Permit Released Twice on Success Debugging Lab

Permit Released Twice on SuccessEvents & ConcurrencyMediumPreparing workspaceAutosaved

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Incident Dossier

Permit Released Twice on Success

A small in-process semaphore gates access to a connection pool. After the team runs a sequence of jobs that succeed, the next acquire returns instantly even though more callers are running than the configured limit allows.

Initial failing signalwithLock concurrency invariant is brokenExpected at most 2 callbacks in flight at once · received 3 or more callbacks ran concurrently

Progress

1Reproduce the bugRun checks

2Edit the fixOpen

3Pass checksOpen

4Submit fixOpen

Reproduction Steps

Run npm test.
Trace what withLock does after a successful fn return.
Count how many times the semaphore is credited per call.
Release the permit exactly once per call.

Focus Mode

Start

src/sem.js

Likely area

src/sem.js

Progressive hints

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

Workspacecreating

Explorer

Preparing workspace files…

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$ workspace boot

Workspace booting...