在任务中重新抛出异常不会使任务进入故障状态

Question

考虑以下场景

 var cancellationTokenSource = new CancellationTokenSource(TimeSpan.FromSeconds(2));
        var startNew = Task.Factory.StartNew(() =>
        {
            var currentThread = Thread.CurrentThread;
            try
            {
                using (cancellationTokenSource.Token.Register(currentThread.Abort))
                    new AutoResetEvent(false).WaitOne(Timeout.InfiniteTimeSpan);
            }
            catch (ThreadAbortException abortException)
            {
                throw new TimeoutException("Operation timeouted", abortException);
            }
        }, cancellationTokenSource.Token, TaskCreationOptions.LongRunning, TaskScheduler.Current);
        startNew.ContinueWith(val => Console.WriteLine("Cancellation handled"), TaskContinuationOptions.OnlyOnCanceled);
        startNew.ContinueWith(val => Console.WriteLine("Fault handled"), TaskContinuationOptions.OnlyOnFaulted);
        startNew.ContinueWith(val => Console.WriteLine("Ran to completion handled"), TaskContinuationOptions.OnlyOnRanToCompletion);

抛开所有关于中止线程是邪恶的讨论，为什么这段代码没有让任务进入故障状态？但是删除 catch 块或调用

Thread.ResetAbort()

似乎可以解决问题

Answer 1

关于线程中止的工作原理：

try {
    try {
        try {
            Thread.CurrentThread.Abort();
        } catch(Exception e) {
            Console.WriteLine(e.GetType());
            throw new Exception();
        }
    } catch(Exception e) {
        Console.WriteLine(e.GetType());
    }
} catch(Exception e) {
    Console.WriteLine(e.GetType());
}

此代码打印：

System.Threading.ThreadAbortException
System.Exception
System.Threading.ThreadAbortException

因此，当您的自定义异常被处理时，ThreadAbortException 将被重新抛出。

ThreadAbortException is a special exception that can be caught by application code, but is re-thrown at the end of the catch block unless ResetAbort is called. MSDN

现在让我们看看一些source:

/// <summary>
/// Executes the task. This method will only be called once, and handles bookeeping associated with
/// self-replicating tasks, in addition to performing necessary exception marshaling.
/// </summary>
private void Execute()
{
    if (IsSelfReplicatingRoot)
    {
        ExecuteSelfReplicating(this);
    }
    else
    {
        try
        {
            InnerInvoke();
        }
        catch (ThreadAbortException tae)
        {
            // Don't record the TAE or call FinishThreadAbortedTask for a child replica task --
            // it's already been done downstream.
            if (!IsChildReplica)
            {
                // Record this exception in the task's exception list
                HandleException(tae);

                // This is a ThreadAbortException and it will be rethrown from this catch clause, causing us to 
                // skip the regular Finish codepath. In order not to leave the task unfinished, we now call 
                // FinishThreadAbortedTask here.
                FinishThreadAbortedTask(true, true);
            }
        }
        catch (Exception exn)
        {
            // Record this exception in the task's exception list
            HandleException(exn);
        }
    }
}

如您所见，ThreadAbortException 案例有特殊的代码路径将任务转移到故障状态。当您通过 TimeoutException 隐藏 ThreadAbortException 时，不会采用该特殊代码路径。因此，当常规代码路径通过将异常记录在任务的异常列表中来处理异常时，ThreadAbortException 将被重新抛出，这会阻止任务正确转换到故障状态。

在任务中重新抛出异常不会使任务进入故障状态

Rethrowing exception in Task doesn't make the Task to go to faulted state

c#

multithreading

task

thread-abort