[RESOLVED] invocation exception using AutoResetEvent

[steve_rm]

Hello,

I am using a background worker to process some login information. However, the background worker has to stop and wait for 2 events to happen. Once these have finished the background worker can complete its job. They are callback that will call the Set() method of the AutoResetEvent.

So I am using AutoResetEvent to set when these 2 events have finished. However, I seemed to be getting this error message

"Exception has been thrown by the target of an invocation."

and Inner exception

"Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index".

The exception usually fires when the registration success leaves scope.

Many thanks for any advice

The code for the background worker.

' Waiting for 'Account in use' and 'Register success or failure'
Private loginWaitEvents() As AutoResetEvent = { New AutoResetEvent(False), New AutoResetEvent(False) }

Private Sub bgwProcessLogin_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
		  Console.WriteLine("Wait until event is set or timeout")
		  loginWaitEvents(0).WaitOne(3000, True)

		  If Me.accountInUseFlag Then
					If Me.lblRegistering.InvokeRequired Then
						Me.lblRegistering.Invoke(New UpdateRegisterLabelDelegate(Me.UpdateRegisterLabel), "Account in use")
					Else
						Me.lblRegistering.Text = "Account in use"
					End If
					' Failed attemp
					e.Cancel = True
					' Reset flag
					Me.accountInUseFlag = False
					Return
		   Else
					' Report current progress
					Me.bgwProcessLogin.ReportProgress(7, "Account accepted")
		   End If

			Console.WriteLine("Just Wait the result of successfull login or not")
			loginWaitEvents(1).WaitOne()

			If Me.registerSuccess Then
					' Report current progress
					Me.bgwProcessLogin.ReportProgress(7, "Register Succesfull")
					' Reset flag
					Me.registerSuccess = False
			Else
					If Me.lblRegistering.InvokeRequired Then
						Me.lblRegistering.Invoke(New UpdateRegisterLabelDelegate(Me.UpdateRegisterLabel), "Failed to register")
					Else
						Me.lblRegistering.Text = "Failed to register"
					End If
					' Failed attemp
					e.Cancel = True
					Return
			End If
End Sub

' Wait for the callback to set the AutoResetEvent

' Error sometimes happens when the function leaves scope.
Private Sub VaxSIPUserAgentOCX_OnSuccessToRegister(ByVal sender As Object, ByVal e As EventArgs)
			Console.WriteLine("OnSuccessToRegister() [ Registered successfully ]")
			Me.registerSuccess = True
			Me.loginWaitEvents(1).Set()
End Sub


' If the flag is not set, then just time out after 3 seconds for the first LoginWaitEvent.waitOne(3000, true)
 Private Sub VaxSIPUserAgentOCX_OnIncomingDiagnostic(ByVal sender As Object, ByVal e As AxVAXSIPUSERAGENTOCXLib._DVaxSIPUserAgentOCXEvents_OnIncomingDiagnosticEvent)
			Dim messageSip As String = e.msgSIP

			'Indicates that a user is already logged on (Accout in use).
			Dim sipErrorCode As String = "600 User Found"
			If messageSip.Contains(sipErrorCode) Then
				' Set flag for account in use
				Me.accountInUseFlag = True
				Console.WriteLine("OnIncomingDiagnostic() WaitEvent.Set() accountInUseFlag: " & Me.accountInUseFlag)
				loginWaitEvents(0).Set()
			End If
 End Sub

[steve_rm]

Hello,

I solved my problem. It was something in the RunWorkercompleted.

However, there is one more thing. The registerSuccess and AccountInUse are global because they are been accessed from 2 different threads. Would it be better to put a lock on them?

Many thanks

[jmcilhinney]

You have a section of code like this:

If Me.accountInUseFlag Then
    '...

It's quite possible that that thread might read the value of the variable and then another thread could change the value while the contents of the If block is being executed. Would that be a problem in the context of your application? If so then you should make that code a critical section, otherwise there's no point.