SyncLock / Multithreading - Child Thread Reading The Values Of _do At The Same Time As Another Child Thread Is Reading The Values

Nov 13, 2009

I have a dictionary object (let's call it _do) I am using to cache some values for use in a multi-threaded program. I have a single controlling parent thread, with a timer function _doTimer() which can kick off child threads with a new instance of class MyThreadObject in each. My parent thread has _do as a property and with each time _doTimer() gets called, it may or may not repopulate _do depending on cacheflag settings. I pass a reference to _do to each instance of MyThreadObject and those threads at some point read the values of _do but DO NOT write to it.

What I want is to ensure that the child threads do not try and read _do whilst the parent thread is writing to it. Same thing but very slightly different -> I also don't want the parent thread to write to _do whilst the child threads are reading from it. However there is no problem with 1 child thread reading the values of _do at the same time as another child thread is reading the values - so ideally I do not want each child thread to completely lock out read access, only locking out Write access.. The code is roughly like this:

[Code]....

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Pass Objects Between Threads Before Child Thread Completes

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What is the best way to pass objects between threads? I would like to create a new thread that creates a new object : Dim myobject as newobject = new newoject Then in my main thread, I would like to use myobject. Ideally I would like to just assign to a global variable but I don't think that is possible. I think I may have to use some form of delegate function (but I think the child thread would need to complete to use a callback). The new thread will not actually end before I need the object reference in the main thread. How should I go about this?

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I have this in the WPF window class:

Public WithEvents mSerialPort As New SerialPort()
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With mSerialPort

[code]....

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I'm learning VB.NET coming from a VB6 and Java background.In my app, I've got a function that validates the fields on a form. All it is doing is reading them, not updating. I've searched and see info about the backgroundWorker class, but all the examples are about updating the fields.I understand the idea of threading and how it works, but have never written code that spawned threads myself. I've always let the language handle it. It seems like a lot of work that I would have to write a sub using the backgroundWorker for every time I wanted to read or update each field. The couple of books I've got that introduce you to the language show you reading or updating the field directly.How do I know what threads are running other than writing the code like I'm used to then running through debugger to figure out what variables are on which thread?

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Aug 26, 2009

I get this error when i request the 'SelectedItem' property of a standard .NET ComboBox control from a BackgroundWorker control.

I know why this exception is raised, however, i thought that read-only operations to controls from different threads were safe?

I know i can turn this off using Form.CheckForIllegalCrossThreadCalls - but i want to make sure that readonly calls from non-ui threads are actually safe or not?

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I'm trying to follow the technique discribed by jmcilhinney in this HTML [URL]..I have all the drawing code in the .Paint event. Reading the above mentioned thread I would need .Invalidate(all or parts of the picturebox) AND .Update() in order to repaint (all or parts of) my PictureBox, however in my case it works without .Update. Am I doing something wrong?

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Sep 8, 2011

Ok so I coded this app that generates a number/word and it will upload to my database. Speed wasn't the issue when my db was under 1million entry. Now that I got about 100million entry it takes a few mins to upload.I worked with threading before but now I want all my threads to access this function that will give them a string. Now here is the problem, if 2 or more thread access the function at the same time, it will crash.How can I by pass that?I read about SyncLock. Can I use SyncLock on my function on each thread?

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Aug 25, 2011

The program i am writing has 5 features, all of which i want to run in their own threads. On the main for I have a listView which contains all the accounts (user password etc). The thread is defined as:

Public fbaThread As New Thread(New ThreadStart(AddressOf fba_Start))

In cmdAdderStart i begin the new thread by:
fbaRun = True
fbaThread.Start()

[Code]....

I have managed to write the UpdateDebug() to update my txtDebug on the main form. But now I am having trouble being able to pull the values from lvAccounts.items().subitems I can accomplish this with global variables but i'm sure this is not the best way to do this.

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Is there any chance to pass values from mdi parent to mdi child.

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Apr 15, 2012

I open a child form from within a parent form

[code]...

now the form customer master has values within a listview. when i doubleclick on a value within the listview i want this form to close and pass the value to a textbox within the parent form. what would the code be? I am relatively new to vb.

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All the code i found for multi-threading is complex and not clear.What i want to do is creating a thread for reading and analyzing a big text file on Form_Load event, so that the form UI building continue without waiting for reading and analyzing the file finish.

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Jan 2, 2012

I am using the BackgroundWorker to do the heavy tasks so the UI thread doesn't get blocked. While the BackgroundWorker can send values to the UI thread using the progress-scheme, how can the BackgroundWorker get some values FROM the UI thread?

Either by asking it or simply by the UI thread sending some values to the BackgroundWorker?

Just accessing a variable of the UI thread like UIForm.x within the BackgroundWorker does not work, it does not seem to have access to the UI variables?

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Feb 23, 2009

I coded a class that scans an object and maps data from a data table into each one of the corresponding properties, it works very well, however I am not able to set the property of one of the child (coplex objects)

Public Class CntrConfHdr
Private m_CntrConfHdrID As Double
Private m_HeaderCode As String

[Code]...

I want to set the value for the child object TypeCurrency.TypeCurrencyID thus I set the value of the variable sTargetPropertyName to TypeCurrency.TypeCurrencyID but the application willnot work stating that the property can not be found.

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Im working with MDI parent/child objects. when closing the child objects i need the child to check to see if it is the last child object before closing. i couldn't find anything on google, maybe im searching for the wrong thing.

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I have a textbox which will accept a user input for a email address or phone number.I want to using a new thread do a search for various results and populate a listbox.I know i need to do this in another thread so my main form will still operate but how can I do this? I've never used threads before and I know it's tricky to get the values from a textbox and also update a list box on another thread.

