How To Multithread A Filestream
Feb 23, 2011
I'm making a type of download manager which downloads parts of a file using HTTPREQUEST.addrange. The parts download without a problem and currently I use 5 instances of the same class to download the parts simultaneously each one downloading a different section of the file. Now my problem is that I don't want to save each part as a file then merge them later, I want to use a singular filestream and append everything asynchronously. In the code below I attempted to use the seek method but it feels like it changes the seek for all of the other parts as well.
[Code]...
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Nov 25, 2008
The goal is to write data to a SQL Server 2008 FILESTREAM file using VB.Net. An "Access Denied" message occurs when creating a FileStream object in the code(see red underlined code below). SQL Server 2008 is configured to "Allow remote clients to have streaming access to FILESTREM data" along with "Enable FILESTREAM for Transaction-SQL access"... What configuration setting is missing and causing the "Access Denied" message? Figure 1.) Code used to stream data to SQL Server managed file
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Nov 17, 2011
how do I multithread using timers. For instance 3 picture boxes that change ever 3 seconds?
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Feb 24, 2011
I have client/server app.I have a class for the tcpclient and a class for the tcplistenerIn my tcpclient class I have a system.timers.timerThe timer elapsed event fires a public event(in the tcpclient class) which the tcplistener class handles.During debugging I see the timer firing its elapsed event and calling raiseevent on the public method, yet the event is never fired in my tcplistener class.
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Sep 5, 2010
I'm working on a project. It is a windows form app which has a webbrowser. The app navigates to a url automatically, checks the url's document, and jumps to another url (depends on the document). It works fine. But, now, the problem is the project needs check many urls, so, I'm trying to make it as a MDI form project. when the start button clicked, it create a control thread, in the thread, it launchs 10 MDI forms (within main form), each form does the work for different urls. once done, then launch the next 10 urls.
It works. However, I noticed that, although 10 MDI forms are open, the navigating part in their webbrowser seems run in sequencial. I thought these 10 MDI forms will load 10 urls at the same time, do the work at the same time, but I found that it seems they do load urls one by one, not at the same time.
so, I did some research, it seems webbrowser can only be run STA mode. does it mean I can not use multithread to load different urls at the same time?
basically, I want to have a multi tab webbrowser, and navigate to different urls in these tabs at the same time.
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Mar 4, 2011
the differences between multi threading and background worker and when I should be using either.
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Mar 3, 2009
On this piece Of code I want to multithread, beginning where the for loop takes the data out of the array arydata. The threads would all do the same task.
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Aug 10, 2009
VB and programming on Windows as such. Mostly c++/gcc/linux. I am trying to build this VB app that shows a streaming video from a camera and that needs to be overlaid with some custom graphics and text. I used the code published here: [URL] to get the capture part to work. It essentially uses the avicap32.dll that most of you would probably know.
My plan:
1) Capture frames using SendMessage(windowHandle, WM_CAP_EDIT_COPY, 0, 0) and then copy from clipboard.
2) Do whatever graphics/text overlay on the obtained bitmap
3) send it to some picturebox on some form that is being shown
4) Do step 1 to 3 in a loop by a spawned worker thread.
Firstly is this a reasonable way to do what I want? or is there a much more efficient/easier way to about?
Now the specific problem: From my main thread directly if I do step 1 to 3 once UIComponent.DrawImage(VideoComponent.GetBitmap()) It shows me once captured image as it should and all is good.
Just to clarify: UIComponent is an object/instance that launches the Form and owns the picturebox I want to display on. VideoComponent is an object/instance that has started the videocapture and owns the picturebox to which the video is being captured. But if I wrap the same call above in a function and launch a thread that would start with that function as its starting point, I see a blank screen. Again, for testing purpose, I am only doing step 1 through 3 just once.
The thread part of the code is like this:
Private drawthread As Thread
public sub main()
drawthread = New Thread(AddressOf threadfunc)
[CODE]........
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Nov 25, 2009
I have this situation: a Form with a System.Timer in it (with AutoReset = False). The form has its main thread and the timer its own thread too (nothing new here). When the user press a button I need to stop the timer, wait until the timer thread has stopped its execution and do something more.
On the other side, the timer updates an item at the form so BeginInvoke is used. The code looks like this:
Button Code: Private Sub ButtonStop_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButtonStop.Click
[Code]...
