rt: fix blocking pool shutdown logic (#1978)

The blocking task queue was not explicitly drained as part of the
blocking pool shutdown logic. It was originally assumed that the
contents of the queue would be dropped when the blocking pool structure
is dropped. However, tasks must be explicitly shutdown, so we must drain
the queue can call `shutdown` on each task.

Fixes #1970, #1946

2 files changed, 34 insertions, 0 deletions

diff --git a/tokio/src/runtime/tests/loom_blocking.rs b/tokio/src/runtime/tests/loom_blocking.rs
new file mode 100644
index 00000000..85e6fb12
--- /dev/null
+++ b/tokio/src/runtime/tests/loom_blocking.rs
@@ -0,0 +1,31 @@
+use crate::runtime::{self, Runtime};
+
+use std::sync::Arc;
+
+#[test]
+fn blocking_shutdown() {
+    loom::model(|| {
+        let v = Arc::new(());
+
+        let rt = mk_runtime(1);
+        rt.enter(|| {
+            for _ in 0..2 {
+                let v = v.clone();
+                crate::task::spawn_blocking(move || {
+                    assert!(1 < Arc::strong_count(&v));
+                });
+            }
+        });
+
+        drop(rt);
+        assert_eq!(1, Arc::strong_count(&v));
+    });
+}
+
+fn mk_runtime(num_threads: usize) -> Runtime {
+    runtime::Builder::new()
+        .threaded_scheduler()
+        .num_threads(num_threads)
+        .build()
+        .unwrap()
+}
diff --git a/tokio/src/runtime/tests/mod.rs b/tokio/src/runtime/tests/mod.rs
index a1910a44..da592f76 100644
--- a/tokio/src/runtime/tests/mod.rs
+++ b/tokio/src/runtime/tests/mod.rs
@@ -2,3 +2,6 @@
 
 #[cfg(loom)]
 pub(crate) mod loom_oneshot;
+
+#[cfg(loom)]
+pub(crate) mod loom_blocking;