记录异常并重新抛出的Polly策略 [英] Polly policy to log exception and rethrow

问题描述

我考虑使用 Polly 来创建政策记录异常并重新抛出。
我没有找到一种允许使用的现成方法，但是我看到的一些选项是

I consider to use Polly to create policy to log exception and rethrow. I didn't find an existing method that allow it out of the box , but some options that I see are

Fallback

// Specify a substitute value or func, calling an action (eg for logging) if the fallback is invoked.
Policy.Handle<Whatever>()  
 .Fallback<UserAvatar>(UserAvatar.Blank, onFallback: (exception, context) =>  
   {   _logger.Log(exception, context);
       throw exception;
  });

问题：是否可以从Fallback引发异常？

Question: is it ok to throw exception from Fallback?

超时

Policy.Timeout(1, T30meoutStrategy.Pessimistic, (context, timespan, task) =>  
   {        task.ContinueWith(t =>
 { // ContinueWith important!: the abandoned task may very well still be executing, when the caller times out on waiting for it!    
   if (t.IsFaulted      )           
  {             
       logger.Error(context,t.Exception);         
       throw exception;
  }   );    

或重试

Policy.Handle<DivideByZeroException>().Retry(0, (exception, retryCount) =>   
  {                logger.Error(context,exception);         
throw exception;
  }   );  

问题：是否支持0次重试？

Question: is 0 retries supported?

或亲吻并写简单的try / catch

Or KISS and write simple try/catch with throw by myself.

以下哪种方法更好？
您的建议是什么？

Which of these methods is better? What are your recommendation?

推荐答案

如果您还没有Polly，可以尝试一下/抓住最简单的。

If you do not already have Polly in the mix, try/catch would seem simplest.

如果您已经有了Polly，请 FallbackPolicy 可以按照您建议的方式安全地重新利用。 onFallback 委托和后备操作或值不受政策的 .Handle<>（）子句约束，因此您可以安全地从 onFallback 委托中抛出异常。

If you already have Polly in the mix, FallbackPolicy can safely be re-purposed in the way you suggest. The onFallback delegate and fallback action or value are not governed by the .Handle<>() clauses of the Policy, so you can safely rethrow an exception from within the onFallback delegate.

 Policy<UserAvatar>.Handle<Whatever>()  
 .Fallback<UserAvatar>(UserAvatar.Blank, onFallback: (exception, context) =>  
   {   _logger.Log(exception, context);
       throw exception;
  });

---

使用 TimeoutPolicy 仅捕获由呼叫者由于超时而较早离开的代表，仅在 TimeoutMode.Pessimistic 中；并非所有例外。

---

The approach your question outlines with TimeoutPolicy would only capture exceptions thrown by delegates the caller had earlier walked away from due to timeout, and only in TimeoutMode.Pessimistic; not all exceptions.

您的问题使用概述的方法.Retry（0，... ）无效。如果未指定重试，则不会调用 onRetry 委托。

The approach your question outlines with .Retry(0, ...) would not work. If no retries are specified, the onRetry delegate would not be invoked.

为避免重新使用 FallbackPolicy 的麻烦，您还可以在Polly的结构内编写自己的 LogThenRethrowPolicy 。 此提交（其中添加了简单的 NoOpPolicy ）说明了添加新策略所需的最低要求。您可以添加类似于 NoOpPolicy 的实现，但只需 try {} catch {/ * log;重新抛出* /}

To avoid the untidiness of repurposing FallbackPolicy, you could also code your own LogThenRethrowPolicy, within Polly's structures. This commit (which added the simple NoOpPolicy) exemplifies the minimum necessary to add a new policy. You could add an implementation similar to NoOpPolicy but just try { } catch { /* log; rethrow */ }

编辑2019年1月：Polly。 Contrib现在还包含一个 Polly.Contrib.LoggingPolicy 可以提供帮助。

EDIT January 2019: Polly.Contrib now also contains a Polly.Contrib.LoggingPolicy which can help with this.

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