Multi Threading - Perform A Specific Operation ?
May 18, 2007
I want to make an application in VB.NET and I want this application to work as follows, There will be an array of items on which I want to perform a specific operation (MyTask), with the help of multiple threads.For example, say, the array is holding 12 items in it, and I want to create 3 threads to do the work,
Thread 1: Reads the first item from the array and goes to perform the specific operation (MyTask).
Thread 2: Reads the second item from the array and goes to perform the operation MyTask
Thread 3: Reads the third itm from the array and goes to perform the Mytask.
Now once Thread 1 completes the operatin MyTask, I want to assign 4th item from the array to the Thread 1 to continue the process.Once Thread 2 completes the operatin MyTask, I want to assign 5th item from the array to the Thread 2 to continue the process and so on... until all the items from the array is processed. Also, the function taking 5 arguments out of which 4 arguments will be same. Only one argument will vary and it will take the keywords one by one as input parameter.
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Feb 10, 2010
I'm adding multi-threading facilities for the first time. I have a function that is wrapped to be run in a separated thread. This function retrieves data (text) from a combobox and it works for sure without multi-threading.
When I call it as multi-threaded, I get the following error when I try to retrieve the data from the cmobobox: Cross-thread operation not valid: Control 'cmb1stBL' accessed from a thread other than the thread it was created on.
It looks like a restriction of thread-safety... I assume that the child thread cannot read from his parent, to make sure that he doesn't change his parent data. So how can I read the data from the combobox? Should I read the comoboxbox data before calling the child thread?
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May 30, 2009
I know .Net and C# pretty well, but never even looked at VB.My problem is: our Win32 COM library is used by a number of clients, and we see that the number of failures is higher for those who use the library from VB (both VB and VB.NET) than for those who use C++, C# or Delphi. One thing about our library is that it is supposed to be used from one thread only - can some threading magic by VB be the cause of failures?
Clients tell us the do not create any extra threads on their own.
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Apr 3, 2012
ok here is my code :
[Code]...
What's happening is, i see the threads stop after the function dwnld is completed. So i first check for the state (12 means background and unstarted). On case 12 start the thread and in case 16 (stopped) remove that particular thread and add a different thread like i add 10 above. Also there is a check when the i counter reaches last number, restart the whole loop by assigning i=0.
The program downloads some web pages, the url is passed from the listbox2. The geturl will pass the url and remove it from the list. So when the listbox is empty, exit the for loop. But the above code is running for only 11 times and it does not restart. I tried using a lable and goto but it simple hangs. What i want is to maintain 10 threads to keep downloading the web pages and when the list is empty, exit the function.
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Aug 25, 2009
I looked around the site and the questions I found relating to this subject were for C# (the application that I am maintaining is written in VB.NET), so I apologize if I overlooked one. Here is where I am calling my thread:
[Code]...
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May 14, 2011
I have a need to build an app that will access about 10 websites and pass data to them, etc.I've read about something called multi-threading when searching Google. I've also seen people say that they use multiple browsers.Which route is better to use? I figure if you have to do some sort of multi-threading that you would access a single browser?
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May 14, 2011
I have a need to build an app that will access about 10 websites and pass data to them, etc.I've read about something called multi-threading when searching Google. I've also seen people say that they use multiple browsers.Which route is better to use? I figure if you have to do some sort of multi-threading that you would access a single browser?Not sure which way I should approach this app.
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Nov 4, 2009
this is the code have written am unable to perfrom the log in operation.[code]
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Apr 25, 2009
Dim Conn As New ADODB.Connection
Dim rs As New ADODB.Recordset
Conn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & "C:Documents and SettingsUserDesktopContribucionescontribuciones.mdb"
rs.Open()
rs.Open("SELECT * FROM master")
rs.MoveFirst()
TextBox1.Text = rs.Fields("sueldoanual").Value
I have this error
The connection cannot be used to perform this operation. It is either closed or invalid in this context.
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Oct 25, 2010
I have a list of items and wish to set one of their properties to a certain value:
applist.ForEach(Function(x) x.PrePaidTypeID = CInt(DBEnums.PrePaidType.NoPrepay))
...but we think this just does a boolean comparison. Is there a way to force VB to assign the integer value rather than compare it?
