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util: cleanup asyncio event loop after stopping
Public commit record
86/100 · Strong
What the developer wrote
Authored by f321x
util: cleanup asyncio event loop after stopping
I noticed many ResourceWarning when running regtests with
PYTHONASYNCIODEBUG=1 and PYTHONDEVMODE=1, each time a daemon
gets stopped the asyncio loop wouldn't get properly cleaned up:
```
(env) user@hp:~/code/electrum-fork$ python3 -m unittest tests.regtest.TestLightningAB.test_lnwatcher_waits_until_fees_go_down
***** test_lnwatcher_waits_until_fees_go_down ******
initializing alice
0.67 | W | asyncio | Executing <Task finished name='Task-1' coro=<run_offline_command() done, defined at /home/user/code/electrum-fork/./run_electrum:229> result={'msg': 'Please keep ... your wallet.', 'path': '/tmp/alice/r...efault_wallet', 'seed': 'fiction sadd...it radar desk'} created at /home/user/code/electrum-fork/electrum/util.py:1760> took 0.280 seconds
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
funding alice
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
f84277454a04243e500cf84c67aad16e04dd7a88ffa849ffcf20ce3f9af277df
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
initializing bob
0.54 | W | asyncio | Executing <Task finished name='Task-1' coro=<run_offline_command() done, defined at /home/user/code/electrum-fork/./run_electrum:229> result={'msg': 'Please keep ... your wallet.', 'path': '/tmp/bob/reg...efault_wallet', 'seed': 'wink loud so...ory myth case'} created at /home/user/code/electrum-fork/electrum/util.py:1760> took 0.195 seconds
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
funding bob
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
f68b651e84dc8547f54dd09129018a2d0d256dedc8ccc48595ae172de895371a
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
mining 1 blocks
starting daemon (PID 38153)
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
/tmp/alice/regtest/wallets/default_wallet
/usr/lib64/python3.14/asyncio/base_events.py:758: ResourceWarning: unclosed event loop <_UnixSelectorEventLoop running=False closed=False debug=True>
```
This commits adds some cleanup to `util.create_and_start_event_loop()`
to
1. cancel remaining tasks
2. shut down asyncgens
3. shutdown the default executor
4. call loop.close() to free the resources allocated to the loop
See https://stackoverflow.com/questions/30765606/whats-the-correct-way-to-clean-up-after-an-interrupted-event-loop
This seems to reliably solve the mentioned `ResourceWarning`.
✓ Descriptive subject✓ Names a concrete action or component✓ Provides detailed explanatory context✓ Mentions testing or verification✓ Links an issue, advisory, or supporting reference
What changed, and why it matters
This commit fixes a housekeeping issue in Electrum's background task manager. When the program stopped an internal 'event loop,' it previously left it partially open, causing Python resource warnings. The patch makes sure remaining tasks are cancelled, generators are shut down, the executor is stopped, and the loop is fully closed. There is no direct security vulnerability described; it is a cleanup that may improve stability and reduce resource leaks during testing.
Recommended action
Treat as a normal stability/maintenance improvement. Review whether the new cleanup order could hide exceptions during shutdown, but no urgent security action is indicated.
Security signals we found
01
Resource leak cleanup in asyncio event loop shutdown
02
No explicit security bug or exploit path described
03
Improves graceful teardown of background tasks and executor threads
Evidence from the diff
The change is in electrum/util.py inside create_and_start_event_loop(). The existing cleanup block now cancels all pending tasks with asyncio.gather(*asyncio.all_tasks(loop), return_exceptions=True), suppresses CancelledError, runs loop.shutdown_asyncgens(), runs loop.shutdown_default_executor() for BaseEventLoop, logs any exception, sets the global loop reference to None, and finally calls loop.close(). The commit message frames this as resolving ResourceWarning messages observed in regtests with PYTHONASYNCIODEBUG=1 and PYTHONDEVMODE=1.
Changed components
electrum/util.pycreate_and_start_event_loop()Inspect captured patch +13 / −1
diff --git a/electrum/util.py b/electrum/util.py
index cc27336..08e60e5 100644
--- a/electrum/util.py
+++ b/electrum/util.py
@@ -52,7 +52,7 @@ import functools
from functools import partial
from abc import abstractmethod, ABC
import enum
-from contextlib import nullcontext
+from contextlib import nullcontext, suppress
import traceback
import inspect
@@ -1704,8 +1704,20 @@ def create_and_start_event_loop() -> Tuple[asyncio.AbstractEventLoop,
loop.run_until_complete(stopping_fut)
finally:
# clean-up
+ try:
+ pending_tasks = asyncio.gather(*asyncio.all_tasks(loop), return_exceptions=True)
+ pending_tasks.cancel()
+ with suppress(asyncio.CancelledError):
+ loop.run_until_complete(pending_tasks)
+ loop.run_until_complete(loop.shutdown_asyncgens())
+ if isinstance(loop, asyncio.BaseEventLoop):
+ loop.run_until_complete(loop.shutdown_default_executor())
+ except Exception as e:
+ _logger.debug(f"exception when cleaning up asyncio event loop: {e}")
+
global _asyncio_event_loop
_asyncio_event_loop = None
+ loop.close()
loop.set_exception_handler(on_exception)
_set_custom_task_factory(loop)
Risk score
Our methodology →Why this scored 19/100
Human-validated context
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