如何更简单的使用Polly

Polly 弹性瞬时错误处理库

Polly是一个C#实现的弹性瞬时错误处理库
它可以帮助我们做一些容错模式处理,比如:

  • 超时与重试(Timeout and Retry)
  • 熔断器(Circuit Breaker)
  • 舱壁隔离(Bulkhead Isolation)
  • 回退(Fallback)

使用也是非常简单的,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
    });

但是每个地方我们都得这样写,个人还是不喜,
那么怎么简化呢?
当然是使用 Norns.Urd 这些AOP框架封装我们常用的东西做成 Attribute

如何实现简化呢?

我们来尝试将 Retry功能 做成 RetryAttribute

  1. 安装 AOP 框架
    自己写多累呀,用现成的多好呀
dotnet add package Norns.Urd
  1. 编写 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));
        }
    }
  1. 考虑到 async 和 sync 在Polly 有差异,那么我们兼容一下吧
    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));
        }
    }
  1. 我们来做个测试吧
    public class RetryTest
    {
        public class DoRetryTest
        {
            public int Count { get; set; }

            [Retry(2)]  // 使用 Retry
            public virtual void Do()
            {
                if (Count < 50)
                {
                    Count++; // 每调用一次就加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); //我们期望调用总共 3 次
        }
    }

是的,就是这样,我们可以在任何地方使用 RetryAttribute

当然,一些常见的方法已经封装在了 Norns.Urd.Extensions.Polly

这里通过Norns.Urd将Polly的各种功能集成为更加方便使用的功能

如何启用 Norns.Urd + Polly, 只需使用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()

有关 Norns.Urd, 大家可以查看 https://fs7744.github.io/Norns.Urd/zh-cn/index.html

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