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bpo-32309: Implement asyncio.to_thread() (pythonGH-20143)
Implements `asyncio.to_thread`, a coroutine for asynchronously running IO-bound functions in a separate thread without blocking the event loop. See the discussion starting from [here](https://github.com/python/cpython/pull/18410GH-issuecomment-628930973) in pythonGH-18410 for context. Automerge-Triggered-By: @aeros (cherry picked from commit cc2bbc2) Co-authored-by: Kyle Stanley <[email protected]>
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"""High-level support for working with threads in asyncio""" | ||
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import functools | ||
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from . import events | ||
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__all__ = "to_thread", | ||
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async def to_thread(func, /, *args, **kwargs): | ||
"""Asynchronously run function *func* in a separate thread. | ||
Any *args and **kwargs supplied for this function are directly passed | ||
to *func*. | ||
Return an asyncio.Future which represents the eventual result of *func*. | ||
""" | ||
loop = events.get_running_loop() | ||
func_call = functools.partial(func, *args, **kwargs) | ||
return await loop.run_in_executor(None, func_call) |
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"""Tests for asyncio/threads.py""" | ||
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import asyncio | ||
import unittest | ||
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from unittest import mock | ||
from test.test_asyncio import utils as test_utils | ||
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def tearDownModule(): | ||
asyncio.set_event_loop_policy(None) | ||
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class ToThreadTests(test_utils.TestCase): | ||
def setUp(self): | ||
super().setUp() | ||
self.loop = asyncio.new_event_loop() | ||
asyncio.set_event_loop(self.loop) | ||
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def tearDown(self): | ||
self.loop.run_until_complete( | ||
self.loop.shutdown_default_executor()) | ||
self.loop.close() | ||
asyncio.set_event_loop(None) | ||
self.loop = None | ||
super().tearDown() | ||
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def test_to_thread(self): | ||
async def main(): | ||
return await asyncio.to_thread(sum, [40, 2]) | ||
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result = self.loop.run_until_complete(main()) | ||
self.assertEqual(result, 42) | ||
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def test_to_thread_exception(self): | ||
def raise_runtime(): | ||
raise RuntimeError("test") | ||
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async def main(): | ||
await asyncio.to_thread(raise_runtime) | ||
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with self.assertRaisesRegex(RuntimeError, "test"): | ||
self.loop.run_until_complete(main()) | ||
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def test_to_thread_once(self): | ||
func = mock.Mock() | ||
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async def main(): | ||
await asyncio.to_thread(func) | ||
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self.loop.run_until_complete(main()) | ||
func.assert_called_once() | ||
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def test_to_thread_concurrent(self): | ||
func = mock.Mock() | ||
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async def main(): | ||
futs = [] | ||
for _ in range(10): | ||
fut = asyncio.to_thread(func) | ||
futs.append(fut) | ||
await asyncio.gather(*futs) | ||
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self.loop.run_until_complete(main()) | ||
self.assertEqual(func.call_count, 10) | ||
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def test_to_thread_args_kwargs(self): | ||
# Unlike run_in_executor(), to_thread() should directly accept kwargs. | ||
func = mock.Mock() | ||
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async def main(): | ||
await asyncio.to_thread(func, 'test', something=True) | ||
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self.loop.run_until_complete(main()) | ||
func.assert_called_once_with('test', something=True) | ||
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if __name__ == "__main__": | ||
unittest.main() |
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Misc/NEWS.d/next/Library/2020-05-17-02-03-09.bpo-32309.KM9psl.rst
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Added a new :term:`coroutine` :func:`asyncio.to_thread`. It is mainly used for | ||
running IO-bound functions in a separate thread to avoid blocking the event | ||
loop, and essentially works as a high-level version of | ||
:meth:`~asyncio.loop.run_in_executor` that can directly take keyword arguments. |