ExecuteQueryRetryAsync.cs

using Microsoft.SharePoint.Client;
using System;
using System.Net;
using System.Threading;
using System.Threading.Tasks;
using static Microsoft.SharePoint.Client.ClientContextExtensions;

public static class ClientContextExtensions
{
    public static async Task ExecuteQueryRetryAsync(this ClientContext clientContext,
            CancellationTokenSource cancellationTokenSource, int retryCount = 3, int backoffDelaySeconds = 30)
    {
        if (retryCount <= 0)
            throw new ArgumentException("Provide a retryCount value greater than zero.");

        if (backoffDelaySeconds <= 0)
            throw new ArgumentException("Provide a backoffDelaySeconds value greater than zero.");
        
        int retryAttempts = 0;

        while(retryAttempts < retryCount)
        {
            try
            {
                await clientContext.ExecuteQueryAsync().ConfigureAwait(false);
                return;
            }
            catch (WebException w)
            {
                var response = w.Response as HttpWebResponse;
                if (response != null && response.StatusCode == (HttpStatusCode)429)
                {
                    Console.WriteLine($"CSOM request exceeded usage limits. Sleeping for {backoffDelaySeconds} seconds before retrying.");
                    await Task.Delay(backoffDelaySeconds * 1000);

                    // Add to retry count and increase delay.
                    retryAttempts++;
                    backoffDelaySeconds = backoffDelaySeconds * 2;
                }
                else
                {
                    throw;
                }
            }
        }

        if (cancellationTokenSource != null)
        {
            // cancel tasks associated with the cancellation token source
            cancellationTokenSource.Cancel();
        }

        throw new MaximumRetryAttemptedException($"CSOM request exceeded usage limits. Maximum ({retryCount}) retries unsuccessful, aborting.");
    }
}