tests: thread stress tests intermittent failures under QEMU (stress_aes, stress_recurse, stress_schedule)
Three thread stress tests fail intermittently under QEMU emulation on CI:
thread/stress_aes.py — times out on QEMU ARM/MIPS/RISCV64. Execution
time approaches or exceeds the configured timeout (70-180s depending on
arch). Observed 7 times in a 20-run log window. Attributed to ~28 of 103
failed runs over 14 months. On RISCV64 it's excluded entirely because it
takes ~180s against a 200s timeout.
thread/stress_recurse.py — was already excluded from qemu_mips,
qemu_arm, qemu_riscv64 with "is flaky" comments. No direct log
observations in the sample window since it was excluded, but the
exclusion predates the analysis period.
thread/stress_schedule.py — crashed once (expected PASS, got
CRASH) on qemu_riscv64 in the 20-run window. Low frequency but a
crash rather than a timeout suggests a real issue.
These may be QEMU-specific timing/emulation issues rather than bugs in
MicroPython's threading, but the crash in stress_schedule suggests at
least some of these are real.
PR #18861 now ignores these failures in CI. stress_aes.py is additionally
excluded on RISCV64 to avoid burning ~180s of CI time on each timeout.
See analysis: https://gist.github.com/andrewleech/5686ed5242e0948d8679c432579e002e
tests: cmdline/repl_lock.py and repl_cont.py intermittent failures
Two REPL tests fail intermittently on CI:
cmdline/repl_lock.py — fails on QEMU ARM and RISCV64. The expected
output shows >>> micropython.heap_lock() but the actual output drops
the >>> prompt prefix. Observed 3 times in 20 runs with logs. This is
a REPL prompt timing issue under QEMU emulation.
cmdline/repl_cont.py — fails on macOS. Differences in quote escaping
in REPL continuation prompts ("'" vs '\''). Observed once in 20 runs.
The macOS job has historically been the second most failure-prone job
(4.3% failure rate, 25 failures over 14 months) with all failures
attributed to REPL-related issues. The August 2025 spike (11 macOS
failures) correlates with the GitHub Actions macOS 15 runner migration.
PR #18861 now ignores these failures in CI.
See analysis: https://gist.github.com/andrewleech/5686ed5242e0948d8679c432579e002e