Bug report
Bug description:
asyncio.shield() never releases a waiter that was cancelled, the cancelled task stays referenced by the shielded task forever. As a result, printing call graph raises an exception
Repro:
import asyncio
async def main():
inner = asyncio.create_task(asyncio.sleep(3600), name="INNER")
async def waiter():
await asyncio.shield(inner)
alive= asyncio.create_task(waiter(), name="ALIVE")
for i in range(2):
t = asyncio.create_task(waiter(), name=f"CANCELLED-{i}")
await asyncio.sleep(0)
t.cancel()
await asyncio.sleep(0)
asyncio.print_call_graph(inner)
inner.cancel()
asyncio.run(main())Expected:
* Task(name='INNER', id=0x35f290b0410)
+ Call stack:
| File '/Users/timofeiivankov/cpython/Lib/asyncio/tasks.py', line 705, in async sleep()
+ Awaited by:
* Task(name='ALIVE', id=0x35f290b0610)
+ Call stack:
| File '/Users/timofeiivankov/cpython/repro.py', line 7, in async main.<locals>.waiter()
Actually:
Traceback (most recent call last):
File "/Users/timofeiivankov/cpython/repro.py", line 19, in <module>
asyncio.run(main())
~~~~~~~~~~~^^^^^^^^
File "/Users/timofeiivankov/cpython/Lib/asyncio/runners.py", line 205, in run
return runner.run(main)
~~~~~~~~~~^^^^^^
File "/Users/timofeiivankov/cpython/Lib/asyncio/runners.py", line 128, in run
return self._loop.run_until_complete(task)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
File "/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py", line 725, in run_until_complete
return future.result()
~~~~~~~~~~~~~^^
File "/Users/timofeiivankov/cpython/repro.py", line 16, in main
asyncio.print_call_graph(inner)
~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^
File "/Users/timofeiivankov/cpython/Lib/asyncio/graph.py", line 276, in print_call_graph
print(format_call_graph(future, depth=depth, limit=limit), file=file)
~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/Users/timofeiivankov/cpython/Lib/asyncio/graph.py", line 260, in format_call_graph
render_level(graph, buf, 0)
~~~~~~~~~~~~^^^^^^^^^^^^^^^
File "/Users/timofeiivankov/cpython/Lib/asyncio/graph.py", line 252, in render_level
render_level(fut, buf, level + 1)
~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
File "/Users/timofeiivankov/cpython/Lib/asyncio/graph.py", line 217, in render_level
if f.f_generator is None:
^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'f_generator'
Proposed fix: add cleanup in _outer_done_callback of asyncio.shield()
def _outer_done_callback(outer):
if not inner.done():
inner.remove_done_callback(_inner_done_callback)
if cur_task is not None:
inner.remove_done_callback(_clear_awaited_by_callback)
futures.future_discard_from_awaited_by(inner, cur_task)
# Keep only one callback to log on cancel
inner.remove_done_callback(_log_on_exception)
inner.add_done_callback(_log_on_exception)I have a fix ready
CPython versions tested on:
CPython main branch
Operating systems tested on:
macOS
Linked PRs
Bug report
Bug description:
asyncio.shield()never releases a waiter that was cancelled, the cancelled task stays referenced by the shielded task forever. As a result, printing call graph raises an exceptionRepro:
Expected:
Actually:
Proposed fix: add cleanup in
_outer_done_callbackofasyncio.shield()I have a fix ready
CPython versions tested on:
CPython main branch
Operating systems tested on:
macOS
Linked PRs