.NET中AggregateException未被捕获致应用崩溃问题求助

问题背景 #

应用在VPN断开测试场景下崩溃：连接VPN启动应用后，运行时断开VPN，随即抛出未被捕获的AggregateException导致应用崩溃，且调用栈中无我方代码。核心代码结构如下：

• 仓储方法GetBatchAsync()在Polly的retryPolicy内被调用
• 重试策略嵌套在Parallel.ForAsync()中
• 已确认问题与"Enable Just My Code"调试设置无关

相关代码 #

Parallel.ForAsync逻辑 #

await Parallel.ForAsync(0, totalBatchesCount, parallelOptions, async (i, cancellationToken) =>
{
    //...
    await retryPolicy.ExecuteAsync(async () =>
    {
        try
        {
            var batch = await _userRepository.GetBatchAsync(startId, endId);
            //...
        }
        catch (Exception ex)
        {
            throw new Exception($"Batch failed for startId: {startId} and endId {endId}", ex);
        }
    });
});

仓储方法 #

public async Task<List<User>> GetBatchAsync(int startId, int endId)
{
    try
    {
        await using var context = await _contextFactory.CreateDbContextAsync();

        return await context.Users
            .Where(u => u.UserId >= startId && u.UserId < endId)
            .Include(u => u.Invoice)
            .AsNoTracking()
            .ToListAsync();
    }
    catch (AggregateException ex)
    {
        Console.WriteLine(ex.ToString());
        throw;
    }
    catch (Exception ex) 
    {
        Console.WriteLine(ex.ToString());
        throw;
    }
}

Polly重试策略 #

var retryPolicy = Policy
    .Handle<Exception>()
    .WaitAndRetryAsync(POLLY_RETRY_COUNT, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)),
        (exception, timeSpan, retryCount, context) =>
        {
            _logger.LogWarning($"Retry {retryCount} due to: {exception.Message}, stack trace: {exception.StackTrace}, inner: {exception?.InnerException?.Message}");
        });

异常信息 #

Unhandled exception. System.AggregateException: One or more errors occurred. (Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding)
 ---> MySql.Data.MySqlClient.MySqlException (0x80004005): Timeout expired.  The timeout period elapsed prior to completion of the operation or the server is not responding
 ---> System.TimeoutException: The operation has timed out.
   at MySql.Data.Common.StreamCreator.<>c.<GetTcpStreamAsync>b__8_1()
   at System.Threading.CancellationTokenSource.Invoke(Delegate d, Object state, CancellationTokenSource source)
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
--- End of stack trace from previous location ---
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state)
   at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean throwOnFirstException)
   --- End of inner exception stack trace ---
   at System.Threading.CancellationTokenSource.ExecuteCallbackHandlers(Boolean throwOnFirstException)
   at System.Threading.TimerQueueTimer.Fire(Boolean isThreadPool)
   at System.Threading.TimerQueue.FireNextTimers()
   at System.Threading.ThreadPoolWorkQueue.Dispatch()
   at System.Threading.PortableThreadPool.WorkerThread.WorkerThreadStart()

问题分析 #

这个未捕获异常的根源在于MySQL客户端底层的CancellationToken回调抛出了异常，该异常发生在ThreadPool线程上，脱离了业务代码的async/await上下文，因此现有try-catch块、Polly重试策略都无法捕获它。

从异常栈可以看到，异常起源于MySql.Data.Common.StreamCreator.GetTcpStreamAsync的超时逻辑，触发CancellationTokenSource.ExecuteCallbackHandlers时抛出了未处理的异常，直接导致应用崩溃。

解决方案 #

1. 注册全局未处理异常捕获（兜底方案） #

在应用启动时添加全局异常处理，确保所有逃脱的异常都能被捕获记录，避免直接崩溃：

// 捕获AppDomain级别的未处理异常
AppDomain.CurrentDomain.UnhandledException += (sender, args) =>
{
    var exception = args.ExceptionObject as Exception;
    _logger.LogCritical(exception, "全局未处理异常");
    // 执行必要的资源清理后优雅退出
};

// 捕获未被观察的Task异常
TaskScheduler.UnobservedTaskException += (sender, args) =>
{
    _logger.LogCritical(args.Exception, "未观察到的Task异常");
    args.SetObserved(); // 标记异常已处理，阻止应用崩溃
};

2. 优化业务代码的异常处理逻辑 #

（1）给Polly传递CancellationToken

确保Parallel.ForAsync的取消令牌传递给Polly的ExecuteAsync方法，让取消信号能正确传递到底层操作：

await Parallel.ForAsync(0, totalBatchesCount, parallelOptions, async (i, cancellationToken) =>
{
    try
    {
        // 计算startId、endId逻辑...
        await retryPolicy.ExecuteAsync(async ct =>
        {
            var batch = await _userRepository.GetBatchAsync(startId, endId, ct);
            // 处理批次数据逻辑...
        }, cancellationToken); // 传递取消令牌
    }
    catch (Exception ex)
    {
        _logger.LogError(ex, $"批次{i}处理失败");
        // 根据业务需求决定是否终止或继续
    }
});

（2）简化仓储层异常处理

仓储层无需额外捕获AggregateException，EF Core异步操作抛出的是具体异常（如MySqlException），直接让异常向上抛出由Polly处理即可：

public async Task<List<User>> GetBatchAsync(int startId, int endId, CancellationToken cancellationToken)
{
    await using var context = await _contextFactory.CreateDbContextAsync(cancellationToken);

    return await context.Users
        .Where(u => u.UserId >= startId && u.UserId < endId)
        .Include(u => u.Invoice)
        .AsNoTracking()
        .ToListAsync(cancellationToken);
}

3. 升级MySQL客户端包 #

这个底层异常可能是MySQL.Data包的已知问题，升级到最新稳定版本（或替换为MySqlConnector）可以修复这类超时回调的异常问题。

4. 替换Parallel.ForAsync为Task.WhenAll（可选） #

如果Parallel.ForAsync的异常处理不够灵活，可以改用Task.WhenAll实现并行处理，异常控制更直观：

var tasks = Enumerable.Range(0, totalBatchesCount)
    .Select(async i =>
    {
        try
        {
            // 计算startId、endId逻辑...
            await retryPolicy.ExecuteAsync(async ct =>
            {
                var batch = await _userRepository.GetBatchAsync(startId, endId, ct);
                // 处理批次数据逻辑...
            }, cancellationToken);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, $"批次{i}处理失败");
        }
    });

await Task.WhenAll(tasks);

内容的提问来源于stack exchange，提问作者Maciejosas