What is best practice when closing a C# application?
I have read that you can use:
Environment.Exit(0); or Application.Exit();
But what is the difference?
Furthermore, with regards to Environment.Exit(0), I have used exit codes before when working with Java but have never fully understood their purpose. What role do they play when exiting an application in C#?
System.Windows.Forms.Application.Exit() - Informs all message pumps that they must terminate, and then closes all application windows after the messages have been processed. This method stops all running message loops on all threads and closes all windows of the application. This method does not force the application to exit. The Exit() method is typically called from within a message loop, and forces Run() to return. To exit a message loop for the current thread only, call ExitThread(). This is the call to use if you are running a Windows Forms application. As a general guideline, use this call if you have called System.Windows.Forms.Application.Run().
System.Environment.Exit(exitCode) - Terminates this process and gives the underlying operating system the specified exit code. This call requires that you have SecurityPermissionFlag.UnmanagedCode permissions. If you do not, a SecurityException error occurs. This is the call to use if you are running a console application.
I hope it is best to use Application.Exit
See also these links:
Application.Exit() vs Application.ExitThread() vs Environment.Exit()
http://geekswithblogs.net/mtreadwell/archive/2004/06/06/6123.aspx
Application.Exit is for Windows Forms applications - it informs all message pumps that they should terminate, waits for them to finish processing events and then terminates the application. Note that it doesn't necessarily force the application to exit.
Environment.Exit is applicable for all Windows applications, however it is mainly intended for use in console applications. It immediately terminates the process with the given exit code.
In general you should use Application.Exit in Windows Forms applications and Environment.Exit in console applications, (although I prefer to let the Main method / entry point run to completion rather than call Environment.Exit in console applications).
For more detail see the MSDN documentation.
What role do they play when exiting an application in C#?
The same as every other application. Basically they get returned to the caller. Irrelvant if ythe start was an iicon double click. Relevant is the call is a batch file that decides whether the app worked on the return code. SO, unless you write a program that needs this, the return dcode IS irrelevant.
But what is the difference?
One comes from environment one from the System.Windows.Forms?.Application. Functionall there should not bbe a lot of difference.
for me best solotion this is
Thread.CurrentThread.Abort();
and force close app.
Try this
System.Windows.Application.Current.Shutdown();
It is work also with NotifyIcon. Place this code in App.xaml.cs
'
protected override void OnExit(ExitEventArgs e)
{
base.OnExit(e);
App.nIcon.Visible = false;
}
Related
Following are the ways by which we can exit an application:
Environment.Exit(0)
Application.Exit()
Form.Close()
What is the difference between these three methods and when to use each one?
The proper method would be Application.Exit(). According to the Documentation, it terminates all message loops and closes all windows thus giving your forms the possibility to execute their cleanup code (in Form.OnClose etc).
Environment.Exit would just kill the process. If some form has e.g. unsaved changes it would not have any chances to ask the user if he wants to save them. Also resources (database connections etc.) could not be released properly, files might not be flushed etc.
Form.Close just does what it says: it closes a form. If you have other forms opened (perhaps not now but in some future version of your application), the application will not terminate.
Keep in mind that if you use multithreading, Application.Exit() will not terminate your threads (and thus the application will keep working in the background, even if the GUI is terminated). Therefore you must take measures to kill your threads, either in the main function (i.e. Program.Main()) or when in the OnClose event of your main form.
they are all fine.
but form.Close() won't close your application
it closes the form and after that
the main-method returns an int (exitcode).
if you want that your application exits with exitcodes use
Environmet.Exit(exitcode) or return the exitcode in the main-method
I'm currently writing quite a simple app, but it makes a change to the OS which gets changed back when the program is closed.
The worry of course, is if the program crashes. I can do everything in my power to prevent it from crashing, or handling things if it does crash - but I can't stop someone from force closing the process (unless I can?)
Is there a way to catch that event and run just a very quick cleanup before the process exits?
I don't think there is anything you can do if your process gets killed - one approach would be to have your app spawn a helper process that is just there for this case. When your app terminates that process can detect that and "fix" the OS setting as desired before it shuts down itself - obviously this only would work if that other process doesn't get killed first.
You can hook UnhandledException. You can't stop the application terminating, but you can log or do some clean up. This allows you to handle the case of application crashes.
It terms of someone actually just killing the process there's nothing you can do about that.
Program defensively.
Write the original settings to a file. Delete the file when closing. When starting, check whether the file is there - if it is, your process was killed and you know what to return the settings to.
Programming 201 - the basics of transactions, applied to system settings wit hthe program runtime as transaction boundary.
If you don't mind a little interop to C or C++ code, and if you're running on Windows Vista or newer, you could make use of the Application Recovery and Restart APIs. These APIs tell Windows to intercept your process when something catastrophic happens, so that you can perhaps call a little cleanup code before Windows kills the process completely.
See http://msdn.microsoft.com/en-us/library/cc948909.aspx.
I'm writing a program which creates no forms at all until one is required. The problem is, it's preventing shutdown from continuing automatically. I've seen discussions about adding an if to form closing events to check if it's due to shutdown, but as I've said, my program is meant to have no forms at all until required.
Is there any event or some other method that will allow me to know when my program should be closing itself to allow for Windows to shut itself down automatically? And it's not multithreaded.
