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We have run out of flags bits in PyTypeObject's tp_flags #134860
Description
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Flags are also an
unsigned intinPyType_Spec, which is part of the stable ABI. See https://docs.python.org/3/c-api/type.html#c.PyType_Spec.flagsLet's add a new field for new internal flags, so they don't clutter the public API. (Moving
_Py_TPFLAGS_STATIC_BUILTINand_Py_TPFLAGS_MATCH_SELFthere would free up two bits.
And also switch touint64_t.Flags are also an
unsigned intinPyType_Spec, which is part of the stable ABI.For new flags we can add slots, and teach
PyType_From*&PyType_GetSlotto handle bits.Reacted by Sergey Miryanov
PyTypeObject'stp_flagsfield is defined as anunsigned long. In effect this means that we have only 32 bits we can use for flags. We have already used all 32 of them.Bits 15 and 16 are reserved for Stackless Python. Since Stackless Python is pining for the fjords, we could recycle those two bits. However that's not going to last long with likely changes necessary for parallelism and performance.
Any change to
PyTypeObjectbreaks both API and ABI, but that's OK because:PyTypeObjectis part of the stable ABI, but its layout is not.The cleanest change, IMO, is to change
unsigned long tp_flagstouint64_t tp_flagswhich gives us another 32 bits, which should last many more years.