Bug report

Bug description:

test_rollover_based_on_st_birthtime_only failed again on main, on the "Windows / Build and test (x64, tail-call)" CI job of 532b9db (2026-09-01): https://github.com/python/cpython/actions/runs/33523218872/job/99907492032

FAIL: test_rollover_based_on_st_birthtime_only (test.test_logging.TimedRotatingFileHandlerTest.test_rollover_based_on_st_birthtime_only)
AssertionError: False is not true : No rotated files found, went back 5 seconds

This is the test that gh-150960 (fixed by GH-150954, which widened the search from 5 to 6 timestamps) was about. The diagnostics the test prints show why it still fails on a slow machine:

Test time: 2026-09-01 15-10-51
The only matching files are: ['test_logging-2-p8i89g4b.log', 'test_logging-2-p8i89g4b.log.2026-09-01_15-10-45']
Contents of test_logging-2-p8i89g4b.log:
2026-09-01 15:10:51,079 testing - new record supposedly in the new file after rollover
Contents of test_logging-2-p8i89g4b.log.2026-09-01_15-10-45:
2026-09-01 15:10:45,004 testing - initial
2026-09-01 15:10:47,105 testing - update before rollover to renew the st_mtime

The rollover happened and is correct. The rotated file is named after the start of the interval, which is the creation time of the log file (TimedRotatingFileHandler.__init__() computes rolloverAt from min(creation_time, modification_time), and doRollover() uses rolloverAt - interval for the suffix), so its suffix is 15-10-45. The test then looks for a rotated file with a timestamp between now and now - 5 s. now was 15:10:51, six seconds after the file was created, because the third add_record() came 3.97 s after the second one instead of about 2.1 s. So the file with suffix 15-10-45 was one second outside the window.

The test's timing (two time.sleep(2.1) calls plus three handler set-ups and emits) is nominally 4.2 s, and any slowdown of more than 0.8 s pushes the rotated file out of the fixed 5-second window. The window should be derived from the time the test actually took, since the suffix can never be older than the moment the log file was created.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows (CI)

Linked PRs

• gh-157161: Fix test_rollover_based_on_st_birthtime_only on slow machines #157162