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Any way to catch an exception occurring on a thread I don't own?

I'm using a crappy third party library because unfortunately I have no choice. This library creates a bunch of threads internally when I call it, and occasionally throws a NullReferenceException on one of these threads. Is there any way for me to catch these exceptions even though I don't own the thread that throws them? I have no way to change the third party code.
As a simple example to show the problem:
public static void main()
{
try
{
var crappyLib = new CrappyLibrary();
crappyLib.DoCrappyThings();
}
catch
{
Console.WriteLine("This never happens");
}
}
// I do not own the following code, I can't change it
public class CrappyLibrary
{
public void DoCrappyThings()
{
var t = new Thread(DoWork);
t.Start();
}
private void DoWork()
{
throw new ThisLibrarySucksException();
}
}

The thing worrying me most in the described case is abnormal thread termination inside that 3rd-party lib. Once a thread is throwing, you can't catch the exception via correct way because you're not the owner of that thread invocation (and it has no idea it should propagate the exception to you; unlike it happens in TPL, let say). So even if handling such exceptions via a global handler this could be incorrect way because the lib can appear in non-consistent state after any of such exceptions.
So the safe way here is to isolate the lib inside some scope and re-launch the scope after any exception. Let say, to load the lib into separate domain.

If your goal is to prevent early termination of your process because of these unhandled exceptions that are not under your control, then there exists the legacyUnhandledExceptionPolicy setting that you can add to your app.config that will prevent unhandled thread exceptions from terminating the whole process.
Obviously, the solution is not perfect, as unhandled exceptions can destabilize the state of the threads. But at least it's an option you can consider.
Please have a look at the documentation about this here to better understand the implications of turning on this setting.
Your app.config would have to look something like this:
<?xml version="1.0" encoding="utf-8"?>
<configuration>
<runtime>
<legacyUnhandledExceptionPolicy enabled="1"/>
</runtime>
</configuration>
EDIT:
Just a thought, but perhaps the above setting, in combination with adding an event handler for AppDomain.UnhandledException can help you with your need.
Using AppDomain.UnhandledException, you can detect the failure, so that you know when you need to trigger a retry, or whatever else it is that you need to do in these cases.
And the legacyUnhandledExceptionPolicy setting would still be useful to prevent the process from shuting down, thus giving you the opportunity to perform the retry.

I hope this is helpful https://msdn.microsoft.com/en-GB/library/system.windows.forms.application.threadexception.aspx
You can try something like that (it's from the article)
Application.ThreadException += new ThreadExceptionEventHandler (ErrorHandlerForm.Form1_UIThreadException);
// Set the unhandled exception mode to force all Windows Forms errors to go through
// our handler.
Application.SetUnhandledExceptionMode(UnhandledExceptionMode.CatchException);
// Add the event handler for handling non-UI thread exceptions to the event.
AppDomain.CurrentDomain.UnhandledException +=
new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);

Global level error handling in C# windows application

I am trying to implement global level error handling in my windows application
I have the button click event for the form which creates some error
label1.Text =
class1.Calculate(Convert.ToSingle(textBox1.Text), Convert.ToSingle(textBox2.Text))
.ToString(CultureInfo.InvariantCulture);
MessageBox.Show("That was really Close");
now I want the control to go to message box, the unhandled error are being handled in the main function as
private static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.ThreadException += new ThreadExceptionEventHandler(Application_ThreadException);
Application.Run(new Form1());
}
private static void Application_ThreadException(object sender, ThreadExceptionEventArgs e)
{
if (e.Exception.InnerException != null)
MessageBox.Show(e.Exception.InnerException.Message.ToString());
else MessageBox.Show(e.Exception.ToString());
}
This code sample does handles the exception but I want the control back to the button Click, that is The MessageBox.Show("That was really Close"); should get called after exception handling

