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
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
This question already has answers here:
How do I properly exit a C# application?
(4 answers)
Closed 6 years ago.
I used to call Application.Exit terminate my application. At some point in time, I start to use a DLL, and I cannot fully terminate my application (a thread is running).
However, I can call Environment.Exit(0) and terminate my app completely.
I have read some useful posts.
[Closing Applications
[http://geekswithblogs.net/mtreadwell/archive/2004/06/06/6123.aspx][2]
It seems
Application.Exit() is recommended for Windows application and
Environment.Exit(exitCode) is recommended for console application
That's what I read from other posts.
===== The reason that I asked this question, and Something is still unclear to me:
Now, I just add Environment.Exit(0) at the end of Application.Exit event handler, since I had the event handler for Application.Exit and save some state information in the handler.
I am still not sure that I use this in a correct way. In other words, does this make sense to call both Application.Exit() and Environment.Exit(exitCode)
If you really just needs to terminate the App instantly and terminate all the threads, then you need to use Environment.Exit(0).
If you want your Forms' Close events to fire and your threads to continue their work, you need to use Application.Exit();
It really depends on your situation. The first is like you terminating the process (Killing it). The Second is like sending a message to the App and politely asking it to finish everything in hand and then close for good. This allows to save some state information by firing the closing events if implemented.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Application.Exit
I have a Winforms app in which Application.Exit() fails to run.
public Form1()
{
InitializeComponent();
path=parseINI();//Gets path from ini file
}
In my case, Application.Exit() is being called from the parseINI method, where it doesn't work. Is the problem that its being called when the app is starting? I stuck it in another method that runs after the form is loaded, and it works there. I did use Environment.Exit in my parseINI method, and that worked (despite it being for console apps rather than WinForms).
EDIT: I should probably add that its there as a check, to make sure a file being read is formatted correctly, if it is, then its not called, otherwise the program exits.
This might be because you still haven't started the application via Application.Run when the Form ctor executes.
The common startup code template goes like this:
Application.Run(new Form1());
If that is the case, you call Application.Exit before Application.Run. So after you have called exit, you effectively call Run, and therefore, the application runs.
Call the Form.Close() method inside parseINI() instead of Application.Exit()
The Environment.Exit() method terminates the application, closing the application thread. Indeed, from the documentation:
Terminates this process and gives the underlying operating system the specified exit code.
Why do you have to shutdown your application from within your parseINI method?
Anyway, the method call for Application.Exit() is not working for you, because, reading the MSDN page:
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.
Then, you can add this line to your constructor, to "run" the application, allowing you to use Application.Exit():
Application.Run(new YourForm());
You can find an interesting discussion here: http://geekswithblogs.net/mtreadwell/archive/2004/06/06/6123.aspx
Read this answer for details.
Furthermore, read this important SO question to better understand the difference between Environment.Exit() and Application.Exit().
I am having problems closing an application that uses WaitForSingleObject() with an INFINITE timout.
The full picture is this. I am doing the following to allow my application to handle the device wakeup event:
Register the event with:
CeRunAppAtEvent("\\\\.\\Notifications\\NamedEvents\\WakeupEvent",
NOTIFICATION_EVENT_WAKEUP);
Start a new thread to wait on:
Thread waitForWakeThread = new Thread(new ThreadStart(WaitForWakeup));
waitForWakeThread.Start();
Then do the following in the target method:
private void WaitForWakeup()
{
IntPtr handle = CreateEvent(IntPtr.Zero, 0, 0, "WakeupEvent");
while (true)
{
WaitForSingleObject(handle, INFINITE);
MessageBox.Show("Wakey wakey");
}
}
This all works fine until I try to close the application when, predictably, WaitForSingleObject continues to wait and does not allow the app to close properly. We only allow one instance of our app to run at a time and we check for this on startup. It appears to continue running until the device is soft reset.
Is there a way to kill the handle that WaitForSingleObject is waiting for, to force it to return?
Many thanks.
Use WaitForMultipleObject instead, and pass 2 handles. The existing one, and one for an event called something like 'exit'. During app shutdown, SetEvent on the exit event, and the WaitForMultipleObject will return and you can get it to exit the thread gracefully.
You need to switch on the return value of WaitForMultipleObject to do the appropriate behaviour depending on which one of the handles was triggered.
Possibly, also, you can set the thread to be a background thread. This will prevent it from stopping your application from shutting down when the main thread terminates.
See:
http://msdn.microsoft.com/en-us/library/system.threading.thread.isbackground.aspx
This is what I would do...
Use the EventWaitHandle class instead of calling CreateEvent directly. There shouldn't be any need to use the Windows API other than CeRunAppAtEvent (and API calls make code ugly...). Get this working first.
Before creating the thread, create a ManualResetEvent variable that is not initially flagged. Call it "TerminateEvent".