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Apr 11, 2009
currently i am working on a project in which i am using datagridview control. if I enter key value in cell than remaining data of that particular row fetch automatically from data base. how? how to delete as row in datagridview? how to update a row in datagridview?
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Mar 13, 2010
how to perform the database operation such reading data and using them for comparison within the VB programming..
Please guide me with explanation as i have very little knowledge regarding the database operation...
i am using VB.Net 2008 as frontend...and MS SQL Server 2008 (express edition ) as back end...
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Mar 3, 2009
I need to be able to call a C++ dll that takes a long time (possibly infinte, it relies on user input)to execute. Im calling this through VB. My VB GUI freezes up when this happens, and I would like to keep the GUI responsive, so that the user can stop this possibly infinte loop. A bit of background, the C++ is trying to keep score on a snooker table using a webcam, and while the VB scoreboard updates easily, I would like to script it so that the analysis is almost continuous, while still allowing the user to interact. Currently the project requires the user to press a button to start the shot analysis, but it would be preferable if the program scripted itself. I have only realised this problem now and the deadline is very soon.
Update: Our lecturer suggested an option to solve the problem, but it would appear that most options here and the one he suggested will not work for us as the processing time required for the webcam image capture is too great to handle due to hardware constraints.
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Jun 26, 2009
SMS Multi Threading
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Sep 28, 2010
I've been reading around trying to find out why I'd be getting this exception to no avail.
I'm using Visual Basic 2010.
Briefly, I have a "Settings Panel" form which takes a while to create (it contains a lot of labels and textboxes), so I create it in another thread.
After it's loaded, it can be viewed by clicking a button which changes the form's visibility to True. I use the following subroutine to handle invokes for my controls:
Public Sub InvokeControl(Of T As Control)(ByVal Control As T, ByVal Action As Action(Of T))
If Control.InvokeRequired Then
[Code]....
The SettingsTable.Create() method generates a bunch of Labels and TextBoxes based on the contents of the application settings and adds them to the SettingsTable.
When I click on the ViewSettingsPanel checkbox, I get a cross-thread violation error.
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Sep 27, 2011
When I try to run my DLL in Autocad, I got the message below.Application attempted to perform an operation not allowed by the security policy. To grant this application the required permission, contact your.I know there are many threads on this error, but Im not sure about one thing.Can I resolved this on our FilesServer or I have to do something on each computers that will use the DLL ?
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Feb 15, 2009
I'm creating a password hash recovery tool that uses brute force. I have the brute force algorithm run in a background worker. It all works, but some similar apps I tried out have performance ~100x bigger then my app. (mine does 50k keys/second, some others do 5m keys/second or more.)I realize this is partly caused by using a .Net language, but I suspect there are ways to significantly speed up the brute force. A lot of ppl say I should use multi threading, but how is this done in practice? Splitting up the passwords to check would slow down my app I think.
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Nov 12, 2010
I have a button click event and inside I do a lot of work. While I am doing this work (not from the UI project) I want to send messages to the UI to display to the user.
[Code]...
and inside DoMyWork which is in another assembly i can call SendMessage which writes to the textbox. The messages will only display though when DoMyWork is complete. How can I update TextBox1.Text on the fly without putting DoMyWork on a BackGround thread or do i have to put it on a BackGround thread? I do actually want to block the user from doing anything while DoMyWork is running
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Sep 9, 2009
I know there are many cases when it's best to multi thread an application but when is it best to multi thread a .net web Application?
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Jun 22, 2010
I made a simple Form1, with Text.Box1 (starting value=1) and Text.Box2 (starting value = 100000), as shown in the attachment: I wanted that, when the Form loads,value of Text.Box1 keeps on increasing by 2 and value of Text.Box2 keeps on
[Code]...
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Aug 20, 2009
One of our products consists of two different services:
- main service that launched at the startup of Wndows
- GUI that launched manualy when needed
GUI is representing data from main service.Main service starts X amount of threads that do some work and gether data.Some minor data and adresses to threads are stored in chache memory, so that GUI will have access to them.Everything works fine in 99% cases, but in some rare cases GUI do not display any data when used on machines with multiple processors (not milti-core). My guess is that it can't access the memory -> probably OS "decided" to run main service on one processor and GUI on another one.Is there any way to access the memory alocated for one processor from the service that runs on another processor?Or is there simple and secure way (same application will be also runing on single processor machines) to specify both services to run on the same processor?
