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Avoid race due to deleted imports when cleaning up objects at interpreter shutdown #973

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Merged
leofang merged 7 commits into from
Sep 27, 2025
Merged

Avoid race due to deleted imports when cleaning up objects at interpreter shutdown #973

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a9165d6
is_shutting_down
brandon-b-miller Sep 16, 2025
28db9df
Update cuda_bindings/cuda/bindings/utils/__init__.py
brandon-b-miller Sep 16, 2025
33f68da
safe_close()
brandon-b-miller Sep 16, 2025
7155fd1
is_finalizing
brandon-b-miller Sep 18, 2025
e0bea0c
merge/resolve/fix
brandon-b-miller Sep 20, 2025
b68a5d1
refactor
brandon-b-miller Sep 26, 2025
013cf22
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brandon-b-miller Sep 26, 2025
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1 change: 0 additions & 1 deletion cuda_bindings/cuda/bindings/utils/__init__.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,5 @@
# SPDX-FileCopyrightText: Copyright (c) 2025 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
# SPDX-License-Identifier: LicenseRef-NVIDIA-SOFTWARE-LICENSE

from typing import Any, Callable

from ._ptx_utils import get_minimal_required_cuda_ver_from_ptx_ver, get_ptx_ver
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11 changes: 9 additions & 2 deletions cuda_core/cuda/core/experimental/_event.pyx
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Expand Up @@ -18,7 +18,7 @@ from cuda.core.experimental._utils.cuda_utils import (
driver,
handle_return,
)

import sys
if TYPE_CHECKING:
import cuda.bindings
from cuda.core.experimental._device import Device
Expand Down Expand Up @@ -108,6 +108,13 @@ cdef class Event:
self._ctx_handle = ctx_handle
return self

cpdef safe_close(self, is_shutting_down=sys.is_finalizing):
"""Destroy the event."""
if self._handle is not None:
if not is_shutting_down():
err, = driver.cuEventDestroy(self._handle)
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@cpcloud cpcloud Sep 16, 2025 •
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What's the issue with this?

Suggested change
err, = driver.cuEventDestroy(self._handle)
if (destroy := getattr(driver, "cuEventDestroy", None)) is not None:
err, = destroy(self._handle)

Then you don't need the global hack.

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@leofang leofang Sep 16, 2025

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We want to use a field-tested solution (see the internal thread) instead of coming up with a new one.

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@cpcloud cpcloud Sep 16, 2025

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How about sys.is_finalizing()? There's probably not a more field tested solution than what's in the standard library.

In this case it also seems particularly suited to the problem being solved here.

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@kkraus14 kkraus14 Sep 16, 2025

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This is definitely better, but this is still a hack where if we run things under tools like cuda-memcheck that check for resource leaks it will still pop.

Additionally, we'd need to carry these checks everywhere that code could be called in __del__ functions, I believe even transitively. I.E. the raise_if_driver_error function.

What if we moved to a __dealloc__ function?

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@leofang leofang Sep 17, 2025 •
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As discussed internally,sys.is_finalizing() - while official - only returns True at the very late stage of interpreter shutdown, later than all of the exit handlers (which this PR is based on). It is unclear to me if this solves the problem. I feel nervous about this. Do we have any known, big projects using this solution?

What if we moved to a __dealloc__ function?

No, we can't do this (yet), because we currently call Python bindings. Once #866 lands we can switch to this, but I need some time to work it out and I prefer this to be fixed independently (and asap).

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@cpcloud cpcloud Sep 17, 2025 •
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Here are the relevant steps, in order, during interpreter shutdown:

  1. wait for threads to shutdown
  2. wait for any pending calls
  3. call atexit handlers (where the flag would be set)
  4. set the interpreter to be officially in finalizing mode (this information is what sys.is_finalizing() uses)
  5. collect garbage (__del__ would be called here)

So, it doesn't really matter which approach we take, and it's overall less code and less hacky code to use a standard library builtin.

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@cpcloud cpcloud Sep 18, 2025

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For reference: https://github.com/python/cpython/blob/4305cc3ef35a35f9b2c163ae0ffeea219da5af5d/Python/pylifecycle.c?plain=1#L2144

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@leofang leofang Oct 3, 2025

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For posterity: Turns out is_finalizing becomes True too late, and this PR does not fix all shutdown errors: #1063. We'll fix this in #1070.

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@cpcloud cpcloud Oct 3, 2025 •
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This makes it sound like the previously proposed solution using atexit would work, but it wouldn't, because __del__ is still called at the same point in the program regardless of where the state of the interpreter is checked.

It would be more helpful to provide thorough reasoning (as I did above). Right now, it just looks like everything I said was incorrect without any description as to why that is.

raise_if_driver_error(err)

cpdef close(self):
"""Destroy the event."""
if self._handle is not None:
Expand All @@ -116,7 +123,7 @@ cdef class Event:
raise_if_driver_error(err)

def __del__(self):
self.close()
self.safe_close()

def __isub__(self, other):
return NotImplemented
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8 changes: 7 additions & 1 deletion cuda_core/cuda/core/experimental/_memory.pyx
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Expand Up @@ -9,6 +9,7 @@ from cuda.core.experimental._utils.cuda_utils cimport (
_check_driver_error as raise_if_driver_error,
check_or_create_options,
)
import sys

from dataclasses import dataclass
from typing import TypeVar, Union, TYPE_CHECKING
Expand Down Expand Up @@ -69,7 +70,12 @@ cdef class Buffer:
return self

def __del__(self):
self.close()
self.safe_close()

cpdef safe_close(self, stream: Stream = None, is_shutting_down=sys.is_finalizing):
if self._ptr and self._mr is not None:
if not is_shutting_down():
self._mr.deallocate(self._ptr, self._size, stream)

cpdef close(self, stream: Stream = None):
"""Deallocate this buffer asynchronously on the given stream.
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9 changes: 8 additions & 1 deletion cuda_core/cuda/core/experimental/_stream.pyx
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Expand Up @@ -8,6 +8,7 @@ from cuda.core.experimental._utils.cuda_utils cimport (
_check_driver_error as raise_if_driver_error,
check_or_create_options,
)
import sys

import cython
import os
Expand Down Expand Up @@ -186,7 +187,13 @@ cdef class Stream:
return self

def __del__(self):
self.close()
self.safe_close()

cpdef safe_close(self, is_shutting_down=sys.is_finalizing):
if self._owner is None:
if self._handle and not self._builtin:
if not is_shutting_down():
handle_return(driver.cuStreamDestroy(self._handle))

cpdef close(self):
"""Destroy the stream.
Expand Down