Simple debounce

Debouncer.cs

using System;
using System.Threading;
using System.Threading.Tasks;

namespace MyNamespace
{
    public class Debouncer : IDisposable
    {
        private readonly CancellationTokenSource cts = new CancellationTokenSource();
        private readonly TimeSpan waitTime;
        private int counter;

        public Debouncer(TimeSpan? waitTime = null)
        {
            this.waitTime = waitTime ?? TimeSpan.FromSeconds(3);
        }

        public void Debouce(Action action)
        {
            var current = Interlocked.Increment(ref this.counter);

            Task.Delay(this.waitTime).ContinueWith(task =>
            {
                // Is this the last task that was queued?
                if (current == this.counter && !this.cts.IsCancellationRequested)
                    action();

                task.Dispose();
            }, this.cts.Token);
        }

        public void Dispose()
        {
            this.cts.Cancel();
        }
    }
}

IConfigurationExtensions.cs

using System;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Primitives;

namespace MyNamespace
{
    public static class IConfigurationExtensions
    {
        /// <summary>
        /// Perform an action when configuration changes. Note this requires config sources to be added with
        /// `reloadOnChange` enabled
        /// </summary>
        /// <param name="config">Configuration to watch for changes</param>
        /// <param name="action">Action to perform when <paramref name="config"/> is changed</param>
        public static void OnChange(this IConfiguration config, Action action)
        {
            // IConfiguration's change detection is based on FileSystemWatcher, which will fire multiple change
            // events for each change - Microsoft's code is buggy in that it doesn't bother to debounce/dedupe
            // https://github.com/aspnet/AspNetCore/issues/2542
            var debouncer = new Debouncer(TimeSpan.FromSeconds(3));

            ChangeToken.OnChange<object>(config.GetReloadToken, _ => debouncer.Debouce(action), null);
        }
    }
}

Program.cs

...

var config = new ConfigurationBuilder()
    .AddJsonFile("appsettings.json", false, true)
    .SetBasePath(Directory.GetCurrentDirectory())
    .Build();
    
config.OnChange(() =>
{
    // TODO: Config has been changed, do stuff here
});

...

Hopefully an async overload will make it into v7 later this year. If this is still important to you please upvote to help prioritise it? :)