mirror of
https://github.com/pnpm/pnpm.git
synced 2026-03-26 11:02:01 -04:00
878a7734a0
## Problem
Every file extracted to the CAS goes through a temp-file-plus-rename cycle: `writeFile(temp, buffer)` then `renameOverwriteSync(temp, fileDest)`. For a typical cold install with ~30k files, this adds ~30k extra rename syscalls.
## Solution
Use `writeFileExclusive()` with `{ flag: 'wx' }` (O_CREAT|O_EXCL) to write directly to the final CAS path when the file doesn't exist — skipping the temp+rename overhead. For recovery paths (corrupt/partial files, EEXIST races), fall back to the existing atomic temp+rename via `optimisticRenameOverwrite`.
### Write paths
- **File doesn't exist (common cold-install path)** → `writeFileExclusive` writes directly, no rename
- **File exists with correct integrity** → return immediately, no write
- **File exists with wrong integrity (corruption/crash)** → atomic temp+rename recovery
- **EEXIST (concurrent write)** → verify integrity; if OK return, otherwise atomic temp+rename recovery
### Concurrent safety
- `writeFileExclusive` (`O_CREAT|O_EXCL`) ensures only one process creates a given CAS file
- Recovery overwrites use the battle-tested `optimisticRenameOverwrite` + `pathTemp` for atomic replacement
- `verifyFileIntegrity` is non-destructive (no `unlinkSync` on mismatch), safe when another process may be mid-write
- A crash mid-`writeFileExclusive` can leave a partial file, recovered on next access via atomic temp+rename
---------
Co-authored-by: Zoltan Kochan <z@kochan.io>