ASP VNext 开源服务容错处理库Polly

背景

Polly是一个.NET弹性和瞬态故障处理库，允许开发人员以流畅和线程安全的方式表达诸如重试，断路器，超时，隔离头和回退之类的策略。

Polly面向.NET Standard 1.1（覆盖范围：.NET Core 1.0，Mono，Xamarin，UWP，WP8.1 +）和.NET Standard 2.0+（覆盖范围：.NET Core 2.0 + 、. NET Core 3.0和更高版本的Mono，Xamarin和UWP目标）。nuget软件包还包括.NET Framework 4.6.1和4.7.2的直接目标。

使用方式

通过NuGet安装

Install-Package Polly

代码实现

故障处理，响应策略

故障处理策略处理您通过策略执行的委托引发的特定异常或返回的结果。

步骤1：指定您希望策略处理的异常/错误

// Single exception type
Policy.Handle<HttpRequestException>()// Single exception type with condition
Policy.Handle<SqlException>(ex => ex.Number == 1205)// Multiple exception types
Policy.Handle<HttpRequestException>().Or<OperationCanceledException>()// Multiple exception types with condition
Policy.Handle<SqlException>(ex => ex.Number == 1205).Or<ArgumentException>(ex => ex.ParamName == "example")// Inner exceptions of ordinary exceptions or AggregateException, with or without conditions
// (HandleInner matches exceptions at both the top-level and inner exceptions)
Policy.HandleInner<HttpRequestException>().OrInner<OperationCanceledException>(ex => ex.CancellationToken != myToken)

步骤2：指定策略应如何处理这些故障

2.1、重试

‍

// Retry once
Policy.Handle<SomeExceptionType>().Retry()// Retry multiple times
Policy.Handle<SomeExceptionType>().Retry(3)// Retry multiple times, calling an action on each retry 
// with the current exception and retry count
Policy.Handle<SomeExceptionType>().Retry(3, onRetry: (exception, retryCount) =>{// Add logic to be executed before each retry, such as logging});// Retry multiple times, calling an action on each retry 
// with the current exception, retry count and context 
// provided to Execute()
Policy.Handle<SomeExceptionType>().Retry(3, onRetry: (exception, retryCount, context) =>{// Add logic to be executed before each retry, such as logging });

2.2、永远重试（直到成功）

// Retry forever
Policy.Handle<SomeExceptionType>().RetryForever()// Retry forever, calling an action on each retry with the 
// current exception
Policy.Handle<SomeExceptionType>().RetryForever(onRetry: exception =>{// Add logic to be executed before each retry, such as logging       });// Retry forever, calling an action on each retry with the
// current exception and context provided to Execute()
Policy.Handle<SomeExceptionType>().RetryForever(onRetry: (exception, context) =>{// Add logic to be executed before each retry, such as logging       });

2.3、等待并重试

// Retry, waiting a specified duration between each retry. 
// (The wait is imposed on catching the failure, before making the next try.)
Policy.Handle<SomeExceptionType>().WaitAndRetry(new[]{TimeSpan.FromSeconds(1),TimeSpan.FromSeconds(2),TimeSpan.FromSeconds(3)});// Retry, waiting a specified duration between each retry, 
// calling an action on each retry with the current exception
// and duration
Policy.Handle<SomeExceptionType>().WaitAndRetry(new[]{TimeSpan.FromSeconds(1),TimeSpan.FromSeconds(2),TimeSpan.FromSeconds(3)}, (exception, timeSpan) => {// Add logic to be executed before each retry, such as logging    }); // Retry, waiting a specified duration between each retry, 
// calling an action on each retry with the current exception, 
// duration and context provided to Execute()
Policy.Handle<SomeExceptionType>().WaitAndRetry(new[]{TimeSpan.FromSeconds(1),TimeSpan.FromSeconds(2),TimeSpan.FromSeconds(3)}, (exception, timeSpan, context) => {// Add logic to be executed before each retry, such as logging    });// Retry, waiting a specified duration between each retry, 
// calling an action on each retry with the current exception, 
// duration, retry count, and context provided to Execute()
Policy.Handle<SomeExceptionType>().WaitAndRetry(new[]{TimeSpan.FromSeconds(1),TimeSpan.FromSeconds(2),TimeSpan.FromSeconds(3)}, (exception, timeSpan, retryCount, context) => {// Add logic to be executed before each retry, such as logging    });// Retry a specified number of times, using a function to 
// calculate the duration to wait between retries based on 
// the current retry attempt (allows for exponential backoff)
// In this case will wait for
//  2 ^ 1 = 2 seconds then
//  2 ^ 2 = 4 seconds then
//  2 ^ 3 = 8 seconds then
//  2 ^ 4 = 16 seconds then
//  2 ^ 5 = 32 seconds
Policy.Handle<SomeExceptionType>().WaitAndRetry(5, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)) );// Retry a specified number of times, using a function to 
// calculate the duration to wait between retries based on 
// the current retry attempt, calling an action on each retry 
// with the current exception, duration and context provided 
// to Execute()
Policy.Handle<SomeExceptionType>().WaitAndRetry(5, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)), (exception, timeSpan, context) => {// Add logic to be executed before each retry, such as logging});// Retry a specified number of times, using a function to 
// calculate the duration to wait between retries based on 
// the current retry attempt, calling an action on each retry 
// with the current exception, duration, retry count, and context 
// provided to Execute()
Policy.Handle<SomeExceptionType>().WaitAndRetry(5, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)), (exception, timeSpan, retryCount, context) => {// Add logic to be executed before each retry, such as logging});