93 lines
3.9 KiB
Python
93 lines
3.9 KiB
Python
"""Shared daemon-thread ThreadPoolExecutor.
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Stdlib ``ThreadPoolExecutor`` workers are non-daemon AND are registered in
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``concurrent.futures.thread._threads_queues``, whose atexit hook
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(``_python_exit``) joins every worker unconditionally — even after
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``shutdown(wait=False)``. A single wedged worker (tool blocked on network
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I/O, hung provider daemon, stuck subagent) therefore blocks interpreter
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exit forever. This is the root cause of multi-minute CLI exits on long
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sessions: every abandoned concurrent-tool batch leaves workers that the
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exit hook insists on joining.
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``DaemonThreadPoolExecutor`` spawns daemon workers and skips the
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``_threads_queues`` registration, so:
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- ``_python_exit`` never joins them, and
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- the interpreter's non-daemon thread join at shutdown skips them.
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Semantics are otherwise identical (initializer/initargs, work queue,
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idle-thread reuse), plus context propagation: ``submit`` snapshots the
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submitting context with ``copy_context()`` and runs each work item inside
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it. Stdlib ``ThreadPoolExecutor`` only does this from Python 3.14; on the
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3.11-3.13 runtimes Hermes ships, a bare pool worker starts with an EMPTY
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Context and silently drops contextvar-based state (profile secret scope,
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HERMES_HOME override) — under the multiplexed gateway a credential read in
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such a worker fails closed with ``UnscopedSecretError``. Propagating by
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default makes every consumer safe even when it forgets
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``propagate_context_to_thread``. Use it for any pool whose work is
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best-effort or independently interruptible and must never hold the process open:
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concurrent tool execution, background memory sync, catalog fan-out,
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subagent timeout wrappers. Do NOT use it for work that must complete
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before exit (durable writes) — those belong on foreground threads with
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explicit bounded joins.
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"""
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from __future__ import annotations
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import threading
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import weakref
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from concurrent.futures import ThreadPoolExecutor
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from concurrent.futures.thread import _worker
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from contextvars import copy_context
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__all__ = ["DaemonThreadPoolExecutor"]
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class DaemonThreadPoolExecutor(ThreadPoolExecutor):
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"""ThreadPoolExecutor variant whose workers do not block process exit."""
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def submit(self, fn, /, *args, **kwargs):
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"""Submit a callable, propagating the caller's contextvars.
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Python 3.14's ``ThreadPoolExecutor`` snapshots the submitting
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context with ``copy_context()`` and runs each work item inside it;
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3.11-3.13 (the runtimes Hermes ships) do not, so a pool worker
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starts with an empty Context and loses the multiplexed profile
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secret scope / HERMES_HOME override. Do it here unconditionally so
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the daemon pool behaves identically on every runtime; on 3.14+ the
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inner ``ctx.run`` re-applies the same immutable context and is a
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no-op.
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"""
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ctx = copy_context()
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def _run_with_context(*call_args, **call_kwargs):
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return ctx.run(fn, *call_args, **call_kwargs)
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return super().submit(_run_with_context, *args, **kwargs)
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def _adjust_thread_count(self) -> None:
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# Mirrors CPython's implementation (3.8–3.13) with two changes:
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# daemon=True and no _threads_queues registration.
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if self._idle_semaphore.acquire(timeout=0):
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return
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def weakref_cb(_, q=self._work_queue):
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q.put(None)
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num_threads = len(self._threads)
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if num_threads < self._max_workers:
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thread_name = "%s_%d" % (self._thread_name_prefix or self, num_threads)
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t = threading.Thread(
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name=thread_name,
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target=_worker,
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args=(
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weakref.ref(self, weakref_cb),
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self._work_queue,
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self._initializer,
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self._initargs,
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),
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daemon=True,
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)
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t.start()
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self._threads.add(t)
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