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
}
);
开源地址
https://github.com/App-vNext/Polly