为什么此后台线程中的未处理异常不会终止我的进程？
Wat*_* v2 5 .net c# multithreading asynchronous
我生成一个前台线程和一个后台线程,在每个线程中抛出一个异常.
using System;
using System.Threading;
namespace OriginalCallStackIsLostOnRethrow
{
class Program
{
static void Main(string[] args)
{
try
{
A2();
// Uncomment this to see how the unhandled
// exception in the foreground thread causes
// the program to terminate
// An exception in this foreground thread
// *does* terminate the program
// var t = new Thread(() => {
// throw new DivideByZeroException();
// });
// t.Start();
}
catch (Exception ex)
{
// I am not expecting anything from the
// threads to come here, which is fine
Console.WriteLine(ex);
}
finally
{
Console.WriteLine("Press any key to exit...");
Console.ReadKey();
}
}
static void A2() { B2(); }
static void B2() { C2(); }
static void C2() { D2(); }
static void D2()
{
Action action = () =>
{
Console.WriteLine($"D2 called on worker #{Thread.CurrentThread.ManagedThreadId}. Exception will occur while running D2");
throw new DivideByZeroException();
Console.WriteLine("Do we get here? Obviously not!");
};
action.BeginInvoke(ar => Console.WriteLine($"D2 completed on worker thread #{Thread.CurrentThread.ManagedThreadId}"), null);
}
}
}
正如所料,前台线程中的未处理异常终止了该进程.但是,后台线程中的未处理异常只是终止线程,并且不会使进程停止,实际上无法观察到并且无声地失败.
因此,该程序产生以下输出:
Press any key to exit...
D2 called on worker #6. Exception will occur while running D2
D2 completed on worker thread #6
这挑战了我对线程中异常处理的理解.我的理解是,无论线程的性质如何,从框架的v2.0开始,未处理的异常将使进程终止.
以下是有关此主题的文档的引用:
线程的前台或后台状态不会影响线程中未处理的异常的结果.在.NET Framework 2.0版中,前台或后台线程中的未处理异常导致应用程序终止.请参阅托管线程中的例外.
从.NET Framework 2.0版开始,公共语言运行库允许线程中大多数未处理的异常自然地继续.在大多数情况下,这意味着未处理的异常会导致应用程序终止.
这是.NET Framework版本1.0和1.1的重大变化,它为许多未处理的异常提供了支持 - 例如,线程池线程中的未处理异常.请参阅本主题后面的"从先前版本更改".
另一个有趣的观察
有趣的是,如果我在完成回调中抛出异常而不是正在执行的实际操作,那么后台线程上的异常确实会导致程序终止.有关代码,请参阅下文.
using System;
using System.Threading;
namespace OriginalCallStackIsLostOnRethrow
{
class Program
{
static void Main(string[] args)
{
try
{
// A2();
A3();
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
finally
{
Console.WriteLine("Press any key to exit...");
Console.ReadKey();
}
}
static void A2() { B2(); }
static void B2() { C2(); }
static void C2() { D2(); }
static void D2()
{
Action action = () =>
{
try
{
Console.WriteLine($"D2 called on worker #{Thread.CurrentThread.ManagedThreadId}. Exception will occur while running D2");
throw new DivideByZeroException();
// Console.WriteLine("Do we get here? Obviously not!");
}
catch(Exception ex)
{
Console.WriteLine(ex);
}
};
action.BeginInvoke(ar => Console.WriteLine($"D2 completed on worker thread #{Thread.CurrentThread.ManagedThreadId}"), null);
}
static void A3() { B3(); }
static void B3() { C3(); }
static void C3() { D3(); }
static void D3()
{
Action action = () => { Console.WriteLine($"D2 called on worker #{Thread.CurrentThread.ManagedThreadId}."); };
action.BeginInvoke(ar =>
{
Console.WriteLine($"D2 completed on worker thread #{Thread.CurrentThread.ManagedThreadId}. Oh, but wait! Exception!");
// This one on the completion callback does terminate the program
throw new DivideByZeroException();
}, null);
}
}
}
另一个有趣的观察
此外,更有趣的是,如果您在要使用APM执行的操作中处理异常,则在catch块中(在catch块中设置断点D2()),Exception除了被调用的lambda之外,没有堆栈跟踪.它甚至没有关于它是如何到达那里的信息.
然而,对于在完成回调中捕获在catch块中的异常,情况并非如此,例如D3().
我在Visual Studio Community 2015 Edition中使用C#6.0编译器,我的程序目标是.NET框架的v4.5.2.
正如 PetSerAl 在问题的评论部分中指出的那样，要获取异常信息，必须EndInvoke从完成回调内部调用，如下所示。
using System;
using System.Runtime.Remoting.Messaging;
using System.Threading;
namespace OriginalCallStackIsLostOnRethrow
{
class Program
{
static void Main(string[] args)
{
try
{
A2();
// A3();
}
catch (Exception ex)
{
Console.WriteLine(ex);
}
finally
{
Console.WriteLine("Press any key to exit...");
Console.ReadKey();
}
}
static void A2() { B2(); }
static void B2() { C2(); }
static void C2() { D2(); }
static void D2()
{
Action action = () =>
{
Console.WriteLine($"D2 called on worker #{Thread.CurrentThread.ManagedThreadId}. Exception will occur while running D2");
throw new DivideByZeroException();
};
action.BeginInvoke(ar =>
{
((Action)((ar as AsyncResult).AsyncDelegate)).EndInvoke(ar);
Console.WriteLine($"D2 completed on worker thread #{Thread.CurrentThread.ManagedThreadId}");
}, null);
}
static void A3() { B3(); }
static void B3() { C3(); }
static void C3() { D3(); }
static void D3()
{
Action action = () => { Console.WriteLine($"D2 called on worker #{Thread.CurrentThread.ManagedThreadId}."); };
action.BeginInvoke(ar =>
{
try
{
Console.WriteLine($"D2 completed on worker thread #{Thread.CurrentThread.ManagedThreadId}. Oh, but wait! Exception!");
throw new DivideByZeroException();
}
catch (Exception ex)
{
throw ex;
}
}, null);
}
}
}
try / catch这很奇怪，并且如果您要在异步执行的操作中放置一个块，为什么堆栈跟踪不会显示仍然是一个谜。
我指的是缺少 StackTrace ，而不是缺少调用堆栈。:-)
