[subinterpreters] Make the type attribute lookup cache per-interpreter

[vstinner]

BPO	42745
Nosy	@vstinner, @pablogsal
PRs	bpo-42745: Make the type cache per-interpreter #23947 bpo-42745: finalize_interp_types() calls _PyType_Fini() #23953

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2020-12-26.00:46:02.836>
created_at = <Date 2020-12-25.22:50:34.708>
labels = ['expert-subinterpreters', 'interpreter-core', '3.10']
title = '[subinterpreters] Make the type attribute lookup cache per-interpreter'
updated_at = <Date 2020-12-26.19:26:19.730>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2020-12-26.19:26:19.730>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2020-12-26.00:46:02.836>
closer = 'vstinner'
components = ['Interpreter Core', 'Subinterpreters']
creation = <Date 2020-12-25.22:50:34.708>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 42745
keywords = ['patch']
message_count = 5.0
messages = ['383777', '383786', '383816', '383820', '383822']
nosy_count = 2.0
nosy_names = ['vstinner', 'pablogsal']
pr_nums = ['23947', '23953']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue42745'
versions = ['Python 3.10']

[vstinner]

Currently, the type lookup cache is shared by all interpreter which causes multiple issues:

• The version tag is currently protected by the GIL, but it would require a new lock if the GIL is made per interpreter (bpo-40512)

• Clearing the cache in an interpreter clears the cache in all interpreters

• The cache has a fixed size of 4096 entries. The cache misses increase with the number of interpreters, since each interpreter has its own types.

I propose to make the type lookup cache per interpreter.

[vstinner]

New changeset 4101018 by Victor Stinner in branch 'master':
bpo-42745: Make the type cache per-interpreter (GH-23947)
4101018

[pablogsal]

4101018 introduced some reference leaks:

https://buildbot.python.org/all/#/builders/384/builds/136

4101018 is the first bad commit
commit 4101018
Author: Victor Stinner <vstinner@python.org>
Date: Sat Dec 26 01:45:43 2020 +0100

bpo-42745: Make the type cache per-interpreter (GH-23947)

Make the type attribute lookup cache per-interpreter.

Add private _PyType_InitCache() function, called by PyInterpreterState_New().

Continue to share next_version_tag between interpreters, since static
types are still shared by interpreters.

Remove MCACHE macro: the cache is no longer disabled if the
EXPERIMENTAL_ISOLATED_SUBINTERPRETERS macro is defined.

Include/internal/pycore_interp.h | 22 +++
Include/internal/pycore_object.h | 3 +
Include/internal/pycore_pylifecycle.h | 2 +-
.../2020-12-25-23-30-58.bpo-42745.XsFoHS.rst | 1 +
Objects/typeobject.c | 178 ++++++++++++---------
Python/pylifecycle.c | 2 +-
Python/pystate.c | 2 +
7 files changed, 128 insertions(+), 82 deletions(-)
create mode 100644 Misc/NEWS.d/next/Core and Builtins/2020-12-25-23-30-58.bpo-42745.XsFoHS.rst
bisect run success

I assume PR 23953 fixes those? If that is so, could we land it before more buildbots start to fail?

[vstinner]

I assume PR 23953 fixes those?

Yes, it fix the 7 tests which leak:

./python -m test -R 3:3 -j0 test__xxsubinterpreters test_ast test_atexit test_capi test_interpreters test_threading

[vstinner]

New changeset f450723 by Victor Stinner in branch 'master':
bpo-42745: finalize_interp_types() calls _PyType_Fini() (GH-23953)
f450723