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Erik Johnston
b4deb24be6
`test_lock_contention` is a performance-regression canary (#16840): the pathological behaviour it guards against spent ~30s spinning the CPU, vs ~0.5s when healthy. The 5s wall-clock alarm it used was calibrated on SQLite, but against PostgreSQL a healthy run already takes 3-4s of wall-clock time (500 sequential acquire/release cycles, each a real database round-trip), so any CI load pushed it over the limit. Add a `cpu_time` mode to `tests/utils.py`'s test_timeout, implemented with [`setitimer(ITIMER_PROF)`](https://docs.python.org/3/library/signal.html#signal.setitimer), which budgets process CPU time instead of wall-clock time. Time spent blocked on the database or lost to a loaded CI runner no longer counts, while a regression to CPU-spinning still trips the alarm mid-spin. A healthy run costs <1s of CPU on either database engine; the budget is 10s. This also subsumes the RISC-V wall-clock carve-out from #18430, which is removed. --------- Co-authored-by: Claude Fable 5 <noreply@anthropic.com>