Replace the WaitForSingleObject API call with WaitHandle.WaitAny(WaitHandle[]) and pass an array containing "TerminateEvent" and the EventWaitHandle class wrapping the CeRunAppAtEvent notification.
Your loop can use the return value of WaitAny to determine what to do. The return value is the array index of the wait handle that unblocked the thread, so you can determine whether to continue the loop or not.
To cleanly end the thread, you can call "Set" on your "TerminateEvent" and then "Join" the thread to wait for it to terminate.
'This all works fine until I try to close the application when, predictably, WaitForSingleObject continues to wait and does not allow the app to close properly.'
Any app can close, no matter what its threads are doing. If you call ExitProcess(0) from any thread in your app, the app will close, no matter if there are threads waiting INFINITE on some API/sychro, sleeping, running on another processor, whatever. The OS will change the state of all theads that are not running to 'never run again' and use its interprocessor driver to hard-interrupt any other processors that are actually running your thread code. Once all the threads are stopped, the OS frees handles, segments etc and your app no longer exists.
Problems arise when developers try to 'cleanly' shut down threads that are stuck - like yours, when the app is closing. So..
Do you have a TThread.WaitFor, or similar, in an OnClose/OnCloseQuery handler, FormDestroy or destructor? If you have, and have no vital reason to ensure that the thread is terminated, just comment it out!
This allows the main form to close and so your code will finally reach the ExitProcess() it has been trying to get at since you clicked on the red cross button
You could, of coure, just call ExitProcess() yourself, but this may leave you with resources leaked in other proceses - database connections, for example.
'216/217 errors on close if I don't stop the threads'. This often happens because developers have followed the er... 'unfortunate' Delphi thread examples and communicate with threads by directly exchanging data between secondary thread fields and main thread fields, (eg. TThread.synchronize). This just sucks and is hell-bent on causing problems, even in the app run, never mind at shutdown when a form has been destroyed and a thread is trying to write to it or a thread has been destroyed and a main-thread form is trying ot call methods on it. It is much safer to communicate asynchronously with threads by means of queueing/PostMessaging objects that outlive both of them, eg. objects created in the thread/form and freed in the form/thread, or by means of a (thread-safe), pool of objects created in an initialization section. Forms can then close/free safely while associated threads may continue to pointlessly fill up objects for handling until the main form closes, ExitProcess() is reached and the OS annihilates the threads.
'My Form handle is invalid because it has closed but my thread tries to post a message to it'. If the PostMessage excepts, exit your thread. A better way is similar to the approach above - only post messages to a window that outlives all forms. Create one in an initialization section with a trivial WndProc that only handles one const message number that all threads use for posting. You can use wParam to pass the TwinControl instance that the thread is trying to communicate with, (usually a form variable), while lParam passes the object being communicated. When it gets a message from a thread, WndProc calls 'Peform' on the TwinControl passed and the TwinControl will get the comms object in a message-handler. A simple global boolean, 'AppClosing', say, can stop the WndProc calling Peform() on TwinControls that are freeing themselves during shutdown. This approach also avoids problems arising when the OS recreates your form window with a different handle - the Delphi form handle is not used and Windows will not recreate/change the handle of the simple form created in initialization.
I have followed these approaches for decades and do not get any shutdown problems, even with apps with dozens of threads slinging objects around on queues.
Rgds,
Martin
Of course the preferable way to solve this is to use WaitForMultipleObjects, or any other suitable function that is able to wait for multiple criterias (such as WaitForMultipleObjects, MsgWaitForMultipleObjects, etc.).
However if you have no control over which function is used - there're some tricky methods to solve this.
You may hack the functions imported from system DLL, by altering in memory the import table of any module. Since WaitForMultipleObjects is exported from kernel32.dll - it's ok.
using this technics you may redirect the function caller into your hands, and there you will be able to use the WaitForMultipleObjects.
What is the best way to kill an application instance?
I am aware of these three methods:
Application.Exit()
Environment.Exit(0)
Process.GetCurrentProcess().Kill()
Can anyone tell me which is better or when using each of the above would be appropriate?
guidelines from c# faq:
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 WinForms 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.
Killing the process is likely not recommended.
If this is a Windows Forms application, use Application.Exit(). That will close the program nicely.
Just a quick answer, I would always use the "Exit" option when it will work. It is a much cleaner way to do it.
To "Kill" a process means exactly that, and therefore the program does not get to do any cleanup work it might want to do (like saving configuration, saving other files, etc...). Unless you know what the process is and that it does not have any "cleanup" to do, and even then, it's just cleaner to use "Exit."
There does not appear to be any difference between the two "Exit" options you mention, I would wager that the first is simply implicitly passing the zero value.
foreach (Process proc in Process.GetProcessesByName("WindowsFormsApplication1.vshost"))
{
proc.Kill();
}