0 {
inner.lock().notify(false);
}
}
/// Notifies all active listeners.
///
/// # Examples
///
/// ```
/// use event_listener::Event;
///
/// let event = Event::new();
///
/// // This notification gets lost because there are no listeners.
/// event.notify_all();
///
/// let listener1 = event.listen();
/// let listener2 = event.listen();
///
/// // Both `listener1` and `listener2` get notified.
/// event.notify_all();
/// ```
#[inline]
pub fn notify_all(&self) {
let inner = self.inner();
// Make sure the notification comes after whatever triggered it.
full_fence();
// Notify if there is at least one listener.
if inner.flags.load(Ordering::Relaxed) & NOTIFIABLE != 0 {
inner.lock().notify(true);
}
}
/// Returns a reference to the inner state.
fn inner(&self) -> &Inner {
let mut inner = self.inner.load(Ordering::Acquire);
// Initialize the state if this is its first use.
if inner.is_null() {
// Allocate on the heap.
let new = Arc::new(Inner {
flags: AtomicUsize::new(0),
list: Mutex::new(List {
head: None,
tail: None,
len: 0,
notifiable: 0,
}),
});
// Convert the heap-allocated state into a raw pointer.
let new = Arc::into_raw(new) as *mut Inner;
// Attempt to replace the null-pointer with the new state pointer.
inner = self.inner.compare_and_swap(inner, new, Ordering::AcqRel);
// Check if the old pointer value was indeed null.
if inner.is_null() {
// If yes, then use the new state pointer.
inner = new;
} else {
// If not, that means a concurrent operation has initialized the state.
// In that case, use the old pointer and deallocate the new one.
unsafe {
drop(Arc::from_raw(new));
}
}
}
unsafe { &*inner }
}
}
impl Drop for Event {
#[inline]
fn drop(&mut self) {
let inner: *mut Inner = *self.inner.get_mut();
// If the state pointer has been initialized, deallocate it.
if !inner.is_null() {
unsafe {
drop(Arc::from_raw(inner));
}
}
}
}
impl fmt::Debug for Event {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Event { .. }")
}
}
impl Default for Event {
fn default() -> Event {
Event::new()
}
}
/// A guard waiting for a notification from an [`Event`].
///
/// There are two ways for a listener to wait for a notification:
///
/// 1. In an asynchronous manner using `.await`.
/// 2. In a blocking manner by calling [`EventListener::wait()`] on it.
///
/// If a notified listener is dropped without receiving a notification, dropping will notify
/// another active listener.
pub struct EventListener {
/// A reference to [`Event`]'s inner state.
inner: Arc<Inner>,
/// A pointer to this listener's entry in the linked list.
entry: Option<NonNull<Entry>>,
}
unsafe impl Send for EventListener {}
unsafe impl Sync for EventListener {}
impl EventListener {
/// Blocks until a notification is received.
///
/// # Examples
///
/// ```
/// use event_listener::Event;
///
/// let event = Event::new();
/// let listener = event.listen();
///
/// // Notify `listener`.
/// event.notify_one();
///
/// // Receive the notification.
/// listener.wait();
/// ```
pub fn wait(self) {
self.wait_internal(None);
}
/// Blocks until a notification is received or a timeout is reached.
///
/// Returns `true` if a notification was received.
///
/// # Examples
///
/// ```
/// use std::time::Duration;
/// use event_listener::Event;
///
/// let event = Event::new();
/// let listener = event.listen();
///
/// // There are no notification so this times out.
/// assert!(!listener.wait_timeout(Duration::from_secs(1)));
/// ```
pub fn wait_timeout(self, timeout: Duration) -> bool {
self.wait_internal(Some(Instant::now() + timeout))
}
/// Blocks until a notification is received or a deadline is reached.
///
/// Returns `true` if a notification was received.
///
/// # Examples
///
/// ```
/// use std::time::{Duration, Instant};
/// use event_listener::Event;
///
/// let event = Event::new();
/// let listener = event.listen();
///
/// // There are no notification so this times out.
