GeezerVison is showing github.com — `call_soon_threadsafe` callbacks from executor no longer run before `await run_in_executor()` returns in 3.14.3 · Issue #144506 · python/cpython
call_soon_threadsafe callbacks from executor no longer run before await run_in_executor() returns in 3.14.3 #144506
DescriptionBug report
Bug description:
Python 3.14.3 introduced a behavior change of how run_in_executor interacts with call_soon_threadsafe. Previously, callbacks scheduled via call_soon_threadsafe from within an executor job were guaranteed to run before await run_in_executor() returned.
This seems to be a direct cause of changes from gh-141696, as monkey-patching the asyncio.futures._chain_future reverts to the old behavior.
Reproducer:
import asyncio
import sys
import threading
from concurrent.futures import ThreadPoolExecutor
print(f"Python version: {sys.version}")
async def test_timing():
loop = asyncio.get_running_loop()
executor = ThreadPoolExecutor(max_workers=1)
results = []
def final_callback():
results.append("final_callback")
def intermediate_callback():
results.append("intermediate_callback")
loop.call_soon(final_callback)
def thread_work():
results.append("thread_work")
loop.call_soon_threadsafe(intermediate_callback)
await loop.run_in_executor(executor, thread_work)
results.append("executor_done")
await asyncio.sleep(0)
results.append("after_sleep_0")
executor.shutdown(wait=False)
final_ran_before_sleep = (
"final_callback" in results
and results.index("final_callback") < results.index("after_sleep_0")
)
return final_ran_before_sleep, results
async def main():
for i in range(20):
success, results = await test_timing()
print(f" Iteration {i+1} {'PASS' if success else 'FAIL'}: {results}")
asyncio.run(main())3.14.2:
Python version: 3.14.2 (main, Feb 5 2026, 13:08:22) [GCC 15.2.1 20260103]
Iteration 1 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
(rest is the same)
3.14.3:
Python version: 3.14.3 (main, Feb 5 2026, 12:15:05) [GCC 15.2.1 20260103]
Iteration 1 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 2 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 3 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 4 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 5 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 6 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 7 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 8 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 9 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 10 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 11 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 12 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 13 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 14 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 15 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 16 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 17 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 18 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 19 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
Iteration 20 FAIL: ['thread_work', 'executor_done', 'intermediate_callback', 'after_sleep_0']
3.14.3, with asyncio.sleep(1e-15), all callbacks run but order changes:
Python version: 3.14.3 (main, Feb 5 2026, 12:15:05) [GCC 15.2.1 20260103]
Iteration 1 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 2 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 3 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 4 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 5 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 6 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 7 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 8 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 9 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 10 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 11 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 12 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 13 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 14 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 15 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 16 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 17 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 18 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
Iteration 19 PASS: ['thread_work', 'intermediate_callback', 'final_callback', 'executor_done', 'after_sleep_0']
Iteration 20 PASS: ['thread_work', 'executor_done', 'intermediate_callback', 'final_callback', 'after_sleep_0']
CPython versions tested on:
3.14
Operating systems tested on:
Linux Activitykumaraditya303 commented on Feb 6, 2026
Previously, callbacks scheduled via call_soon_threadsafe from within an executor job were guaranteed to run before await run_in_executor() returned.
Hmm, AFAIK this was never guaranteed, it just happened to work like that on previous versions. If you change the call_soon to call_later with small delay such as 0.001 in intermediate_callback then you would see this behaviour on older versions as well. kumaraditya303 commented on Mar 21, 2026 I'll close this as this is being fixed on home-assistant side.
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