If you don't want the method to stop on an exception then you need to handle the exception at that point. You could have the catch call some kind of global error handling method but you will need a try catch in that method.
Global level exception handling is for exceptions that you can't deal with immediately and need to catch before the program dies, usually for logging and such like.
Global level exception handling is not a substitute for handling exceptions at the correct place. If you expect code to throw an exception and it is one you can deal with then you should put a try/catch at that point of the code. In the example above you say you want to carry on running the method so clearly the error is not a fatal one so you should deal with it in the normal way.
Often though it should be noted that exceptions that you can handle are ones that can be avoided. For example checking what you pass to a method before passing it. The ones that can't be removed entirely are usually ones to do with external resources (eg reading files). I'm sure there are a lot of other exceptions but as somebody wise once said "Exceptions are for exceptional circumstances". If you can foresee them you should try to avoid them.
In this case I assume the exception is related to invalid input in your text boxes. In this case you should use Single.TryParse to verify the input before passing it on to your method. If either of the values fails to parse you can then let the user know that properly.

handling errors through the async dll stack

I'm trying to handle errors that are passed through 2 dlls I've created. So Console.exe calls dll 1. dll 1 completes an async MQ message read and the handler calls dll 2. If dll 2 errors it passes the Exception (throw) without a problem. But the dll 1 (async) handler catch the throw from dll 2 and give me an unhandled by user message.. I have followed the msdn code to add in the IAsyncResult to keep the hander alive but the issue persists.
can anyone advise on how I should handle this stack and get the handler error returned to the console.exe program so I can present it to the user. Code below:-
Console.exe (snippet)
try
{
_msmq.MSMQ_GetMessage(_msgPath);
//set up the print of the number of queue messages
Console.WriteLine("Main thread: starting a timer");
Timer t = new Timer(ComputeBoundOp, _msgPath, 0, 2000);
Console.Write("Press any key to continue . . .");
Console.ReadKey(true);
t.Dispose(); // Cancel the timer now
}
catch (MessageQueueException _msgQex)
{
Console.WriteLine("An error occurred with the queue:- " + _msgQex);
}
catch (Exception _ex)
{
Console.WriteLine("An error occurred with the queue:- " + _ex);
}
dll 1
public void MSMQ_GetMessage(string _MQ_Path)
{
try
{
//set the correct message queue
MessageQueue _msgQ = new MessageQueue(_MQ_Path, QueueAccessMode.ReceiveAndAdmin);
//set the format of the message queue
_msgQ.Formatter = new XmlMessageFormatter(new Type[] { typeof(_TwitterStreamFeed) });
_msgQ.ReceiveCompleted += new ReceiveCompletedEventHandler(_msgQ_RecieveCompleted);
IAsyncResult _result = _msgQ.BeginReceive();
_asyncList.Add(_result); // asyncList is a global variable of type System.Collections - > this allows the callback to remain open and therefore nit garbage collected while the async thread runs off on it's own
}
catch (Exception _ex)
{
throw new Exception("_msgQ_get Message threw the following error :- " + _ex);
}
}
//method to process message
public void _msgQ_RecieveCompleted(object sender, ReceiveCompletedEventArgs e)
{
try
{
//queue that have received a message
MessageQueue _mq = (MessageQueue)sender;
//get the messge off the queue
Message _mqmsg = _mq.EndReceive(e.AsyncResult);
//set the values back into a formatted struct
//now process your SQL....
Azure_SQL _azuresql = new Azure_SQL();
_azuresql.writeMessageToStorage((_TwitterStreamFeed)_mqmsg.Body);
//refresh queue just in case any changes occurred (optional)
_mq.Refresh();
//tell MessageQueue to receive next message when it arrives
_mq.BeginReceive();
}
catch (Exception _ex)
{
throw;
}
dll 2
public void writeMessageToStorage(_TwitterStreamFeed _msmq_message_as_TSF)
{
try
{
// now do something with the class - i..e write the values to the database
SqlConnection _azurecon = new SqlConnection(_AzuzeSQLConnection);
SqlCommand _sqlcmd = new SqlCommand();
//Setup the command string to call the stored procedure
//Add the parameter to the parameters collection of the command
blah blah blah......... Do SQL writing to Db
_azurecon.Open();
SqlDataReader _sqldr_tweet_place = _sqlcmd_place.ExecuteReader(CommandBehavior.CloseConnection);
}
//now close things off
_azurecon.Close();
}
catch (Exception _ex)
{
// Throw the error to preserve the original
throw;
}

