On 1/12/21 4:09 PM, Victor Stinner wrote:
On Tue, Jan 12, 2021 at 3:28 PM Petr Viktorin <encu...@gmail.com> wrote:
If a type is immutable and has no references to heap-allocated objects,
it could stay as a static type.
The issue is that very many types don't fit that. For example, if some
method needs to raise a module-specific exception, that's a reference to
a heap-allocated type, because custom exceptions generally aren't static.
(...)
I don't see why we would need to destroy immutable static objects. They
don't need to be freed.
I'm not sure of your definition of "immutable" here. At the C level,
many immutable Python objects are mutable. For example, a str instance
*can* be modified with the C level, and computing hash(<my string>)
modifies the object as well (the internal cached hash value).
Any type contains at least one Python object: the __mro__ tuple. Most
types also contain a __subclass__ dictionary (by default, it's NULL).
These objects are created at Python startup, but not destroyed at
Python exit. See also tp_bases (tuple) and tp_dict (dict).
Ah, right. __subclasses__ is the reason these need to be heap types (if
they allow subclassing, which – isn't).
If __mro__ is a tuple of static types, it could probably be made static
as well; hashes could be protected by a lock.
I tried once to "finalize" static types, but it didn't go well:
* https://github.com/python/cpython/pull/20763
* https://bugs.python.org/issue1635741#msg371119
It doesn't look to be safe to clear static types. Many functions rely
on the fact that static types are "always there" and are never
finalized. Also, only a few static types are cleared by my PR: many
static types are left unchanged. For example, static types of the _io
module. It seems like a safer approach is to continue the work on
bpo-40077: "Convert static types to PyType_FromSpec()".
Yes, seems so. And perhaps this has enough subtle details to want a PEP?
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