Throttle

Throttle.cs

await using var limiter = new FixedWindowRateLimiter(new FixedWindowRateLimiterOptions() { Window = TimeSpan.FromSeconds(1), PermitLimit = 1, AutoReplenishment = true, QueueLimit = 1 });
var source = Ints();
await foreach (var item in Debounce(source, limiter))
{
    Console.WriteLine($"{DateTime.Now} {item}");
}

static async IAsyncEnumerable<int> Ints()
{
    for (int i = 0; i < 106; i += 5)
    {
        await Task.Delay(i * 10);
        yield return i;
    }
}

static async IAsyncEnumerable<T> Debounce<T>(IAsyncEnumerable<T> source, RateLimiter limiter)
{
    var ch = Channel.CreateBounded<T>(new BoundedChannelOptions(1) { FullMode = BoundedChannelFullMode.DropOldest, SingleReader = true, SingleWriter = true });
    _ = EnumerateSource(source);

    while (true)
    {
        using var lease = await limiter.AcquireAsync();
        if (await ch.Reader.WaitToReadAsync() && ch.Reader.TryRead(out var item))
            yield return item;
        else
            break;
    }

    async Task EnumerateSource(IAsyncEnumerable<T> source)
    {
        await foreach (var item in source)
            ch.Writer.TryWrite(item);

        ch.Writer.Complete();
    }
}