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//! A shutdown channel.
//!
//! Each worker holds the `Sender` half. When all the `Sender` halves are
//! dropped, the `Receiver` receives a notification.
use crate::loom::sync::Arc;
use crate::sync::oneshot;
use std::time::Duration;
#[derive(Debug, Clone)]
pub(super) struct Sender {
_tx: Arc<oneshot::Sender<()>>,
}
#[derive(Debug)]
pub(super) struct Receiver {
rx: oneshot::Receiver<()>,
}
pub(super) fn channel() -> (Sender, Receiver) {
let (tx, rx) = oneshot::channel();
let tx = Sender { _tx: Arc::new(tx) };
let rx = Receiver { rx };
(tx, rx)
}
impl Receiver {
/// Blocks the current thread until all `Sender` handles drop.
///
/// If `timeout` is `Some`, the thread is blocked for **at most** `timeout`
/// duration. If `timeout` is `None`, then the thread is blocked until the
/// shutdown signal is received.
///
/// If the timeout has elapsed, it returns `false`, otherwise it returns `true`.
pub(crate) fn wait(&mut self, timeout: Option<Duration>) -> bool {
use crate::runtime::context::try_enter_blocking_region;
if timeout == Some(Duration::from_nanos(0)) {
return false;
}
let mut e = match try_enter_blocking_region() {
Some(enter) => enter,
_ => {
if std::thread::panicking() {
// Don't panic in a panic
return false;
} else {
panic!(
"Cannot drop a runtime in a context where blocking is not allowed. \
This happens when a runtime is dropped from within an asynchronous context."
);
}
}
};
// The oneshot completes with an Err
//
// If blocking fails to wait, this indicates a problem parking the
// current thread (usually, shutting down a runtime stored in a
// thread-local).
if let Some(timeout) = timeout {
e.block_on_timeout(&mut self.rx, timeout).is_ok()
} else {
let _ = e.block_on(&mut self.rx);
true
}
}
}