AsyncSemaphore

A simple wrapper around a SemaphoreSlim featuring:

• Automatic releasing without try/finally blocks by utilising the IDisposable using pattern
• Guarantee that release can only be called once per WaitAsync call
• Analyzers to help you implement the desired pattern
• An IAsyncSemaphore interface for if you need to mock

Install

dotnet add package AsyncSemaphore

Usage

private readonly AsyncSemaphore _asyncSemaphore = new AsyncSemaphore(1);

public async Task MyMethod()
{
    // Just assign the `IDisposable` returned from `WaitAsync` to a variable and use the using statement with it
    using var lockHandle = await _asyncSemaphore.WaitAsync();

    // Do whatever you want - Even if we throw exceptions, we'll release the semaphore once we leave this method's scope
    await DoSomethingInsideLock();
}

or scoped:

private readonly AsyncSemaphore _asyncSemaphore = new AsyncSemaphore(1);

public async Task MyMethod()
{
    // or create your own scope with {} braces - And after you leave that scope, your lock will be released
    using (await _asyncSemaphore.WaitAsync())
    {
        await DoSomethingInsideLock();
    }

    await DoSomethingAfterLockReleased();
}

Benchmarks and allocations can be seen below.

BenchmarkDotNet v0.15.8, Linux Ubuntu 25.10 (Questing Quokka)
12th Gen Intel Core i7-12700K 0.80GHz, 1 CPU, 20 logical and 12 physical cores
.NET SDK 10.0.101
  [Host]     : .NET 10.0.1 (10.0.1, 10.0.125.57005), X64 RyuJIT x86-64-v3
  DefaultJob : .NET 10.0.1 (10.0.1, 10.0.125.57005), X64 RyuJIT x86-64-v3

Method	Mean	Error	StdDev	Allocated
Raw_Semaphore_Slim	29.95 ns	0.054 ns	0.048 ns	-
AsyncSemaphore_With_Inherited_Scope	35.38 ns	0.097 ns	0.081 ns	-
AsyncSemaphore_With_Braced_Scope	35.72 ns	0.247 ns	0.231 ns	-