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Sep 10, 2010
I have a question regarding the synchronization in multi threading.
I have a function called send which i am calling in a for loop for every data row.
This function creates threads to send emails to different people.
Public Sub send(ByVal Conn As Data.DataRow, ByVal job As Data.DataRow)
MyThread = New Thread(AddressOf Me.start)
MyThread.Start()
End Sub
But every thread created is writing to a log file at different points of time. So, there are very high chances that 2 threads write to the same file at the same time. So, do i need to use any kind of synchronization mechanisms here ? or is it fine without them ?
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Dec 11, 2010
I've been raking my brain for quite some time on this. Is there any way with VB.NET that I can use multiple IP's in one instance of a program? For example, I want to be able to navigate to a web page 10 times at once, with each one using a different IP. I want them to be parallel (multi-threaded) rather than going sequentially. Going sequentially, I could just do the action, change the IP, do the action, change the IP.
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Jan 10, 2012
I have a button and when it's clicked a HTTP request is sent out to a website to do a few things, but because its got to load the external resources it makes the interface frozen. I've moved the HTTP onto another thread using the follow
VB.NET Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim Thread1 As New System.Threading.Thread(AddressOf check_accounts)
[Code]...
When i want to update a label that is on my main form (from the check_accounts sub). I know that isn't the right way, but i have no idea what the right way is. All the documentation i can find is very (excuse me for this) nerdy and really doesn't offer much insight on how to incorporate it into a project.
I want to be able to have a numericupdown box that can let the user change the amount of threads they want to use. I assume more threads allow the http requests to be done faster and at the same time?Also if i wanted to pause the HTTP requests, would the best method to use be pausing the thread?
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Jun 10, 2010
This error occurs when I want to add my app to the startup keys
My.Computer.Registry.LocalMachine.OpenSubKey("SOFTWAREMicrosoftWindowsCurrentVersionRun", True).SetValue(Application.ProductName, app)
[code].....
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Jun 15, 2009
I am working on adding multi-threading to my application. I have done two applications using multi-threading following a tutorial of sorts, and modifying the code to "get my feet wet."
This is the first time I am trying multi-threading within my own application, and I feel I should be beyond this type of problem, but after a 3 hour search on the forums, I can not find a solution, so I am posting this thread.
The section of code with the error
vb.net
Imports System.Threading
Imports SldWorks
Imports SwConst
[Code]......
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Aug 29, 2010
using multi-threading in my application.Basically what i am trying to do from within a form event is initiate a class instance and then run a function of that class (via a thread) that changes certain member values of that class.Those class member values are then used to update values on the main form.Ive created a simple example below but i cant seem to get it to work.The class values are not updating and im struggling to understand how this threading works.
Class FormMain
Private Sub BtnClick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles myformbtn.Click()
Dim myFileCounter As New FileCounter()
[code]....
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Apr 12, 2011
I'm creating an app that needs to navigate to multiple websites, logs me in and then submits my documentation.I've read that multi-threading can handle this task but then I've read something about backgroundworker.
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Dec 18, 2010
Download file using Multithreading
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Jun 20, 2012
We working with a Modem type interface that use's the Comm port for two way communication. The App starts and sets up the Comm port, and sends config info to the 'Modem'. Trick here is you have specific timing issues that need to be considered, and we got it all sorted, by using Threading.
You send The Config command to the modem and wait X ms for the confirmation reply (Single Byte), If no reply, send a Wake up command, wait X ms and send Config command again. Once confirmed that the modem is in config mode, send parameters, Waiting for confirmation of each one. Once config is set, send the 'Return to normal mode' command and wait for confirmation. [Code]
The SwitchModemMode sub runs under the Comms thread and not the main thread, like the Checkmodem sub at the top. Mostly because the Comms thread Raises the Data Event, which in turn calls the SwitchModemMode. Now because of that the Thread that is supposed to be checking for the input and setting the Flag, is actually the one waiting for the Flag to be set. And Yes App.DoEvents could solve it here, however that can/will mess with the Timing needed with these commands. I'm looking for how to pass the Raised event to the Main thread.
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