Async Callback From ThreadPool?
Jun 12, 2009
I have a bunch of operations that need to be executed simultaneously. For this I'm using the thread pool to execute the tasks. I'd like to know if it's possible to consume some sort of Async Callback (similar to BackgroundWorker.DoWorkComplete) when each thread is finished. The reasoning behind this is that I have a windows service running that uses IPC to update a GUI and I need to know the time at which each specific thread finishes I've used background workers to do a set of tasks and they work perfectly, however, they take longer than I would like. I've timed the execution on my BGW method for a designated number of said tasks and it took 27 seconds, and the same set of tasks takes 4 seconds using the threadpool method. I've also tried using managed threads, to the same effect as the background workers.
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Nov 15, 2009
I have a method that is asynchronously called when System.Net.Sockets.NetworkStream.BeginRead completes.
skDelegate = New AsyncCallback(AddressOf skDataReceived)
skStream.BeginRead(skBuffer, 0, 100000, skDelegate, New Object)
In that callback method, I need to interact with the UI thread.
Sub skDataReceived(ByVal result As IAsyncResult)
CType(My.Application.OpenForms.Item("frmMain"), frmMain).refreshStats(d1, d2)
End Sub
This causes an exception after the method completes. (when End Sub is executed)
[Code]...
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May 28, 2012
I am an absolute beginner on ASP.net (VB.) Please pardon me if the question is too obvious for the experienced members.I tried to make a simple WebRequest in the async mode in case the target URL takes long to provide the data. In my code below, I just want to see if the callback block (RespCallback) is called correctly every time. If all goes well, lblResult should have the string '123' appended to it every time I click the button which calls the 'GetData' sub.
However, the lblResult only shows 123 after the first click. After the subsequent click, the lblResult only gets appended with '12', as if RespCallback is never called. When I tried to debug this in Visual Studio, the execution actually stepped right into the RespCallback part and the lblResult.Text watch actually shows '123123' but the resulting Web page always shows only '12312'
I am sure I am missing something basic here, but I just don't know what. I was even guessing that it has to do with browser cache (hence the result changes for the second time) but I don't know how to fix that either.
[Code]...
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Jun 4, 2011
I m trying to move all my drive's files into h drive firstly i have added all drives in threadpool for scanning and when scanning of any drive finish (Without waiting for other drive's complete ) it will move file's to h drive but it is not working as i wanted that's why i need two threadpool - one threadpool for scanning files and second threadpool for moving file's into drive's
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Jun 3, 2010
I'm trying to write a 'developer friendly' wrapper for the Windows API EnumWindows - the problem is that the API uses a callback function that gets invoked on another thread, where as I want my wrapper function to simplify this and make it more useful by working like any other normal synchronous function and just returning a value.
Now if the API just called the callback once that would be fine, as I would just call the API and make the wrapper function wait until it got a signal from the callback function telling it to continue... but the API calls the callback function over 100 times (once for every window handle that exists). The biggest problem is that there is nothing that indicates that any particular call to this callback function is the last one, so my wrapper function has no idea when it is safe to continue and return the list of window handles to the caller.
The only solution I could think of is to do this:
1. The wrapper function calls the API and starts a timer that waits 2 seconds before it raises the Elapsed event. The wrapper function then pauses until it receives a signal (ManualResetEvent)
2. Each time the callback function is raised by the API on a different thread, it stops the timer (so this is before the 2 seconds have elapsed), adds the current window handle that was passed in by the API to the list of handles, then starts the timer again.
3. If the timer reaches its 2 second interval then it is assumed that we are at the end of the windows because otherwise the callback would have stopped the timer. So the timer's Elapsed event handler is what signals the original thread (that the wrapper function is executing on) to continue as we now have a complete list of windows to return.
This works fine and does exactly what I want... but I dont like it.
I dont like forcing the caller to wait an extra 2 seconds after the API has done its last callback but more importantly I dont like assuming that the API will never take longer than 2 seconds between callbacks. In reality on my PC it is never anywhere near that long between callbacks, it is something like 200 miliseconds, but I have no idea how long it would be on a slower PC and I want this to be completely reliable.
[URL]
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Jan 1, 2010
how this is written in VB.NET? This was an example I found on [URL]
ThreadPool.QueueUserWorkItem(delegate
{
var channelFactory = new ChannelFactory<ISimpleService>("*");
var simpleService = channelFactory.CreateChannel();
var asyncResult = simpleService.BeginGetGreeting("Daniel", null, null);
[code]....
