c# – Polly超时政策澄清

我试图让timout政策正常工作.
在集成api时我有以下要求.

>创建一个http请求以调用endpoint1并传递transactionID并捕获结果
>如果http请求在20秒内没有回答,则发送具有相同transactionID的取消请求并捕获结果

对于这项任务,我想使用Polly,在我看来这是一个很好的组件,可以帮助处理瞬态故障.然而,由于我对这项技术很陌生,我只想确定我是否正确实施.

首先,我和Polly一起创建了一个超时策略

var timeoutPolicy =
    Policy.TimeoutAsync(
        TimeSpan.FromSeconds( 20 ),
        TimeoutStrategy.Optimistic,
        async ( context, timespan, task ) => {
            //write here the cancel request 
        } );

之后我准备执行该政策

var policyResult = await timeoutPolicy.ExecuteAndCaptureAsync( async () => {
    //make here the request 1
} );

我从文档中得到的是,如果在timeoutPolicy.ExecuteAndCaptureAsync委托内发生了一个timout,Polly会自动调用onTimeout委托.对？

不过我的问题是：

>如果在执行委托内发生异常,会发生什么？我应该将这个polly构造包装在try catch中吗？
>当我分析政策结果时,我如何理解超时是否发生？

解决方法:

What I got from the documentation is that if a timeout occurs inside the
ExecuteAndCaptureAsync delegate Polly automagically invoke the
onTimeout delegate. Right?

Correct.

What happens if inside the execute delegate an exception occurs?

因为您使用的是ExecuteAndCaptureAsync(…),所以例外是placed in policyResult.FinalException.

Should I wrap that polly construct in a try catch?

因为您正在使用ExecuteAndCaptureAsync(..),所以异常放在policyResult.FinalException中,因此您不需要try-catch.

When I analyze the policy result how do I understand if the timeout has happened or not?

TimeoutPolicy throws TimeoutRejectedException超时.因为您正在使用ExecuteAndCaptureAsync(…),所以您应该在policyResult.FinalException中找到该异常.

还有一些评论.使用TimeoutStrategy.Optimisitic,即based on co-operative cancellation by CancellationToken,您应该执行取消令牌的委托：

var policyResult = await timeoutPolicy.ExecuteAndCaptureAsync(async (ct) => {
    //make request 1, in a form which responds to the cancellation token ct
}, userCancellationToken /* CancellationToken.None is acceptable. Polly will merge its timing-out CancellationToken into ct, during policy execution. */
);

其次,作为在onRetryAsync中调用取消请求的替代方法：async(context,timespan,task)=> {…},您可以选择使用下面的模式使代码更顺序/更少嵌套：

var policyResult = await timeoutPolicy.ExecuteAndCaptureAsync(async (ct) => {
    //make request 1, in a form which responds to the cancellation token ct
}, CancellationToken.None);

if (policyResult.Outcome == OutcomeType.Failure && policyResult.FinalException is TimeoutRejectedException)
{
    //write here the cancel request 
}

更新：调用取消请求将以任何方式工作 – 从onRetryAsync内部,或顺序,如上所述.顺序版本的一个优点是,如果取消请求因异常而失败,它可以更容易推断出现的情况.使用嵌套方法(在onRetryAsync中调用取消请求),最终捕获到policyResult.FinalException中的异常可能来自初始请求或取消请求 – 并且可能很难分辨哪个.

标签：c,polly,transient-failure
来源： https://codeday.me/bug/20190622/1265424.html