C# 如何使用dotnet core和Polly添加动态重试策略

我有一个DotnetCore（2.1）控制台应用程序，我正在使用Polly用重试策略包装我的代码段。这适用于下面所示的简单用例：

private void ProcessRun() 
{
    var policy = Policy.Handle<SocketException>().WaitAndRetryAsync(
                 retryCount: 3
                 sleepDurationProvider: attempt => TimeSpan.FromSeconds(10),
                 onRetry: (exception, calculatedWaitDuration) => 
                 {
                    Console.WriteLine($"Retry policy executed for type SocketException");
                 });

    try
    {
        CancellationTokenSource _cts = new CancellationTokenSource()

        PollyRetryWaitPolicy.ExecuteAsync(async token => {
           MyOperation(token);
        }, _cts.Token)
        .ContinueWith(p => {
           if (p.IsFaulted || p.Status == TaskStatus.Canceled)
           {
                Console.WriteLine("faulted or was cancelled");
           }
        })
        .ConfigureAwait(false);
    }
    catch (Exception ex) {
     Console.WriteLine($"Exception has occurred: {ex.Message}");
    }
}

执行代码时，将按预期捕获套接字异常

我正在寻找一种灵活的方法，用多个策略而不是一个策略来包装代码。我修改了代码，动态地添加了许多包装的Polly重试策略，以允许捕获多个错误类型，并轻松地更改我正在查找的异常。我将代码更改为：

internal PolicyWrap PollyRetryWaitPolicy;

public void AddRetryWaitPolicy<T>(int waitTimeInSeconds, int retryAttempts)
    where T: Exception
{

    // Setup the polly policy that will be added to the executing code.
    var policy = Policy.Handle<T>().WaitAndRetryAsync(
                retryCount: retryAttempts, 
                sleepDurationProvider: attempt => TimeSpan.FromSeconds(waitTimeInSeconds), 
                onRetry: (exception, calculatedWaitDuration) => 
                {
                    Console.WriteLine($"Retry policy executed for type {typeof(T).Name}");
                });

    if (host.PollyRetryWaitPolicy == null)
    {
        // NOTE: Only add this timeout policy as it seems to need at least one
        // policy before it can wrap! (suppose that makes sense).
        var timeoutPolicy = Policy
            .TimeoutAsync(TimeSpan.FromSeconds(waitTimeInSeconds), TimeoutStrategy.Pessimistic);
        PollyRetryWaitPolicy = policy.WrapAsync(timeoutPolicy);
    }
    else
    {
        PollyRetryWaitPolicy.WrapAsync(policy);
    }
}

private void ProcessRun() 
{
    AddRetryWaitPolicy<SocketException>(10, 5);
    AddRetryWaitPolicy<InvalidOperationException>(5, 2);

    try
    {
        Console.WriteLine($"Calling HostedProcess.Run() method. AwaitResult: {awaitResult}");

        CancellationTokenSource _cts = new CancellationTokenSource()

        PollyRetryWaitPolicy.ExecuteAsync(async token => {
           MyOperation(token);
        }, _cts.Token)
        .ContinueWith(p => {
           if (p.IsFaulted || p.Status == TaskStatus.Canceled)
           {
                Console.WriteLine("Process has faulted or was cancelled");
           }
        })
        .ConfigureAwait(false);
    }
    catch (Exception ex) {
     Console.WriteLine($"Exception has occurred: {ex.Message}");
    }
}

但当我尝试以下操作时，它不会按预期重试2次（根本不会重试）：

我做错了什么？以上所有内容的要点是根据需要动态地执行多个策略。除了暴政，还有更好的办法吗

提前感谢您的指点

这里：

if (host.PollyRetryWaitPolicy == null)
{
    // NOTE: Only add this timeout policy as it seems to need at least one
    // policy before it can wrap! (suppose that makes sense).
    var timeoutPolicy = Policy
        .TimeoutAsync(TimeSpan.FromSeconds(waitTimeInSeconds), TimeoutStrategy.Pessimistic);
    PollyRetryWaitPolicy = policy.WrapAsync(timeoutPolicy);
}
else
{
    PollyRetryWaitPolicy.WrapAsync(policy);
}

在wrap中，

if

分支和

else

分支对重试策略和超时策略的排序方法不一致

• 在

  if

  分支中，超时策略包装在重试策略中。因此，超时将作为每次尝试的超时
• 在

  else

  分支中，任何现有的重试和超时策略都被包装在新的重试策略之外。因此，超时策略在新的重试策略之外。
  • 新的重试策略设置为在

    waitTimeInSeconds

    之后重试；但是超时策略也设置为在

    waitTimeInSeconds

    之后执行超时。因此，一旦发生第一次重试（对于第二次或后续配置的重试策略），超时将中止整个执行。因此，正如您所观察到的，重试从未发生

要解决此问题，您可以将

else

分支更改为：

PollyRetryWaitPolicy = policy.WrapAsync(PollyRetryWaitPolicy);

---

背景：请参阅。根据您是将

TimeoutPolicy

放置在

RetryPolicy

内部还是外部，

TimeoutPolicy

作为每次尝试的超时（内部时），还是作为所有尝试的总超时（外部时）

private void MyOperation() 
{
    Thread.Sleep(2000);
    throw new InvalidOperationException();
}

if (host.PollyRetryWaitPolicy == null)
{
    // NOTE: Only add this timeout policy as it seems to need at least one
    // policy before it can wrap! (suppose that makes sense).
    var timeoutPolicy = Policy
        .TimeoutAsync(TimeSpan.FromSeconds(waitTimeInSeconds), TimeoutStrategy.Pessimistic);
    PollyRetryWaitPolicy = policy.WrapAsync(timeoutPolicy);
}
else
{
    PollyRetryWaitPolicy.WrapAsync(policy);
}

PollyRetryWaitPolicy = policy.WrapAsync(PollyRetryWaitPolicy);