[API Proposal]: RateLimiter uses TimeProvider

Background and motivation

Rate limiters in the System.Threading.RateLimiting namespace is not designed to accept TimeProvider.

Therefore, we need to wait for the actual time to elapse when testing functions that use them.

For faster testing, please make sure that rate limiters accepts TimeProvider and does not have to wait for the actual time to elapse.

API Proposal

namespace System.Threading.RateLimiting;

public sealed class FixedWindowRateLimiterOptions
{
    public TimeProvider TimeProvider { get; set; } = TimeProvider.System;
}

public sealed class SlidingWindowRateLimiterOptions
{
    public TimeProvider TimeProvider { get; set; } = TimeProvider.System;
}

public sealed class TokenBucketRateLimiterOptions
{
    public TimeProvider TimeProvider { get; set; } = TimeProvider.System;
}

API Usage

var timeProvider = new FakeTimeProvider();

var options = new TokenBucketRateLimiterOptions
{
    TokenLimit = 1,
    TokensPerPeriod = 1,
    AutoReplenishment = true,
    ReplenishmentPeriod = TimeSpan.FromSeconds(10),
    TimeProvider = timeProvider
};

using var limiter = new TokenBucketRateLimiter(options);

using (var lease = limiter.AttemptAcquire())
{
    Assert.True(lease.IsAcquired);
}

timeProvider.Advance(TimeSpan.FromSeconds(10));

// If TimeProvider is not supported, we need to actually stop the thread here.
// Thread.Sleep(TimeSpan.FromSeconds(10));

using (var lease = limiter.AttemptAcquire())
{
    Assert.True(lease.IsAcquired);
}

Alternative Designs

No response

Risks