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a5c8fc28a4
When two HTTP requests arrived simultaneously for the same package on
a cold in-memory cache (bc._caches[name] === undefined), they would
both:
1. Enter getPackages, see no warm cache,
2. Read and parse the same _cache/{pkg}.json independently,
3. Both call transformAndUpdate, which re-runs _classify on every
build.
The first call populates bc._targetsByBuildIdCache as it classifies.
The second call then hits the cache shortcut at the top of _classify
and skips the projInfo.oses/arches/libcs/formats/triplets
accumulation block entirely. Its projInfo ends up with empty tracking
arrays (because the prior Object.assign(projInfo, meta) reset them),
and that poisoned projInfo gets written to bc._caches[name],
overwriting the first call's good cache.
After this, every subsequent installer request returns errPackage
because serve-installer.js checks projInfo.oses.includes(hostTarget.os)
— and projInfo.oses is now [].
Fix: a per-name in-flight promise. Concurrent callers for a cold
package share a single load. Calls for warm packages take the fast
path with no synchronization.
Reproduced reliably with Promise.all of 6 cold-cache calls for the
same package: 1/6 succeeded before the fix, 6/6 after. On staging at
HTTP concurrency=12, installer cand-only-errors went from 24-229
(cause-dependent) to 0.