/// assert!(!listener.wait_deadline(Instant::now() + Duration::from_secs(1)));
/// ```
pub fn wait_deadline(self, deadline: Instant) -> bool {
self.wait_internal(Some(deadline))
}
fn wait_internal(mut self, deadline: Option<Instant>) -> bool {
// Take out the entry pointer and set it to `None`.
let entry = match self.entry.take() {
None => unreachable!("cannot wait twice on an `EventListener`"),
Some(entry) => entry,
};
// Set this listener's state to `Waiting`.
{
let mut list = self.inner.lock();
let e = unsafe { entry.as_ref() };
// Do a dummy replace operation in order to take out the state.
match e.state.replace(State::Notified) {
State::Notified => {
// If this listener has been notified, remove it from the list and return.
list.remove(entry);
return true;
}
// Otherwise, set the state to `Waiting`.
_ => e.state.set(State::Waiting(thread::current())),
}
}
// Wait until a notification is received or the timeout is reached.
loop {
match deadline {
None => thread::park(),
Some(deadline) => {
// Check for timeout.
let now = Instant::now();
if now >= deadline {
return false;
}
// Park until the deadline.
thread::park_timeout(deadline - now);
}
}
let mut list = self.inner.lock();
let e = unsafe { entry.as_ref() };
// Do a dummy replace operation in order to take out the state.
match e.state.replace(State::Notified) {
State::Notified => {
// If this listener has been notified, remove it from the list and return.
list.remove(entry);
return true;
}
// Otherwise, set the state back to `Waiting`.
state => e.state.set(state),
}
}
}
}
impl fmt::Debug for EventListener {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("EventListener { .. }")
}
}
impl Future for EventListener {
type Output = ();
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
let mut list = self.inner.lock();
let entry = match self.entry {
None => unreachable!("cannot poll a completed `EventListener` future"),
Some(entry) => entry,
};
let state = unsafe { &entry.as_ref().state };
// Do a dummy replace operation in order to take out the state.
match state.replace(State::Notified) {
State::Notified => {
// If this listener has been notified, remove it from the list and return.
list.remove(entry);
drop(list);
self.entry = None;
return Poll::Ready(());
}
State::Created => {
// If the listener was just created, put it in the `Polling` state.
state.set(State::Polling(cx.waker().clone()));
}
State::Polling(w) => {
// If the listener was in the `Pooling` state, keep it.
state.set(State::Polling(w));
}
State::Waiting(_) => {
unreachable!("cannot poll and wait on `EventListener` at the same time")
}
}
Poll::Pending
}
}
impl Drop for EventListener {
fn drop(&mut self) {
// If this listener has never picked up a notification...
if let Some(entry) = self.entry.take() {
let mut list = self.inner.lock();
// But if a notification was delivered to it...
if list.remove(entry).is_notified() {
// Then pass it on to another active listener.
list.notify(false);
}
}
}
}
/// A guard holding the linked list locked.
struct ListGuard<'a> {
/// A reference to [`Event`]'s inner state.
inner: &'a Inner,
/// The actual guard that acquired the linked list.
guard: MutexGuard<'a, List>,
}
impl Drop for ListGuard<'_> {
#[inline]
fn drop(&mut self) {
let list = &mut **self;
let mut flags = 0;
// Set the `NOTIFIED` flag if there is at least one notified listener.
if list.len - list.notifiable > 0 {
flags |= NOTIFIED;
}
// Set the `NOTIFIABLE` flag if there is at least one notifiable listener.
if list.notifiable > 0 {
flags |= NOTIFIABLE;
}
self.inner.flags.store(flags, Ordering::Release);
}
}
impl Deref for ListGuard<'_> {
type Target = List;
#[inline]
fn deref(&self) -> &List {
&*self.guard
}
}
impl DerefMut for ListGuard<'_> {
#[inline]
fn deref_mut(&mut self) -> &mut List {
&mut *self.guard
}
}
/// The state of a listener.
enum State {
/// It has just been created.
Created,
/// It has received a notification.
Notified,
/// An async task is polling it.
Polling(Waker),
/// A thread is blocked on it.
