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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
//! Machinery for [tasks](https://html.spec.whatwg.org/multipage/#concept-task).
use std::fmt;
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
macro_rules! task {
($name:ident: move || $body:tt) => {{
#[allow(non_camel_case_types)]
struct $name<F>(F);
impl<F> crate::task::TaskOnce for $name<F>
where
F: ::std::ops::FnOnce() + Send,
{
fn name(&self) -> &'static str {
stringify!($name)
}
fn run_once(self) {
(self.0)();
}
}
$name(move || $body)
}};
}
/// A task that can be run. The name method is for profiling purposes.
pub trait TaskOnce: Send {
#[allow(unsafe_code)]
fn name(&self) -> &'static str {
::std::any::type_name::<Self>()
}
fn run_once(self);
}
/// A boxed version of `TaskOnce`.
pub trait TaskBox: Send {
fn name(&self) -> &'static str;
fn run_box(self: Box<Self>);
}
impl<T> TaskBox for T
where
T: TaskOnce,
{
fn name(&self) -> &'static str {
TaskOnce::name(self)
}
fn run_box(self: Box<Self>) {
self.run_once()
}
}
impl fmt::Debug for dyn TaskBox {
fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
fmt.debug_tuple(self.name())
.field(&format_args!("..."))
.finish()
}
}
/// Encapsulated state required to create cancellable tasks from non-script threads.
pub struct TaskCanceller {
pub cancelled: Option<Arc<AtomicBool>>,
}
impl TaskCanceller {
/// Returns a wrapped `task` that will be cancelled if the `TaskCanceller`
/// says so.
pub fn wrap_task<T>(&self, task: T) -> impl TaskOnce
where
T: TaskOnce,
{
CancellableTask {
cancelled: self.cancelled.clone(),
inner: task,
}
}
}
/// A task that can be cancelled by toggling a shared flag.
pub struct CancellableTask<T: TaskOnce> {
cancelled: Option<Arc<AtomicBool>>,
inner: T,
}
impl<T> CancellableTask<T>
where
T: TaskOnce,
{
fn is_cancelled(&self) -> bool {
self.cancelled
.as_ref()
.map_or(false, |cancelled| cancelled.load(Ordering::SeqCst))
}
}
impl<T> TaskOnce for CancellableTask<T>
where
T: TaskOnce,
{
fn name(&self) -> &'static str {
self.inner.name()
}
fn run_once(self) {
if !self.is_cancelled() {
self.inner.run_once()
}
}
}
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