rt: fix panic in task abort when off rt (#3159)

A call to `JoinHandle::abort` releases a task. When called from outside of the runtime,
this panics due to the current implementation checking for a thread-local worker context.

This change makes accessing the thread-local context optional under release, by falling
back to remotely marking a task remotely as dropped. Behaving the same as if the core
was stolen by another worker.

Fixes #3157

1 files changed, 26 insertions, 0 deletions

diff --git a/tokio/tests/task_abort.rs b/tokio/tests/task_abort.rs
new file mode 100644
index 00000000..e84f19c3
--- /dev/null
+++ b/tokio/tests/task_abort.rs
@@ -0,0 +1,26 @@
+#![warn(rust_2018_idioms)]
+#![cfg(feature = "full")]
+
+/// Checks that a suspended task can be aborted without panicking as reported in
+/// issue #3157: <https://github.com/tokio-rs/tokio/issues/3157>.
+#[test]
+fn test_abort_without_panic_3157() {
+    let rt = tokio::runtime::Builder::new_multi_thread()
+        .enable_time()
+        .worker_threads(1)
+        .build()
+        .unwrap();
+
+    rt.block_on(async move {
+        let handle = tokio::spawn(async move {
+            println!("task started");
+            tokio::time::sleep(std::time::Duration::new(100, 0)).await
+        });
+
+        // wait for task to sleep.
+        tokio::time::sleep(std::time::Duration::new(1, 0)).await;
+
+        handle.abort();
+        let _ = handle.await;
+    });
+}