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Aug 13, 2010

In one application, I need use 4 simultaneous threads.When the threads finished, I need to update the text of a TextBox.So, I create 4 Textbox, and I wanna the threads change the text to FINISHED.Each thread change one distinct TB.I use this "example"

Dim Terminados As Integer = 0
Private Sub frmEnviarMensagem_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Timer1.Enabled = True
Timer1.Start()

[code]....

The problem is, I have an error in the red lines.The error is: INVALIDOPERATIONEXCEPTION "Cross-Thread operation not valid: Control tbPlaca1 Accessed from a thread other than the thread it was created on."I don't use cross threading. Each TB only was accessed for the correspondent thread, and for the "main program".

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Nov 3, 2011

This is the error message I am getting:

"Cross-thread operation not valid: Control 'Panel1' accessed from a thread other than the thread it was created on." The reason I am getting this error is because I am opening up a new form and then calling these three things:

Panel1.Show()
Label1.Show()
Label2.Show()

why I get this error message because it doesn't occur normally if I open Form2 after closing Form1, it only occurs when I open Form2 after closing Form4.

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Error - Cross-thread Operation Not Valid: Control 'txt1' Accessed From A Thread Other Than The Thread It Was Created On

Jul 21, 2009

I have done a program using vb2005 to display reading from my microcontroller bs2 board but have encountered some problems. My code are as follows.

Dim Stop_Rx As Boolean
Private Sub btnRead_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnRead.Click
SerialPort1.Open()

[code]....

I've encounter an error which is, (Cross-thread operation not valid: Control 'txt1' accessed from a thread other than the thread it was created on.)

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Jun 21, 2012

When my client try to connect to server I'm getting this error : Cross-thread operation not valid: Control 'l_users' accessed from a thread other than the thread it was created on.

Private Sub _socketManager_onConnectionAccept(ByVal SocketID As String) Handles _socketManager.onConnectionAccept
l_Users.Items.Add(SocketID)
End Sub

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Feb 17, 2012

Would anyone be able to help me here please. I'm fairly new to VB.net and threading so im just trying to figure out what is happening.When I debug this I am getting the error thread operation not valid: Control 'ProgressBar1' accessed from a thread other than the thread it was created on.

I'm a little lost as to why the error is occuring or how to fix it. I've had to put the progress bar in a separate thread otherwise the GUI crashes

[Code]...

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Sep 2, 2010

My understanding is that thread.join will suspend the execution of code on the calling thread until the spawned thread finishes or is aborted...

With that in mind, I tried this:

For i = 1 to 50
threads = New Thread(AddressOf test)
threads.IsBackground = True
threads.SetApartmentState(ApartmentState.STA)

[CODE]...

However, the rest of the code runs when the loop finishes, not waiting for all the spawned threads to finish. Since the rest of the code needs the threads to finish (otherwise the rest will error).

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Jun 6, 2010

I have written an application that loads a form - frmCad as well as AutoCad. It does this via a class which detects when AutoCad quits.

Friend Class CadApp Private WithEvents AppObject As AcadApplication... Private Sub AppObject_BeginQuit(ByRef Cancel As Boolean) Handles AppObject.BeginQuit RaiseEvent Quit() End SubEnd Class

My main class loads frmCad as well as CadApp.

Public Class Cad Private WithEvents frmCad As CadForm Private WithEvents app As CadApp... Public Sub ShowForm() If frmCad Is Nothing Then frmCad = New CadForm frmCad.Visible = True End Sub... Private Sub app_Quit() Handles app.Quit frmCad.Dispose() frmCad = Nothing.... End Sub

When I debug the program, it stops at frmCad.Dispose()The program continues to execute, but all the code after it fails to work.Looking more carefully I get an error message which contains:-Cross-thread operation not valid: Control 'Autocad' accessed from a thread other than the thread it was created on.

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Feb 9, 2011

My error:Cross-thread operation not valid: Control 'label2' accessed from a thread other than the thread it was created on. I want to be able to give my Public RunBot() sub access to edit Labels, buttons, etc without an error.

[Code]...

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Apr 1, 2010

I'm getting the 'System.InvalidOperationException' error on acccessing a thread from other than where it was created. My code is:

'Required by the Windows Form Designer
Public components As System.ComponentModel.IContainer ' changed from private

[code]....

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Jun 6, 2009

My problem is Cross-thread operation not valid: Control 'statusHO' accessed from a thread other than the thread it was created on.

System.InvalidOperationException was unhandled
Message="Cross-thread operation not valid: Control 'statusHO' accessed from a thread other than the thread it was created on."
Source="System.Windows.Forms"
StackTrace:

[Code]...

i used it andit works fine then. but as it is mentioned its not a good practice to use it. So what should i do? is it ok if i use this as i am not able to use correct practice. Mine application is not for enterprise purpose. its just my class project, and it works fine even if i put application working in background. System works ok. I dont know how to correct this error.As i dont have that much knowlege of threads.

So please guide me how to fix this in correct way otherwise i am force to go for bad programming practice
Please refer to Windows Mobile Developer Center > Smart Device Development Forums > Windows Mobile Development > Appendtext not working for all my code details

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Dim lvi As ListViewItem
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[code]....

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[code]....

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sLine = srTrad.ReadLine()

so what I get is �2C0A0B453238�. Then I try to put them in pairs and reading as a HEX value, but I can�t. The only thing I get is the hex value of �2�, �C�, and so on. This is not what I�m looking for.

The second way is storing the values in a variable of type Byte:

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[Code]...

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Private Sub LoadData()
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[Code]......

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[Code].....

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