Question

How to asynchronously save an entity to Windows Azure Table Service?

The code below works synchronously but raises an exception when trying to save asynchronously.

This statement:

context.BeginSaveChangesWithRetries(SaveChangesOptions.Batch,
    (asyncResult => context.EndSaveChanges(asyncResult)), null);

Results in System.ArgumentException: “The current object did not originate the async result. Parameter name: asyncResult”.

Additionally, what’s the correct pattern for creating the service context when saving asynchronously? Should I create a separate context for each write operation? Is it too expensive (e.g. requiring a call over the network)?

TableStorageWriter.cs:

using System;
using System.Data.Services.Client;
using System.Diagnostics;
using Microsoft.WindowsAzure;
using Microsoft.WindowsAzure.StorageClient;

namespace WorkerRole1
{
    public class TableStorageWriter
    {
        private const string _tableName = "StorageTest";
        private readonly CloudStorageAccount _storageAccount;
        private CloudTableClient _tableClient;

        public TableStorageWriter()
        {
            _storageAccount = CloudStorageAccount.Parse(CloudConfigurationManager.GetSetting("StorageConnectionString"));
            _tableClient = _storageAccount.CreateCloudTableClient();
            _tableClient.CreateTableIfNotExist(_tableName);
        }

        public void Write(string message)
        {
            try
            {
                DateTime now = DateTime.UtcNow;
                var entity = new StorageTestEntity
                    {
                        Message = message,
                        PartitionKey = string.Format("{0:yyyy-MM-dd}", now),
                        RowKey = string.Format("{0:HH:mm:ss.fff}-{1}", now, Guid.NewGuid())
                    };

                // Should I get this context before each write? It is efficient?
                TableServiceContext context = _tableClient.GetDataServiceContext();

                context.AddObject(_tableName, entity);

                // This statement works but it's synchronous
                context.SaveChangesWithRetries();

                // This attempt at saving asynchronously results in System.ArgumentException:
                // The current object did not originate the async result. Parameter name: asyncResult
                // context.BeginSaveChangesWithRetries(SaveChangesOptions.Batch,
                //                                  (asyncResult => context.EndSaveChanges(asyncResult)), null);
            }
            catch (StorageClientException e)
            {
                Debug.WriteLine("Error: {0}", e.Message);
                Debug.WriteLine("Extended error info: {0} : {1}",
                                e.ExtendedErrorInformation.ErrorCode,
                                e.ExtendedErrorInformation.ErrorMessage);
            }
        }
    }

    internal class StorageTestEntity : TableServiceEntity
    {
        public string Message { get; set; }
    }
}

Called from WorkerRole.cs:

using System.Net;
using System.Threading;
using Microsoft.WindowsAzure.ServiceRuntime;
using log4net;

namespace WorkerRole1
{
    public class WorkerRole : RoleEntryPoint
    {
        public override void Run()
        {
            var storageWriter = new TableStorageWriter();
            while (true)
            {
                Thread.Sleep(10000);
                storageWriter.Write("Working...");
            }
        }

        public override bool OnStart()
        {
            ServicePointManager.DefaultConnectionLimit = 12;
            return base.OnStart();
        }
    }
}

Examples using Windows Azure SDK for .NET 1.8.

Answer 1

You should call EndSaveChangesWithRetries instead of EndSaveChanges, as otherwise the IAsyncResult object returned by BeginSaveChangesWithRetries cannot be used by EndSaveChanges. So, could you please try changing your End method call as below?

context.BeginSaveChangesWithRetries(SaveChangesOptions.Batch,
    (asyncResult => context.EndSaveChangesWithRetries(asyncResult)),
    null);

And for your other question, I would recommend creating a new TableServiceContext for each call, as DataServiceContext is not stateless (MSDN) and the way you implemented TableStorageWriter.Write with the asynchronous call might allow concurrent operations. Actually, in Storage Client Library 2.0, we explicitly prevented concurrent operations that uses a single TableServiceContext object. Moreover, creating a TableServiceContext does not result in a request to Azure Storage.