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asyncio subprocess spawn does not record the awaiting task #157259
Description
Bug report
Bug description:
The internal subprocess pipe-connect task registers no awaited_by edge
Repro:
import asyncio, sys
async def main():
spawn = asyncio.create_task(
asyncio.create_subprocess_exec(sys.executable, '-c', 'pass',
stdin=asyncio.subprocess.PIPE),
name='spawn')
await asyncio.sleep(0)
await asyncio.sleep(0)
for t in asyncio.all_tasks() - {asyncio.current_task()}:
asyncio.print_call_graph(t)
proc = await spawn
await proc.wait()
asyncio.run(main())Actual:
* Task(name='spawn', id=0x103e00b90)
+ Call stack:
| File '/Users/timofeiivankov/cpython/Lib/asyncio/unix_events.py', line 211, in async _UnixSelectorEventLoop._make_subprocess_transport()
| File '/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py', line 1839, in async BaseEventLoop.subprocess_exec()
| File '/Users/timofeiivankov/cpython/Lib/asyncio/subprocess.py', line 249, in async create_subprocess_exec()
* Task(name='Task-2', id=0x103b7d0a0)
+ Call stack:
| File '/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py', line 1753, in async BaseEventLoop.connect_write_pipe()
| File '/Users/timofeiivankov/cpython/Lib/asyncio/base_subprocess.py', line 188, in async BaseSubprocessTransport._connect_pipes()
Expected:
* Task(name='spawn', id=0x105620b90)
+ Call stack:
| File '/Users/timofeiivankov/cpython/Lib/asyncio/unix_events.py', line 211, in async _UnixSelectorEventLoop._make_subprocess_transport()
| File '/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py', line 1839, in async BaseEventLoop.subprocess_exec()
| File '/Users/timofeiivankov/cpython/Lib/asyncio/subprocess.py', line 249, in async create_subprocess_exec()
* Task(name='Task-2', id=0x10539d0a0)
+ Call stack:
| File '/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py', line 1753, in async BaseEventLoop.connect_write_pipe()
| File '/Users/timofeiivankov/cpython/Lib/asyncio/base_subprocess.py', line 194, in async BaseSubprocessTransport._connect_pipes()
+ Awaited by:
* Task(name='spawn', id=0x105620b90)
+ Call stack:
| File '/Users/timofeiivankov/cpython/Lib/asyncio/unix_events.py', line 211, in async _UnixSelectorEventLoop._make_subprocess_transport()
| File '/Users/timofeiivankov/cpython/Lib/asyncio/base_events.py', line 1839, in async BaseEventLoop.subprocess_exec()
| File '/Users/timofeiivankov/cpython/Lib/asyncio/subprocess.py', line 249, in async create_subprocess_exec()
Proposed fix: register the edge in BaseSubprocessTransport.__init__ and discard it in doe callback
I have a fix ready for that
CPython versions tested on:
CPython main branch
Operating systems tested on:
macOS
Activity
kumaraditya303 commentedon Sep 10, 2026
There is little value in recording for internal tasks
deadlovelll commentedon Sep 10, 2026
The docs say no exception for internal tasks (ascynio-graph.rst:125) :
For example we have same bookkeeping in
staggered_race()for its internalrun_one_corotasksSo i think this should be supported too
pythongh-157259: Skip subprocess call graph test on platforms without…