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 策略并想要返回IAsyncPolicy，但它给出了错误，

从 Polly.Retry.RetryPolicy < System.Net.Http.HttpResponseMessage> 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

按如下方式调整您的代码：

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。
• 等待并重试策略是通用的IAsyncPolicy<HttpResponseMessage>，因为它处理HttpResponseMessage结果。

要将这些组合到 PolicyWrap 中，请使用.Wrap(...)实例方法语法：

return timeoutPolicy.WrapAsync(waitAndRetryPolicy);

由于生成的 PolicyWrap 处理HttpResponseMessage，它也是类型IAsyncPolicy<HttpResponseMessage>，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。