Question

我们目前有一个天真的RetryWrapper，它会在发生异常时重试给定的函数：

public T Repeat<T, TException>(Func<T> work, TimeSpan retryInterval, int maxExecutionCount = 3) where TException : Exception
{ 
   ...

对于retryInterval，我们使用以下逻辑来＆＃34;等待＆＃34;在下一次尝试之前。

_stopwatch.Start();
while (_stopwatch.Elapsed <= retryInterval)
{
  // do nothing but actuallky it does! lots of CPU usage specially if retryInterval is high
}
_stopwatch.Reset();

我不是特别喜欢这种逻辑，理想情况下我更希望重试逻辑不会发生在主线程上，你能想到更好的方法吗？

注意：我很乐意考虑.Net＆gt; = 3.5

的答案

Answer 1

只要您的方法签名返回T，主线程就必须阻塞，直到完成所有重试。但是，您可以通过让线程休眠而不是执行手动重置事件来减少CPU：

Thread.Sleep(retryInterval);

如果您愿意更改API，可以将其设置为不阻止主线程。例如，您可以使用异步方法：

public async Task<T> RepeatAsync<T, TException>(Func<T> work, TimeSpan retryInterval, int maxExecutionCount = 3) where TException : Exception
{
     for (var i = 0; i < maxExecutionCount; ++i)
     {
        try { return work(); }
        catch (TException ex)
        {
            // allow the program to continue in this case
        }
        // this will use a system timer under the hood, so no thread is consumed while
        // waiting
        await Task.Delay(retryInterval);
     }
}

这可以与以下内容同步使用：

RepeatAsync<T, TException>(work, retryInterval).Result;

但是，您也可以启动任务，然后再等待它：

var task = RepeatAsync<T, TException>(work, retryInterval);

// do other work here

// later, if you need the result, just do
var result = task.Result;
// or, if the current method is async:
var result = await task;

// alternatively, you could just schedule some code to run asynchronously
// when the task finishes:
task.ContinueWith(t => {
    if (t.IsFaulted) { /* log t.Exception */ }
    else { /* success case */ }
});

Answer 2

考虑使用Transient Fault Handling Application Block

Microsoft企业库瞬态故障处理应用程序 Block允许开发人员通过添加使应用程序更具弹性强大的瞬态故障处理逻辑。瞬态故障是错误由于某些临时条件（如网络）而发生的情况连接问题或服务不可用。通常，如果您重试短时间内导致瞬态错误的操作，你发现错误消失了。

它可以作为NuGet包使用。

using Microsoft.Practices.TransientFaultHandling;
using Microsoft.Practices.EnterpriseLibrary.WindowsAzure.TransientFaultHandling;
...
// Define your retry strategy: retry 5 times, starting 1 second apart
// and adding 2 seconds to the interval each retry.
var retryStrategy = new Incremental(5, TimeSpan.FromSeconds(1), 
  TimeSpan.FromSeconds(2));

// Define your retry policy using the retry strategy and the Windows Azure storage
// transient fault detection strategy.
var retryPolicy =
  new RetryPolicy<StorageTransientErrorDetectionStrategy>(retryStrategy);

// Receive notifications about retries.
retryPolicy.Retrying += (sender, args) =>
    {
        // Log details of the retry.
        var msg = String.Format("Retry - Count:{0}, Delay:{1}, Exception:{2}",
            args.CurrentRetryCount, args.Delay, args.LastException);
        Trace.WriteLine(msg, "Information");
    };

try
{
  // Do some work that may result in a transient fault.
  retryPolicy.ExecuteAction(
    () =>
    {
        // Your method goes here!
    });
}
catch (Exception)
{
  // All the retries failed.
}

Answer 3

如何使用计时器代替秒表？

例如：

    TimeSpan retryInterval = new TimeSpan(0, 0, 5);
    DateTime startTime;
    DateTime retryTime;
    Timer checkInterval = new Timer();

    private void waitMethod()
    {
        checkInterval.Interval = 1000;
        checkInterval.Tick += checkInterval_Tick;         
        startTime = DateTime.Now;
        retryTime = startTime + retryInterval;
        checkInterval.Start();
    }

    void checkInterval_Tick(object sender, EventArgs e)
    {
        if (DateTime.Now >= retryTime)
        {
            checkInterval.Stop();

            // Retry Interval Elapsed
        }   
    }

在C＃中实现Retry Wrapper的最佳方法是什么？

3 个答案: