Incident Dossier

Lock Around the Wrong Axis

A reservation system handles thousands of requests per second. Two callers each asking for unrelated slots, but both issued by the same user account, block each other. Throughput collapses to the number of users instead of the number of slots.

Initial failing signaltwo reservations for the same owner serializeExpected behavior: peak in-flight == 2 · actual behavior: peak in-flight == 1

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Look at the lock key passed to `_withLock`.
Two distinct slots share the same key (the owner), so they serialize.
Lock on the slot identity, not the caller.

Focus Mode

Start

src/slots.js

Likely area

src/slots.js

Challenge Coach

Hints reveal broad direction first, then narrow toward the suspect path without showing hidden tests or exact solution code.

TopicEvents & Concurrency

DifficultyMedium

Est. time18 min

Workspacepreparing

Explorer

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Evidence Map

Failing signal loaded from challenge API
Workspace files loaded from workspace API
Results rendered only after API run/submit

Autosaved

workspace

Outputread-onlyready$ prepare workspace

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