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use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};
/// Converts a function to a future that completes on poll.
pub(crate) struct BlockingTask<T> {
func: Option<T>,
}
impl<T> BlockingTask<T> {
/// Initializes a new blocking task from the given function.
pub(crate) fn new(func: T) -> BlockingTask<T> {
BlockingTask { func: Some(func) }
}
}
// The closure `F` is never pinned
impl<T> Unpin for BlockingTask<T> {}
impl<T, R> Future for BlockingTask<T>
where
T: FnOnce() -> R + Send + 'static,
R: Send + 'static,
{
type Output = R;
fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<R> {
let me = &mut *self;
let func = me
.func
.take()
.expect("[internal exception] blocking task ran twice.");
// This is a little subtle:
// For convenience, we'd like _every_ call tokio ever makes to Task::poll() to be budgeted
// using coop. However, the way things are currently modeled, even running a blocking task
// currently goes through Task::poll(), and so is subject to budgeting. That isn't really
// what we want; a blocking task may itself want to run tasks (it might be a Worker!), so
// we want it to start without any budgeting.
crate::runtime::coop::stop();
Poll::Ready(func())
}
}