Wait for application to close VB.NET

I am designing an application and I am in a very early stage of the design process but I am hoping to get some advise on the best way forward. What I need is a mechanism that will control the close-down of an application. E.g before the application starts of its sets a flag in the db like a "critical section flag=true". If the user tries to close the application while the code is in this critical section the application will wait until "critical section flag=false" before it closes down. Any suggestions on the best design approach for this?
jes12345Asked:
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Meir RivkinFull stack Software EngineerCommented:
what kind of applciation are you talking about?console app? winforms?
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jes12345Author Commented:
This is not decided but probably a winform running hidden in the system tray.
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AndyAinscowFreelance programmer / ConsultantCommented:
Does the app have any user interface?

Don't forget - the user can kill tasks with the 'task manager'.  You probably wouldn't be able to stop that.
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Meir RivkinFull stack Software EngineerCommented:
i'd create an abstract class which responsible for keeping the app alive if the critical flag is set to true which mean the app is still in critical processing.
the abstract class will inherit Form object (System.Windows.Forms) and the main form of every application will be of this type (the abstract class).
the abstract class will handle the OnFormClosing event and will check the status of the critical flag.
while the flag equals to true then do nothing, otherwise call the form base class OnFormClosing to complete the closing procedure of the main form and the application itself.
the critical processing will be taken place in other thread which upon compete it will set the critical flag.
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nepaluzCommented:
handle the Main Form closing event and populate with your code:

Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
    'handle your routine to test here
End Sub

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jes12345Author Commented:
I have believe I have sketched out a possible solution. Any comments?
Public Class Form1

    Friend WithEvents BackgroundWorker1 As System.ComponentModel.BackgroundWorker

    Private Sub form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing

        While True
            If System.IO.File.Exists("EXIT_OK.txt") Then
                System.Environment.Exit(0)
            End If
        End While

    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        My.Computer.FileSystem.DeleteFile("EXIT_OK.txt")
        Me.BackgroundWorker1 = New System.ComponentModel.BackgroundWorker
    End Sub

    Private Sub BackgroundWorker1_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork

        For i As Integer = 0 To 500
            Debug.WriteLine(CStr(i))
            System.Threading.Thread.Sleep(10)

            If i = 500 Then
                My.Computer.FileSystem.WriteAllText("EXIT_OK.txt", "", False)
            End If
        Next
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        BackgroundWorker1.RunWorkerAsync()
    End Sub
End Class

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AndyAinscowFreelance programmer / ConsultantCommented:
Try to kill it with the task manager - does that get around your method?
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nepaluzCommented:
I believe you have to hold the "Form Closing" position till you are thru. Something like firing off a BGWorker from there would do the job.

As it stands, I believe your app will exit notwithstanding.
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ladarlingCommented:
That wouldnt work....
You have to set the cancel flag of the FormClosingEventArgs object like:
e.Cancel = True
And instead of testing for a file system object or another flag (especially one thats generated out of the control of the UI Thread)  you could more easily test for the workers .IsBusy property and then handle the backgroundworker.RunWorkerCompleted event.
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