On Fri., 6 Dec. 2019, 3:31 am Christian Tismer, <tis...@stackless.com> wrote:
> Hi guys, > > during the last few weeks I have been struggling quite much > in order to make PySide run with Python 3.8 at all. > > The expected problems were refcounting leaks due to changed > handling of heaptypes. But in fact, the runtime behavior was > much worse, because I always got negative refcounts! > > After exhaustive searching through the different 3.8 commits, I could > isolate the three problems with logarithmic search. > > The hard problem was this: > Whenever PySide creates a new type, it crashes in PyType_Ready. > The reason is the existence of the Py_TPFLAGS_METHOD_DESCRIPTOR > flag. > During the PyType_Ready call, the function mro() is called. > This mro() call results in a negative refcount, because something > behaves differently since this flag is set by default in mro(). > > When I patched this flag away during the type_new call, everything > worked ok. I don't understand why this problem affects PySide > at all. Here is the code that would normally be only the newType line: > > > // PYSIDE-939: This is a temporary patch that circumvents the problem > // with Py_TPFLAGS_METHOD_DESCRIPTOR until this is finally solved. > PyObject *ob_PyType_Type = reinterpret_cast<PyObject *>(&PyType_Type); > PyObject *mro = PyObject_GetAttr(ob_PyType_Type, > Shiboken::PyName::mro()); > auto hold = Py_TYPE(mro)->tp_flags; > Py_TYPE(mro)->tp_flags &= ~Py_TPFLAGS_METHOD_DESCRIPTOR; > auto *newType = reinterpret_cast<SbkObjectType *>(type_new(metatype, > args, kwds)); > Py_TYPE(mro)->tp_flags = hold; > Isn't this manipulating the flags in the tuple type, rather than anything on a custom object? Or is "mro" a custom object rather than an MRO tuple? If anything, given the combination of factors required to reproduce the problem, I would guess that there might be a ref counting problem in the __set_owner__ invocations when called on a new type rather than a regular instance, and that was somehow affected by the change to increment the type refcount in PyObject_Init rather than PyType_GenericAlloc. Cheers, Nick. >
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