Pause and resume a Thread (Background Worker)

Question

I am working in VB.Net and I need to pause one thread as it waits for the other to finish.

I've seen a very close question but can't seem to figure it out (And couldn't comment on that post Pause/Resume loop in Background worker)

My scenario is that I have 2 background workers. Worker1 is passing fileNames to Worker2 which processes the files. I need to pause Worker1 if Worker2 hasn't finished. I.e. Worker1 only releases the next fileName after Worker2 has finished

Any ideas on how to do this?

WORKING CODE AFTER COMMENTS FROM @user1666788

Code below is for the scenario stated above of two background workers where one has to wait for the other to finish before proceeding.

Dim isFinished as boolean
Dim currentFiile as integer

Private Sub StartWork_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles StartWork.Click
    bgWorker1.WorkerSupportsCancellation = True
    isFinished = True
    currentFile = 0
    bgWorker1.RunWorkerAsync()
End Sub

Private Sub bgWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgWorker1.DoWork
    If isFinished = False Then
        bgWorker1.CancelAsync()
    End If
    isFinished = False
    For i = currentFile To fileNames.Count - 1
        Dim fileName As String = fileNames(i)
        LoadRules(myValidator.GetFileType(fileName))
        If i = fileNames.Count Then bgWorker1.CancelAsync()
        Exit Sub
    Next
End Sub

Private Function LoadRules(ByVal fileType As String) As Boolean
    ' Function to load some rules for file processing
    Try

        ' Start Thread for actual file processing using bgworker2
        bgWorker2.WorkerSupportsCancellation = True
        bgWorker2.RunWorkerAsync()
        Return True
    Catch ex As Exception

    End Try
End Function

Private Sub bgWorker2_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgWorker2.DoWork

    Try

         ' Do your thing here
         ' for x is 0 to 1million
         ' next

        ' Mark is finished to true
        isFinished = True

        ' Set currentFile
        currentFile += 1

        ' The bgWorker1 is restarted when bgWorker2 has finished.
        ' Note however that bgWorker1 will "Continue" where it left off due to the property "currentFile"
        bgWorker1.RunWorkerAsync()

        '++++++++++++++++++++++++++++++++++++
    Catch ex As Exception

    End Try
End Sub

There you go. Its working as expected. Now need to figure out how to "monitor" progress of writing a file to disk so that I can start off another process after the file has fully been created.....

@HansPassant I've "quick solved" my problem as per the suggestion in answer one below. However, I've Googled BlockingCollection and it looks like it would solve the above in a much more "professional" way. Do you have a sample implementation or a detailed guide? — lukik, Sep 19 '12 at 04:12

score 1 · Accepted Answer · answered Sep 18 '12 at 21:25

I had a similar issue as this. from what I've been told by VS it can't be done. However I found a way around the subroutines for pausing/resuming threads no longer being used.

The easiest way is to check progress, and if it's still working end the call. Here is an example, imagine S1 as your first thread and S2 as your second.

sub S1()

if(processingfile)then exit sub

'Insert code here for sending next file for processing

end sub

sub S2()
processingfile = true

'Insert code for processing files

processingfile = false

end sub

That is more or less how I worked around the problem. I hope my advice helped :)

Oh and one more thing, you might want to sleep the first thread before checking if the file is processing so that it doesn't use up a bunch of CPU power. But that's just a guess, I haven't tried it without a short sleeping period

Thanks! It worked like a charm. I'll edit my post to show the code I've come up with. — lukik, Sep 19 '12 at 01:52

Pause and resume a Thread (Background Worker)

1 Answers1