Ensure that cancel scopes are entered and exited in the same task

Only checks on asyncio; trio support is not there yet.

docs/versionhistory.rst

@@ -11,6 +11,8 @@ This library adheres to `Semantic Versioning 2.0 <http:https://semver.org/>`_.
  * ``run_sync_in_worker_thread()`` → ``anyio.to_thread.run_sync()``
  * ``run_async_from_thread()`` → ``anyio.from_thread.run()``
  * ``run_sync_from_thread()`` → ``anyio.from_thread.run_sync()``
+- Added check that cancel scopes are entered and exited in the same task (only done on asyncio for
+ now)
 
 **3.0.0rc2**
 

src/anyio/_backends/_asyncio.py

@@ -265,19 +265,22 @@ def __exit__(self, exc_type: Optional[Type[BaseException]], exc_val: Optional[Ba
  exc_tb: Optional[TracebackType]) -> Optional[bool]:
  if not self._active:
  raise RuntimeError('This cancel scope is not active')
+ if current_task() is not self._host_task:
+ raise RuntimeError('Attempted to exit cancel scope in a different task than it was '
+ 'entered in')
+
+ assert self._host_task is not None
+ host_task_state = _task_states.get(self._host_task)
+ if host_task_state is None or host_task_state.cancel_scope is not self:
+ raise RuntimeError("Attempted to exit a cancel scope that isn't the current tasks's "
+ "current cancel scope")
 
  self._active = False
  if self._timeout_handle:
  self._timeout_handle.cancel()
  self._timeout_handle = None
 
- assert self._host_task is not None
  self._tasks.remove(self._host_task)
- host_task_state = _task_states.get(self._host_task)
- if host_task_state is None or host_task_state.cancel_scope is not self:
- raise RuntimeError("Cancel scope task corruption detected.\n"
- "This means that you tried to exit a cancel scope that wasn't the"
- "last entered cancel scope in the current host task.")
 
  host_task_state.cancel_scope = self._parent_scope
 

tests/test_taskgroups.py

@@ -867,3 +867,20 @@ async def test_cancelscope_exit_before_enter():
  """Test that a RuntimeError is raised if one tries to exit a cancel scope before entering."""
  scope = CancelScope()
  pytest.raises(RuntimeError, scope.__exit__, None, None, None)
+
+
+@pytest.mark.parametrize('anyio_backend', ['asyncio']) # trio does not check for this yet
+async def test_cancelscope_exit_in_wrong_task():
+ async def enter_scope(scope):
+ scope.__enter__()
+
+ async def exit_scope(scope):
+ scope.__exit__(None, None, None)
+
+ scope = CancelScope()
+ async with create_task_group() as tg:
+ tg.spawn(enter_scope, scope)
+
+ with pytest.raises(RuntimeError):
+ async with create_task_group() as tg:
+ tg.spawn(exit_scope, scope)