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lostmsu opened this issue Sep 11, 2020 · 6 comments
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Multiple assertion failures for Python classes derived from System.Exception in debug builds #1218

lostmsu opened this issue Sep 11, 2020 · 6 comments

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@lostmsu
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lostmsu commented Sep 11, 2020 •
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Environment

  • Pythonnet version: 2.5.1
  • Python version: 3.8
  • Operating System: Win 10 64

Details

In debug build (DebugWinPY3) this test:

pythonnet/src/tests/test_constructors.py

Line 41 in 61d1b7c

class Sub(System.Exception):

fails this assertion:

pythonnet/src/runtime/interop.cs

Line 92 in 61d1b7c

Debug.Assert(typeSize > 0 && typeSize <= ExceptionOffset.Size());

Python type object for Sub class gets an unknown extra field of size IntPtr.Size, causing it to be larger than its base type object (reflected) System.Exception.

See also #1196 (comment) for previous discussion.

@koubaa @amos402
@lostmsu
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lostmsu commented Sep 11, 2020

It seems that the reason is that System.Exception has no weak list associated with it:

Marshal.ReadInt32(type, TypeOffset.tp_weaklistoffset) // type == Sub
80
Marshal.ReadInt32(Marshal.ReadIntPtr(type, TypeOffset.tp_base), TypeOffset.tp_weaklistoffset)
0

@amos402
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amos402 commented Sep 11, 2020

Because it used tp_basicsize as the slot to save GCHandle, you can test it on soft-shutdown branch, it should be fine.
https://github.com/amos402/pythonnet/blob/12c0206b94173935864e0434ec22898753ffb6b5/src/runtime/interop.cs#L116-L117
I changed the slot.

@lostmsu
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lostmsu commented Sep 11, 2020

@amos402 not exactly sure what you mean. The reflected System.Exception should already have a slot for GCHandle. If that would be the reason, size of Sub would be equal to size of System.Exception, but it is not.

@amos402
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amos402 commented Sep 11, 2020

image
Trust me, it fixed.
image

The reason is as I said. The size of Sub come from type(System.Exception)->tp_basicsize, they're not equal.

@koubaa
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koubaa commented Sep 13, 2020

@lostmsu @amos402 I just took Amos's interop changes from the soft shutdown branch and applied them to master, and this issue goes away. I'll submit a PR soon with this change, even if it doesn't fix my PyType_FromSpec it could still make the soft shutdown branch easier to review without these changes

@koubaa koubaa mentioned this issue Sep 13, 2020
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@koubaa
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koubaa commented Oct 24, 2020

Fixed in master

@filmor filmor closed this as completed Oct 24, 2020
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apply amos interop changes from soft shutdown koubaa/pythonnet
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@filmor @lostmsu @amos402 @koubaa