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Merged
merged 3 commits into from
Aug 30, 2019
Merged

bpo-37140: Fix StructUnionType_paramfunc() #15612

merged 3 commits into from
Aug 30, 2019

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vstinner
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@vstinner vstinner commented Aug 30, 2019 •
edited by bedevere-bot
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Fix a ctypes regression of Python 3.8. When a ctypes.Structure is
passed by copy to a function, ctypes internals created a temporary
object which had the side effect of calling the structure finalizer
(del) twice. The Python semantics requires a finalizer to be
called exactly once. Fix ctypes internals to no longer call the
finalizer twice.

Create a new internal StructParam_Type which is only used by
_ctypes_callproc() to call PyMem_Free(ptr) on Py_DECREF(argument).
StructUnionType_paramfunc() creates such object.

https://bugs.python.org/issue37140

@vstinner
bpo-37140: Fix StructUnionType_paramfunc()
2579e56 
Fix a ctypes regression of Python 3.8. When a ctypes.Structure is
passed by copy to a function, ctypes internals created a temporary
object which had the side effect of calling the structure finalizer
(__del__) twice. The Python semantics requires a finalizer to be
called exactly once. Fix ctypes internals to no longer call the
finalizer twice.

Create a new internal StructParam_Type which is only used by
_ctypes_callproc() to call PyMem_Free(ptr) on Py_DECREF(argument).
StructUnionType_paramfunc() creates such object.
@vstinner vstinner mentioned this pull request Aug 30, 2019
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I wrote an unit test. I made sure that the unit test fails without the fix:

FAIL: test_pass_by_value_finalizer (ctypes.test.test_structures.StructureTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/vstinner/python/master/Lib/ctypes/test/test_structures.py", line 449, in test_pass_by_value_finalizer
    self.assertEqual(finalizer_calls, [])
AssertionError: Lists differ: ['called'] != []

First list contains 1 additional elements.
First extra element 0:
'called'

- ['called']
+ []

Without the fix, Test.del() is called once internally during the call to the C function ("func()"), and then a second time when the object is destroyed (s = None).

serge-sans-paille
serge-sans-paille reviewed Aug 30, 2019
View reviewed changes
Modules/_ctypes/_ctypes.c
(PyObject *)Py_TYPE(self), new_ptr);
copied_self->b_needsfree = 1;

obj = (&StructParam_Type)->tp_alloc(&StructParam_Type, 0);
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s/obj/arg_obj/ to increase readability ?

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I chose "obj" name to get "parg->obj = obj" which looks nice to me :-)

Lib/ctypes/test/test_structures.py
s = None
support.gc_collect()
self.assertEqual(finalizer_calls, ["called"])

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<3 the test case

@vstinner vstinner merged commit 96b4087 into python:master Aug 30, 2019
@vstinner vstinner deleted the ctypes_struct_param branch August 30, 2019 12:30
@miss-islington
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Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.8.
🐍🍒⛏🤖

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GH-15613 is a backport of this pull request to the 3.8 branch.

miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Aug 30, 2019
@vstinner @miss-islington
bpo-37140: Fix StructUnionType_paramfunc() (pythonGH-15612)
a1c6b17 
Fix a ctypes regression of Python 3.8. When a ctypes.Structure is
passed by copy to a function, ctypes internals created a temporary
object which had the side effect of calling the structure finalizer
(__del__) twice. The Python semantics requires a finalizer to be
called exactly once. Fix ctypes internals to no longer call the
finalizer twice.

Create a new internal StructParam_Type which is only used by
_ctypes_callproc() to call PyMem_Free(ptr) on Py_DECREF(argument).
StructUnionType_paramfunc() creates such object.
(cherry picked from commit 96b4087)

Co-authored-by: Victor Stinner <[email protected]>
miss-islington added a commit that referenced this pull request Aug 30, 2019
@miss-islington @vstinner
bpo-37140: Fix StructUnionType_paramfunc() (GH-15612)
17f61ed 
Fix a ctypes regression of Python 3.8. When a ctypes.Structure is
passed by copy to a function, ctypes internals created a temporary
object which had the side effect of calling the structure finalizer
(__del__) twice. The Python semantics requires a finalizer to be
called exactly once. Fix ctypes internals to no longer call the
finalizer twice.

Create a new internal StructParam_Type which is only used by
_ctypes_callproc() to call PyMem_Free(ptr) on Py_DECREF(argument).
StructUnionType_paramfunc() creates such object.
(cherry picked from commit 96b4087)

Co-authored-by: Victor Stinner <[email protected]>
lisroach pushed a commit to lisroach/cpython that referenced this pull request Sep 10, 2019
@vstinner @lisroach
bpo-37140: Fix StructUnionType_paramfunc() (pythonGH-15612)
8c06825 
Fix a ctypes regression of Python 3.8. When a ctypes.Structure is
passed by copy to a function, ctypes internals created a temporary
object which had the side effect of calling the structure finalizer
(__del__) twice. The Python semantics requires a finalizer to be
called exactly once. Fix ctypes internals to no longer call the
finalizer twice.

Create a new internal StructParam_Type which is only used by
_ctypes_callproc() to call PyMem_Free(ptr) on Py_DECREF(argument).
StructUnionType_paramfunc() creates such object.
DinoV pushed a commit to DinoV/cpython that referenced this pull request Jan 14, 2020
@vstinner @DinoV
bpo-37140: Fix StructUnionType_paramfunc() (pythonGH-15612)
082c315 
Fix a ctypes regression of Python 3.8. When a ctypes.Structure is
passed by copy to a function, ctypes internals created a temporary
object which had the side effect of calling the structure finalizer
(__del__) twice. The Python semantics requires a finalizer to be
called exactly once. Fix ctypes internals to no longer call the
finalizer twice.

Create a new internal StructParam_Type which is only used by
_ctypes_callproc() to call PyMem_Free(ptr) on Py_DECREF(argument).
StructUnionType_paramfunc() creates such object.
websurfer5 pushed a commit to websurfer5/cpython that referenced this pull request Jul 20, 2020
@vstinner @websurfer5
bpo-37140: Fix StructUnionType_paramfunc() (pythonGH-15612)
18c22ef 
Fix a ctypes regression of Python 3.8. When a ctypes.Structure is
passed by copy to a function, ctypes internals created a temporary
object which had the side effect of calling the structure finalizer
(__del__) twice. The Python semantics requires a finalizer to be
called exactly once. Fix ctypes internals to no longer call the
finalizer twice.

Create a new internal StructParam_Type which is only used by
_ctypes_callproc() to call PyMem_Free(ptr) on Py_DECREF(argument).
StructUnionType_paramfunc() creates such object.
@ynkdir ynkdir mentioned this pull request Dec 12, 2022
Merged
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@vstinner @miss-islington @bedevere-bot @serge-sans-paille @the-knights-who-say-ni