How would you limit concurrent async operations in C#?

Using SemaphoreSlim for concurrency limits

Use SemaphoreSlim to bound concurrent asynchronous work without blocking threads unnecessarily.

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I can use SemaphoreSlim to limit how many async operations run at the same time. Each operation awaits WaitAsync, does the work, and releases the semaphore in a finally block. This is useful when I have many items to process but do not want to call a dependency hundreds of times at once. It is different from a lock because it allows a controlled number of concurrent operations, not just one.

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Concurrency limits, SemaphoreSlim, async-safe waiting, downstream protection, and avoiding unbounded fan-out.

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Concurrency limits are a real production concern. This drill checks whether a candidate can prevent one feature from overwhelming a database, API, queue, or external provider.
I can use SemaphoreSlim to limit how many async operations run at the same time. Each operation awaits WaitAsync, does the work, and releases the semaphore in a finally block. This is useful when I have many items to process but do not want to call a dependency hundreds of times at once. It is different from a lock because it allows a controlled number of concurrent operations, not just one.
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For example, if I need to call an external API for 500 customers, I would not start 500 requests at once. I might allow 10 concurrent calls using SemaphoreSlim, pass cancellation tokens, and record failures per item. The trade-off is throughput versus safety: higher concurrency may finish faster but can trigger rate limits, timeouts, or database pressure. The limit should come from dependency capacity, not a random number.

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Forgetting to release the semaphore in a finally block.
Using a local semaphore when a global distributed limit is required.
Choosing a concurrency value without measuring dependency capacity.
Blocking with Wait() instead of awaiting WaitAsync().
Ignoring cancellation while waiting for the semaphore.

How would you limit concurrent async operations in C#?

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