Neil Schemenauer <nas-pyt...@arctrix.com> added the comment:
Hello Eddie, Thank you for putting what looks to be significant effort into this PR. It would be great if we can get this fixed. There is a real issue about breaking 3rd party extensions. So, we want to proceed with care. I wonder, if we are going to break extensions already, could we just remove the whole concept of heap allocated types? If you look through the CPython source code, I think you will find a lot of tricky code that deals with the Py_TPFLAGS_HEAPTYPE case. If we could remove heap types, we could remove all those cases. That would give some performance improvement but more importantly would simplify the implementation. If PyType_FromSpec() is now working correctly, could we just move everything that the currently a heap type to use that? Obviously we have to give 3rd party extensions a lot of time to get themselves updated. Maybe give a deprecation warning if Py_TPFLAGS_HEAPTYPE is used. You could have a configuration option for Python that enables or disables the Py_TPFLAGS_HEAPTYPE support. Once we think extensions have been given enough time to update themselves, we can remove Py_TPFLAGS_HEAPTYPE. Some other possible advantages of getting rid of heap types: - GC objects will always have the GC header allocated (because CPython controls the allocation of the chunk of memory for the type) - might be possible to eliminate GC headers and use bitmaps. I have been experimenting with the idea but it seems to require that we don't use heap types. Initially I was interested in the bitmap idea because of memory savings. After more tinkering, I think the big win will be in eliminating linked-list traversals. On modern CPUs, that's slow and iterating over a bitmap should be much faster. - I suspect heap types are difficult to support for PyPy. I haven't looked into that but it seems tricky when you have non-refcounting GC - type_is_gc() is ugly and would go away. Based on my profiling, PyObject_IS_GC() is pretty expensive. A lot of types have the tp_is_gc slot set (more than you would expect). - In the very long term, using PyType_FromSpec() could give us the freedom to change the structure layout of types. I don't have any specific ideas about that but it seems like a better design. ---------- nosy: +nascheme _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue35810> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
