我正在尝试扩展this answer on SO,以使WCF客户端在出现瞬时网络故障时重试并处理other situations that require a retry such as authentication expiration.
问题:
需要处理哪些WCF异常,正确的处理方式是什么?
除了proxy.abort()
之外,还有一些我希望看到的示例技术:
由于不太可能一个人知道所有异常或解决异常的方法,因此请分享您所知道的。我将在下面的代码示例中汇总答案和方法。
// USAGE SAMPLE
//int newOrderId = 0; // need a value for definite assignment
//Service<IOrderService>.Use(orderService=>
//{
// newOrderId = orderService.PlaceOrder(request);
//}
/// <summary>
/// A safe WCF Proxy suitable when sessionmode=false
/// </summary>
/// <param name="codeBlock"></param>
public static void Use(UseServiceDelegateVoid<T> codeBlock)
{
IClientChannel proxy = (IClientChannel)_channelFactory.CreateChannel();
bool success = false;
try
{
codeBlock((T)proxy);
proxy.Close();
success = true;
}
catch (CommunicationObjectAbortedException e)
{
// Object should be discarded if this is reached.
// Debugging discovered the following exception here:
// "Connection can not be established because it has been aborted"
throw e;
}
catch (CommunicationObjectFaultedException e)
{
throw e;
}
catch (MessageSecurityException e)
{
throw e;
}
catch (ChannelTerminatedException)
{
proxy.Abort(); // Possibly retry?
}
catch (ServerTooBusyException)
{
proxy.Abort(); // Possibly retry?
}
catch (EndpointNotFoundException)
{
proxy.Abort(); // Possibly retry?
}
catch (FaultException)
{
proxy.Abort();
}
catch (CommunicationException)
{
proxy.Abort();
}
catch (TimeoutException)
{
// Sample error found during debug:
// The message could not be transferred within the allotted timeout of
// 00:01:00. There was no space available in the reliable channel's
// transfer window. The time allotted to this operation may have been a
// portion of a longer timeout.
proxy.Abort();
}
catch (ObjectDisposedException )
{
//todo: handle this duplex callback exception. Occurs when client disappears.
// Source: https://stackoverflow.com/questions/1427926/detecting-client-death-in-wcf-duplex-contracts/1428238#1428238
}
finally
{
if (!success)
{
proxy.Abort();
}
}
}
最佳答案
编辑:多次关闭和重新打开客户端似乎有些效率低下。我是exploring solutions here,如果找到一个,它将更新并扩展此代码。 (或者,如果David Khaykin发布了答案,我会将其标记为已接受)
经过几年的修改后,下面的代码是我首选的处理WCF重试和处理异常的策略(after seeing this blog posting from the wayback machine)。
我调查了每个异常,以及该异常的处理方法,并注意到了一个共同特征。每个需要从通用基类继承的“重试”的异常。我还注意到,使客户端进入无效状态的每个permFail异常也来自共享基类。
下面的示例捕获客户端可以通过的每个WCF异常,并且可以针对您自己的自定义 channel 错误进行扩展。
WCF客户端用法示例
生成客户端代理后,就可以实现它。
Service<IOrderService>.Use(orderService=>
{
orderService.PlaceOrder(request);
}
ServiceDelegate.cs
将此文件添加到您的解决方案。除非您要更改重试次数或要处理的异常,否则无需对此文件进行任何更改。
public delegate void UseServiceDelegate<T>(T proxy);
public static class Service<T>
{
public static ChannelFactory<T> _channelFactory = new ChannelFactory<T>("");
public static void Use(UseServiceDelegate<T> codeBlock)
{
IClientChannel proxy = null;
bool success = false;
Exception mostRecentEx = null;
int millsecondsToSleep = 1000;
for(int i=0; i<5; i++) // Attempt a maximum of 5 times
{
// Proxy cann't be reused
proxy = (IClientChannel)_channelFactory.CreateChannel();
try
{
codeBlock((T)proxy);
proxy.Close();
success = true;
break;
}
catch (FaultException customFaultEx)
{
mostRecentEx = customFaultEx;
proxy.Abort();
// Custom resolution for this app-level exception
Thread.Sleep(millsecondsToSleep * (i + 1));
}
// The following is typically thrown on the client when a channel is terminated due to the server closing the connection.
catch (ChannelTerminatedException cte)
{
mostRecentEx = cte;
proxy.Abort();
// delay (backoff) and retry
Thread.Sleep(millsecondsToSleep * (i + 1));
}
// The following is thrown when a remote endpoint could not be found or reached. The endpoint may not be found or
// reachable because the remote endpoint is down, the remote endpoint is unreachable, or because the remote network is unreachable.
catch (EndpointNotFoundException enfe)
{
mostRecentEx = enfe;
proxy.Abort();
// delay (backoff) and retry
Thread.Sleep(millsecondsToSleep * (i + 1));
}
// The following exception that is thrown when a server is too busy to accept a message.
catch (ServerTooBusyException stbe)
{
mostRecentEx = stbe;
proxy.Abort();
// delay (backoff) and retry
Thread.Sleep(millsecondsToSleep * (i + 1));
}
catch (TimeoutException timeoutEx)
{
mostRecentEx = timeoutEx;
proxy.Abort();
// delay (backoff) and retry
Thread.Sleep(millsecondsToSleep * (i + 1));
}
catch (CommunicationException comException)
{
mostRecentEx = comException;
proxy.Abort();
// delay (backoff) and retry
Thread.Sleep(millsecondsToSleep * (i + 1));
}
catch(Exception e)
{
// rethrow any other exception not defined here
// You may want to define a custom Exception class to pass information such as failure count, and failure type
proxy.Abort();
throw e;
}
}
if (success == false && mostRecentEx != null)
{
proxy.Abort();
throw new Exception("WCF call failed after 5 retries.", mostRecentEx );
}
}
}