HttpThrottleDemo

Read the full article at :

https://dev.to/stevsharp/semaphoreslim-in-net-a-practical-guide-with-the-rest-of-the-toolbox-1mh7

A tiny console that shows SemaphoreSlim based throttling for async HTTP work. You set a max concurrency, it runs a batch of requests, it reports latency and the highest concurrency observed.

Requirements

• .NET 9 SDK

Quick start

git clone <your-repo-url>
cd HttpThrottleDemo
dotnet run -- -c 8 -n 100 -t 30 -u "https://httpbin.org/delay/1?i={i}"

What it does

• Limits parallel requests with a SemaphoreSlim
• Supports Ctrl+C and a global timeout
• Prints success and failure counts, average and P95 latency, max in flight

Usage

dotnet run -- [options]

Options

• -c, --concurrency max parallel requests, default 8
• -n, --total total requests, default 100
• -t, --timeout global timeout in seconds, default 30
• -u, --url URL template, use {i} as index placeholder
• -h, --help show help

Examples

# 12 concurrent requests, 200 total, 45 seconds timeout
dotnet run -- -c 12 -n 200 -t 45 -u "https://httpbin.org/delay/1?i={i}"

# Low concurrency against your own API
dotnet run -- -c 4 -n 50 -u "https://example.com/items/{i}"

How it works

HttpThrottler.RunAsync accepts a delegate Func<CancellationToken, Task<T>> and a token.

• The token cancels waiting to enter, and it also flows into your HTTP call, so both admission and the work can be canceled with one source.
• The permit is released in finally, even if the work fails or is canceled.

Files

• HttpThrottleDemo.csproj
• Program.cs with HttpThrottler and minimal options parsing

That is it. Tune -c for your API and network, keep an eye on the summary to verify the limit behaves as expected.

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