fix(cli): make mops install safe under parallel invocations - #543
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Kamirus merged 3 commits intoMay 22, 2026
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Concurrent `mops install` runs against the same project (editor watcher, vscode-motoko fixture installer, CI matrix) used to race in two places — global cache writes and local `.mops/<pkg>` copies — leaving zero-byte / truncated files that surfaced later as missing completions or type-check errors. GitHub installs were strictly worse because `mkdirSync(cacheDir)` ran before the download, so a peer process saw an empty dir as cached. Cache writes now stage into a sibling `.staging-*` dir and atomically rename onto the canonical path; the loser of a race discards its staging silently. `mops install`, `mops add`, and the local `.mops/` sync follow the same pattern. The shared `.mops/_tmp/` zip dir used by GitHub installs is also per-invocation (`mkdtemp`) now. Stale staging dirs from crashed runs are swept on the next install (mtime threshold so a sibling that is mid-staging is never clobbered). Refs LANG-1310, caffeinelabs/vscode-motoko#461. Co-authored-by: Cursor <cursoragent@cursor.com>
…github - commitStagingDir only swallows EPERM/EEXIST/ENOTEMPTY when dest exists. - Parallel-install test isolates the global cache via XDG_CACHE_HOME so the global-write code path actually executes (was a hot-cache no-op). - Sweep covers <rootDir>/.mops/_github/ and the github zip download dir (renamed to .staging-github-dl-). - Migrate dead-but-exported addCache to the staging pattern. - SIGINT exits 130 (POSIX convention). - Trim comments; CHANGELOG note about `mops cache clean` for upgrades. Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Cursor <cursoragent@cursor.com>
Kamirus
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May 22, 2026 08:55
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Why
Two
mopsprocesses installing into the same project (editor watcher, vscode-motoko's fixture installer, CI matrix sharing a global cache) race on cache writes and leave zero-byte / truncated files in.mops/. Symptom downstream: missing completions, hover, type-check errors. v2.13.2's concurrent-invocations fix coveredcheck/build/check-stablescratch dirs, not the install cache path.Two race windows:
install-mops-dep.ts):Promise.all(mkdir + writeFile)writes directly intocacheDirwhileisDepCached = fs.existsSync(cacheDir)— peer sees "cached" mid-write and copies a half-populated tree..mops/<pkg>(syncLocalCache): two concurrent installs both missexistsSync(dest)and interleave writes viancp.GitHub installs were strictly worse —
mkdirSync(cacheDir)ran before the download, so peers saw an empty dir as cached. The shared.mops/_tmp/zip dir was also clobbered by concurrent github installs.What
Cache writes stage into a sibling
.staging-*dir (mkdtemp, same filesystem) and atomicallyrenameonto the canonical path. Race-loser catchesENOTEMPTY/EEXIST/EPERM(only whendestexists, to avoid masking real Windows AV / permission errors), drops its staging, and observes a complete cache. Applies to mops registry installs, github installs, local.mops/sync, and the github zip download dir. Stale staging is swept on the next install with a 1h mtime cutoff.Test plan
mops installruns against an isolatedXDG_CACHE_HOMEproduce no zero-byte files and no.staging-*leftovers (cold-cache path actually exercised).parallel builds of the same canister both succeedstill passes.npm run check+npm run lintclean.Refs LANG-1310, caffeinelabs/vscode-motoko#461.