fix: hang on double shutdown

deadpool.py

@@ -642,6 +642,9 @@ def submit(
         return fut
 
     def shutdown(self, wait: bool = True, *, cancel_futures: bool = False) -> None:
+        if self.closed:
+            return
+
         logger.debug(f"shutdown: {wait=} {cancel_futures=}")
 
         # No more new tasks can be submitted
@@ -706,16 +709,14 @@ def __enter__(self):
         return self
 
     def __exit__(self, exc_type, exc_val, exc_tb):
-        if not self.closed:
-            kwargs = {}
-            if self.shutdown_wait is not None:
-                kwargs["wait"] = self.shutdown_wait
-
-            if self.shutdown_cancel_futures is not None:
-                kwargs["cancel_futures"] = self.shutdown_cancel_futures
+        kwargs = {}
+        if self.shutdown_wait is not None:
+            kwargs["wait"] = self.shutdown_wait
 
-            self.shutdown(**kwargs)
+        if self.shutdown_cancel_futures is not None:
+            kwargs["cancel_futures"] = self.shutdown_cancel_futures
 
+        self.shutdown(**kwargs)
         self.runner_thread.join()
         return False
 

tests/test_deadpool.py

@@ -344,6 +344,14 @@ def test_shutdown(logging_initializer, wait, cancel_futures):
     assert result == 123
 
 
+@pytest.mark.parametrize("wait", [True, False])
+def test_shutdown_idempotent(wait):
+    """Calling shutdown() twice must not deadlock."""
+    d = deadpool.Deadpool(max_workers=2)
+    d.shutdown(wait=wait)
+    d.shutdown(wait=wait)
+
+
 @pytest.mark.parametrize("wait", [True, False])
 @pytest.mark.parametrize("cancel_futures", [True, False])
 def test_shutdown_manual(logging_initializer, wait, cancel_futures):