我需要在Azure Web实例中实现一些线程后续逻辑。 我有一些像这样的代码：
lock (_bookingLock)
{
// Check for a free time
bool isTimeFree = _scheduleService.IsTimeFree(dateTimeGuidId);
//* race condition here
if (isTimeFree)
{
// Make a booking. So this time is busy
newBookingId = _paymentService.CreateBooking(dateTimeGuidId).ToString();
}
}
但我无法在多实例环境中使用 lock 而我无法省略锁定，因为*存在竞争条件。这里最好的方法是什么？
答案 0 :(得分：4)
我决定使用blob租约。我升级smarx's code以使用Azure存储客户端版本2或3，并编写了一个附加方法。这是完整的代码：
using Microsoft.WindowsAzure.Storage;
using Microsoft.WindowsAzure.Storage.Blob;
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Globalization;
using System.Linq;
using System.Net;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.WindowsAzure.Storage.Shared.Protocol;
using Microsoft.WindowsAzure.Storage.Blob.Protocol;
using System.Configuration;
namespace TerminalManager.Domain.Foundation.BlobLeases
{
public class AutoRenewLease : IDisposable
{
public bool HasLease { get { return leaseId != null; } }
AccessCondition _accessCondition;
private CloudBlockBlob blob;
private string leaseId;
private Thread renewalThread;
private bool disposed = false;
public static void DoOnce(CloudBlockBlob blob, Action action) { DoOnce(blob, action, TimeSpan.FromSeconds(5)); }
public static void DoOnce(CloudBlockBlob blob, Action action, TimeSpan pollingFrequency)
{
// blob.Exists has the side effect of calling blob.FetchAttributes, which populates the metadata collection
while (!blob.Exists() || blob.Metadata["progress"] != "done")
{
using (var arl = new AutoRenewLease(blob))
{
if (arl.HasLease)
{
action();
blob.Metadata["progress"] = "done";
AccessCondition ac = new AccessCondition();
ac.LeaseId = arl.leaseId;
blob.SetMetadata(ac);
}
else
{
Thread.Sleep(pollingFrequency);
}
}
}
}
/// <summary>
/// Выполнить последовательно
/// </summary>
/// <param name="lockBlobName">имя блоба - просто буквы</param>
/// <param name="action"></param>
/// <param name="cnStrName">из конфига</param>
/// <param name="containerName">из конфига</param>
/// <param name="pollingFrequency"></param>
public static void DoConsequence(string lockBlobName, Action action,
string cnStrName = "StorageConnectionString",
string containerName = "leasesContainer", TimeSpan? pollingFrequency = null)
{
//http://www.windowsazure.com/en-us/develop/net/how-to-guides/blob-storage/
// Формат пути к блобу
//http://<storage account>.blob.core.windows.net/<container>/<blob>
// Блобовский аккаунт
var account = CloudStorageAccount.Parse(ConfigurationManager.ConnectionStrings[cnStrName].ConnectionString); //CloudStorageAccount.Parse("UseDevelopmentStorage=true"); // Не работает на SDK 2.2 // or your real connection string
var blobs = account.CreateCloudBlobClient();
// Контейнер - типа папки
var container = blobs
.GetContainerReference(ConfigurationManager.AppSettings[containerName]);
container.CreateIfNotExists();
var blob = container.GetBlockBlobReference(lockBlobName);
bool jobDone = false;
while (!jobDone)
{
using (var arl = new AutoRenewLease(blob))
{
if (arl.HasLease)
{
// Some Sync Work here
action();
jobDone = true;
}
else
{
Thread.Sleep(pollingFrequency ?? TimeSpan.FromMilliseconds(300));
}
}
}
}
public static void DoEvery(CloudBlockBlob blob, TimeSpan interval, Action action)
{
while (true)
{
var lastPerformed = DateTimeOffset.MinValue;
using (var arl = new AutoRenewLease(blob))
{
if (arl.HasLease)
{
blob.FetchAttributes();
DateTimeOffset.TryParseExact(blob.Metadata["lastPerformed"], "R", CultureInfo.CurrentCulture, DateTimeStyles.AdjustToUniversal, out lastPerformed);
if (DateTimeOffset.UtcNow >= lastPerformed + interval)
{
action();
lastPerformed = DateTimeOffset.UtcNow;
blob.Metadata["lastPerformed"] = lastPerformed.ToString("R");
AccessCondition ac = new AccessCondition();
ac.LeaseId = arl.leaseId;
blob.SetMetadata(ac);
}
}
}
var timeLeft = (lastPerformed + interval) - DateTimeOffset.UtcNow;
var minimum = TimeSpan.FromSeconds(5); // so we're not polling the leased blob too fast
Thread.Sleep(
timeLeft > minimum
? timeLeft
: minimum);
}
}
public AutoRenewLease(CloudBlockBlob blob)
{
this.blob = blob;
blob.Container.CreateIfNotExists();
try
{
if (!blob.Exists())
{
blob.UploadFromByteArray(new byte[0], 0, 0, AccessCondition.GenerateIfNoneMatchCondition("*"));// new BlobRequestOptions { AccessCondition = AccessCondition.IfNoneMatch("*") });
}
}
catch (StorageException e)
{
if (e.RequestInformation.HttpStatusCode != (int)HttpStatusCode.PreconditionFailed // 412 from trying to modify a blob that's leased
&& e.RequestInformation.ExtendedErrorInformation.ErrorCode != BlobErrorCodeStrings.BlobAlreadyExists
)
{
throw;
}
}
try
{
leaseId = blob.AcquireLease(TimeSpan.FromSeconds(60), null);
_accessCondition = new AccessCondition { LeaseId = leaseId };
}
catch (Exception)
{
Trace.WriteLine("==========> Lease rejected! <==========");
}
if (HasLease)
{
renewalThread = new Thread(() =>
{
while (true)
{
Thread.Sleep(TimeSpan.FromSeconds(40));
var ac = new AccessCondition();
ac.LeaseId = leaseId;
blob.RenewLease(ac);//.RenewLease(leaseId);
}
});
renewalThread.Start();
}
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!disposed)
{
if (disposing)
{
if (renewalThread != null)
{
renewalThread.Abort();
blob.ReleaseLease(_accessCondition);
renewalThread = null;
}
}
disposed = true;
}
}
~AutoRenewLease()
{
Dispose(false);
}
}
}
以下是如何使用它（不要忘记blob连接字符串和目录名称的setup config）：
// lock analog
AutoRenewLease.DoConsequence("testBlob2", () =>
{
// Some task
if (collection == 0)
{
Thread.Sleep(1000 * 2);
collection++;
}
Trace.WriteLine(tNo + " =====Collection=" + collection);
Trace.WriteLine(tNo + " =====MustBe = 1");
});
答案 1 :(得分：1)
我强烈建议通过一系列消息对此进行建模。您可以通过Azure Service Bus发送消息（命令）来创建预订。只有一个消费者会处理消息，您不需要“锁定”。此外，您可以扩展到多个使用者，以便您可以同时处理多个命令。事件还可用于通知消费者状态的变化（如创建或更新预订）并执行他们需要做的事情。