如何异步保存实体到Windows Azure Table Service?
下面的代码同步工作,但在尝试异步保存时引发异常。
此声明:
context.BeginSaveChangesWithRetries(SaveChangesOptions.Batch,
(asyncResult => context.EndSaveChanges(asyncResult)), null);
在 System.ArgumentException 中的结果:"当前对象没有产生异步结果。参数名称:异步结果"。
此外,异步保存时创建服务上下文的正确模式是什么?我是否应该为每个写入操作创建一个单独的上下文?是否太贵(例如,需要通过网络呼叫)?
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; }
}
}
从 workerRole.cs 调用:
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();
}
}
}
使用 Windows Azure SDK for .NET 1.8 的示例。
而不是 EndSaveChanges,否则 BeginSaveChangesWithRetry 返回的 IAsyncResult 对象不能被 EndSaveChanges 使用。那么,您能否尝试更改您的 End 方法调用,如下所示?
context.BeginSaveChangesWithRetries(SaveChangesOptions.Batch,
(asyncResult => context.EndSaveChangesWithRetries(asyncResult)),
null);
对于您的另一个问题,我建议为每个调用创建一个新的 TableServiceContext,因为 DataServiceContext 不是无状态 (MSDN),并且使用异步调用实现 TableStorageWriter.Write 的方式可能允许并发操作。实际上,在存储客户端库 2.0 中,我们显式阻止了使用单个 TableServiceContext 对象的并发操作。此外,创建 TableServiceContext 不会导致对 Azure 存储的请求。