The reason for this is that, internally, the MessageQueue class is explicitly swallowing the exception. Where the MessageQueue class raises the ReceiveCompleted event, it's inside of a try-catch statement - and the catch block is empty. Suffice it to say, if an exception occurs inside your ReceiveCompleted event handler, _msgQ_RecieveCompleted(), nothing's ever going to know it happened.
I see a couple of options, in order of preference.
Option 1 - Shift where the asynchronous call is made
Since this exception-swallowing behavior only occurs when using BeginReceive(), in MSMQ_GetMessage(), you can switch from using BeginReceive() to just Receive(). Then, make your call to MSMQ_GetMessage() asynchronous and any exception that gets thrown will be propagated as expected.
As a side note, a new(er) alternative for making asynchronous calls is available; the Task<> class. As opposed to the Thread class, Task<> has exception handling functionality built in. It does, however, require Framework 4 or higher. There is a good explanation of it's use described in the answer here.
Option 2 - Use a custom event
If refactoring the asynchronous call isn't an option, you can create a custom event in your class in 'dll 2' and subscribe to that event in 'Console.exe'. So when an exception occurs in _msgQ_RecieveCompleted(), you can raise the event and 'Console.exe' will be notified.

The MessageQueue.BeginReceive() method uses the standard .NET APM (Asynchronous Programming Model) pattern. It is very important to understand how it works to know how to properly deal with exceptions. Be sure to read the MSDN article, there are lots of other googable resources available.
In APM, the callback that tells you that a message was received in executed on a thread-pool thread. Which is a very efficient way to get code to run quickly. It is however also a very troublesome way when something goes wrong. The EndReceive() method call is likely to throw an exception, it does so to tell you that the receive operation could not be completed. A standard exception it will throw is ObjectDisposedException. Which will happen when the MessageQueue object gets disposed. In your case when your program terminates. You need to catch that exception and exit from your event handler, it is an expected exception and signals that nothing more useful is going to happen next since the queue was closed.
Then there's a raft of possible exceptions that can be raised by major mishaps in the message queue plumbing. Plus whatever you do with the message. Looks like you execute some Azure code, plenty of ways that can fall over. If you let such an exception escape from the callback method, like you do, then there's no catch clause anywhere in the call stack that is going to handle the exception. The standard way .NET deals with unhandled exceptions is to raise the AppDomain.UnhandledException event and terminate your program. If you didn't actually implement that event then there's nothing decent to look at to diagnose the reason your program ended, the Windows Error Reporting dialog has no good diagnostic.
Whether or not you should try to handle the exception and prevent the program from terminating is up to you. But it pretty strongly fits the "don't shoot the messenger" pattern, it is very unlikely your program can meaningfully continue to execute when such an exception is raised. It invariably takes a human to fix the problem, like restoring the network connection or fixing the message queue. If you do catch it then the odds that the same exception is raised over and over again is fairly likely. After all, there wasn't anything decent you could do in your code to repair the network.
So the best guidance here is to not try, just make sure that IT staff has a good diagnostic so they can repair the problem. Do implement the AppDomain.UnhandledException and display and log the e.UnhandledException.ToString() value. This will also let you learn the number of ways that your program can fail. There might be some conditions that are common enough to warrant catching, something like a temporary network outage. At that point you'll also know what to do about it, in other words what kind of code to write in the catch clause. There is no possible way you know what to write right now, you should therefore not try.
Last but not least, do note that you got yourself into this pickle because you used BeginReceive() unnecessarily. You've already got a perfectly good thread to do work on. But it doesn't do anything useful, it is stuck in the Console.ReadKey() method. Particularly in .NET 4.5 a very tricky method to call, it prevents other threads from writing anything to the console. So your error reporting won't work, it will deadlock when it tries to use Console.WriteLine() to write a diagnostic.
You might as well use MessageQueue.Read() instead. Now dealing with exceptions is a lot easier since they occur on the same thread. The MessageQueue.SynchronizingObject can also be helpful to get completion callbacks to occur on the main thread, but that only works in a GUI app, not in a console app.

