New submission from Dima Tisnek <dim...@gmail.com>:
Cancelling a deadlocked group of tasks results in MaximumRecursionError Inspired by https://stackoverflow.com/questions/55341189/handling-asyncio-deadlocks Given the following test-asyncio.py: ``` import asyncio async def test(): async def f(): await g_task async def g(): await f_task f_task = asyncio.create_task(f()) g_task = asyncio.create_task(g()) async def release(): await asyncio.sleep(5) f_task.cancel() await asyncio.gather(f_task, g_task, release()) asyncio.run(test()) ``` Results in: ``` Traceback (most recent call last): File ".../python3.8/asyncio/runners.py", line 43, in run return loop.run_until_complete(main) File ".../python3.8/asyncio/base_events.py", line 589, in run_until_complete return future.result() File "test-asyncio.py", line 18, in test await asyncio.gather(f_task, g_task, release()) File "test-asyncio.py", line 16, in release f_task.cancel() RecursionError: maximum recursion depth exceeded while calling a Python object During handling of the above exception, another exception occurred: Traceback (most recent call last): File "test-asyncio.py", line 20, in <module> asyncio.run(test()) File ".../python3.8/asyncio/runners.py", line 46, in run _cancel_all_tasks(loop) File ".../python3.8/asyncio/runners.py", line 59, in _cancel_all_tasks task.cancel() RecursionError: maximum recursion depth exceeded while calling a Python object Exception in default exception handler Traceback (most recent call last): File ".../python3.8/asyncio/base_events.py", line 1644, in call_exception_handler self.default_exception_handler(context) File ".../python3.8/asyncio/base_events.py", line 1615, in default_exception_handler value = repr(value) File ".../python3.8/asyncio/base_tasks.py", line 21, in _task_repr_info info.insert(3, f'wait_for={task._fut_waiter!r}') File ".../python3.8/asyncio/base_tasks.py", line 21, in _task_repr_info info.insert(3, f'wait_for={task._fut_waiter!r}') File ".../python3.8/asyncio/base_tasks.py", line 21, in _task_repr_info info.insert(3, f'wait_for={task._fut_waiter!r}') [Previous line repeated 326 more times] File ".../python3.8/asyncio/base_tasks.py", line 9, in _task_repr_info info = base_futures._future_repr_info(task) File ".../python3.8/asyncio/base_futures.py", line 57, in _future_repr_info info.append(_format_callbacks(future._callbacks)) File ".../python3.8/asyncio/base_futures.py", line 36, in _format_callbacks cb = '{}, {}'.format(format_cb(cb[0][0]), format_cb(cb[1][0])) File ".../python3.8/asyncio/base_futures.py", line 31, in format_cb return format_helpers._format_callback_source(callback, ()) File ".../python3.8/asyncio/format_helpers.py", line 23, in _format_callback_source func_repr = _format_callback(func, args, None) File ".../python3.8/asyncio/format_helpers.py", line 56, in _format_callback func_repr += _format_args_and_kwargs(args, kwargs) File ".../python3.8/asyncio/format_helpers.py", line 41, in _format_args_and_kwargs return '({})'.format(', '.join(items)) RecursionError: maximum recursion depth exceeded while calling a Python object Exception in default exception handler Traceback (most recent call last): File ".../python3.8/asyncio/base_events.py", line 1644, in call_exception_handler self.default_exception_handler(context) File ".../python3.8/asyncio/base_events.py", line 1615, in default_exception_handler value = repr(value) File ".../python3.8/asyncio/base_tasks.py", line 21, in _task_repr_info info.insert(3, f'wait_for={task._fut_waiter!r}') File ".../python3.8/asyncio/base_tasks.py", line 21, in _task_repr_info info.insert(3, f'wait_for={task._fut_waiter!r}') File ".../python3.8/asyncio/base_tasks.py", line 21, in _task_repr_info info.insert(3, f'wait_for={task._fut_waiter!r}') [Previous line repeated 326 more times] File ".../python3.8/asyncio/base_tasks.py", line 9, in _task_repr_info info = base_futures._future_repr_info(task) File ".../python3.8/asyncio/base_futures.py", line 57, in _future_repr_info info.append(_format_callbacks(future._callbacks)) File ".../python3.8/asyncio/base_futures.py", line 36, in _format_callbacks cb = '{}, {}'.format(format_cb(cb[0][0]), format_cb(cb[1][0])) File ".../python3.8/asyncio/base_futures.py", line 31, in format_cb return format_helpers._format_callback_source(callback, ()) File ".../python3.8/asyncio/format_helpers.py", line 23, in _format_callback_source func_repr = _format_callback(func, args, None) File ".../python3.8/asyncio/format_helpers.py", line 56, in _format_callback func_repr += _format_args_and_kwargs(args, kwargs) File ".../python3.8/asyncio/format_helpers.py", line 41, in _format_args_and_kwargs return '({})'.format(', '.join(items)) RecursionError: maximum recursion depth exceeded while calling a Python object ``` ---------- components: asyncio messages: 339006 nosy: Dima.Tisnek, asvetlov, yselivanov priority: normal severity: normal status: open title: task.cancel unbound recursion versions: Python 3.7, Python 3.8, Python 3.9 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