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fix(tools): support CPython 3.14 ThreadPoolExecutor internals in DaemonThreadPoolExecutor #69209

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fix(tools): support CPython 3.14 ThreadPoolExecutor internals in DaemonThreadPoolExecutor #69209

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29 changes: 23 additions & 6 deletions tools/daemon_pool.py
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Original file line number Diff line number Diff line change
Expand Up @@ -33,12 +33,19 @@

__all__ = ["DaemonThreadPoolExecutor"]

# CPython 3.14 reworked ThreadPoolExecutor internals: per-worker state
# (initializer/initargs) moved into a WorkerContext built by the new
# ``prepare_context()`` classmethod, and ``_worker`` now takes
# ``(executor_ref, ctx, work_queue)`` instead of
# ``(executor_ref, work_queue, initializer, initargs)``.
_HAS_WORKER_CONTEXT = hasattr(ThreadPoolExecutor, "prepare_context")


class DaemonThreadPoolExecutor(ThreadPoolExecutor):
"""ThreadPoolExecutor variant whose workers do not block process exit."""

def _adjust_thread_count(self) -> None:
# Mirrors CPython's implementation (3.8–3.13) with two changes:
# Mirrors CPython's implementation (3.8–3.14) with two changes:
# daemon=True and no _threads_queues registration.
if self._idle_semaphore.acquire(timeout=0):
return
Expand All @@ -49,15 +56,25 @@ def weakref_cb(_, q=self._work_queue):
num_threads = len(self._threads)
if num_threads < self._max_workers:
thread_name = "%s_%d" % (self._thread_name_prefix or self, num_threads)
t = threading.Thread(
name=thread_name,
target=_worker,
args=(
if _HAS_WORKER_CONTEXT:
# CPython 3.14+ worker signature.
worker_args = (
weakref.ref(self, weakref_cb),
self._create_worker_context(),
self._work_queue,
)
else:

@teknium1 teknium1 Jul 30, 2026

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Please add a mocked regression test for this branch. CI currently supports Python <3.14, so the normal daemon-pool submission tests cannot execute this WorkerContext tuple.

# CPython 3.8–3.13 worker signature.
worker_args = (
weakref.ref(self, weakref_cb),
self._work_queue,
self._initializer,
self._initargs,
),
)
t = threading.Thread(
name=thread_name,
target=_worker,
args=worker_args,
daemon=True,
)
t.start()
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