executor.submit(wait_on_future)
-.. class:: ThreadPoolExecutor(max_workers)
+.. class:: ThreadPoolExecutor(max_workers=None)
An :class:`Executor` subclass that uses a pool of at most *max_workers*
threads to execute calls asynchronously.
+ .. versionchanged:: 3.5
+ If *max_workers* is ``None`` or
+ not given, it will default to the number of processors on the machine,
+ multiplied by ``5``, assuming that :class:`ThreadPoolExecutor` is often
+ used to overlap I/O instead of CPU work and the number of workers
+ should be higher than the number of workers
+ for :class:`ProcessPoolExecutor`.
+
.. _threadpoolexecutor-example:
import queue
import threading
import weakref
+import os
# Workers are created as daemon threads. This is done to allow the interpreter
# to exit when there are still idle threads in a ThreadPoolExecutor's thread
_base.LOGGER.critical('Exception in worker', exc_info=True)
class ThreadPoolExecutor(_base.Executor):
- def __init__(self, max_workers):
+ def __init__(self, max_workers=None):
"""Initializes a new ThreadPoolExecutor instance.
Args:
max_workers: The maximum number of threads that can be used to
execute the given calls.
"""
+ if max_workers is None:
+ # Use this number because ThreadPoolExecutor is often
+ # used to overlap I/O instead of CPU work.
+ max_workers = (os.cpu_count() or 1) * 5
if max_workers <= 0:
raise ValueError("max_workers must be greater than 0")
from test.script_helper import assert_python_ok
+import os
import sys
import threading
import time
self.executor.shutdown(wait=True)
self.assertCountEqual(finished, range(10))
+ def test_default_workers(self):
+ executor = self.executor_type()
+ self.assertEqual(executor._max_workers,
+ (os.cpu_count() or 1) * 5)
+
class ProcessPoolExecutorTest(ProcessPoolMixin, ExecutorTest, unittest.TestCase):
def test_killed_child(self):
Library
-------
+- Issue #21527: Add a default number of workers to ThreadPoolExecutor equal
+ to 5 times the number of CPUs. Patch by Claudiu Popa.
+
- Issue #22216: smtplib now resets its state more completely after a quit. The
most obvious consequence of the previous behavior was a STARTTLS failure
during a connect/starttls/quit/connect/starttls sequence.