[issue39511] [subinterpreters] Per-interpreter singletons (None, True, False, etc.)

[STINNER Victor]

STINNER Victor <vstinner at python.org> added the comment:

I vaguely recall discussions about immortal Python objects.

(*) Instagram gc.freeze()

* https://docs.python.org/dev/library/gc.html#gc.freeze
* https://instagram-engineering.com/dismissing-python-garbage-collection-at-instagram-4dca40b29172

(*) Python immortal strings

* PyUnicode_InternImmortal()
* SSTATE_INTERNED_IMMORTAL
* They are only destroyed if Python is compiled with Valgrind or Purify support: unicode_release_interned() function

(*) COUNT_ALLOCS

* When Python is built with COUNT_ALLOCS macro defined, types are immortal
* Many tests have to be skipped if COUNT_ALLOCS is used
* I plan to remove COUNT_ALLOCS feature in bpo-39489 :-)

(*) Static types

* Types which are not allocated on the heap but "static" are immortal
* These types cause various issues and should go away
* For example, they are incompatible with multi-phase initialization module (PEP 489) and stable ABI (PEP 384)

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