""" Modified ThreadPoolExecutor to support threads leaving the thread pool This includes a global `secede` method that a submitted function can call to have its thread leave the ThreadPoolExecutor's thread pool. This allows the thread pool to allocate another thread if necessary and so is useful when a function realises that it is going to be a long-running job that doesn't want to take up space. When the function finishes its thread will terminate gracefully. This code copies and modifies two functions from the `concurrent.futures.thread` module, notably `_worker` and ThreadPoolExecutor._adjust_thread_count` to allow for checking against a global `threading.local` state. These functions are subject to the following license, which is included as a comment at the end of this file: https://docs.python.org/3/license.html ... and are under copyright by the Python Software Foundation Copyright 2001-2016 Python Software Foundation; All Rights Reserved """ import itertools import logging import os import queue import threading from . import _concurrent_futures_thread as thread from .metrics import time logger = logging.getLogger(__name__) thread_state = threading.local() def _worker(executor, work_queue): thread_state.proceed = True thread_state.executor = executor try: while thread_state.proceed: with executor._rejoin_lock: if executor._rejoin_list: rejoin_thread, rejoin_event = executor._rejoin_list.pop() executor._threads.add(rejoin_thread) executor._threads.remove(threading.current_thread()) rejoin_event.set() break try: task = work_queue.get(timeout=1) except queue.Empty: continue if task is not None: # sentinel task.run() del task elif thread._shutdown or executor is None or executor._shutdown: work_queue.put(None) return del executor except BaseException: logger.critical("Exception in worker", exc_info=True) finally: del thread_state.proceed del thread_state.executor class ThreadPoolExecutor(thread.ThreadPoolExecutor): # Used to assign unique thread names _counter = itertools.count() def __init__(self, *args, **kwargs): super().__init__(*args, **kwargs) self._rejoin_list = [] self._rejoin_lock = threading.Lock() self._thread_name_prefix = kwargs.get( "thread_name_prefix", "DaskThreadPoolExecutor" ) def _adjust_thread_count(self): if len(self._threads) < self._max_workers: t = threading.Thread( target=_worker, name=self._thread_name_prefix + "-%d-%d" % (os.getpid(), next(self._counter)), args=(self, self._work_queue), ) t.daemon = True self._threads.add(t) t.start() def shutdown(self, wait=True, timeout=None): with threads_lock: with self._shutdown_lock: self._shutdown = True self._work_queue.put(None) if timeout is not None: deadline = time() + timeout if wait: for t in self._threads: if timeout is not None: timeout2 = max(deadline - time(), 0) else: timeout2 = None t.join(timeout=timeout2) def secede(adjust=True): """Have this thread secede from the ThreadPoolExecutor See Also -------- rejoin : rejoin the thread pool """ thread_state.proceed = False with threads_lock: thread_state.executor._threads.remove(threading.current_thread()) if adjust: thread_state.executor._adjust_thread_count() def rejoin(): """Have this thread rejoin the ThreadPoolExecutor This will block until a new slot opens up in the executor. The next thread to finish a task will leave the pool to allow this one to join. See Also -------- secede : leave the thread pool """ thread = threading.current_thread() event = threading.Event() e = thread_state.executor with e._rejoin_lock: e._rejoin_list.append((thread, event)) e.submit(lambda: None) event.wait() thread_state.proceed = True threads_lock = threading.Lock() """ PSF LICENSE AGREEMENT FOR PYTHON 3.5.2 ====================================== 1. This LICENSE AGREEMENT is between the Python Software Foundation ("PSF"), and the Individual or Organization ("Licensee") accessing and otherwise using Python 3.5.2 software in source or binary form and its associated documentation. 2. 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BY WAY OF EXAMPLE, BUT NOT LIMITATION, PSF MAKES NO AND DISCLAIMS ANY REPRESENTATION OR WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE OR THAT THE USE OF PYTHON 3.5.2 WILL NOT INFRINGE ANY THIRD PARTY RIGHTS. 5. PSF SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF PYTHON 3.5.2 FOR ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS A RESULT OF MODIFYING, DISTRIBUTING, OR OTHERWISE USING PYTHON 3.5.2, OR ANY DERIVATIVE THEREOF, EVEN IF ADVISED OF THE POSSIBILITY THEREOF. 6. This License Agreement will automatically terminate upon a material breach of its terms and conditions. 7. Nothing in this License Agreement shall be deemed to create any relationship of agency, partnership, or joint venture between PSF and Licensee. This License Agreement does not grant permission to use PSF trademarks or trade name in a trademark sense to endorse or promote products or services of Licensee, or any third party. 8. 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