Fix poll_expired incorrectly returning Pending when there are no outstanding requests.

tarpc/src/server.rs

@@ -333,6 +333,7 @@ where
     type Item = Result<TrackedRequest<Req>, ChannelError<T::Error>>;
 
     fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
+        #[derive(Debug)]
         enum ReceiverStatus {
             Ready,
             Pending,
@@ -388,6 +389,11 @@ where
                 Poll::Pending => Pending,
             };
 
+            tracing::trace!(
+                "Expired requests: {:?}, Inbound: {:?}",
+                expiration_status,
+                request_status
+            );
             match (expiration_status, request_status) {
                 (Ready, _) | (_, Ready) => continue,
                 (Closed, Closed) => return Poll::Ready(None),

tarpc/src/server/in_flight_requests.rs

@@ -98,6 +98,11 @@ impl InFlightRequests {
         &mut self,
         cx: &mut Context,
     ) -> Poll<Option<Result<u64, tokio::time::error::Error>>> {
+        if self.deadlines.is_empty() {
+            // TODO(https://github.com/tokio-rs/tokio/issues/4161)
+            // This is a workaround for DelayQueue not always treating this case correctly.
+            return Poll::Ready(None);
+        }
         self.deadlines.poll_expired(cx).map_ok(|expired| {
             if let Some(RequestData {
                 abort_handle, span, ..
@@ -184,6 +189,8 @@ mod tests {
     #[tokio::test]
     async fn remove_request_doesnt_abort() {
         let mut in_flight_requests = InFlightRequests::default();
+        assert!(in_flight_requests.deadlines.is_empty());
+
         let abort_registration = in_flight_requests
             .start_request(
                 0,
@@ -198,9 +205,11 @@ mod tests {
             in_flight_requests.poll_expired(&mut noop_context()),
             Poll::Pending
         );
+        assert!(!in_flight_requests.deadlines.is_empty());
 
         assert_matches!(in_flight_requests.remove_request(0), Some(_));
         // Postcondition: No pending expirations
+        assert!(in_flight_requests.deadlines.is_empty());
         assert_matches!(
             in_flight_requests.poll_expired(&mut noop_context()),
             Poll::Ready(None)