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
它能够帮助咱们作一些容错模式处理，好比：

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

使用也是很是简单的，好比：

// 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
    });

可是每一个地方咱们都得这样写，我的仍是不喜，
那么怎么简化呢？
固然是使用 Norns.Urd 这些AOP框架封装咱们经常使用的东西作成 Attribute 啦

如何实现简化呢？

咱们来尝试将 Retry功能 作成 RetryAttribute吧

1. 安装 AOP 框架
   本身写多累呀，用现成的多好呀

dotnet add package Norns.Urd

2. 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));
        }
    }

3. 考虑到 async 和 sync 在Polly 有差别，那么咱们兼容一下吧

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));
        }
    }

4. 咱们来作个测试吧

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); //咱们指望调用总共 3 次
        }
    }

是的，就是这样，咱们能够在任何地方使用 RetryAttribute

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

这里经过Norns.Urd将Polly的各类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, 你们能够查看 https://fs7744.github.io/Norns.Urd/zh-cn/index.html