I understand that there are a few ways to exit an application, such as Application.Exit(), Application.ExitThread(), Environment.Exit(), etc.
I have an external "commons" library, and I'm trying to create a generic FailIf method that logs the failure to the logs, does this and that and this and that, then finally exits the application... here's a short version of it.
public static void FailIf(Boolean fail, String message, Int32 exitCode = 1)
{
if (String.IsNullOrEmpty(message))
throw new ArgumentNullException("message");
if (fail)
{
//Do whatever I need to do
//Currently Environment.Exit(exitCode)
Environment.Exit(exitCode);
}
}
I have read that using Environment.Exit isn't the best way to handle things when it comes to WinForm apps, and also when working with WPF apps and Silverlight there are different ways to exit... My question is really:
What do I put to exit gracefully to cover all application types?
Read this about the difference between using Environment and Application :
Application.Exit Vs Environment.Exit
There's an example of what you want to do in the bottom of that page:
if (System.Windows.Forms.Application.MessageLoop)
{
// Use this since we are a WinForms app
System.Windows.Forms.Application.Exit();
}
else
{
// Use this since we are a console app
System.Environment.Exit(1);
}
If it's just an abort, use Environment.Exit(). If it's something very critical (that can't handle any sort of cleanup), use Environment.FailFast().
I would recommend using basic exception handling, so instead of System.Environment.Exit(1) throw new ApplicationException(message) which bubbles up the exception to the main method, in your case something like this:
try{
Application.Run(new MyForm());
}
catch(ApplicationException){
// do custom cleanup/reporting
}
Just make sure you throw the exception from the main thread, else invoke on it before throwing ofcourse
Related
So I'm working with cmdlets in C# and using a base cmdlet which derives from PSCmdlet.
Like this: Child <- Parent <- PSCmdlet.
We login to a system using methods in the Parent cmdlet. But sometimes things don't always go right with exceptions, crashes and so on. So it doesn't really logout properly.
My question is as follows:
Is there a method existing that I can implement/override in the Parent cmdlet that will run no matter what happens so that we properly can logout? Kind of like try finally.
I have checked out EndProcessing() and StopProcessing() but they aren't really up to the task in unforeseen situations.
Edit: To clarify, there are multiple cmdlets and the situation is not just about login. There are multiple exceptions that can occur based on code and user-input.
The solution for my problem, as #PetSerAl suggested, was to implement IDisposable in the Parent class.
Using Dispose() I could then add whatever methods needed to finalize the cmdlet no matter what happens.
This sounds like a good case to use Try-catch:
try
{
UserLogin();
OtherMethod();
}
catch(UnauthorizedException au)
{
Console.WriteLine("Unauthorized user... shutting down");
//Closing Code...
Environment.Exit(0);
}
catch(OtherException oe)
{
//Closing Code...
Environment.Exit(0);
}
...
Where you would (if not already) throw the UnauthorizedException() exception within UserLogin() or which ever method you are using to test credentials.
This concept can also be applied to the other areas of code that you are expecting exceptions to be thrown. If the exceptions are because of code not working properly, Try-Catch should not be used to suppress that error as it should be corrected. Exceptions/errors based off of User-Input could be wrapped with Try-Catch.
I am currently writing system tests for a legacy windows forms application.
In my test, I call the Program.Main() method, which in turn calls Application.Run(new MainForm()); at some point.
Is there a way to replace Application.Run() with something that I can control?
Specifically, I need to be able to stop the execution and catch unhandled exceptions.
You could modify Program.Main to accept a form as an input parameter, with a default of MainForm. Reference types can't have non-null defaults but we can accomplish the same thing by using two prototypes:
class Program
{
//Normal entry point
static public void Main()
{
Main(new MainForm());
}
//Internal & test entry point
static public void Main(Form form)
{
DoSomeSetup();
Application.Run(form);
}
}
When you run the program in the normal way, it'll use a MainForm.
But when you run it from your test project, you can call it like this:
Program.Main(new FormICanControl());
And then you can control it.
//Arrange
var t = new TestForm();
//Act
Program.Main(t);
t.ExecuteSomeTest();
//Assert
Assert.AreEqual(t.ResultCode, 0, "Test failed.");
To "stop the execution", you can ask Main thread to exit by calling Application.ExitThread() and in dreadful situations when it does't respond you may kill the Main thread with .Abort() as a last resort.
The exceptions won't be automatically collected for you anywhere, but you can catch them in a process of testing using
Application.ThreadExceptionHandler
AppDomain.CurrentDomain.UnhandledException
Testing a real-life app without Application might be a problem because people often do some tricks by calling Application.DoEvents(..) and doing other stuff with messages pump.
I am trying to catch exceptions for my form client not being able to establish a connection to a server with this in the Connect callback:
try
{
client.EndConnect(async);
}
catch (Exception e)
{
client.Close();
return;
}
This works fine but this behavior is encapsulated in to a class so I want to call throw; instead of return; so that the client class can handle it instead, like so:
try
{
client.Connect(host, port);
}
catch
{
Console.WriteLine("Could not connect to: " + host + ":" + port.ToString());
}
So why not just call throw; then? Well, for some reason if I call throw;, throw new Exception();, or basically anything other than return; the program failsfast. I'm really not sure what's causing this. I tried removing client.Close(); to see if it was the problem but nothing. If I don't call return; the program just immediately exits with no error.
