plugin: watchtower: call start_watching() threadsafe
What the developer wrote
Authored by f321x
plugin: watchtower: call start_watching() threadsafe
Launch `WatchtowerPlugin.watchtower.start_watching()` through
asyncio.run_coroutine_threadsafe instead of ensure_future to prevent the
following exception from happening when running python with
`PYTHONASYNCIODEBUG=1`.
```
20251103T165007.087746Z | ERROR | plugin.Plugins | cannot initialize plugin watchtower: Error loading watchtower plugin: RuntimeError('Non-thread-safe operation invoked on an event loop other than the current one')
Traceback (most recent call last):
File "/home/user/code/electrum-fork/electrum/plugin.py", line 629, in load_plugin_by_name
plugin = module.Plugin(self, self.config, name)
File "/home/user/code/electrum-fork/electrum/plugins/watchtower/watchtower.py", line 59, in __init__
asyncio.ensure_future(self.watchtower.start_watching())
~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/lib64/python3.14/asyncio/tasks.py", line 732, in ensure_future
return loop.create_task(coro_or_future)
~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^
File "/usr/lib64/python3.14/asyncio/base_events.py", line 468, in create_task
return self._task_factory(self, coro, **kwargs)
~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^
File "/home/user/code/electrum-fork/electrum/util.py", line 1773, in factory
task = asyncio.Task(coro, loop=loop_, **kwargs)
File "/usr/lib64/python3.14/asyncio/base_events.py", line 829, in call_soon
self._check_thread()
~~~~~~~~~~~~~~~~~~^^
File "/usr/lib64/python3.14/asyncio/base_events.py", line 866, in _check_thread
raise RuntimeError(
"Non-thread-safe operation invoked on an event loop other "
"than the current one")
RuntimeError: Non-thread-safe operation invoked on an event loop other than the current one
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/home/user/code/electrum-fork/electrum/plugin.py", line 184, in load_plugins
self.load_plugin_by_name(name)
~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^
File "/home/user/code/electrum-fork/electrum/plugin.py", line 631, in load_plugin_by_name
raise Exception(f"Error loading {name} plugin: {repr(e)}") from e
Exception: Error loading watchtower plugin: RuntimeError('Non-thread-safe operation invoked on an event loop other than the current one')
```
What changed, and why it matters
This is a small bug-fix patch for Electrum's watchtower plugin. It changes how a background monitoring task is started so it is scheduled on the correct event loop thread, preventing a crash when running Python with extra asyncio debugging enabled. The crash is a reliability issue, not a security vulnerability that can be exploited by an attacker.
Treat as a routine stability/reliability fix. No urgent security response is needed. Users running the watchtower plugin with PYTHONASYNCIODEBUG=1 will benefit from the corrected scheduling behavior.
Security signals we found
Thread-safety fix in asyncio task scheduling
Crash-only symptom (RuntimeError on plugin load)
No attacker-controlled input or privilege boundary crossed
No memory corruption, injection, or cryptographic weakness
Evidence from the diff
The commit replaces asyncio.ensure_future(self.watchtower.start_watching()) with asyncio.run_coroutine_threadsafe(self.watchtower.start_watching(), self.network.asyncio_loop). The original code created a task on the wrong event loop from a non-event-loop thread, which raises RuntimeError under PYTHONASYNCIODEBUG=1 and is generally unsafe. The fix schedules the coroutine onto the network’s asyncio loop in a thread-safe manner, matching the pattern already used for the WatchTowerServer task on the next line.
Changed components
electrum/plugins/watchtower/watchtower.pyWatchtowerPlugin initializationInspect captured patch +1 / −1
diff --git a/electrum/plugins/watchtower/watchtower.py b/electrum/plugins/watchtower/watchtower.py
index 6bb08a8..04212c2 100644
--- a/electrum/plugins/watchtower/watchtower.py
+++ b/electrum/plugins/watchtower/watchtower.py
@@ -56,7 +56,7 @@ class WatchtowerPlugin(BasePlugin):
return
self.watchtower = WatchTower(self.network)
- asyncio.ensure_future(self.watchtower.start_watching())
+ asyncio.run_coroutine_threadsafe(self.watchtower.start_watching(), self.network.asyncio_loop)
if watchtower_port := self.config.WATCHTOWER_SERVER_PORT:
self.server = WatchTowerServer(self.watchtower, self.network, watchtower_port)
asyncio.run_coroutine_threadsafe(self.network.taskgroup.spawn(self.server.run), self.network.asyncio_loop)
Why this scored 24/100
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