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Jun 26, 2011
i have this code which i run with queued 10,000, even when a max of 50 is set but the threadpool counts goes to high.
Public Sub DoWork(ByVal objItem As Object)
Dim objUrl as String = DirectCast(objItem, string)
Try
If objUrl Is Nothing Then
[code]....
EDIT:i use a this code to check the number of runing threads each second
Sub Timer1Tick(sender As Object, e As EventArgs)
tsslthreads.Text=string.Format ("Threads: {0}", Process.GetCurrentProcess().Threads.Count)
End Sub
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Jan 11, 2009
I'm currently writing an application that is used to automate a certain task. Currently, it uses the threadpool (using up to 25 threads per the enduser's option). Each thread calls a function which will usually take about two minutes to finish, but it uses a While loop in order to repeat the process. This is my code to start the threads:
Private Sub ProcessAllItems()
For i As Integer = 1 To Me.numThreads.Value Step 1
Threading.ThreadPool.QueueUserWorkItem(New Threading.WaitCallback(AddressOf ProcessItem), i)
Next i
End Sub
The function "ProcessItem()" is the function that contains the While loop. The control "Me.numThreads" is a NumericUpDown control whose max value is set to 25. My question is...is this a good method to follow? To my knowledge after .NET Framework SP1 there is a max of 250 threads/CPU. However I've read the the threadpool is normally used for processing short-lived tasks. Should I be using background workers instead? If so, how could I start up to 25 background workers during runtime depending on the value of "Me.numThreads"?
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Jul 2, 2009
currently i am using a threadpool that contain a number of thread. This number of thread can be different everytime, sometimes 5, sometimes 10, sometimes 15 and so on (multiple of 5). So now i have it working good by using for loop to queue the thread into threadpool. Now the problems is i do not know how to make the progress bar depending on my threadpool. I want my progress bar to complete only when all the thread are done. After searching google, i found that maybe it can be solve by using AutoResetEvent(false), but after i apply to my program, it still did not work, my program hang at xEvent.WaitOne() method and didnt proceed further, anyone can explain to me how to solve the problem? Or got any other ways? For your information, only 5 threads can be running at the same time as the requirement state so (so i set the setmaxthread to 5 already).
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Mar 15, 2011
anybody familiar with these error? "There were not enough free threads in the ThreadPool object to complete the operation".im calling a web service in my windows application client.
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Jun 5, 2010
whipped up this code real quick which uses a ThreadPool on Form Load to iterate through my subnet and tell me if there's a device communicating at each IP address.
some questions: Why am I able to update BOTH my label at the top AND the listbox, but I'm only using an .Invoke on the Listbox?How can I know how many threads are currently being used while that is executing?
What does the SyncLock do?I'm aware some people don't like the use of Application.DoEvents(). Is it ok to be using it in this instance or is there a better practice?For those wanting to try it out, drag a Label and a Listbox to a new form. Label is called "currentIPTextbox", Listbox is default name.
[Code]...
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Feb 12, 2010
I prepare data to be processed, and saved to file. Since this process is slow, I want to delegate it to a parallel thread, so the main routine can end his work faster. The data is processed and saved to file by the "Sub ProcesarDatos", a routine on his instance of "FileProcessor class".
I call the code this way:
Dim
fp As
New
FileProcessor(DatosDeArchivo, Archivo & ".txt", Me)
ThreadPool.QueueUserWorkItem
(NewSystem.Threading.WaitCallback _
AddressOffp.ProcesarDatos))
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Feb 14, 2012
I am using VB.NET 2008.Every now and then, ThreadPool.QueueUserWorkItem can take up to 500 msI checked the available thread, and it's not 0.What can cause ThreadPool.QueueUserWorkItem to take long sometimes, and how can I make it faster ?
Do While Not TerminateRisk
While qRiskSync.Count > 0
sItem = qRiskSync.Dequeue
[code]....
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Mar 9, 2012
can somebody give ThreadPool example for application thats needs to get information to datagridview from thousands of sources? My application needs to work fast and without freezing and lag, but I cant figure out this threadpool thing. And would be nice if you could add this thing to example that when I set domainupdown value to 25 as example, it sets threads to 25. So its making work 25x faster. I haven't find any good example for this, only some C# examples but they haven't work after i converted those to vb.net.
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Nov 20, 2009
I have a app that gathers and store updated data from a list of websites. My app use threadpool and each thread visits a site within the list and gathers the data. I want to create a stop button to stop/ prevent threadpool from running once it is clicked. How do I go about doing this?
