perf(client): create DispatchGone error only if needed

src/client/dispatch.rs

@@ -226,28 +226,31 @@ pub(crate) enum Callback<T, U> {
 
 impl<T, U> Drop for Callback<T, U> {
  fn drop(&mut self) {
- // FIXME(nox): What errors do we want here?
- let error = crate::Error::new_user_dispatch_gone().with(if std::thread::panicking() {
- "user code panicked"
- } else {
- "runtime dropped the dispatch task"
- });
-
  match self {
  Callback::Retry(tx) => {
  if let Some(tx) = tx.take() {
- let _ = tx.send(Err((error, None)));
+ let _ = tx.send(Err((dispatch_gone(), None)));
  }
  }
  Callback::NoRetry(tx) => {
  if let Some(tx) = tx.take() {
- let _ = tx.send(Err(error));
+ let _ = tx.send(Err(dispatch_gone()));
  }
  }
  }
  }
 }
 
+#[cold]
+fn dispatch_gone() -> crate::Error {
+ // FIXME(nox): What errors do we want here?
+ crate::Error::new_user_dispatch_gone().with(if std::thread::panicking() {
+ "user code panicked"
+ } else {
+ "runtime dropped the dispatch task"
+ })
+}
+
 impl<T, U> Callback<T, U> {
  #[cfg(feature = "http2")]
  pub(crate) fn is_canceled(&self) -> bool {