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Bypass the pathological case of too many threads #17615

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Bypass the pathological case of too many threads #17615

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22 changes: 19 additions & 3 deletions Lib/concurrent/futures/thread.py
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Original file line number Diff line number Diff line change
Expand Up @@ -122,13 +122,16 @@ class ThreadPoolExecutor(_base.Executor):
_counter = itertools.count().__next__

def __init__(self, max_workers=None, thread_name_prefix='',
shrink_on_exception=False,
initializer=None, initargs=()):
"""Initializes a new ThreadPoolExecutor instance.

Args:
max_workers: The maximum number of threads that can be used to
execute the given calls.
thread_name_prefix: An optional name prefix to give our threads.
shrink_on_exception: If no more threads can be created shrink the
pool decreasing max_workers instead of throwing exception
initializer: A callable used to initialize worker threads.
initargs: A tuple of arguments to pass to the initializer.
"""
Expand All @@ -149,6 +152,7 @@ def __init__(self, max_workers=None, thread_name_prefix='',

self._max_workers = max_workers
self._work_queue = queue.SimpleQueue()
self._shrink_on_exception = shrink_on_exception
self._idle_semaphore = threading.Semaphore(0)
self._threads = set()
self._broken = False
Expand Down Expand Up @@ -198,9 +202,16 @@ def weakref_cb(_, q=self._work_queue):
self._initializer,
self._initargs))
t.daemon = True
t.start()
self._threads.add(t)
_threads_queues[t] = self._work_queue
try:
t.start()
except RuntimeError:
if self._shrink_on_exception:
self._max_workers = num_threads
else:
raise
else:
self._threads.add(t)
_threads_queues[t] = self._work_queue

def _initializer_failed(self):
with self._shutdown_lock:
Expand All @@ -215,6 +226,11 @@ def _initializer_failed(self):
if work_item is not None:
work_item.future.set_exception(BrokenThreadPool(self._broken))

def set_size(self, new_max_workers:int)->int:
if new_max_workers > 0:
self._max_workers = new_max_workers
return self._max_workers

def shutdown(self, wait=True):
with self._shutdown_lock:
self._shutdown = True
Expand Down