c# 如何更簡單的使用Polly

Polly是一個C#實現的彈性瞬時錯誤處理庫
它可以幫助我們做一些容錯模式處理,比如:

  • 超時與重試(Timeout and Retry)
  • 熔斷器(Circuit Breaker)
  • 艙壁隔離(Bulkhead Isolation)
  • 回退(Fallback)

使用也是非常簡單的,比如:

// 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
 });

但是每個地方我們都得這樣寫,個人還是不喜,
那麼怎麼簡化呢?
當然是使用 Norns.Urd 這些AOP框架封裝我們常用的東西做成 Attribute 啦

如何實現簡化呢?

我們來嘗試將 Retry功能 做成 RetryAttribute吧

1.安裝 AOP 框架

自己寫多累呀,用現成的多好呀

dotnet add package Norns.Urd

2.編寫 Retry InterceptorAttribute

 public class RetryAttribute : AbstractInterceptorAttribute
 {
 private readonly int retryCount;

 public RetryAttribute(int retryCount)
 {
  this.retryCount = retryCount;
 }

 public override async Task InvokeAsync(AspectContext context, AsyncAspectDelegate next)
 {
  await Policy.Handle<Exception>()
  .RetryAsync(retryCount)
  .ExecuteAsync(() => next(context));
 }
 }

3.考慮到 async 和 sync 在Polly 有差異,那麼我們兼容一下吧

 public class RetryAttribute : AbstractInterceptorAttribute
 {
 private readonly int retryCount;

 public RetryAttribute(int retryCount)
 {
  this.retryCount = retryCount;
 }

 public override void Invoke(AspectContext context, AspectDelegate next)
 {
  Policy.Handle<Exception>()
  .Retry(retryCount)
  .Execute(() => next(context));
 }

 public override async Task InvokeAsync(AspectContext context, AsyncAspectDelegate next)
 {
  await Policy.Handle<Exception>()
  .RetryAsync(retryCount)
  .ExecuteAsync(() => next(context));
 }
 }

4.我們來做個測試吧

 public class RetryTest
 {
 public class DoRetryTest
 {
  public int Count { get; set; }

  [Retry(2)] // 使用 Retry
  public virtual void Do()
  {
  if (Count < 50)
  {
   Count++; // 每調用一次就加1
   throw new FieldAccessException();
  }
  }
 }

 public DoRetryTest Mock()
 {
  return new ServiceCollection()
  .AddTransient<DoRetryTest>()
  .ConfigureAop()
  .BuildServiceProvider()
  .GetRequiredService<DoRetryTest>();
 }

 [Fact]
 public void RetryWhenSync()
 {
  var sut = Mock();
  Assert.Throws<FieldAccessException>(() => sut.Do());
  Assert.Equal(3, sut.Count); //我們期望調用總共 3 次
 }
 }

是的,就是這樣,我們可以在任何地方使用 RetryAttribute

當然,一些常見的方法已經封裝在瞭 Norns.Urd.Extensions.Polly

這裡通過Norns.Urd將Polly的各種功能集成為更加方便使用的功能

如何啟用 Norns.Urd + Polly, 隻需使用EnablePolly()

如:

new ServiceCollection()
 .AddTransient<DoTimeoutTest>()
 .ConfigureAop(i => i.EnablePolly())

TimeoutAttribute

[Timeout(seconds: 1)] // timeout 1 seconds, when timeout will throw TimeoutRejectedException
double Wait(double seconds);

[Timeout(timeSpan: "00:00:00.100")] // timeout 100 milliseconds, only work on async method when no CancellationToken
async Task<double> WaitAsync(double seconds, CancellationToken cancellationToken = default);

[Timeout(timeSpan: "00:00:01")] // timeout 1 seconds, but no work on async method when no CancellationToken
async Task<double> NoCancellationTokenWaitAsync(double seconds);

RetryAttribute

[Retry(retryCount: 2, ExceptionType = typeof(AccessViolationException))] // retry 2 times when if throw Exception
void Do()

CircuitBreakerAttribute

[CircuitBreaker(exceptionsAllowedBeforeBreaking: 3, durationOfBreak: "00:00:01")] 
//or
[AdvancedCircuitBreaker(failureThreshold: 0.1, samplingDuration: "00:00:01", minimumThroughput: 3, durationOfBreak: "00:00:01")]
void Do()

BulkheadAttribute

[Bulkhead(maxParallelization: 5, maxQueuingActions: 10)]
void Do()

有關 Norns.Urd, 大傢可以查看 https://fs7744.github.io/Norns.Urd/zh-cn/index.html

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