diff options
| -rw-r--r-- | Doc/library/concurrent.futures.rst | 10 | ||||
| -rw-r--r-- | Lib/concurrent/futures/thread.py | 7 | ||||
| -rw-r--r-- | Lib/test/test_concurrent_futures.py | 6 | ||||
| -rw-r--r-- | Misc/NEWS | 3 |
4 files changed, 24 insertions, 2 deletions
diff --git a/Doc/library/concurrent.futures.rst b/Doc/library/concurrent.futures.rst index 08c926a6d4..e487817dfb 100644 --- a/Doc/library/concurrent.futures.rst +++ b/Doc/library/concurrent.futures.rst @@ -115,11 +115,19 @@ And:: 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: diff --git a/Lib/concurrent/futures/thread.py b/Lib/concurrent/futures/thread.py index 8d6081cf15..3ae442d987 100644 --- a/Lib/concurrent/futures/thread.py +++ b/Lib/concurrent/futures/thread.py @@ -10,6 +10,7 @@ from concurrent.futures import _base 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 @@ -80,13 +81,17 @@ def _worker(executor_reference, work_queue): _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") diff --git a/Lib/test/test_concurrent_futures.py b/Lib/test/test_concurrent_futures.py index 83184c3267..11560e65ac 100644 --- a/Lib/test/test_concurrent_futures.py +++ b/Lib/test/test_concurrent_futures.py @@ -11,6 +11,7 @@ test.support.import_module('threading') from test.script_helper import assert_python_ok +import os import sys import threading import time @@ -444,6 +445,11 @@ class ThreadPoolExecutorTest(ThreadPoolMixin, ExecutorTest, unittest.TestCase): 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): @@ -129,6 +129,9 @@ Core and Builtins 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. |