Fix Python 3.12+ fork warning in async connection tests (apache#56019)

Author: kaxil

task-sdk/tests/conftest.py

@@ -175,6 +175,48 @@ def _disable_ol_plugin():
     airflow.plugins_manager.plugins = None
 
 
+@pytest.fixture(autouse=True)
+def _cleanup_async_resources(request):
+    """
+    Clean up async resources that can cause Python 3.12 fork warnings.
+
+    Problem: asgiref.sync.sync_to_async (used in _async_get_connection) creates
+    ThreadPoolExecutors that persist between tests. When supervisor.py calls
+    os.fork() in subsequent tests, Python 3.12+ warns about forking a
+    multi-threaded process.
+
+    Solution: Clean up asgiref's ThreadPoolExecutors after async tests to ensure
+    subsequent tests start with a clean thread environment.
+    """
+    yield
+
+    # Only clean up after async tests to avoid unnecessary overhead
+    if "asyncio" in request.keywords:
+        # Clean up asgiref ThreadPoolExecutors that persist between tests
+        # These are created by sync_to_async() calls in async connection retrieval
+        try:
+            from asgiref.sync import SyncToAsync
+
+            # SyncToAsync maintains a class-level executor for performance
+            # We need to shut it down to prevent multi-threading warnings on fork()
+            if hasattr(SyncToAsync, "single_thread_executor") and SyncToAsync.single_thread_executor:
+                if not SyncToAsync.single_thread_executor._shutdown:
+                    SyncToAsync.single_thread_executor.shutdown(wait=True)
+                SyncToAsync.single_thread_executor = None
+
+            # SyncToAsync also maintains a WeakKeyDictionary of context-specific executors
+            # Clean these up too to ensure complete thread cleanup
+            if hasattr(SyncToAsync, "context_to_thread_executor"):
+                for executor in list(SyncToAsync.context_to_thread_executor.values()):
+                    if hasattr(executor, "shutdown") and not getattr(executor, "_shutdown", True):
+                        executor.shutdown(wait=True)
+                SyncToAsync.context_to_thread_executor.clear()
+
+        except (ImportError, AttributeError):
+            # If asgiref structure changes, fail gracefully
+            pass
+
+
 class MakeTIContextCallable(Protocol):
     def __call__(
         self,