The point is that I wait the main thread to let the timer thread to end its work.The problem is that this code deadlocks when the user clicks the button when the BeginInvoke is going to be called. How a simple thing like this one can be done? Looks like I cannot find a good solution to this problem
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Aug 9, 2009
SERVER
Im using this code:
Imports System.Threading
Imports System.Net.Sockets
[code]....
but when i tried to run the application, it hangs even if i wait several minutes.., is there something wrong with the code..
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Apr 30, 2011
I have a multithread program and in a thread i read a stram from ftp server and write them to a file and close it and in another thread open saved file and read it for process.but sometime when i want to open saved file i receive a error that say : cannot open file , because another user open it .i create 2 filter that surly file saved and closed , but i don't success.
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Jan 21, 2010
I have a program with 3 forms; each has a different role behind them. Form 1 loads when the program executes and the other 2 load by clicking on buttons from form 1. I would like to implement a multithreaded approach where even after clicking on form2 and form 3 I can still execute other form 1 options while form2 and form 3 contents execute. I read through some tutorials and still not to sure how to implement. I figured I need to create instances of the forms 2 and 3 but how to call the threads and control them? I did try a simple one and had some error concerning delegates.
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May 18, 2011
The server connects, the clients connect, one client sends a message to the server, and the server broadcasts it to the other clients. But what I want to do now is to also have the server communicate with the clients. But when I click on the server form, it freezes, and I cant do nothing.
I think this is because of me not creating a thread for the communication(I saw this on another forum), but I dont know how to do that. I copied basically all the chat program code from a site, and I dont know much of sockets and what not.
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May 18, 2011
i'm doing a chat for a project, and it works like this. The server connects, the clients connect, one client sends a message to the server, and the server broadcasts it to the other clients. But what I want to do now is to also have the server communicate with the clients. But when I click on the server form, it freezes, and I cant do nothing. I think this is because of me not creating a thread for the communication(I saw this on another forum), but I dont know how to do that. I copied basically all the chat program code from a site, and I dont know much of sockets and what not.
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Nov 15, 2011
How can I use a text box on a multithreaded client so that it will appear in the command line of the multithreaded server?We were given this code to work around/tear apart:
Imports System.Net.Sockets
Imports System.Text
Module Module1
[code]....
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Jun 27, 2011
i am new with multithreading in vbnet. i got this error.Cross-thread operation not valid: Control 'lvSample' accessed from a thread other than thethread it was created on.this is my code.
Private Sub xFormLoad(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim t As Threading.Thread
[code].....
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Jan 21, 2010
I have a thread executing the following:
vb
Do UpdateVis()
System.Threading.Thread.Sleep(Interval)
Loop
UpdateVis is as follows:
[Code]...
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May 27, 2009
I am trying to successfully multithread a piece of software I have been working on. I have an array of threads 'gen' already working, calling to a method taking a single integer as a parameter (done via typecasting).Now in this thread, when the function gets processed (for each thread a roughly 500 iteration while loop) the index seems to be getting mixed up. As far as I can tell, my threads are messing with eachother and warping values. Now this is happening in locally declared variables inside this function, not global variables.It may be useful to know that I am using a WebRequest via a call to another method. Don't know if that makes a difference or not.
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Jul 7, 2009
I'm trying to manipulate something that is in a different thread, and I know I need to do something by the way of Invoked procedure, but I'm unclear on how. I looked up some examples here on the forums and tried to follow the basic template, but I continue to have the same problem. how to use invoke correctly.
Private Sub getMessage()
For Me.infiniteCounter = 1 To 2
'Try
[CODE]...........................
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Aug 16, 2009
I currently have a browser go through the same list of sites one by one and gather updates. The problem though this takes awhile. Can a browser be multithreaded, (so it could visit several sites at a time) and if so would this take up a lot of server resources?
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Aug 31, 2009
I am doing this within a thread:For Each item As ListViewItem In lvUsers.Items and I am getting: Cross-thread operation not valid: Control 'lvUsers' accessed from a thread other than the thread it was created on.I have been able to adjust a control in a way using something like:
Public Delegate Sub ListAddNameInvoker(ByVal text As String)
Public Sub ListAddName(ByVal text As String)
If lvUsers.InvokeRequired Then
[code]....