Replacing the standard exception/error form in .net

I was thinking, is it possible to "override" or maybe replace the standard winforms .net Exception form??
I am talking about this dude:
Is it possible, during the scope of the hole program, to override this windows? I mean automatically, without having to perform try/catch.

You can handle System.Windows.Forms.Application.ThreadException event to show your custom message.

You should handle both the following events:
AppDomain.CurrentDomain.UnhandledException
Application.ThreadException
In those handlers you could display a custom form that you made.

This is the ThreadExceptionDialog class, it derives from the Form class. Deriving from it to alter the dialog is a lost cause, you can't easily get to the embedded controls. You can create your own Form derived class to make your own dialog just as well, just give it a constructor that takes an Exception argument. Implement an event handler for Application.ThreadException to display it.
Do note the fundamental flaw in the dialog. It expects the user to make the right choice when she needs to click a button to dismiss the dialog. With, in general, fairly obscure information about what exactly went wrong. It means something to you, rarely anything more than 'oh crap' to the user. Clicking the Continue button is not typically the right thing to do.
To avoid the user having to make such a difficult choice, call Application.SetUnhandledExceptionMode() in your Main() method, passing ThrowException so that the event is never raised. Every unhandled exception now goes through AppDomain.UnhandledException. Including the ones that were raised in a worker thread, exceptions that don't produce the dialog. Write an event handler for it and display and/or log the value of e.ExceptionObject.ToString(). It is up to you to sort out a way to get that info to your desk, or the user's IT staff, so you can improve your product and they can get their machines stable.

In webforms, you can handle Application_Error in global.asax. But it seems like you're talking about winforms. In that case:
try adding the following code into your main starter method:
Application.ThreadException += new System.Threading.ThreadExceptionEventHandler(ExceptionHandler.OnThreadException);
And define the ExceptionHandler class as follows:
/// <summary>
/// Main thread error handler.
/// </summary>
public sealed class ExceptionHandler
{
private ExceptionHandler()
{}
/// <summary>
/// Handles an exception on the main thread.
/// </summary>
/// <param name="sender"></param>
/// <param name="t"></param>
public static void OnThreadException(object sender, ThreadExceptionEventArgs t)
{
DialogResult result = DialogResult.Cancel;
try
{
result = ShowThreadExceptionDialog(t.Exception);
}
catch
{
try
{
MessageBox.Show("Fatal Error", "Application Error", MessageBoxButtons.OK, MessageBoxIcon.Stop);
}
finally
{
Application.Exit();
}
}
// Exits the program when the user clicks Abort.
if (result == DialogResult.Abort)
Application.Exit();
}
// Creates the error message and displays it.
private static DialogResult ShowThreadExceptionDialog(Exception e)
{
string errorMsg = "An error occurred please contact the adminstrator with the following information:\n\n";
errorMsg = errorMsg + e.Message + "\n\nStack Trace:\n" + e.StackTrace;
return MessageBox.Show(errorMsg, "Application Error", MessageBoxButtons.AbortRetryIgnore, MessageBoxIcon.Stop);
}
}
taken from: http://www.eggheadcafe.com/community/aspnet/2/27469/any-method-for-handling-error-globally-in-c.aspx

Check this link.
From the page:
Introduction
One of the things that impressed me when I first started learning .NET was its enhanced exception-handling functionality. By this I mean such features as easy access to the type of exception thrown, full stack trace and inner exceptions. This makes it easy to still get full information in those places where you just catch a top-level System.Exception. I find this convenient since, if you don't need to take specific action on a particular type of exception, it is tedious to have successive catch handlers for each type of exception that may be thrown. In any case, even if you do catch specific exceptions you usually also need to catch System.Exception just to cover yourself and prevent program crashes. Thus I find that I end up catching System.Exception all over the place in my code. A typical scenario is that in Windows Forms and ASP.NET Web Forms applications, all of my non-trivial event handlers end up containing try-catch System.Exception blocks.
The trouble is that this does still clutter up the code somewhat and doesn't really seem quite right. Is there a better way?

