พื้นฐานความทนทาน: การลองใหม่และการหน่วงเพิ่ม

เหตุผลที่ต้องลองใหม่และเพิ่มเวลาหน่วง

จัดประเภทข้อผิดพลาด

ตัวช่วยเพิ่มเวลาหน่วง

using System;
using System.Threading;
using System.Threading.Tasks;

public static class Backoff
{
  // Compute delay = min(base * 2^attempt, cap) + jitter
  public static int ComputeDelayMs(int attempt, int baseMs, int capMs, int jitterMs, Random rng)
  {
    long exp = (long)baseMs << attempt; // base * 2^attempt
    if (exp > capMs) exp = capMs;
    int jitter = rng.Next(0, jitterMs + 1); // [0..jitterMs]
    return (int)exp + jitter;
  }
}

public class Program
{
  public static void Main(string[] args)
  {
    Random rng = new Random(123);
    for (int i = 0; i < 5; i++)
    {
      int d = Backoff.ComputeDelayMs(i, 100, 2000, 50, rng);
      Console.WriteLine("Attempt " + i + " -> " + d + " ms");
    }
  }
}

ตัวห่อการลองใหม่

using System;
using System.Threading;
using System.Threading.Tasks;

public class Program
{
  static readonly Random Rng = new Random();

  // Simulate an operation that sometimes fails transiently.
  static async Task<string> FlakyAsync()
  {
    await Task.Delay(60);
    // 50% chance of transient failure
    if (DateTime.UtcNow.Ticks % 2 == 0) throw new TimeoutException("Transient");
    return "OK";
  }

  static async Task<T> RetryAsync<T>(Func<Task<T>> action, int maxAttempts)
  {
    int baseMs = 100, capMs = 2000, jitterMs = 50;
    for (int attempt = 0; attempt < maxAttempts; attempt++)
    {
      try
      {
        return await action();
      }
      catch (TimeoutException)
      {
        if (attempt == maxAttempts - 1) throw; // out of retries
        int delay = Backoff.ComputeDelayMs(attempt, baseMs, capMs, jitterMs, Rng);
        await Task.Delay(delay);
      }
      catch (Exception)
      {
        // Non-transient (unknown) -> do not retry
        throw;
      }
    }
    throw new InvalidOperationException("Unreachable");
  }

  public static void Main(string[] args)
  {
    try
    {
      string s = RetryAsync(FlakyAsync, 5).GetAwaiter().GetResult();
      Console.WriteLine("Result: " + s);
    }
    catch (Exception ex)
    {
      Console.WriteLine("Failed: " + ex.GetType().Name);
    }
  }
}

การลองใหม่ภายใต้งบเวลา

using System;
using System.Threading;
using System.Threading.Tasks;

public static class RetryUtil
{
  static readonly Random Rng = new Random();

  public static async Task<T> RetryAsync<T>(Func<CancellationToken, Task<T>> action, int maxAttempts, CancellationToken ct)
  {
    int baseMs = 100, capMs = 1500, jitterMs = 50;
    for (int attempt = 0; attempt < maxAttempts; attempt++)
    {
      ct.ThrowIfCancellationRequested();
      try
      {
        return await action(ct);
      }
      catch (TimeoutException)
      {
        if (attempt == maxAttempts - 1) throw;
        int delay = Backoff.ComputeDelayMs(attempt, baseMs, capMs, jitterMs, Rng);
        await Task.Delay(delay, ct); // pass token so we can abort waiting
      }
    }
    throw new InvalidOperationException("Unreachable");
  }
}

public class Program
{
  static async Task<string> SometimesSlowAsync(CancellationToken ct)
  {
    await Task.Delay(200, ct);
    if (DateTime.UtcNow.Millisecond % 3 != 0) throw new TimeoutException("Transient");
    return "OK";
  }

  public static void Main(string[] args)
  {
    var cts = new CancellationTokenSource();
    cts.CancelAfter(800); // overall budget

    try
    {
      string s = RetryUtil.RetryAsync(SometimesSlowAsync, 5, cts.Token).GetAwaiter().GetResult();
      Console.WriteLine("Done: " + s);
    }
    catch (OperationCanceledException) { Console.WriteLine("Canceled"); }
    catch (Exception ex) { Console.WriteLine("Failed: " + ex.Message); }
  }
}

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