cython

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"""
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Check that the @cython.no_gc_clear decorator disables generation of the
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tp_clear slot so that __dealloc__ will still see the original reference
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contents.
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Discussed here: https://article.gmane.org/gmane.comp.python.cython.devel/14986
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"""
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cimport cython
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from cpython.ref cimport PyObject, Py_TYPE
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# Pull tp_clear for PyTypeObject as I did not find another way to access it
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# from Cython code.
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cdef extern from *:
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    ctypedef struct PyTypeObject:
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        void (*tp_clear)(object)
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    ctypedef struct __pyx_CyFunctionObject:
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        PyObject* func_closure
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def is_tp_clear_null(obj):
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    return (<PyTypeObject*>Py_TYPE(obj)).tp_clear is NULL
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def is_closure_tp_clear_null(func):
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    return is_tp_clear_null(
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        <object>(<__pyx_CyFunctionObject*>func).func_closure)
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@cython.no_gc_clear
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cdef class DisableTpClear:
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    """
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    An extension type that has a tp_clear method generated to test that it
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    actually clears the references to NULL.
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    >>> uut = DisableTpClear()
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    >>> is_tp_clear_null(uut)
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    True
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    >>> uut.call_tp_clear()
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    >>> type(uut.requires_cleanup) == list
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    True
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    >>> del uut
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    """
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    cdef public object requires_cleanup
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    def __cinit__(self):
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        self.requires_cleanup = [
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                "Some object that needs cleaning in __dealloc__"]
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    def call_tp_clear(self):
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        cdef PyTypeObject *pto = Py_TYPE(self)
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        if pto.tp_clear != NULL:
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            pto.tp_clear(self)
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cdef class ReallowTpClear(DisableTpClear):
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    """
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    >>> import gc
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    >>> obj = ReallowTpClear()
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    >>> is_tp_clear_null(obj)
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    False
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    >>> obj.attr = obj  # create hard reference cycle
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    >>> del obj; _ignore = gc.collect()
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    # Problem: cannot really validate that the cycle was cleaned up without using weakrefs etc...
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    """
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    cdef public object attr
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def test_closure_without_clear(str x):
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    """
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    >>> c = test_closure_without_clear('abc')
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    >>> is_tp_clear_null(c)
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    False
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    >>> is_closure_tp_clear_null(c)
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    True
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    >>> c('cba')
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    'abcxyzcba'
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    """
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    def c(str s):
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        return x + 'xyz' + s
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    return c
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def test_closure_with_clear(list x):
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    """
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    >>> c = test_closure_with_clear(list('abc'))
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    >>> is_tp_clear_null(c)
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    False
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    >>> is_closure_tp_clear_null(c)
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    False
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    >>> c('cba')
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    'abcxyzcba'
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    """
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    def c(str s):
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        return ''.join(x) + 'xyz' + s
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    return c
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