Globally catch exceptions in a WPF application?

We have a WPF application where parts of it may throw exceptions at runtime. I'd like to globally catch any unhandled exceptions and log them, but otherwise continue program execution as if nothing happened (kinda like VB's On Error Resume Next).
Is this possible in C#? And if so, where exactly would I need to put the exception handling code?
Currently I can't see any single point where I could wrap a try/catch around and which would catch all exceptions that could occur. Even then, I would have left whatever has been executed because of the catch. Or am I thinking in horribly wrong directions here?
ETA: Because many people below pointed it out: The application is not for controlling nuclear power plants. If it crashes, it's not that big a deal, but it throws random exceptions that are mostly UI-related that are a nuisance in the context where it would be used. There were (and probably still are) a few of those and since it uses a plugin architecture and may be extended by others (also students in that case; so no experienced developers that are able to write completely error-free code).
As for the exceptions that get caught: I do log them to a log file, including the complete stack trace. That was the whole point of that exercise. Just to counter those people that were taking my analogy to VB's OERN too literally.
I know that blindly ignoring certain classes of errors is dangerous and might corrupt my application instance. As said before, this program isn't mission-critical for anyone. No-one in their right mind would bet the survival of the human civilization on it. It's simply a little tool for testing certain design approaches wrt. software engineering.
For the immediate use of the application there are not many things that can happen on an exception:
No exception handling – error dialog and application exit. Experiment has to be repeated, though likely with another subject. No errors have been logged, which is unfortunate.
Generic exception handling – benign error trapped, no harm done. This should be the common case judged from all errors we were seeing during development. Ignoring this kind of errors should have no immediate consequences; the core data structures are tested well enough that they will easily survive this.
Generic exception handling – serious error trapped, possibly crash at a later point. This may happen rarely. We've never seen it so far. The error is logged anyway and a crash might be inevitable. So this is conceptually similar to the very first case, except that we have a stack trace. And in the majority of cases the user won't even notice.
As for the experiment data generated by the program: A serious error would at worst just cause no data to be recorded. Subtle changes that change the result of the experiment ever so slightly are pretty unlikely. And even in that case, if the results seem dubious the error was logged; one can still throw away that data point if it's a total outlier.
To summarize: Yes, I consider myself still at least partially sane and I don't consider a global exception handling routine which leaves the program running to be necessarily totally evil. As said twice before, such a decision might be valid, depending on the application. In this case it was judged a valid decision and not total and utter bullshit. For any other application that decision might look different. But please don't accuse me or the other people who worked on that project to potentially blow up the world just because we're ignoring errors.
Side note: There is exactly one user for that application. It's not something like Windows or Office that gets used by millions where the cost of having exceptions bubble to the user at all would be very different in the first place already.

Use the Application.DispatcherUnhandledException Event. See this question for a summary (see Drew Noakes' answer).
Be aware that there'll be still exceptions which preclude a successful resuming of your application, like after a stack overflow, exhausted memory, or lost network connectivity while you're trying to save to the database.

Example code using NLog that will catch exceptions thrown from all threads in the AppDomain, from the UI dispatcher thread and from the async functions:
App.xaml.cs :
public partial class App : Application
{
private static Logger _logger = LogManager.GetCurrentClassLogger();
protected override void OnStartup(StartupEventArgs e)
{
base.OnStartup(e);
SetupExceptionHandling();
}
private void SetupExceptionHandling()
{
AppDomain.CurrentDomain.UnhandledException += (s, e) =>
LogUnhandledException((Exception)e.ExceptionObject, "AppDomain.CurrentDomain.UnhandledException");
DispatcherUnhandledException += (s, e) =>
{
LogUnhandledException(e.Exception, "Application.Current.DispatcherUnhandledException");
e.Handled = true;
};
TaskScheduler.UnobservedTaskException += (s, e) =>
{
LogUnhandledException(e.Exception, "TaskScheduler.UnobservedTaskException");
e.SetObserved();
};
}
private void LogUnhandledException(Exception exception, string source)
{
string message = $"Unhandled exception ({source})";
try
{
System.Reflection.AssemblyName assemblyName = System.Reflection.Assembly.GetExecutingAssembly().GetName();
message = string.Format("Unhandled exception in {0} v{1}", assemblyName.Name, assemblyName.Version);
}
catch (Exception ex)
{
_logger.Error(ex, "Exception in LogUnhandledException");
}
finally
{
_logger.Error(exception, message);
}
}

