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gh-142615: disallow multiple initializations of asyncio tasks and futures #142616

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Merged

kumaraditya303 merged 11 commits into python:main from kumaraditya303:immutable-task

Jan 3, 2026

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Merged

gh-142615: disallow multiple initializations of asyncio tasks and futures #142616

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37f8e99

disallow multiple initializations of asyncio tasks and futures

kumaraditya303 Dec 12, 2025

ffa9ec9

do the same for python tasks

kumaraditya303 Dec 12, 2025

4eb0119

add tests

kumaraditya303 Dec 12, 2025

a457ba1

📜🤖 Added by blurb_it.

blurb-it[bot] Dec 12, 2025

82a7fd0

fix news

kumaraditya303 Dec 12, 2025

5ae2e22

fmt

kumaraditya303 Dec 12, 2025

3e697f6

make error message same for both implementations

kumaraditya303 Dec 12, 2025

09983fc

Merge branch 'main' into immutable-task

kumaraditya303 Dec 29, 2025

ed666f9

remove redundant ref counting

kumaraditya303 Dec 29, 2025

080a0c8

fix compilation

kumaraditya303 Dec 29, 2025

c85880b

Merge branch 'main' into immutable-task

kumaraditya303 Jan 3, 2026

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disallow multiple initializations of asyncio tasks and futures

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kumaraditya303 committed Dec 12, 2025

commit 37f8e990ac4819e20018f39c91623265fe17ffcc

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27 changes: 0 additions & 27 deletions 27 Lib/test/test_asyncio/test_futures.py

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -1091,33 +1091,6 @@ def __getattribute__(self, name):
		fut.add_done_callback(fut_callback_0)
		self.assertRaises(ReachableCode, fut.set_result, "boom")

		def test_use_after_free_on_fut_context_0_with_evil__getattribute__(self):
		# see: https://github.com/python/cpython/issues/125984

		class EvilEventLoop(SimpleEvilEventLoop):
		def call_soon(self, args, *kwargs):
		super().call_soon(args, *kwargs)
		raise ReachableCode

		def __getattribute__(self, name):
		if name == 'call_soon':
		# resets the future's event loop
		fut.__init__(loop=SimpleEvilEventLoop())
		return object.__getattribute__(self, name)

		evil_loop = EvilEventLoop()
		with mock.patch.object(self, 'loop', evil_loop):
		fut = self._new_future()
		self.assertIs(fut.get_loop(), evil_loop)

		fut_callback_0 = mock.Mock()
		fut_context_0 = mock.Mock()
		fut.add_done_callback(fut_callback_0, context=fut_context_0)
		del fut_context_0
		del fut_callback_0
		self.assertRaises(ReachableCode, fut.set_result, "boom")


		@unittest.skipUnless(hasattr(futures, '_CFuture'),
		'requires the C _asyncio module')
		class CFutureDoneCallbackTests(BaseFutureDoneCallbackTests,
Expand Down

36 changes: 0 additions & 36 deletions 36 Lib/test/test_asyncio/test_tasks.py

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -2776,29 +2776,6 @@ def test_get_context(self):
		finally:
		loop.close()

		def test_proper_refcounts(self):
		# see: https://github.com/python/cpython/issues/126083
		class Break:
		def __str__(self):
		raise RuntimeError("break")

		obj = object()
		initial_refcount = sys.getrefcount(obj)

		coro = coroutine_function()
		with contextlib.closing(asyncio.EventLoop()) as loop:
		task = asyncio.Task.__new__(asyncio.Task)
		for _ in range(5):
		with self.assertRaisesRegex(RuntimeError, 'break'):
		task.__init__(coro, loop=loop, context=obj, name=Break())

		coro.close()
		task._log_destroy_pending = False
		del task

		self.assertEqual(sys.getrefcount(obj), initial_refcount)


		def add_subclass_tests(cls):
		BaseTask = cls.Task
		BaseFuture = cls.Future
Expand Down Expand Up		@@ -2921,19 +2898,6 @@ class CTask_CFuture_Tests(BaseTaskTests, SetMethodsTest,
		all_tasks = getattr(tasks, '_c_all_tasks', None)
		current_task = staticmethod(getattr(tasks, '_c_current_task', None))

		@support.refcount_test
		def test_refleaks_in_task___init__(self):
		gettotalrefcount = support.get_attribute(sys, 'gettotalrefcount')
		async def coro():
		pass
		task = self.new_task(self.loop, coro())
		self.loop.run_until_complete(task)
		refs_before = gettotalrefcount()
		for i in range(100):
		task.__init__(coro(), loop=self.loop)
		self.loop.run_until_complete(task)
		self.assertAlmostEqual(gettotalrefcount() - refs_before, 0, delta=10)

		def test_del__log_destroy_pending_segfault(self):
		async def coro():
		pass
Expand Down

19 changes: 6 additions & 13 deletions 19 Modules/_asynciomodule.c

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -498,21 +498,14 @@ future_schedule_callbacks(asyncio_state state, FutureObj fut)
		static int
		future_init(FutureObj fut, PyObject loop)
		{
		if (fut->fut_loop != NULL) {
		PyErr_Format(PyExc_RuntimeError,
		"%T object is already initialized", fut);
		return -1;
		}

		PyObject *res;
		int is_true;

		Py_CLEAR(fut->fut_loop);
		Py_CLEAR(fut->fut_callback0);
		Py_CLEAR(fut->fut_context0);
		Py_CLEAR(fut->fut_callbacks);
		Py_CLEAR(fut->fut_result);
		Py_CLEAR(fut->fut_exception);
		Py_CLEAR(fut->fut_exception_tb);
		Py_CLEAR(fut->fut_source_tb);
		Py_CLEAR(fut->fut_cancel_msg);
		Py_CLEAR(fut->fut_cancelled_exc);
		Py_CLEAR(fut->fut_awaited_by);

		fut->fut_state = STATE_PENDING;
		fut->fut_log_tb = 0;
		fut->fut_blocking = 0;
Expand Down

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