test: acquire_then_drop (#40)

Signed-off-by: tison <[email protected]>

Author: tisonkun

mea/src/semaphore/tests.rs

@@ -12,7 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+use std::future::Future;
+use std::pin::pin;
 use std::sync::Arc;
+use std::task::Context;
+use std::task::RawWaker;
+use std::task::RawWakerVTable;
+use std::task::Waker;
 use std::vec::Vec;
 
 use super::*;
@@ -137,6 +143,22 @@ fn try_acquire_concurrently() {
     assert_eq!(s.available_permits(), 1);
 }
 
+#[test]
+fn acquire_then_drop() {
+    let waker = noop_waker();
+    let mut context = Context::from_waker(&waker);
+
+    let s = Semaphore::new(1);
+    let p1 = s.try_acquire(1).unwrap();
+    {
+        let p2 = s.acquire(1);
+        let poll = pin!(p2).poll(&mut context);
+        assert!(poll.is_pending());
+    }
+    drop(p1);
+    assert_eq!(s.available_permits(), 1);
+}
+
 #[tokio::test]
 async fn acquire_then_forget_exact() {
     let s = Arc::new(Semaphore::new(5));
@@ -161,3 +183,21 @@ async fn acquire_then_forget_exact() {
     acquired.wait().await;
     assert_eq!(s.available_permits(), 3);
 }
+
+fn noop_waker() -> Waker {
+    const NOOP: RawWaker = {
+        const VTABLE: RawWakerVTable = RawWakerVTable::new(
+            // Cloning just returns a new no-op raw waker
+            |_| NOOP,
+            // `wake` does nothing
+            |_| {},
+            // `wake_by_ref` does nothing
+            |_| {},
+            // Dropping does nothing as we don't allocate anything
+            |_| {},
+        );
+        RawWaker::new(std::ptr::null(), &VTABLE)
+    };
+
+    unsafe { Waker::from_raw(NOOP) }
+}