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 啦
如何实现简化呢？
我们来尝试将 Retry功能 做成 RetryAttribute吧
- 安装 AOP 框架
自己写多累呀，用现成的多好呀
dotnet add package Norns.Urd
- 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));
}
}
- 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));
}
}
- 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
