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Issue #11635: Don't use polling in worker threads and processes launched by 

concurrent.futures.
This commit is contained in:
Antoine Pitrou 2011-03-26 19:29:44 +01:00
parent d9faa201ce
commit c13d454e84
3 changed files with 95 additions and 78 deletions
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110
Lib/concurrent/futures/process.py
View File

@ -66,28 +66,17 @@ import weakref
# workers to exit when their work queues are empty and then waits until the
# threads/processes finish.
_thread_references = set()
_threads_queues = weakref.WeakKeyDictionary()
_shutdown = False
def _python_exit():
global _shutdown
_shutdown = True
for thread_reference in _thread_references:
thread = thread_reference()
if thread is not None:
thread.join()
def _remove_dead_thread_references():
"""Remove inactive threads from _thread_references.
Should be called periodically to prevent memory leaks in scenarios such as:
>>> while True:
>>> ... t = ThreadPoolExecutor(max_workers=5)
>>> ... t.map(int, ['1', '2', '3', '4', '5'])
"""
for thread_reference in set(_thread_references):
if thread_reference() is None:
_thread_references.discard(thread_reference)
items = list(_threads_queues.items())
for t, q in items:
q.put(None)
for t, q in items:
t.join()
# Controls how many more calls than processes will be queued in the call queue.
# A smaller number will mean that processes spend more time idle waiting for
@ -130,11 +119,15 @@ def _process_worker(call_queue, result_queue, shutdown):
"""
while True:
try:
call_item = call_queue.get(block=True, timeout=0.1)
call_item = call_queue.get(block=True)
except queue.Empty:
if shutdown.is_set():
return
else:
if call_item is None:
# Wake up queue management thread
result_queue.put(None)
return
try:
r = call_item.fn(*call_item.args, **call_item.kwargs)
except BaseException as e:
@ -209,40 +202,56 @@ def _queue_manangement_worker(executor_reference,
process workers that they should exit when their work queue is
empty.
"""
nb_shutdown_processes = 0
def shutdown_one_process():
"""Tell a worker to terminate, which will in turn wake us again"""
nonlocal nb_shutdown_processes
call_queue.put(None)
nb_shutdown_processes += 1
while True:
_add_call_item_to_queue(pending_work_items,
work_ids_queue,
call_queue)
try:
result_item = result_queue.get(block=True, timeout=0.1)
result_item = result_queue.get(block=True)
except queue.Empty:
executor = executor_reference()
# No more work items can be added if:
# - The interpreter is shutting down OR
# - The executor that owns this worker has been collected OR
# - The executor that owns this worker has been shutdown.
if _shutdown or executor is None or executor._shutdown_thread:
# Since no new work items can be added, it is safe to shutdown
# this thread if there are no pending work items.
if not pending_work_items:
shutdown_process_event.set()
# If .join() is not called on the created processes then
# some multiprocessing.Queue methods may deadlock on Mac OS
# X.
for p in processes:
p.join()
return
del executor
pass
else:
work_item = pending_work_items[result_item.work_id]
del pending_work_items[result_item.work_id]
if result_item is not None:
work_item = pending_work_items[result_item.work_id]
del pending_work_items[result_item.work_id]
if result_item.exception:
work_item.future.set_exception(result_item.exception)
if result_item.exception:
work_item.future.set_exception(result_item.exception)
else:
work_item.future.set_result(result_item.result)
continue
# If we come here, we either got a timeout or were explicitly woken up.
# In either case, check whether we should start shutting down.
executor = executor_reference()
# No more work items can be added if:
# - The interpreter is shutting down OR
# - The executor that owns this worker has been collected OR
# - The executor that owns this worker has been shutdown.
if _shutdown or executor is None or executor._shutdown_thread:
# Since no new work items can be added, it is safe to shutdown
# this thread if there are no pending work items.
if not pending_work_items:
shutdown_process_event.set()
while nb_shutdown_processes < len(processes):
shutdown_one_process()
# If .join() is not called on the created processes then
# some multiprocessing.Queue methods may deadlock on Mac OS
# X.
for p in processes:
p.join()
return
else:
work_item.future.set_result(result_item.result)
# Start shutting down by telling a process it can exit.
shutdown_one_process()
del executor
_system_limits_checked = False
_system_limited = None
@ -279,7 +288,6 @@ class ProcessPoolExecutor(_base.Executor):
worker processes will be created as the machine has processors.
"""
_check_system_limits()
_remove_dead_thread_references()
if max_workers is None:
self._max_workers = multiprocessing.cpu_count()
@ -304,10 +312,14 @@ class ProcessPoolExecutor(_base.Executor):
self._pending_work_items = {}
def _start_queue_management_thread(self):
# When the executor gets lost, the weakref callback will wake up
# the queue management thread.
def weakref_cb(_, q=self._result_queue):
q.put(None)
if self._queue_management_thread is None:
self._queue_management_thread = threading.Thread(
target=_queue_manangement_worker,
args=(weakref.ref(self),
args=(weakref.ref(self, weakref_cb),
self._processes,
self._pending_work_items,
self._work_ids,
@ -316,7 +328,7 @@ class ProcessPoolExecutor(_base.Executor):
self._shutdown_process_event))
self._queue_management_thread.daemon = True
self._queue_management_thread.start()
_thread_references.add(weakref.ref(self._queue_management_thread))
_threads_queues[self._queue_management_thread] = self._result_queue
def _adjust_process_count(self):
for _ in range(len(self._processes), self._max_workers):
@ -339,6 +351,8 @@ class ProcessPoolExecutor(_base.Executor):
self._pending_work_items[self._queue_count] = w
self._work_ids.put(self._queue_count)
self._queue_count += 1
# Wake up queue management thread
self._result_queue.put(None)
self._start_queue_management_thread()
self._adjust_process_count()
@ -348,8 +362,10 @@ class ProcessPoolExecutor(_base.Executor):
def shutdown(self, wait=True):
with self._shutdown_lock:
self._shutdown_thread = True
if wait:
if self._queue_management_thread:
if self._queue_management_thread:
# Wake up queue management thread
self._result_queue.put(None)
if wait:
self._queue_management_thread.join()
# To reduce the risk of openning too many files, remove references to
# objects that use file descriptors.

