1 files changed, 71 insertions, 0 deletions
diff --git a/third_party/rust/tokio/src/runtime/blocking/shutdown.rs b/third_party/rust/tokio/src/runtime/blocking/shutdown.rs
new file mode 100644
index 0000000000..e6f4674183
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/blocking/shutdown.rs
@@ -0,0 +1,71 @@
+//! 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::enter::try_enter;
+
+        if timeout == Some(Duration::from_nanos(0)) {
+            return false;
+        }
+
+        let mut e = match try_enter(false) {
+            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
+        }
+    }
+}