You can use the SystemEvents class, to "listen to" users logging out, or shutting down.
If I understand the documentation correctly (and a deep study with Reflector confirms this):
The systemevents will spawn a new thread that receives the messages from windows (it has its own messagepump).
When an event is received, your code will be called, from the new thread. You should be aware of this.
You could always add a dummy form which you open minimized, with no icon on the taskbar - it won't have any visual impact, but will be sent the form closing event - where you could note the shutdown event, and presumably shut down/stop whatever else there is that your application is doing.
Handling the Microsoft.Win32.SystemEvents.SessionEnding event, and checking if it's an actual shutdown with System.Environment.HasShutdownStarted
I have a console daemon that is run by a GUI application. When the GUI application is terminated I'd like to stop the daemon as well.
How can I do it in a gentle way on windows?
On Linux, I would just use SIGTERM is there a similar mechanism on windows for console applications?
To provide a bit more detail, the daemon app is written in python and the gui is written in C# & windows forms.
Define "gentle" :)
I'm assuming there is already a communication mechanism in place between the daemon and the GUI. Just introduce a "quit" command and send it.
If you want to kill the daemon even if it's busy doing something (or is frozen), use TerminateProcess().
To have the best of both, you can send "quit", then wait on the process handle for some time (WaitForSingleObject()). If the daemon process does not die in, say, 5 sec, then terminate it.
If the main thread of the daemon is prone to long periods of busy activity, have the daemon start a background thread that does nothing but waits for a named event. To signal that thread, open the event by name from GUI, then raise it. It's up to the daemon what to do upon event detection, but at least it will be a controlled shutdown.
Windows doesn't have signals in the way you're thinking.
There's some infrastructure for changing how the (faked) SIGTERM and SIGBREAK are handled by console apps, mostly SetConsoleCtrlHandler and GenerateConsoleCtrlEvent but both are only of use in the console application itself; not from outside.
It's worth noting that all a windows console app does when it receives a SIGTERM is call ExitProcess, nothing special. I'm not 100% on what the python equivalent is called, but whatever standard "exit" call should be equivalent.
I'd suggest writing some code to signal the console app, causing it to call ExitProcess itself. If that's not an option, use TerminateProcess (equivalent Process.Kill) to close the console process from the outside; attempting to "fake" an ExitProcess is dangerous for reasons noted in the MSDN article.
We run a C# console application that starts multiple threads to do work. The main function looks something like this:
try
{
DoWork();
}
catch (Exception err)
{
Logging.Log("Exception " + err.ToString());
}
Logging.Log("Finished");
The DoWork() function reads new jobs from a database, and spawns threads to process one work item each. Since last week, the application has started disappearing mysteriously. It disappears from the processes list and there is no entry in the event logs. The log file shows work up to a certain point: it does not log an exception, or the "Finished" line.
Any clue(s) on how a C# application can vanish like that?
EDIT: Threads are created like:
new Thread(SomeObj.StartFunc).Start();
Some of the disappearances occur when no threads are running.
P.S. We installed DebugDiag with a rule to create a crash dump whenever our program crashed. It did not create any dump files when the process disappeared.
You need to have a similar catch block at the top level of the function that every thread works. If there is an uncaught exception on a thread it will kill the application, and the catch block on the main thread is not going to help.
What's the identity that you're using to run the console application?
Also, you might want to use SetConsoleCtrlHandler to capture the console events. Look at this blog post for more details. We had a similar issue when the console application was run under a service account, and it would occasionally get terminated. I'm not sure if this is what you're running into. Let me know I can post some code.
UPDATE: It looks like your scenario resembles what we had experienced. In your console event handler, you need to check for the LogOff event and return true. Look at this KB article.
public static void inputHandler(ConsoleCtrl.ConsoleEvent consoleEvent)
{
if (ConsoleEvent == ConsoleCtrl.ConsoleEvent.CtrlLogOff)
return true;
return false;
}
It's possible that one of the threads that the DoWork method is spawning is throwing an exception. The default behavior in this case is for the process to terminate. You can stop this from happening by using the AppDomain.UnhandledException event to override the default behavior.
A console program quits when the main function exits. Since DoWork just spawns a few threads it's returning control to main right away, and since Main has nothing else to do it exits and the program ends. At this time the threads spawned by DoWork are also killed.
That it worked before means either there was something in DoWork() to wait on those threads that now returns right away (is broken) or that part still works but a thread that used to take a long time to return now aborts and returns right away.
It could perhaps be the Logging.Log function that throws your exception.
I have managed to make programs disappear without a trace in a similar fashion to you (no exception traces and no termination log messages) in the past. Almost all the time it was related to killing the stack (the name of this website always reminds me).
It is possible that you are suddenly trying to process far more data than usual, or using re-entrant routines, or being 'clever' with pointers.
DISCLAIMER: My experience was with a Win32 C++ application, not C#.
It could be a memory leak. If your application takes too much memory, Windows will kill it. You can check how much memory you are using: if it grows over time, you may have a memory leak.
Another possibility is that somewhere, you have code calling Environment.Exit(). Try a full text search through your code to double-check. You never know!
Be careful; there are some exceptions that cannot be caught: OutOfMemoryException and StackOverflowException.
Therefore your program will die terribly, but silently.