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95 lines
2.4 KiB
Rust
95 lines
2.4 KiB
Rust
use std::future::Future;
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use std::pin::Pin;
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use crate::task::{Context, Poll, Task};
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/// A handle that awaits the result of a task.
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///
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/// Dropping a [`JoinHandle`] will detach the task, meaning that there is no longer
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/// a handle to the task and no way to `join` on it.
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///
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/// Created when a task is [spawned].
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///
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/// [spawned]: fn.spawn.html
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#[derive(Debug)]
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pub struct JoinHandle<T> {
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handle: Option<InnerHandle<T>>,
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task: Task,
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}
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#[cfg(not(target_os = "unknown"))]
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type InnerHandle<T> = async_executor::Task<T>;
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#[cfg(target_arch = "wasm32")]
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type InnerHandle<T> = futures_channel::oneshot::Receiver<T>;
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impl<T> JoinHandle<T> {
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/// Creates a new `JoinHandle`.
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pub(crate) fn new(inner: InnerHandle<T>, task: Task) -> JoinHandle<T> {
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JoinHandle {
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handle: Some(inner),
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task,
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}
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}
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/// Returns a handle to the underlying task.
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///
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/// # Examples
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///
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/// ```
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/// # async_std::task::block_on(async {
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/// #
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/// use async_std::task;
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///
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/// let handle = task::spawn(async {
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/// 1 + 2
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/// });
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/// println!("id = {}", handle.task().id());
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/// #
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/// # })
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pub fn task(&self) -> &Task {
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&self.task
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}
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/// Cancel this task.
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#[cfg(not(target_os = "unknown"))]
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pub async fn cancel(mut self) -> Option<T> {
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let handle = self.handle.take().unwrap();
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handle.cancel().await
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}
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/// Cancel this task.
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#[cfg(target_arch = "wasm32")]
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pub async fn cancel(mut self) -> Option<T> {
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let mut handle = self.handle.take().unwrap();
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handle.close();
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handle.await.ok()
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}
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}
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#[cfg(not(target_os = "unknown"))]
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impl<T> Drop for JoinHandle<T> {
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fn drop(&mut self) {
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if let Some(handle) = self.handle.take() {
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handle.detach();
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}
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}
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}
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impl<T> Future for JoinHandle<T> {
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type Output = T;
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#[cfg(not(target_os = "unknown"))]
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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Pin::new(&mut self.handle.as_mut().unwrap()).poll(cx)
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}
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#[cfg(target_arch = "wasm32")]
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fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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match Pin::new(&mut self.handle.as_mut().unwrap()).poll(cx) {
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Poll::Ready(Ok(t)) => Poll::Ready(t),
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Poll::Ready(Err(_)) => unreachable!("channel must not be canceled"),
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Poll::Pending => Poll::Pending,
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}
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}
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}
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