Question on threading

svanwass

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: -Steve

David Mujica

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. :) Good luck.

svanwass

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

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?

svanwass

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

Luc Pattyn

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. :)

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svanwass

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 Pattyn

svanwass wrote:

that doesn't work

:confused:

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svanwass

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 Pattyn

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. :)

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svanwass

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 Pattyn

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) :)

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Tieske8

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

Spectre_001

Save the thread class instances that you create into an array or IList. Once you have started all of your threads, you can loop through the array or list checking either the State or IsAlive property of each thread until all indicate that they are finished. This way, you don't have to block your main thread while waiting for the other threads to finish. Your main thread can continue working and just check periodically to see if all worker threads have finished.

Kevin Rucker, Application Programmer QSS Group, Inc. United States Coast Guard OSC Kevin.D.Rucker@uscg.mil "Programming is an art form that fights back." -- Chad Hower

svanwass

Seems like I have a lot to learn about the proper handeling of threads. Would any of you have a recommendation on the topic but in relations to c#? I dislike VB...

Spectre_001

Free e-book on C# threading: www.albahari.com/threading/threading.pdf

Kevin Rucker, Application Programmer QSS Group, Inc. United States Coast Guard OSC Kevin.D.Rucker@uscg.mil "Programming is an art form that fights back." -- Chad Hower

Jason Christian

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.

SLDWorks

This site has been so helpful in the past for me over 8 years. I am self taught .net, and have used it primarily with SolidWorks API since 2003. Thread for me is simply threads, and delegates. I run threads in order to crunch data. It keep the main form thread alive while crunching the info. Many times the threads have to send stuff back to the main threaded form. In order to do this without cross thread violations, we need to use delegates. My technique for sending info into a thread, and having the thread call back is rather simple. If I need to create lets say 100 threads. I will use a thread in order to do that. The thread that creates the 100 threads will sleep, only to awake and see if all threads have died. When all threads have died, the main thread cruches and then dies. The main form thread never stalls out, and gets tickled from all sides by all threads from a delegates sub. Here is the code I wrote to explain the most on these topics. Things to note are as follows: Each thread can create its node without limitations. The main thread relys on all threads being done creation. Then the assumtion is made that all thread nodes exist. This can only be true because all threads are not alive. So the main thread changes the display name of each treenode, and then dies itself. The threads and delegates take object arrays, so you can pack them full of anything, both in and out of the thread. The form is very much alive through the whole process. If only a form could speak, because this one is far from a deep sleep. Cheers, Sean P (Sldprt[ItsAboutTime])

Imports System.Threading

Public Class Form1

Dim t1 As Thread
Dim t2 As Thread()
Dim c As Collection

Dim treeview As TreeView

Private Sub Form1\_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load


    tMain()


End Sub

Sub tMain()

    c = New Collection

    treeview = New TreeView
    Me.Controls.Add(treeview)
    treeview.Size = New Size(200, 400)
    treeview.Location = New Point(10, 6)
    treeview.Visible = True

    c.Add(100, "StartData")

    t1 = New Thread(AddressOf MainThreading)

    t1.Start(New Object() {c})

End Sub

Sub MainThreading(ByVal args As Object)

    With CType(args(0), Collection)

        ReDim t2(.Item("StartData"))

        Dim i As Integer

        For i = 0 To UBound(t2)

            .Add(i, "ThreadKey" & i)