mirror of https://github.com/python/cpython
241 lines
8.5 KiB
Python
241 lines
8.5 KiB
Python
# Adapted with permission from the EdgeDB project;
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# license: PSFL.
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__all__ = ("TaskGroup",)
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from . import events
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from . import exceptions
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from . import tasks
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class TaskGroup:
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"""Asynchronous context manager for managing groups of tasks.
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Example use:
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async with asyncio.TaskGroup() as group:
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task1 = group.create_task(some_coroutine(...))
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task2 = group.create_task(other_coroutine(...))
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print("Both tasks have completed now.")
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All tasks are awaited when the context manager exits.
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Any exceptions other than `asyncio.CancelledError` raised within
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a task will cancel all remaining tasks and wait for them to exit.
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The exceptions are then combined and raised as an `ExceptionGroup`.
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"""
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def __init__(self):
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self._entered = False
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self._exiting = False
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self._aborting = False
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self._loop = None
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self._parent_task = None
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self._parent_cancel_requested = False
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self._tasks = set()
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self._errors = []
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self._base_error = None
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self._on_completed_fut = None
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def __repr__(self):
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info = ['']
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if self._tasks:
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info.append(f'tasks={len(self._tasks)}')
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if self._errors:
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info.append(f'errors={len(self._errors)}')
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if self._aborting:
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info.append('cancelling')
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elif self._entered:
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info.append('entered')
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info_str = ' '.join(info)
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return f'<TaskGroup{info_str}>'
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async def __aenter__(self):
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if self._entered:
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raise RuntimeError(
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f"TaskGroup {self!r} has already been entered")
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if self._loop is None:
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self._loop = events.get_running_loop()
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self._parent_task = tasks.current_task(self._loop)
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if self._parent_task is None:
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raise RuntimeError(
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f'TaskGroup {self!r} cannot determine the parent task')
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self._entered = True
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return self
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async def __aexit__(self, et, exc, tb):
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self._exiting = True
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if (exc is not None and
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self._is_base_error(exc) and
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self._base_error is None):
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self._base_error = exc
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propagate_cancellation_error = \
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exc if et is exceptions.CancelledError else None
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if self._parent_cancel_requested:
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# If this flag is set we *must* call uncancel().
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if self._parent_task.uncancel() == 0:
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# If there are no pending cancellations left,
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# don't propagate CancelledError.
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propagate_cancellation_error = None
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if et is not None:
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if not self._aborting:
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# Our parent task is being cancelled:
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#
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# async with TaskGroup() as g:
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# g.create_task(...)
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# await ... # <- CancelledError
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#
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# or there's an exception in "async with":
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#
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# async with TaskGroup() as g:
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# g.create_task(...)
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# 1 / 0
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#
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self._abort()
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# We use while-loop here because "self._on_completed_fut"
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# can be cancelled multiple times if our parent task
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# is being cancelled repeatedly (or even once, when
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# our own cancellation is already in progress)
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while self._tasks:
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if self._on_completed_fut is None:
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self._on_completed_fut = self._loop.create_future()
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try:
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await self._on_completed_fut
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except exceptions.CancelledError as ex:
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if not self._aborting:
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# Our parent task is being cancelled:
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#
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# async def wrapper():
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# async with TaskGroup() as g:
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# g.create_task(foo)
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#
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# "wrapper" is being cancelled while "foo" is
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# still running.
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propagate_cancellation_error = ex
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self._abort()
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self._on_completed_fut = None
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assert not self._tasks
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if self._base_error is not None:
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raise self._base_error
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# Propagate CancelledError if there is one, except if there
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# are other errors -- those have priority.
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if propagate_cancellation_error and not self._errors:
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raise propagate_cancellation_error
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if et is not None and et is not exceptions.CancelledError:
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self._errors.append(exc)
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if self._errors:
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# Exceptions are heavy objects that can have object
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# cycles (bad for GC); let's not keep a reference to
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# a bunch of them.
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try:
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me = BaseExceptionGroup('unhandled errors in a TaskGroup', self._errors)
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raise me from None
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finally:
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self._errors = None
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def create_task(self, coro, *, name=None, context=None):
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"""Create a new task in this group and return it.
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Similar to `asyncio.create_task`.
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"""
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if not self._entered:
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raise RuntimeError(f"TaskGroup {self!r} has not been entered")
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if self._exiting and not self._tasks:
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raise RuntimeError(f"TaskGroup {self!r} is finished")
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if self._aborting:
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raise RuntimeError(f"TaskGroup {self!r} is shutting down")
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if context is None:
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task = self._loop.create_task(coro)
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else:
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task = self._loop.create_task(coro, context=context)
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task.set_name(name)
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# optimization: Immediately call the done callback if the task is
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# already done (e.g. if the coro was able to complete eagerly),
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# and skip scheduling a done callback
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if task.done():
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self._on_task_done(task)
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else:
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self._tasks.add(task)
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task.add_done_callback(self._on_task_done)
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return task
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# Since Python 3.8 Tasks propagate all exceptions correctly,
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# except for KeyboardInterrupt and SystemExit which are
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# still considered special.
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def _is_base_error(self, exc: BaseException) -> bool:
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assert isinstance(exc, BaseException)
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return isinstance(exc, (SystemExit, KeyboardInterrupt))
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def _abort(self):
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self._aborting = True
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for t in self._tasks:
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if not t.done():
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t.cancel()
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def _on_task_done(self, task):
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self._tasks.discard(task)
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if self._on_completed_fut is not None and not self._tasks:
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if not self._on_completed_fut.done():
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self._on_completed_fut.set_result(True)
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if task.cancelled():
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return
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exc = task.exception()
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if exc is None:
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return
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self._errors.append(exc)
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if self._is_base_error(exc) and self._base_error is None:
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self._base_error = exc
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if self._parent_task.done():
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# Not sure if this case is possible, but we want to handle
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# it anyways.
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self._loop.call_exception_handler({
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'message': f'Task {task!r} has errored out but its parent '
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f'task {self._parent_task} is already completed',
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'exception': exc,
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'task': task,
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})
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return
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if not self._aborting and not self._parent_cancel_requested:
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# If parent task *is not* being cancelled, it means that we want
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# to manually cancel it to abort whatever is being run right now
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# in the TaskGroup. But we want to mark parent task as
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# "not cancelled" later in __aexit__. Example situation that
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# we need to handle:
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#
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# async def foo():
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# try:
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# async with TaskGroup() as g:
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# g.create_task(crash_soon())
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# await something # <- this needs to be canceled
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# # by the TaskGroup, e.g.
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# # foo() needs to be cancelled
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# except Exception:
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# # Ignore any exceptions raised in the TaskGroup
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# pass
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# await something_else # this line has to be called
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# # after TaskGroup is finished.
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self._abort()
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self._parent_cancel_requested = True
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self._parent_task.cancel()
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