Be more principled about when blocking is ok (#2410)

This enables `block_in_place` to be used in more contexts. Specifically,
it allows you to block whenever you are off the tokio runtime (like if
you are not using tokio, are in a `spawn_blocking` closure, etc.), and
in the threaded scheduler's `block_on`. Blocking in `LocalSet` and the
basic scheduler's` block_on` is still disallowed.

Fixes #2327.
Fixes #2393.

1 files changed, 2 insertions, 0 deletions

diff --git a/tokio/src/task/local.rs b/tokio/src/task/local.rs
index edecb04b..9af50cee 100644
--- a/tokio/src/task/local.rs
+++ b/tokio/src/task/local.rs
@@ -520,6 +520,8 @@ impl<T: Future> Future for RunUntil<'_, T> {
                 .waker
                 .register_by_ref(cx.waker());
 
+            let _no_blocking = crate::runtime::enter::disallow_blocking();
+
             if let Poll::Ready(output) = me.future.poll(cx) {
                 return Poll::Ready(output);
             }