60
Lib/concurrent/futures/thread.py
View File

@ -25,28 +25,17 @@ import weakref
# workers to exit when their work queues are empty and then waits until the
# threads finish.
_thread_references = set()
_threads_queues = weakref.WeakKeyDictionary()
_shutdown = False
def _python_exit():
global _shutdown
_shutdown = True
for thread_reference in _thread_references:
thread = thread_reference()
if thread is not None:
thread.join()
def _remove_dead_thread_references():
"""Remove inactive threads from _thread_references.
Should be called periodically to prevent memory leaks in scenarios such as:
>>> while True:
... t = ThreadPoolExecutor(max_workers=5)
... t.map(int, ['1', '2', '3', '4', '5'])
"""
for thread_reference in set(_thread_references):
if thread_reference() is None:
_thread_references.discard(thread_reference)
items = list(_threads_queues.items())
for t, q in items:
q.put(None)
for t, q in items:
t.join()
atexit.register(_python_exit)
@ -72,18 +61,23 @@ def _worker(executor_reference, work_queue):
try:
while True:
try:
work_item = work_queue.get(block=True, timeout=0.1)
work_item = work_queue.get(block=True)
except queue.Empty:
executor = executor_reference()
# Exit if:
# - The interpreter is shutting down OR
# - The executor that owns the worker has been collected OR
# - The executor that owns the worker has been shutdown.
if _shutdown or executor is None or executor._shutdown:
return
del executor
pass
else:
work_item.run()
if work_item is not None:
work_item.run()
continue
executor = executor_reference()
# Exit if:
# - The interpreter is shutting down OR
# - The executor that owns the worker has been collected OR
# - The executor that owns the worker has been shutdown.
if _shutdown or executor is None or executor._shutdown:
# Notice other workers
work_queue.put(None)
return
del executor
except BaseException as e:
_base.LOGGER.critical('Exception in worker', exc_info=True)
@ -95,8 +89,6 @@ class ThreadPoolExecutor(_base.Executor):
max_workers: The maximum number of threads that can be used to
execute the given calls.
"""
_remove_dead_thread_references()
self._max_workers = max_workers
self._work_queue = queue.Queue()
self._threads = set()
@ -117,19 +109,25 @@ class ThreadPoolExecutor(_base.Executor):
submit.__doc__ = _base.Executor.submit.__doc__
def _adjust_thread_count(self):
# When the executor gets lost, the weakref callback will wake up
# the worker threads.
def weakref_cb(_, q=self._work_queue):
q.put(None)
# TODO(bquinlan): Should avoid creating new threads if there are more
# idle threads than items in the work queue.
if len(self._threads) < self._max_workers:
t = threading.Thread(target=_worker,
args=(weakref.ref(self), self._work_queue))
args=(weakref.ref(self, weakref_cb),
self._work_queue))
t.daemon = True
t.start()
self._threads.add(t)
_thread_references.add(weakref.ref(t))
_threads_queues[t] = self._work_queue
def shutdown(self, wait=True):
with self._shutdown_lock:
self._shutdown = True
self._work_queue.put(None)
if wait:
for t in self._threads:
t.join()

3
Misc/NEWS
View File

@ -53,6 +53,9 @@ Core and Builtins
Library
-------
- Issue #11635: Don't use polling in worker threads and processes launched by
concurrent.futures.
- Issue #11628: cmp_to_key generated class should use __slots__
- Issue #11666: let help() display named tuple attributes and methods