Waiting(Thread),
}
impl State {
/// Returns `true` if this is the `Notified` state.
#[inline]
fn is_notified(&self) -> bool {
match self {
State::Notified => true,
State::Created | State::Polling(_) | State::Waiting(_) => false,
}
}
}
/// An entry representing a registered listener.
struct Entry {
/// THe state of this listener.
state: Cell<State>,
/// Previous entry in the linked list.
prev: Cell<Option<NonNull<Entry>>>,
/// Next entry in the linked list.
next: Cell<Option<NonNull<Entry>>>,
}
/// A linked list of entries.
struct List {
/// First entry in the list.
head: Option<NonNull<Entry>>,
/// Last entry in the list.
tail: Option<NonNull<Entry>>,
/// Total number of entries in the list.
len: usize,
/// Number of notifiable entries in the list.
///
/// Notifiable entries are those that haven't been notified yet.
notifiable: usize,
}
impl List {
/// Inserts a new entry into the list.
fn insert(&mut self) -> NonNull<Entry> {
unsafe {
// Allocate an entry that is going to become the new tail.
let entry = NonNull::new_unchecked(Box::into_raw(Box::new(Entry {
state: Cell::new(State::Created),
prev: Cell::new(self.tail),
next: Cell::new(None),
})));
// Replace the tail with the new entry.
match mem::replace(&mut self.tail, Some(entry)) {
None => self.head = Some(entry),
Some(t) => t.as_ref().next.set(Some(entry)),
}
// Bump the total count and the count of notifiable entries.
self.len += 1;
self.notifiable += 1;
entry
}
}
/// Removes an entry from the list and returns its state.
fn remove(&mut self, entry: NonNull<Entry>) -> State {
unsafe {
let prev = entry.as_ref().prev.get();
let next = entry.as_ref().next.get();
// Unlink from the previous entry.
match prev {
None => self.head = next,
Some(p) => p.as_ref().next.set(next),
}
// Unlink from the next entry.
match next {
None => self.tail = prev,
Some(n) => n.as_ref().prev.set(prev),
}
// Deallocate and extract the state.
let entry = Box::from_raw(entry.as_ptr());
let state = entry.state.into_inner();
// Update the counters.
if !state.is_notified() {
self.notifiable -= 1;
}
self.len -= 1;
state
}
}
/// Notifies an entry.
#[cold]
fn notify(&mut self, notify_all: bool) {
let mut entry = self.tail;
// Iterate over the entries in the list.
while let Some(e) = entry {
let e = unsafe { e.as_ref() };
// Set the state of this entry to `Notified`.
let state = e.state.replace(State::Notified);
let is_notified = state.is_notified();
// Wake the task or unpark the thread.
match state {
State::Notified => {}
State::Created => {}
State::Polling(w) => w.wake(),
State::Waiting(t) => t.unpark(),
}
// Update the count of notifiable entries.
if !is_notified {
self.notifiable -= 1;
}
// If all entries need to be notified, go to the next one.
if notify_all {
entry = e.prev.get();
} else {
break;
}
}
}
}
/// Equivalent to `atomic::fence(Ordering::SeqCst)`, but in some cases faster.
#[inline]
fn full_fence() {
if cfg!(any(target_arch = "x86", target_arch = "x86_64")) {
// HACK(stjepang): On x86 architectures there are two different ways of executing
// a `SeqCst` fence.
//
// 1. `atomic::fence(SeqCst)`, which compiles into a `mfence` instruction.
// 2. `_.compare_and_swap(_, _, SeqCst)`, which compiles into a `lock cmpxchg` instruction.
//
// Both instructions have the effect of a full barrier, but empirical benchmarks have shown
// that the second one is sometimes a bit faster.
//
// The ideal solution here would be to use inline assembly, but we're instead creating a
// temporary atomic variable and compare-and-exchanging its value. No sane compiler to
// x86 platforms is going to optimize this away.
let a = AtomicUsize::new(0);
a.compare_and_swap(0, 1, Ordering::SeqCst);
} else {
atomic::fence(Ordering::SeqCst);
}
}