But how do I get data from a control and pass it to another thread?
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Sep 3, 2009
I have simple ASP.net web form. With a simple click on a button i need to call a the Multithread process in order to execute my querry in SQL Server DB. I know that my querry willl take up to 45 min to be executed. While the process is running i need to display some status information like: Starting time, Time elapsed, % of completed...So after running the process i got the following error message: "Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding."So i have 2 problems to fix:
Avoid getting timeout while processing/calling the stored procedure. I tried to add cmd.CommandTimeout = 1000 but it didn't work out!
Display correctly Time elapsed and % Completed while processing.
Here's my code in the main form:
Imports System
Imports System.Data
Imports System.Configuration
[code]....
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Aug 25, 2011
I am attempting to read specific lines of GIANT text files (> 150 MB) with hundreds of thousands of lines. The files are contained on an FTP site. I can successfully open the files using FTPwebrequest and streamreader but to get to a specific line using streamreader, you have to read every line before it. Obviously this takes a lot of time when you need to get to the millionth line.
A much faster way, I think, would be to use filestream and the filestream.position function. However, I'm not sure how to open a file as a filestream from FTP. I have tried:
Dim ftpaddress as string = "ftp://####@ftp.textfile.asc+"
Dim fileStream1 As New FileStream(ftpaddress, IO.FileMode.Open, IO.FileAccess.Read)
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Aug 15, 2011
i searched a bit but i cant find something useful.i need to take my files to filestream (i can do this with file paths)and i wanna save this files to somewhere else on my program. Is it possible that with the using FileStream?
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Feb 23, 2009
I am trying to read in a file and store the byte position of each line read so that I can write out to another file the records in any order that I want. I am doing more manipulation of the lines, hence why I need the line position from the original file, but for simplicity sake, I am just including code to display the problem I am encountering. When I read in the file, I am getting the correct file position, but when I write out the lines, every 1024 characters it is re-writing whatever current line it is on. I am assume there is some buffer that is coming into play that I am not familiar with,
[Code]...
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Jul 27, 2009
VB.NET application which allows user to split a file in smaller files. However the stand alone executable of the application,had a permission problem using filestream to read a file without an OutOfMemory exception, while selecting to split locatein certain directories like "C:".To solve the problem i checked My Project window and the "Security" tab, and i tried checking the checkbox: "Enable ClickOnce Security Setting" and selecting "fulltrust application". This added to my app.manifest these lines of code:
<applicationRequestMinimum>
<defaultAssemblyRequest permissionSetReference="Custom" />
<PermissionSet class="System.Security.PermissionSet" version="1" Unrestricted="true"
[code].....
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Jul 5, 2011
I'm working on a project to extract documents from a SQL Database and writing those documents to a network drive. However some of the files pointed at in the DB are encrypted files (RijndaelManaged)that reside on another network driveI have been able to retrieve, and decrypt the files using streams. Now aving problems saving or converting the Memorystream into an actual file.
Here is my code
Public
Sub ExtractDocument(ByVal ThisDocumentInfo
[code].....
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Mar 1, 2009
I am using BinaryFormatters (System.Runtime.Serialization.Formatters.Binary.BinaryFormatter) and FileStreams (System.IO.FileStream) to perform simple Open, Save, and Save As commands. I am using a separate FileStream and BinaryFormatter in each method.
My issue is that there is a delay for between four and ten or so seconds after performing any of those abilities before you can perform any other of them. Apparently the file is open in "another process", which (my guess) is the FileStream.Let's say I save and close a file in my app. I then go File > Open and select the same file and go to open it. I get that error returned.This isn't really an issue with the code, it's more me asking what the reasons are for why this is happening. What would be a way to work around this?
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Feb 18, 2010
I have a filestream, and I want to save a file from that filestream? Like there are bytes in that file stream, and from those I want a "file.exe" to automatically appear on my desktop.
I'm using a code snippet, and I think this is the important part:
Dim fstr As New FileStream("file.exe", FileMode.OpenOrCreate, FileAccess.Write)
fstr.Write(validArg1, validArg2, validArg3)
fstr.Close()
Do I have to use a for loop? Or is there a function like this:
IO.File.WriteAllBytes(myPath, fstr.AllBytes)
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Aug 24, 2011
Filestream URI format not supported?
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