问题出在Internet Explorer 7/6中对单个服务器的最大并发连接数。它只有2! http://msdn.microsoft.com/en-us/library/cc304129(VS.85).aspx
如果我们有3个(例如)并发服务调用,其中两个将立即发送到服务器,但第三个将在队列中等待。发送计时器(对应于sendTimeout
)也在请求处于队列中时运行。如果前两个服务请求会长时间运行,那么第三个服务请求将会生成TimeoutException,尽管它没有发送到服务器(并且我们不会在服务器端看到有关此请求的任何信息,也无法使用Fiddler ...)。
在更真实的情况下,如果我们有大约12个并发呼叫并且默认1分钟发送超时,并且如果服务呼叫平均处理超过10秒,则比我们可以容易地获得最后两个呼叫的超时例外(12/2 * 10秒= 60秒),因为他们会等待所有其他人。
解决的办法是:
- 最大限度地减少并发服务呼叫数。
- 增加
sendTimeout
值客户端配置。
- 实现关键服务的自动重试功能。
- 实施请求管理队列。
在我的情况下,我做了1-3件事情,这就够了。
这是我实现自动重试功能:
public static class ClientBaseExtender
{
/// <summary>
/// Tries to execute async service call. If <see cref="TimeoutException"/> occured retries again.
/// </summary>
/// <typeparam name="TChannel">ServiceClient class.</typeparam>
/// <typeparam name="TArgs">Type of service client method return argument.</typeparam>
/// <param name="client">ServiceClient instance.</param>
/// <param name="tryExecute">Delegate that execute starting of service call.</param>
/// <param name="onCompletedSubcribe">Delegate that subcribes an event handler to the OnCompleted event of the service client method.</param>
/// <param name="onCompleted">Delegate that executes when service call is succeeded.</param>
/// <param name="onError">Delegate that executes when service call fails.</param>
/// <param name="maxAttempts">Maximum attempts to execute service call before error if <see cref="TimeoutException"/> occured (by default 5).</param>
public static void ExecuteAsyncRepeatedly<TChannel, TArgs>(this ClientBase<TChannel> client, Action tryExecute,
Action<EventHandler<TArgs>> onCompletedSubcribe, EventHandler<TArgs> onCompleted,
EventHandler<TArgs> onError, int maxAttempts)
where TChannel : class
where TArgs : AsyncCompletedEventArgs
{
int attempts = 0;
var serviceName = client.GetType().Name;
onCompletedSubcribe((s, e) =>
{
if (e.Error == null) // Everything is OK
{
if (onCompleted != null)
onCompleted(s, e);
((ICommunicationObject)client).Close();
Debug.WriteLine("[{1}] Service '{0}' closed.", serviceName, DateTime.Now);
}
else if (e.Error is TimeoutException)
{
attempts++;
if (attempts >= maxAttempts) // Final timeout after n attempts
{
Debug.WriteLine("[{2}], Final Timeout occured in '{0}' service after {1} attempts.", serviceName, attempts, DateTime.Now);
if (onError != null)
onError(s, e);
client.Abort();
Debug.WriteLine("[{1}] Service '{0}' aborted.", serviceName, DateTime.Now);
return;
}
// Local timeout
Debug.WriteLine("[{2}] Timeout occured in '{0}' service (attempt #{1}).", serviceName, attempts, DateTime.Now);
Debug.WriteLine("[{2}] Attempt #{0} to execute call to '{1}' service.", attempts + 1, serviceName, DateTime.Now);
tryExecute(); // Try again.
}
else
{
if (onError != null)
onError(s, e);
client.Abort();
Debug.WriteLine("[{1}] Service '{0}' aborted.", serviceName, DateTime.Now);
}
});
Debug.WriteLine("[{2}] Attempt #{0} to execute call to '{1}' service.", attempts + 1, serviceName, DateTime.Now);
tryExecute(); // First attempt to execute
}
}
这里是一个用法:
var client = new MyServiceClient();
client.ExecuteAsyncRepeatedly(() => client.MyOperationAsync(...),
(EventHandler<MyOperationCompletedEventArgs> handler) => client.MyOperationCompleted += handler,
(s, e) => // OnCompleted
{
Do(e.Result);
},
(s, e) => // OnError
{
HandleError(e.Error);
}
);
希望这会有所帮助。
我在这里有一个困惑..你如何使用ClientBaseExtender?您的代理是否从ClientBaseExtender派生?但是代理类已经从System.ServiceModel.ClientBase派生。那么你如何使用MyServiceClient插件ClientBaseExtender? – 2010-08-24 09:40:20
不,ClientBaseExtender为ClientBase提供扩展方法(http://msdn.microsoft.com/en-us/library/bb383977.aspx)。所以你可以在ClientBase的任何继承者中使用这个方法。 – 2010-08-26 13:18:09