Python 3.12: can't create new thread at interpreter shutdown

[robhudson]

• gevent version: 24.2.1 from pypi
• Python version: cPython 3.12.2 via python:3.12-slim-bookworm Docker
• Operating System: Ubuntu via python:3.12-slim-bookworm Docker

Description:

Running gunicorn + gevent, received reports via Sentry:

RuntimeError: can't create new thread at interpreter shutdown
  File "newrelic/core/application.py", line 1346, in harvest
    self._active_session.send_span_events(spans.sampling_info, span_samples)
  File "newrelic/core/data_collector.py", line 133, in send_span_events
    return self._protocol.send("span_event_data", payload)
  File "newrelic/core/agent_protocol.py", line 230, in send
    response = self.client.send_request(path=path, params=params, headers=headers, payload=payload)
  File "newrelic/common/agent_http.py", line 446, in send_request
    response = self._connection.request_encode_url(
  File "newrelic/packages/urllib3/request.py", line 96, in request_encode_url
    return self.urlopen(method, url, **extra_kw)
  File "newrelic/packages/urllib3/connectionpool.py", line 703, in urlopen
    httplib_response = self._make_request(
  File "newrelic/packages/urllib3/connectionpool.py", line 386, in _make_request
    self._validate_conn(conn)
  File "newrelic/packages/urllib3/connectionpool.py", line 1042, in _validate_conn
    conn.connect()
  File "newrelic/packages/urllib3/connection.py", line 363, in connect
    self.sock = conn = self._new_conn()
  File "newrelic/packages/urllib3/connection.py", line 174, in _new_conn
    conn = connection.create_connection(
  File "newrelic/packages/urllib3/util/connection.py", line 72, in create_connection
    for res in socket.getaddrinfo(host, port, family, socket.SOCK_STREAM):
  File "gevent/_socketcommon.py", line 225, in getaddrinfo
    addrlist = get_hub().resolver.getaddrinfo(host, port, family, type, proto, flags)
  File "gevent/resolver/thread.py", line 63, in getaddrinfo
    return self.pool.apply(_socket.getaddrinfo, args, kwargs)
  File "gevent/pool.py", line 161, in apply
    return self.spawn(func, *args, **kwds).get()
  File "gevent/threadpool.py", line 546, in spawn
    self.adjust()
  File "gevent/threadpool.py", line 492, in adjust
    self._adjust_step()
  File "gevent/threadpool.py", line 472, in _adjust_step
    self._add_thread()
  File "gevent/threadpool.py", line 499, in _add_thread
    self._WorkerGreenlet(self)
  File "gevent/threadpool.py", line 106, in __init__
    start_new_thread(self._begin, ())