Visual Basic

12-Nov-10 8:41

I am attempting to write a multithreaded application.

The idea is to have a scripted exe run that takes a list of devices, strips out one device and its information into an array, creates a new object of a class. which contains a backgroundworker that contains a telnet object, to telnet to said device and perform simple work (just login at this time). I have 100 device I am doing this for.

So far, everything looks like it works. All 100 devices have a new class object and bgw worker created for them. My problem lies in how to determine when those have completed their work. This is a problem because the rest of the exe needs to process the results of my simple work but can only be done after all have completed.

How can I tell when the work is done? I was thinking about writing something into the RunWorkerCompleted event that tallys but that seems like not the best idea. Sigh | :sigh:

-Steve

Thread manager

David Mujica12-Nov-10 9:33

David Mujica

12-Nov-10 9:33

So, if all of your work is being done in these worker threads, then your main application just becomes a thread manager. Right? (lets take that as true)

1) The thread manager keeps an array of status; one slot for each thread dispatched. (running/WorkDone)

2) Each thread should throw an event which represents "WorkDone"; the thread manager will
listen for this event and update the corresponding array slot.

3) When all threads have been dispatched and begin their work, the thread manager just loops around and sleeps periodically checking if all status array slots have a "WorkDone" status; when that occurs you can continue with you process.

Maybe extend you status array to have a start time so that you can determine if a thread is taking too long, you can take corrective action.

Just a thought. Smile | :)

Good luck.

Re: Thread manager

svanwass12-Nov-10 9:57

12-Nov-10 9:57

So, if all of your work is being done in these worker threads, then your main application just becomes a thread manager. Right? (lets take that as true)

Yes

2) Each thread should throw an event which represents "WorkDone"; the thread manager will
listen for this event and update the corresponding array slot.

How can I make the thread throw a custom event? Conversly, how do I make the thread manager listen?

Re: Thread manager

svanwass12-Nov-10 10:23

12-Nov-10 10:23

OK so I attempted it and I think I ran into an issue with scope.

In the worker thread, I created an event

Public Event IamDone(ByVal sender As Object, ByVal IP As String)

I call that event in the RunWorkerCompleted sub

RaiseEvent IamDone(Me, "111")

And now I am trippng up on how to create the handler in my thread manager. I assumed it would be

AddHandler myworkerthreadclass.IamDone, Addressof myworkerthreadclass.IamDone

but that doenst work

Re: Thread manager

Jason Christian17-Nov-10 6:06

Jason Christian

17-Nov-10 6:06

Why don't use just use the RunWorkerCompleted event, instead of creating a new event to raise? In RunWorkerCompleted you should be able to get the key to the device, and use that to update your status collection.

Or if you are on .NET 4.0 you can use one of the parallel collection to handle this much cleaner.

Luc Pattyn12-Nov-10 10:23

12-Nov-10 10:23

Hi,

1.
Yes, you want the RunWorkerCompleted event handler to do something your main thread can notice. Lots of things are possible, here is one example:
have a global variable that is initialized to the number of jobs, and gets decremented (see Interlocked.Decrement) by each RunWorkerCompleted handler, which on top of that, by checking for zero, raises a signal (see e.g. ManualResetEvent)

2.
It is a bad idea to launch many BackGroundWorkers, as that would be too expensive. The better approach would be to have:
- a small number of BackGroundWorkers (say two times the number of cores your system has, Environment.ProcessorCount);
- a queue of jobs, filled by the main thread, and queried by those BackGroundWorkers (use a lock!);
- and probably a queue of results, filled by those BackGroundWorkers (use another lock), and emptied by the main thread when it gets its "all done" signal.

Smile | :)

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svanwass16-Nov-10 6:30

16-Nov-10 6:30

OK so I attempted it and I think I ran into an issue with scope.

In the worker thread, I created an event

Public Event IamDone(ByVal sender As Object, ByVal IP As String)

I call that event in the RunWorkerCompleted sub

RaiseEvent IamDone(Me, "111")

And now I am trippng up on how to create the handler in my thread manager. I assumed it would be

AddHandler myworkerthreadclass.IamDone, Addressof myworkerthreadclass.IamDone

but that doesn't work

Luc Pattyn16-Nov-10 7:08

16-Nov-10 7:08

svanwass wrote:
that doesn't work

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svanwass16-Nov-10 9:24

16-Nov-10 9:24

I wrote a simple simple version of what I'm attempting.

http://www.4shared.com/file/-tIHs2FE/CustomEventsVB.html[^]

Does that help explain my issue?

Luc Pattyn16-Nov-10 9:41

16-Nov-10 9:41

people here are unlikely to download anything just to maybe understand a question; what you should do is explain the symptoms ("doesn't work" tells us nothing) and tell how it differs from your expectations, then ask a specific question and/or show a relevant code snippet.

Smile | :)

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svanwass16-Nov-10 9:50

16-Nov-10 9:50

My apologies.

Main Form

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim passing(0, 3) As String
        passing(0, 0) = "10.1.1.1"
        passing(0, 1) = "10.1.1.2"
        passing(0, 2) = "10.1.1.3"
        passing(0, 3) = "10.1.1.4"
        Dim myworker As New Foo(passing)
    End Sub

   Private Sub IHeardThat() Handles Foo.IamDone
          'this does NOT work
    End Sub
End Class

My Foo class

Imports System.ComponentModel
Imports System.IO
Imports System.Threading
Public Class Foo

    Public WithEvents backgroundWorker1 As System.ComponentModel.BackgroundWorker
    Public Event IamDone(ByVal sender As Object, ByVal IP As String)

    Dim devicelist(,) As String
    Dim txtFile
    Public Sub New(ByVal Value As String(,))
        devicelist = Value
        backgroundWorker1 = New BackgroundWorker

        backgroundWorker1.WorkerReportsProgress = True
        backgroundWorker1.RunWorkerAsync(devicelist)
    End Sub
    Private Sub backgroundWorker1_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs) Handles backgroundWorker1.DoWork

        ' Get the BackgroundWorker object that raised this event.
        Dim worker As BackgroundWorker = CType(sender, BackgroundWorker)
        Dim myargs As String(,) = e.Argument

    End Sub
    Private Sub backgroundWorker1_RunWorkerCompleted(ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs) Handles backgroundWorker1.RunWorkerCompleted

            RaiseEvent IamDone(Me, "Done")
        End If
    End Sub 
   
End Class

So that's basically it. I attempted to write a sub that would handle the custom event but the form class doesnt see the foo class event.

Does that make sense?

Luc Pattyn16-Nov-10 11:29

16-Nov-10 11:29

does that compile at all?

svanwass wrote:
Private Sub IHeardThat() Handles Foo.IamDone

The IamDone event is not static/shared, how can this work?

Dim myworker As New Foo(passing)
AddHandler myworker.IamDone, AddressOf IHeardThat

does work but is not OK as the handler is added while the BGW is alrady running, so there is a race condition.
possible solutions:
1. pass the delegate to the Foo constructor, so it can add the handler on time;
2. don't start the BGW from the Foo constructor, add a method the caller should call after having set the handler.

General advice:
1. consider making Foo inherit from BGW.
2. start every VB file with "option strict on"
3. tell Visual not to launch the app as long as there are compile errors
4. tell Visual to treat all warnings as errors

(2+3+4 will be a PITA at first, but it will soon teach you to write correct code)

Smile | :)

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Tieske817-Nov-10 1:43

Tieske8

17-Nov-10 1:43

I think the best way would be using a waithandle that signals when done. If you combine the waithandles for all processes, you can use the WaitHandle.WaitAll Method.

See this MSDN article for an example