从Silverlight应用程序同时调用WCF服务时出现TimeoutException

Question

分析日志文件我注意到在Silverlight客户端,大约1%的服务调用以TimeoutException结束.服务(wcf)非常简单,不执行长计算.根据日志,对服务的所有调用总是在1秒内处理(即使在客户端上发生TimeoutException!),因此它不是服务器超时.

那有什么不对？可以是配置还是网络问题？我怎么能避免呢？哪些其他日志记录信息可以帮助您本地化此问题？

我想到的唯一一种解决方法是在超时后重试服务调用.

我将在这个问题上给予任何帮助!

更新:启动时,应用程序执行17个服务调用,同时执行12个服务调用(可能是失败原因？).

更新: WCF日志未包含有关此问题的有用信息.似乎有些服务调用没有到达服务器端.

Answer 1

问题在于Internet Explorer 7/6中与单个服务器的最大并发连接数.它只有2个!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.sendTimeout当请求在队列中时,发送计时器(对应于)也在运行.如果前两个服务请求将运行很长时间,那么第三个将生成TimeoutException但它没有被发送到服务器(我们将不会在服务器端看到有关此请求的任何信息,并且无法通过Fiddler捕获它...).

在更实际的情况下,如果我们有大约12个并发呼叫和默认1分钟发送超时,并且如果服务呼叫平均处理超过10秒,我们可以轻松获得最后两个呼叫的超时异常(12/2*10秒= 60秒) )因为他们会等待所有其他人.

解决方案是:

1. 最小化并发服务调用的数量.
2. 增加客户端配置的sendTimeout值.
3. 为关键服务实现自动重试功能.
4. 实现请求队列以管理它们.

在我的情况下,我做了1-3件事,这就足够了.

这是我自动重试功能的实现:

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.