New Feature in .NET 7: Rate Limiting

As its name implies, rate limiting limits how much of a particular resource can be accessed. An example could be that your application can send through hundreds of requests in a minute, but you are not sure if the application or database is capable of overseeing that many requests. In such a case, programmers can put a rate limiter in the application to oversee the number of requests they would like to handle in a given amount of time (such as a minute) and then reject any requests beyond that point before accessing the database.

In this manner, rate limiting allows your application to oversee a safe number of requests without (potentially) experiencing failures from a connected database.

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How to Use RateLimiter in .NET

The RateLimiter abstract base class is illustrated in the .NET code example below:

public abstract class RateLimiter : IAsyncDisposable, IDisposable
{
    public abstract int GetAvailablePermits();
    public abstract TimeSpan? IdleDuration { get; }

    public RateLimitLease Acquire(int permitCount = 1);
    public ValueTask WaitAsync(int permitCount = 1, CancellationToken = default);

    public void Dispose();
    public ValueTask DisposeAsync();
}

RateLimiter can be found inside the System.Threading.RateLimiting NuGet package.

Using the Acquire Method in .NET

In the following example, we acquire a permit via the Acquire method. If the permit has been acquired, we can perform a given action, or else we can make use of error handling:

RateLimiter rlMyLimiter = GetLimiter();
using RateLimitLease rlMyRateLimitLease = rlMyLimiter.Acquire(permitCount: 1);
if (rlMyRateLimitLease.IsAcquired)
{
    // Anything in here is protected by the limiter
}
else
{
    // Here, error logic could be added
}

Concurrent Rate Limiters in .NET

The next .NET code example shows a concurrent rate limiter making use of queueing permits, which checks if a permit is available or not:

RateLimiter rlMyLimiter  = new ConcurrencyLimiter(
    new ConcurrencyLimiterOptions(permitLimit: 2, queueProcessingOrder: QueueProcessingOrder.OldestFirst, queueLimit: 2));

// First thread
using RateLimitLease rlMyRateLimitLease = rlMyLimiter.Acquire(permitCount: 2);
if (rlMyRateLimitLease.IsAcquired) 
{
	//Anything in here is protected by the limiter
}
else
{
    // Here, error logic could be added for Second Thread
}

// Second Thread
using RateLimitLease rlMyRateLimitLease = await rlMyLimiter.WaitAsync(permitCount: 2);
if (rlMyRateLimitLease.IsAcquired) 
{
	//Anything in here is protected by the limiter
}
else
{
    // Here, error logic could be added for Second Thread
}

Token Bucket Rate Limiter in .NET

The next code example shows the use of a token bucket rate limiter, which developers can use to set the tokens that can get added per period, and how often this should occur:

RateLimiter rlMyLimiter = new TokenBucketRateLimiter(new TokenBucketRateLimiterOptions(tokenLimit: 5, queueProcessingOrder: QueueProcessingOrder.OldestFirst,
    queueLimit: 1, replenishmentPeriod: TimeSpan.FromSeconds(5), tokensPerPeriod: 1, autoReplenishment: true));
using RateLimitLease rlMyRateLimitLease1 = await rlMyLimiter.WaitAsync(5);

using RateLimitLease rlMyRateLimitLease2 = await rlMyLimiter.WaitAsync();

You can learn more about the RateLimiter API in .NET from its official documentation.

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