benchmark_lock.ts

A machine-wide benchmark lock: one measuring process at a time. Two benchmark runs at once don't give two noisy results, they give two wrong ones, because each changes the other's caches, frequency ceiling, and scheduling.

The lock is a file at a fixed path, BENCHMARK_LOCK_PATH, shared by every checkout and every tool on the machine that uses this module. It is created exclusively and names its holder. Acquiring never waits: a second run is refused, not queued. A holder whose process is gone is stale, and its lock is taken over.

Two limits, both narrow. A process id reused by an unrelated process makes a stale lock look held, and the refusal names the file to delete. And two runs that take over the same stale lock in the same instant can both believe they hold it, so release reports whether the lock was still this process's, and a caller that lost it should discard what it measured. A parent killed outright (SIGKILL) also leaves any child it was waiting on running, with the lock looking stale.

The lock is shared on purpose, so any local user can block benchmarks by creating the file; the refusal names it. On Windows the default path is under the per-user temp directory, so there the lock is per user.

Node-only: it uses node:fs, node:os, and process.