尝试包装 2 个 Polly 策略时出现转换错误

Question

我正在尝试包装两个 Polly 策略并想返回IAsyncPolicy，但它给出了错误，

从 Polly.Retry.RetryPolicy转换为 Polly.IAsyncPolicy

public static IAsyncPolicy CreateDefaultRetryPolicy()
{
var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromSeconds(180));
var waitAndRetryPolicy = Polly.Policy
.Handle<HttpRequestException>()
.OrResult<HttpResponseMessage>(r => r.StatusCode == HttpStatusCode.InternalServerError)
.WaitAndRetryAsync(3, retryAttempt => TimeSpan.FromSeconds(Math.Pow(3, retryAttempt)),
(result, timeSpan, context) =>
{
});
return Policy.WrapAsync(timeoutPolicy, waitAndRetryPolicy);
}

如何包装并返回？

Answer 1

按如下方式调整代码：

public static IAsyncPolicy<HttpResponseMessage> CreateDefaultRetryPolicy()
{
var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromSeconds(180));
var waitAndRetryPolicy = Polly.Policy
.Handle<HttpRequestException>()
.OrResult<HttpResponseMessage>(r => r.StatusCode == HttpStatusCode.InternalServerError)
.WaitAndRetryAsync(3, retryAttempt => TimeSpan.FromSeconds(Math.Pow(3, retryAttempt)),
(result, timeSpan, context) =>
{
});
return timeoutPolicy.WrapAsync(waitAndRetryPolicy);
}

解释

• 超时策略是非通用的，IAsyncPolicy。
• 等待重试策略是通用的，IAsyncPolicy<HttpResponseMessage>，因为它处理HttpResponseMessage结果。

要在 PolicyWrap 中组合这些内容，请使用.Wrap(...)实例方法语法：

return timeoutPolicy.WrapAsync(waitAndRetryPolicy);

由于生成的PolicyWrap处理HttpResponseMessage，它也属于IAsyncPolicy<HttpResponseMessage>类型，因此方法返回类型更改为该类型。

Polly 文档涵盖了 wiki 中非通用策略和通用策略之间的差异。