lix/doc/manual/rl-next/libstore-random.md
Lily Ballard 69957a971e libstore: replace random() calls with atomic counter
random() is not thread-safe, it relies on global state, and calling it
from worker threads can result in multiple threads producing the same
value. It also doesn't guarantee unique values even in single-threaded
use.

Use an atomic counter for the use-case of generating temporary paths,
and switch to a thread-local RNG for the one remaining call.

This will probably fix https://github.com/NixOS/nix/issues/7273 though
I'm not willing to risk corrupting my store to find out.

Change-Id: I4c4c4c9796613573ffefd29cc8efe3d07839facc
2024-10-30 19:54:43 -07:00

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Markdown

---
synopsis: Fix potential store corruption with auto-optimise-store
issues: [7273]
cls: [2100]
category: Fixes
credits: lilyball
---
Optimising store paths (and other operations involving temporary files) no longer use `random(3)`
to generate filenames. On darwin systems this was observed to potentially cause store corruption
when using [`auto-optimise-store`](@docroot@/command-ref/conf-file.md#conf-auto-optimise-store),
though this corruption was possible on any system whose `random(3)` does not have locking around
the global state.