---
title: "Counting UNENFORCED fallbacks in the ledger and the background CLI"
canonical: https://dxdev.com/blog/exclusive-create-lock-failed-under-load/
datePublished: 2026-10-03
---
The `spawn_budget` lock failed open under load.

## The old lock

It was built on `O_EXCL` plus `unlink`. Under load it failed open, so the fallback path ran with the budget unenforced.

## The replacement

The lock is now `statefile.file_lock`, a kernel byte-range lock, with a retry on `PermissionError`. The commit that made the change carries tests.

## Counting the fallbacks

The change had a second part. The `UNENFORCED` fallbacks are now counted in the ledger and shown by the CLI `background`, so a lock that fails open shows up as a number instead of passing silently.