On 1/12/21 7:16 PM, Neil Schemenauer wrote:
On 2021-01-12, Victor Stinner wrote:
It seems like a safer approach is to continue the work on
bpo-40077: "Convert static types to PyType_FromSpec()".
I agree that trying to convert static types is a good idea. Another
possible bonus might be that we can gain some performance by
integrating garbage collection with the Python object memory
allocator. Static types frustrate that effort.
Could we have something easier to use than PyType_FromSpec(), for
the purposes of coverting existing code? I was thinking of
something like:
static PyTypeObject Foo_TypeStatic = {
}
static PyTypeObject *Foo_Type;
PyInit_foo(void)
{
Foo_Type = PyType_FromStatic(&Foo_TypeStatic);
}
The PyType_FromStatic() would return a new heap type, created by
copying the static type. The static type could be marked as being
unusable (e.g. with a type flag).
Unfortunately, it's not just the creation that needs to be changed.
You also need to decref Foo_Type somewhere.
Your example is for "single-phase init" modules (pre-PEP 489). Those
don't have a dealloc hook, so they will leak memory (e.g. in multiple
Py_Initialize/Py_Finalize cycles).
Multi-phase init (PEP 489) allows multiple module instances of extension
modules. Assigning PyType_FromStatic's result to a static pointer would
mean that every instance of the module will create a new type, and
overwrite any existing one. And the deallocation will either leave a
dangling pointer or NULL the pointer for other module instances.
So, you need to make the type part of the module state, so that the
module has proper ownership of the type. And that means you need to
access the type from the module state any time you need to use it.
At that point, IMO, PyType_FromStatic saves you so little work that it's
not worth supporting a third variation of type creation code.
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