Unable to diligently close the excel process running in memory

Question

I have developed a VB.Net code for retrieving data from excel file .I load this data in one form and update it back in excel after making necessary modifications in data. This complete flow works fine but most of the times I have observed that even if I close the form; the already loaded excel process does not get closed properly.

I tried all possible ways to close it but could not be able to resolve the issue. Find below code which I am using for connecting to excel and let me know if any other approach I may need to follow to resolve this issue.

Note: I do not want to kill the excel process as it will kill other instances of the excel

Dim connectionString As String

connectionString = "Provider=Microsoft.Jet.OLEDB.4.0; Data Source=" & ExcelFilePath & "; Extended Properties=excel 8.0; Persist Security Info=False"

    excelSheetConnection = New ADODB.Connection

    If excelSheetConnection.State = 1 Then excelSheetConnection.Close()
    excelSheetConnection.Open(connectionString)
    objRsExcelSheet = New ADODB.Recordset

    If objRsExcelSheet.State = 1 Then objRsExcelSheet.Close()
    Try
        If TestID = "" Then
            objRsExcelSheet.Open("Select * from [" & ActiveSheet & "$]", excelSheetConnection, 1, 1)
        Else
            objRsExcelSheet.Open("Select Test_ID,Test_Description,Expected_Result,Type,UI_Element,Action,Data,Risk from [" & ActiveSheet & "$] WHERE TEST_Id LIKE '" & TestID & ".%'", excelSheetConnection, 1, 1)
        End If
        getExcelData = objRsExcelSheet
    Catch errObj As System.Runtime.InteropServices.COMException
        MsgBox(errObj.Message, , errObj.Source)
        Return Nothing
    End Try

    excelSheetConnection = Nothing
    objRsExcelSheet = Nothing

Answer 1

You are using the old VB6 COM interfaces. There isn't any evidence in your code snippet of you ever calling Close() on the RecordSet. You can't call Close() on the Connection since you set it to Nothing.

As written, Excel won't exit until the garbage collector runs and the finalizer thread releases the reference counts on the COM interfaces. Which can take a long time if your program doesn't exit or goes dormant after processing the data. You really should consider uplifting this code to use the classes in System.Data.Oledb so you can properly Dispose() everything when you're done with the objects.

The Q&D solution is to force the finalizer thread to run:

    GC.Collect()
    GC.WaitForPendingFinalizers()
    GC.Collect()

Run this after you're done using the RecordSet. It isn't otherwise recommended.