Anyone know what's going on here?
Edit: I do not understand why I am getting downvoted so much. I showed how I am attempting to catch these exceptions and am asking why they are not working properly. I think the problem may be (not sure, just came up with this) because within the asynchronous callback, because it is a new thread in the ThreadPool, calling throw; does not do anything because, because it is not synchronous, there is nothing to throw back to and the application dies. Even with this knowledge, I am not sure how to solve this problem unless I put some sort of try-catch on the entire program.
I suppose a solution could be just sticking with return; because there is nothing to throw back to (due to the asynchronous callback nature of the method) and instead raise an event indicating a failure of connection. Regardless, many thanks for the downvotes and helping me solve this problem. Oh wait...
What's happening is that the EndConnect is not happening on the same thread as your BeginConnect. When EndConnect throws an exception, it is caught by the worker thread's unhandled exception handler, which fails fast (the other option is that it gets ignored and you never find out that your code isn't working).
You have to come up with a way to tell your main form thread that the connect failed.
As others have pointed out, you'll need to catch your exception one way or another to avoid program termination.
For some ideas on how you can do that "globally", see How to catch ALL exceptions/crashes in a .NET app. Whether this is actually a good idea depends on the specific needs of your program...
Relevant for WinForms:
Can't tell based on your question alone, but in case this is actually a WinForms application, you may need to be cognizant of the difference in behavior of modal forms that throw exceptions, depending on whether the debugger is active or not. Let's say we have two forms - the second one is shown as a modal child of the first one:
If application was started through debugger, second form is closed and and stack unwinding goes all the way to the first form's catch block (if any).
If application is started outside debugger, stack unwinding stops before second form is closed and generic exception message is displayed. The second form stays open and catch block in the first form is never reached.
I was looking at some other question and then I had this question:
Who calls the Main() method?
If I want to exit/quit the application (when I get some exception in the Main() method itself), is it a good idea to use return; statement from the catch block in the Main() method?
Please note that I am not starting any thread in the Main() method explicitly. When we start the application, are there any threads start automatically in the background?
Application.Exit() does not guarantee an application to quit
(EDITED point) Environment.Exit() is another option.
Can use of return; statement to quit the application be a good idea? If no, what are those (subtle) things because of which it may not be good idea?
In comparison, which is the best approach to quit?
If your application is going to terminate due to an unexpected error, you may wish to use Environment.FailFast which will "crash" the application with a specified message that gets written to the event log and offers the user an opportunity to submit the crash data to Microsoft. As the developer, Microsoft can make the crash data available to you.
But if you just want to return an error condition to the calling process (such as in the case of a console application) you can modify your Main method signature to return an int and then return a non-zero value which by convention implies an error condition.
Who calls the Main() method?
CLR
If I want to exit/quit the application (when I get some exception in the Main() method itself), is it a good idea to use return; statement from the catch block in the Main() method?
Yes, with the caveat that you don't have other foreground threads.
You could put a giant try/catch block around all of Main(), or set up the AppDomain.UnhandledException event. This is not directly relevant, but look at Environment.Exit, you're right about Application.Exit since all it does is close all windows. Environment.Exit also allows you to specify a value other than 0 as the exit status (errorlevel) if you have declared void Main() instead of int Main().
Application.Exit() is for Form based applications. The best way to handle an exception in Main:
static void Main(string[] args) {
try {
// code here
} catch {
// do any clean up and return
// optionally specify an exit code
Environment.Exit(1 /* or any number other than zero since this is an error condition */);
}
}
1) The OS basically calls the Main method. It start address is specified PE header of the .exe (if I remember correctly).
2) Yes use the return statement from the catch block.
I have an app, and after about 20 minutes of idle time the program just crashes. ("Windows has encountered an error and needs to close...")
I have no idea why this is happening. What is the best way to go about debugging something like this?
Generally crashes in .Net applications are caused by an unhandled exception - i.e. an exception in a thread in that application that was not caught in a try-catch block of some sort:
try
{
// Some code that may throw an exception
}
catch (Exception ex)
{
Console.WriteLine(ex.ToString());
}
A good first place to check for information about this exception is the application event log, often however you will find that the .Net framework posts only minimal information about the crash - if this is the case then you need to catch and handle the exception yourself, recording enough information to allow you to diagnose the error.
Typically there are two way that you might do this:
1. Ensure that the code for each thread of your application is contained in a try-catch block.
This is the easiest method - unless your application has multiple user threads (you will know if it has), this simply requires that you place a try-catch block around the entry point of your application, for example in a Windows Forms application:
// Probably found somewhere in Program.cs
[STAThread]
static void Main()
{
try
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
catch (Exception ex)
{
MessageBox.Show(ex.ToString());
}
}
If you are working on a console application then you will need to use something other than MessageBox (see the first example).
If you spawn multiple threads then the entry point method for each thread should also catch all exceptions in a similar way.
2. Handle the UnhandledException event of the current App Domain
This event will be fired whenever any thread throws an unhandled exception in the current App Domain. Generally speaking it is best to use the first method instead, however this event is still useful in some situations.
Example:
static void Main()
{
AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);
// The rest of your application
}
static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
{
Console.WriteLine(e.ExceptionObject.ToString());
}
Of course it is worth pointing out that the error still might not be caught by either of the above two methods (which is possible if the error is caused by a native module loaded in the same process), however this should probably do the trick.
Finally - Good luck!