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The permit you never gave back

A throttle that stops throttling, then stops working entirely.

Intermediate18 min on the clock5 graded checks · 100 pointsResources and ConcurrencyPro

Graded by reading your code against the checklist below.

What you build

Share one semaphore rather than creating one per call
Wait asynchronously instead of blocking
Release in a finally, so an exception cannot strand the permit
Pass the cancellation token to the wait
Dispose the semaphore

Done means

One shared semaphore, awaited with the token, released in a finally, and disposed.

How it is graded

Published in full, before you start — every point is one of these and there is nothing else.

Release runs in a finally+35Limiting how much runs at once
The wait is asynchronous+20Limiting how much runs at once
One semaphore, shared+20Limiting how much runs at once
The wait honours cancellation+15Limiting how much runs at once
The semaphore is disposed+10Giving resources back

What it teaches

Limiting how much runs at onceintermediate

A SemaphoreSlim caps concurrency, but only if it is shared and only if every permit comes back — a Release skipped by an exception drains the pool and the service hangs rather than erroring.

Giving resources backbeginner

A file handle or socket you opened is yours to release — the Dispose pattern is how a caller gets to say "I am finished with this" instead of waiting for a collection that may never come.

The rest of Resources and Concurrency

Giving the handle backBeginner · 15 min The leak you can readBeginner · 15 min What you lock onIntermediate · 15 min The app that stops answeringIntermediate · 18 min A deadline and a request to stopAdvanced · 20 min The scoped thing inside the singletonAdvanced · 20 min