"""
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
"""
from . import _concurrent_futures_thread as thread
import os
import logging
import queue
import threading
import itertools
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(ThreadPoolExecutor, self).__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()
[docs]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. Subject to the terms and conditions of this License Agreement, PSF hereby
grants Licensee a nonexclusive, royalty-free, world-wide license to reproduce,
analyze, test, perform and/or display publicly, prepare derivative works,
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version, provided, however, that PSF's License Agreement and PSF's notice of
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Reserved" are retained in Python 3.5.2 alone or in any derivative version
prepared by Licensee.
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incorporates Python 3.5.2 or any part thereof, and wants to make the
derivative work available to others as provided herein, then Licensee hereby
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3.5.2.
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PSF MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED. 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
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7. Nothing in this License Agreement shall be deemed to create any relationship
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Agreement does not grant permission to use PSF trademarks or trade name in a
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third party.
8. By copying, installing or otherwise using Python 3.5.2, Licensee agrees
to be bound by the terms and conditions of this License Agreement.
"""