Intermittent "unrecognized configuration name" failure on iOS and Android

Bug report

Bug description:

The iOS buildbot is seeing an intermittent testing failure in `test_posix.PosixTester.test_confstr:

======================================================================
ERROR: test_confstr (test.test_posix.PosixTester.test_confstr)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/buildbot/Library/Developer/XCTestDevices/4FED991E-7280-4D2F-B63A-C7FECDE66EAD/data/Containers/Bundle/Application/0809D9E4-34B6-4223-A3AD-079D76671D9D/iOSTestbed.app/python/lib/python3.13/test/test_posix.py", line 569, in test_confstr
    self.assertEqual(len(posix.confstr("CS_PATH")) > 0, True)
                         ~~~~~~~~~~~~~^^^^^^^^^^^
ValueError: unrecognized configuration name
----------------------------------------------------------------------

See this PR for the buildbot report; this build is the resulting failure.

The failure appears to be completely transient, affecting ~1 in 10 builds; the next buildbot run almost always passes, with no changes addressing this issue.

I've been unsuccessful reproducing the test locally.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Other

Linked PRs

Until we have time to work out why this is happening, should we skip this test? It's posting iOS buildbot failures on GitHub about once a day, and we don't want to train everyone to ignore them.

I've pushed up #118452 to skip the test on iOS (for now, at least).

gh-118201 - Disable the flaky POSIX test_confstr test on iOS (GH-118452)

Doing a full audit of the failures the buildbot has seen, it appears there's another cluster of tests that fail intermittently for a reason that appears similar to the test_posix test.

Out of 118 builds to date, we've seen:

4 instances of:

======================================================================
ERROR: test_fpathconf (test.test_os.TestInvalidFD.test_fpathconf)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/buildbot/Library/Developer/XCTestDevices/85DA13F3-B7FB-4094-B3E2-5936BFB3D984/data/Containers/Bundle/Application/B95FE44D-AA6C-427B-B3B5-68EB2D062669/iOSTestbed.app/python/lib/python3.13/test/test_os.py", line 2369, in test_fpathconf
    self.check(os.pathconf, "PC_NAME_MAX")
    ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/buildbot/Library/Developer/XCTestDevices/85DA13F3-B7FB-4094-B3E2-5936BFB3D984/data/Containers/Bundle/Application/B95FE44D-AA6C-427B-B3B5-68EB2D062669/iOSTestbed.app/python/lib/python3.13/test/test_os.py", line 2293, in check
    f(os_helper.make_bad_fd(), *args, **kwargs)
    ~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: unrecognized configuration name

2 instances of:

======================================================================
ERROR: test_fd_count (test.test_support.TestSupport.test_fd_count)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/buildbot/Library/Developer/XCTestDevices/4A852A8A-CCCB-441C-8D72-E2EEA20B0EDD/data/Containers/Bundle/Application/9A737A54-B46D-42BE-AACA-F5780789C07E/iOSTestbed.app/python/lib/python3.13/test/test_support.py", line 558, in test_fd_count
    start = os_helper.fd_count()
            ~~~~~~~~~~~~~~~~~~^^
  File "/Users/buildbot/Library/Developer/XCTestDevices/4A852A8A-CCCB-441C-8D72-E2EEA20B0EDD/data/Containers/Bundle/Application/9A737A54-B46D-42BE-AACA-F5780789C07E/iOSTestbed.app/python/lib/python3.13/test/support/os_helper.py", line 634, in fd_count
    MAXFD = os.sysconf("SC_OPEN_MAX")
            ~~~~~~~~~~^^^^^^^^^^^^^^^
ValueError: unrecognized configuration name

2 instances of:

======================================================================
ERROR: test_many_opens (test.test_zipfile.test_core.TestsWithMultipleOpens.test_many_opens)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/buildbot/Library/Developer/XCTestDevices/82B8EC8A-A9A7-4E96-9E26-0D22DE1C6647/data/Containers/Bundle/Application/2BF4ED76-6DB4-44F1-931E-A2CC4F6603B5/iOSTestbed.app/python/lib/python3.13/test/test_zipfile/test_core.py", line 2901, in test_many_opens
    startcount = fd_count()
                 ~~~~~~~~^^
  File "/Users/buildbot/Library/Developer/XCTestDevices/82B8EC8A-A9A7-4E96-9E26-0D22DE1C6647/data/Containers/Bundle/Application/2BF4ED76-6DB4-44F1-931E-A2CC4F6603B5/iOSTestbed.app/python/lib/python3.13/test/support/os_helper.py", line 634, in fd_count
    MAXFD = os.sysconf("SC_OPEN_MAX")
            ~~~~~~~~~~^^^^^^^^^^^^^^^
ValueError: unrecognized configuration name

The common thread here is the call in os_helper.fd_count() to os.sysconf(); it is raising ValueError rather than OSError; however, as with the test_posix failure, the issue appears to be that a POSIX-specific system configuration variable isn't (reliably) available at runtime.

gh-118201: Accomodate flaky behavior of `os.sysconf` on iOS (GH-118453)

pythongh-118201 - Disable the flaky POSIX test_confstr test on iOS (p…

pythongh-118201: Accomodate flaky behavior of `os.sysconf` on iOS (py…

Triage: the linked PRs are merged, is this ready to be closed or is there more to do?

Yes - this is fully resolved.