AppDomain.UnhandledException Event
This event provides notification of uncaught exceptions. It allows the
application to log information about the exception before the system
default handler reports the exception to the user and terminates the
application.
public App()
{
AppDomain currentDomain = AppDomain.CurrentDomain;
currentDomain.UnhandledException += new UnhandledExceptionEventHandler(MyHandler);
}
static void MyHandler(object sender, UnhandledExceptionEventArgs args)
{
Exception e = (Exception) args.ExceptionObject;
Console.WriteLine("MyHandler caught : " + e.Message);
Console.WriteLine("Runtime terminating: {0}", args.IsTerminating);
}
If the UnhandledException event is handled in the default application
domain, it is raised there for any unhandled exception in any thread,
no matter what application domain the thread started in. If the thread
started in an application domain that has an event handler for
UnhandledException, the event is raised in that application domain. If
that application domain is not the default application domain, and
there is also an event handler in the default application domain, the
event is raised in both application domains.
For example, suppose a thread starts in application domain "AD1",
calls a method in application domain "AD2", and from there calls a
method in application domain "AD3", where it throws an exception. The
first application domain in which the UnhandledException event can be
raised is "AD1". If that application domain is not the default
application domain, the event can also be raised in the default
application domain.

In addition what others mentioned here, note that combining the Application.DispatcherUnhandledException (and its similars) with
<configuration>
<runtime>
<legacyUnhandledExceptionPolicy enabled="1" />
</runtime>
</configuration>
in the app.config will prevent your secondary threads exception from shutting down the application.

Here is complete example using NLog
using NLog;
using System;
using System.Windows;
namespace MyApp
{
/// <summary>
/// Interaction logic for App.xaml
/// </summary>
public partial class App : Application
{
private static Logger logger = LogManager.GetCurrentClassLogger();
public App()
{
var currentDomain = AppDomain.CurrentDomain;
currentDomain.UnhandledException += CurrentDomain_UnhandledException;
}
private void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
{
var ex = (Exception)e.ExceptionObject;
logger.Error("UnhandledException caught : " + ex.Message);
logger.Error("UnhandledException StackTrace : " + ex.StackTrace);
logger.Fatal("Runtime terminating: {0}", e.IsTerminating);
}
}
}

in Wpf application Project follow this Steps:
in App.xaml.cs file:
using 'System.Windows.Threading'
create App_DispatcherUnhandledException method same example.
example:
using System.Windows;
using System.Windows.Threading;
namespace Test
{
public partial class App : Application
{
void App_DispatcherUnhandledException(object sender,
DispatcherUnhandledExceptionEventArgs e)
{
// Process unhandled exception
// Prevent default unhandled exception processing
e.Handled = true;
}
}
}
in App.xaml:
add DispatcherUnhandledException="App_DispatcherUnhandledException"
for Example:
<Application x:Class="eValGr.UI.Light.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:eValGr.UI.Light"
DispatcherUnhandledException="Application_DispatcherUnhandledException">
<Application.Resources>
</Application.Resources>
</Application>

Like "VB's On Error Resume Next?" That sounds kind of scary. First recommendation is don't do it. Second recommendation is don't do it and don't think about it. You need to isolate your faults better. As to how to approach this problem, it depends on how you're code is structured. If you are using a pattern like MVC or the like then this shouldn't be too difficult and would definitely not require a global exception swallower. Secondly, look for a good logging library like log4net or use tracing. We'd need to know more details like what kinds of exceptions you're talking about and what parts of your application may result in exceptions being thrown.