Fixed timeout errors not propagating from nested scopes (agronholm#59)

Check all parents for cancellation, not just the immediate one.

Fixes agronholm#58.

anyio/_backends/asyncio.py

@@ -233,7 +233,7 @@ async def __aexit__(self, exc_type, exc_val, exc_tb):
         if all(isinstance(exc, CancelledError) for exc in exceptions):
             if self._timeout_expired:
                 return True
-            elif self._parent_scope is None or not self._parent_scope.cancel_called:
+            elif not self._parent_cancelled():
                 # This scope was directly cancelled
                 return True
 
@@ -246,9 +246,32 @@ async def _cancel(self):
                 # Only deliver the cancellation if the task is already running
                 if task._coro.cr_await is not None:
                     task.cancel()
-            elif not cancel_scope.shield:
+            elif not cancel_scope._shielded_to(self):
                 await cancel_scope._cancel()
 
+    def _shielded_to(self, parent: Optional['CancelScope']) -> bool:
+        # Check whether this task or any parent up to (but not including) the "parent" argument is
+        # shielded
+        cancel_scope = self  # type: Optional[CancelScope]
+        while cancel_scope is not None and cancel_scope is not parent:
+            if cancel_scope._shield:
+                return True
+            else:
+                cancel_scope = cancel_scope._parent_scope
+
+        return False
+
+    def _parent_cancelled(self) -> bool:
+        # Check whether any parent has been cancelled
+        cancel_scope = self._parent_scope
+        while cancel_scope is not None and not cancel_scope._shield:
+            if cancel_scope._cancel_called:
+                return True
+            else:
+                cancel_scope = cancel_scope._parent_scope
+
+        return False
+
     async def cancel(self):
         if self._cancel_called:
             return
@@ -379,8 +402,7 @@ async def __aexit__(self, exc_type, exc_val, exc_tb):
             await asyncio.wait(self.cancel_scope._tasks)
 
         self._active = False
-        if (not self.cancel_scope._parent_scope
-                or not self.cancel_scope._parent_scope.cancel_called):
+        if not self.cancel_scope._parent_cancelled():
             exceptions = [exc for exc in self._exceptions if not isinstance(exc, CancelledError)]
         else:
             exceptions = self._exceptions

anyio/_backends/curio.py

@@ -112,7 +112,7 @@ async def __aexit__(self, exc_type, exc_val, exc_tb):
         if all(isinstance(exc, CancelledError) for exc in exceptions):
             if self._timeout_expired:
                 return True
-            elif self._parent_scope is None or not self._parent_scope.cancel_called:
+            elif not self._parent_cancelled():
                 # This scope was directly cancelled
                 return True
 
@@ -125,9 +125,32 @@ async def _cancel(self):
                 # Only deliver the cancellation if the task is already running
                 if task.coro.cr_await is not None:
                     await task.cancel(blocking=False)
-            elif not cancel_scope.shield:
+            elif not cancel_scope._shielded_to(self):
                 await cancel_scope._cancel()
 
+    def _shielded_to(self, parent: 'CancelScope') -> bool:
+        # Check whether this task or any parent up to (but not including) the "parent" argument is
+        # shielded
+        cancel_scope = self  # type: Optional[CancelScope]
+        while cancel_scope is not None and cancel_scope is not parent:
+            if cancel_scope._shield:
+                return True
+            else:
+                cancel_scope = cancel_scope._parent_scope
+
+        return False
+
+    def _parent_cancelled(self) -> bool:
+        # Check whether any parent has been cancelled
+        cancel_scope = self._parent_scope
+        while cancel_scope is not None and not cancel_scope._shield:
+            if cancel_scope._cancel_called:
+                return True
+            else:
+                cancel_scope = cancel_scope._parent_scope
+
+        return False
+
     async def cancel(self):
         if self._cancel_called:
             return
@@ -256,8 +279,7 @@ async def __aexit__(self, exc_type, exc_val, exc_tb):
                 await task.wait()
 
         self._active = False
-        if (not self.cancel_scope._parent_scope
-                or not self.cancel_scope._parent_scope.cancel_called):
+        if not self.cancel_scope._parent_cancelled():
             exceptions = [exc for exc in self._exceptions if not isinstance(exc, CancelledError)]
         else:
             exceptions = self._exceptions

docs/versionhistory.rst

@@ -6,6 +6,7 @@ This library adheres to `Semantic Versioning <http://semver.org/>`_.
 **UNRELEASED**
 
 - Fixed pathlib2_ compatibility with ``anyio.aopen()``
+- Fixed timeouts not propagating from nested scopes on asyncio and curio (PR by Matthias Urlichs)
 
  .. _pathlib2: https://pypi.org/project/pathlib2/
 

tests/test_taskgroups.py

@@ -430,3 +430,39 @@ async def test_catch_cancellation():
             raise
 
     assert finalizer_done
+
+
+@pytest.mark.anyio
+async def test_nested_fail_after():
+    async def killer(scope):
+        await wait_all_tasks_blocked()
+        await scope.cancel()
+
+    async with create_task_group() as tg:
+        async with open_cancel_scope() as scope:
+            async with open_cancel_scope():
+                await tg.spawn(killer, scope)
+                async with fail_after(1):
+                    await sleep(2)
+                    pytest.fail('Execution should not reach this point')
+
+                pytest.fail('Execution should not reach this point either')
+
+            pytest.fail('Execution should also not reach this point')
+
+    assert scope.cancel_called
+
+
+@pytest.mark.anyio
+async def test_nested_shield():
+    async def killer(scope):
+        await wait_all_tasks_blocked()
+        await scope.cancel()
+
+    with pytest.raises(TimeoutError):
+        async with create_task_group() as tg:
+            async with open_cancel_scope() as scope:
+                async with open_cancel_scope(shield=True):
+                    await tg.spawn(killer, scope)
+                    async with fail_after(0.2):
+                        await sleep(2)