Background worker not working right

Question

I have created a background worker to go and run a pretty long task that includes creating more threads which will read from a file of urls and crawl each. I tried following it through debugging and found that the background process ends prematurely for no apparent reason. Is there something wrong in the logic of my code that is causing this. I will try and paste as much as possible to make sense.

            While Not myreader.EndOfData
                        Try
                            currentRow = myreader.ReadFields()
                            Dim currentField As String
                            For Each currentField In currentRow
                                itemCount = itemCount + 1
                                searchItem = currentField
                                generateSearchFromFile(currentField)
                                processQuerySearch()
                            Next
                        Catch ex As Microsoft.VisualBasic.FileIO.MalformedLineException
                            Console.WriteLine(ex.Message.ToString)
                        End Try

                    End While

This first bit of code is the loop to input from file and this is what the background worker does. The next bit of code is where the background worker creates threads to work all the 'landingPages'. After about 10 threads are created the background worker exits this sub and skips the file input loop and exits the program.

     Try
                For Each landingPage As String In landingPages
                    pgbar.Timer1.Stop()
                    If VisitedPages.Contains(landingPage) Then
                        Continue For
                    Else
                        Dim thread = New Thread(AddressOf processQuery)
                        count = count + 1
                        thread.Name = "Worm" & count
                        thread.Start(landingPage)
                        If numThread >= 10 Then
                            For Each thread In ThreadList
                                thread.Join()
                            Next
                             numThread = 0
                            Continue For
                        Else
                            numThread = numThread + 1
                            SyncLock ThreadList
                                ThreadList.Add(thread)
                            End SyncLock
                        End If
                    End If
                   Next

My main program where I create the background thread is as follows:

Private Sub btnSearch_Click(ByVal sender As System.Object, ByVal e As    System.EventArgs) Handles btnSearch.Click

    isClicked = True
    ProgressBar1.Value = 10
    Me.BackgroundWorker1.RunWorkerAsync()
    Timer1.Interval = 10000
     ....

background do work function is not shown but basically calls this function in another class....

BlogDiscoverObj.start()

now where I tried to wait for all the threads was here in the second block of code above: Dim thread = New Thread(AddressOf processQuery) count = count + 1 thread.Name = "Worm" & count thread.Start(landingPage) If numThread >= 10 Then For Each thread In ThreadList thread.Join() Next numThread = 0 Continue For Else numThread = numThread + 1 SyncLock ThreadList ThreadList.Add(thread) End SyncLock End If End If Next

           Thread.Sleep(1000)
           For Each Thread In ThreadList
                Thread.Join()
            Next

hope this is clearer

Also my main thread runs a forms from where this background is called to run but the main thread is supposed to wait for the background process to end unless the user selects another option from the main form.

Answer 1

How does your main program look like ? You are starting some background threads. A background thread is stopped, whenever no more foreground threads for the program exists.

You need to wait for the threads you started to finish before exiting your Main().