test_interpreters: when TestInterpreterAttrs.test_id_type() is run alone, it fails with an assertion error

[vstinner]

BPO	43962
Nosy	@vstinner, @ericsnowcurrently, @miss-islington, @nanjekyejoannah
PRs	bpo-43962: Fix _PyInterpreterState_IDIncref() #25683 [3.9] bpo-43962: Fix _PyInterpreterState_IDIncref() (GH-25683) #25685 [3.8] bpo-43962: Fix _PyInterpreterState_IDIncref() (GH-25683) #25686

^{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 = None
created_at = <Date 2021-04-27.22:55:01.625>
labels = ['tests', '3.10']
title = 'test_interpreters: when TestInterpreterAttrs.test_id_type() is run alone, it fails with an assertion error'
updated_at = <Date 2021-04-28.13:47:01.117>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2021-04-28.13:47:01.117>
actor = 'vstinner'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Tests']
creation = <Date 2021-04-27.22:55:01.625>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 43962
keywords = ['patch']
message_count = 4.0
messages = ['392145', '392183', '392187', '392197']
nosy_count = 4.0
nosy_names = ['vstinner', 'eric.snow', 'miss-islington', 'nanjekyejoannah']
pr_nums = ['25683', '25685', '25686']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue43962'
versions = ['Python 3.10']

[vstinner]

Example on Linux.

$ ./python -m test test_interpreters -m test.test_interpreters.TestInterpreterAttrs.test_id_type
0:00:00 load avg: 1.20 Run tests sequentially
0:00:00 load avg: 1.20 [1/1] test_interpreters
python: Python/pystate.c:561: _PyInterpreterState_IDDecref: Assertion `interp->id_refcount != 0' failed.
Fatal Python error: Aborted

Current thread 0x00007f05eab42740 (most recent call first):
File "/home/vstinner/python/master/Lib/unittest/case.py", line 549 in _callTestMethod
File "/home/vstinner/python/master/Lib/unittest/case.py", line 592 in run
File "/home/vstinner/python/master/Lib/unittest/case.py", line 652 in __call__
File "/home/vstinner/python/master/Lib/unittest/suite.py", line 122 in run
File "/home/vstinner/python/master/Lib/unittest/suite.py", line 84 in __call__
File "/home/vstinner/python/master/Lib/unittest/suite.py", line 122 in run
File "/home/vstinner/python/master/Lib/unittest/suite.py", line 84 in __call__
File "/home/vstinner/python/master/Lib/unittest/suite.py", line 122 in run
File "/home/vstinner/python/master/Lib/unittest/suite.py", line 84 in __call__
File "/home/vstinner/python/master/Lib/test/support/testresult.py", line 169 in run
File "/home/vstinner/python/master/Lib/test/support/init.py", line 959 in _run_suite
File "/home/vstinner/python/master/Lib/test/support/init.py", line 1082 in run_unittest
File "/home/vstinner/python/master/Lib/test/libregrtest/runtest.py", line 210 in _test_module
File "/home/vstinner/python/master/Lib/test/libregrtest/runtest.py", line 246 in _runtest_inner2
File "/home/vstinner/python/master/Lib/test/libregrtest/runtest.py", line 282 in _runtest_inner
File "/home/vstinner/python/master/Lib/test/libregrtest/runtest.py", line 154 in _runtest
File "/home/vstinner/python/master/Lib/test/libregrtest/runtest.py", line 194 in runtest
File "/home/vstinner/python/master/Lib/test/libregrtest/main.py", line 423 in run_tests_sequential
File "/home/vstinner/python/master/Lib/test/libregrtest/main.py", line 521 in run_tests
File "/home/vstinner/python/master/Lib/test/libregrtest/main.py", line 694 in _main
File "/home/vstinner/python/master/Lib/test/libregrtest/main.py", line 641 in main
File "/home/vstinner/python/master/Lib/test/libregrtest/main.py", line 719 in main
File "/home/vstinner/python/master/Lib/test/main.py", line 2 in <module>
File "/home/vstinner/python/master/Lib/runpy.py", line 86 in _run_code
File "/home/vstinner/python/master/Lib/runpy.py", line 196 in _run_module_as_main

Extension modules: _testcapi, _xxsubinterpreters (total: 2)
Abandon (core dumped)

When the whole test case is run, it's fine:

$ ./python -m test test_interpreters -m TestInterpreterAttrs -v
== CPython 3.10.0a7+ (heads/master:6bd9288b80, Apr 27 2021, 22:16:25) [GCC 11.0.1 20210324 (Red Hat 11.0.1-0)]
== Linux-5.11.15-300.fc34.x86_64-x86_64-with-glibc2.33 little-endian
== cwd: /home/vstinner/python/master/build/test_python_16394æ
== CPU count: 8
== encodings: locale=UTF-8, FS=utf-8
0:00:00 load avg: 1.39 Run tests sequentially
0:00:00 load avg: 1.39 [1/1] test_interpreters
test_custom_id (test.test_interpreters.TestInterpreterAttrs) ... ok
test_custom_isolated_default (test.test_interpreters.TestInterpreterAttrs) ... skipped 'not ready yet (see bpo-32604)'
test_custom_isolated_explicit (test.test_interpreters.TestInterpreterAttrs) ... ok
test_equality (test.test_interpreters.TestInterpreterAttrs) ... ok
test_id_readonly (test.test_interpreters.TestInterpreterAttrs) ... ok
test_id_type (test.test_interpreters.TestInterpreterAttrs) ... ok
test_isolated_readonly (test.test_interpreters.TestInterpreterAttrs) ... ok
test_main_id (test.test_interpreters.TestInterpreterAttrs) ... ok
test_main_isolated (test.test_interpreters.TestInterpreterAttrs) ... skipped 'not ready yet (see bpo-32604)'
test_subinterpreter_isolated_default (test.test_interpreters.TestInterpreterAttrs) ... skipped 'not ready yet (see bpo-32604)'
test_subinterpreter_isolated_explicit (test.test_interpreters.TestInterpreterAttrs) ... ok

---

Ran 11 tests in 0.159s

OK (skipped=3)

== Tests result: SUCCESS ==

1 test OK.

Total duration: 285 ms
Tests result: SUCCESS

[vstinner]

Creating an _interpreters.InterpreterID object calls newinterpid() which calls _PyInterpreterState_IDIncref(interp).

_PyInterpreterState_IDIncref(interp) does nothing if interp->id_mutex is NULL.

Calling _interpreters.get_current() calls interp_get_current() which calls _PyInterpreterState_IDInitref().

_PyInterpreterState_IDInitref() creates the id_mutex and initializes id_refcount to 0.

Later, when the _interpreters.InterpreterID object is deallocated, interpid_dealloc() calls _PyInterpreterState_IDDecref(). Since id_mutex was created in the meanwhile, _PyInterpreterState_IDDecref() now decrements id_refcnt.

... It doesn't work: _PyInterpreterState_IDIncref() should always increase the reference count.

[vstinner]

New changeset 32c5a17 by Victor Stinner in branch 'master':
bpo-43962: Fix _PyInterpreterState_IDIncref() (GH-25683)
32c5a17

[vstinner]

New changeset 77db337 by Victor Stinner in branch '3.8':
bpo-43962: Fix _PyInterpreterState_IDIncref() (GH-25683) (GH-25686)
77db337

[kumaraditya303]

Closing as it seems fixed.