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Jul 1, 2009
currently i am using a threadpool that contain a number of thread. This number of thread can be different everytime, sometimes 5, sometimes 10, sometimes 15 and so on (multiple of 5). So now i have it working good by using for loop to queue the thread into threadpool. Now the problems is i do not know how to make the progress bar depending on my threadpool. I want my progress bar to complete only when all the thread are done. After searching google, i found that maybe it can be solve by using AutoResetEvent(false), but after i apply to my program, it still did not work, my program hang at xEvent.WaitOne() method and didnt proceed further, anyone can explain to me how to solve the problem? Or got any other ways? For your information, only 5 threads can be running at the same time as the requirement state so (so i set the setmaxthread to 5 already).
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Sep 15, 2009
I want to open a VB.net form using a ThreadPool with a maximum of 10 threads. I need to do this because, the form should open based on a live event and i need atmost 10 forms on the desktop at a time. If i open the form on every live event without using a ThreadPool, the desktop will be floaded with many forms. I am using QueueUserWorkItem method of threadpool to queue a method which opens the form. In this queued method, there is form1.show() statement called. But after displaying the form, this method finishes execution and again we have 10 threads available in the system. I somehow want to either keep this method running so that 1 thread is occupied or i want to keep the thread alive till the form1 is closed by the user. I want the 11th form to appear on the desktop, only when any of the existing forms out of the 10 (already on desktop) is closed.
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Jun 4, 2009
When using teh system.threading.timer or threading.threadpool. queueuserworkitem, you are able to pass an object.
But wouldn't the garbage collector destroy the object even before the callback can be executed?[code]...
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Oct 11, 2010
Been trying to implementing ThreadPool over a large and variable amount of data like the following:
public sub ProcessWorkItem(byval state as object)
Dim originalState as CustomStateInfo = CType(state, CustomStateInfo)
'Do stuff
[Code]....
This of course will bomb out if we have more than 64 items/threads being placed on the ThreadPool.
So, how would one process say x amount of items until there are no more items left to process?
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Feb 7, 2010
Every time that I want to make a thread in the ThreadPool I make a stupid little function like Worker_O below.[code]...
Is there a way in VB .net to cast from Sub(i as integer) to Sub(o as object) without making Worker_O? Worker_O is ugly to me.
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Aug 14, 2009
I have a task that needs to be executed many times in a thread, so as to keep my GUI responsive. Right now I'm using the ThreadPool to accomplish the tasks, and it works perfectly. I get all the data I expect back from the threads, life's good. When those tasks are finished, I then fire off another set of threads to accomplish another set of tasks, in the same fashion. The work method of these threads uses a call to RegistryKey.OpenRemoteBaseKey, which does exactly that, opens a remote registry key. The problem is: if the user running the application does not have permission to open the remote registry the call will throw an IOException, but I expect this behaviour because the user does not have permission to do it. However, the call itself can take FOREVER.
I wrote the application initially to use delegate methods and used the WaitHandle.WaitOne() method on AutoResetEvents in a state object I passed to each delegate. I tried the WaitOne method using a timeout, which worked fine until I realized that even though the WaitOne timed out, the thread was still running. This is a problem because (from what I understand) processes are only given a certain number of ThreadPool threads and, once used, they must be finished in order to be released back to the threadpool. In my work method, I also have a variable that can be signalled when the thread should be stopped, but that (obviously) only works on code that I've written.how can I cancel a thread that's stuck on a .NET method? Is there some sort of garbage collection method I can call if I give it a handle?
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May 5, 2009
The error is:
Method 'Private Sub ProcessToolWork()'
does not have a signature compatible
with delegate 'Delegate Sub
[code].....
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Sep 13, 2011
Learning about threads at the moment, barely managing to wrap my head around it, anyway I was wondering how you would go about making threads run sequentially from threadpool if you added them with
threadpool.queueuserworkitem()
In my code currently I know it is not running sequentially as I set it up to call a function and print a number each call. I gather this could be achieved with using synch lock but not quite sure how.
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Jun 28, 2011
what is the best way of detecting if all the threads in the threadpool have finished working,
is there anyway to stop all the threads?
[URL]
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Jun 19, 2012
I'm trying to use a .DLL which Callbacks a Function of my project, but I can't get it to work.
Declaration from .h file of .DLL
void DLL_EXPORT SetEntity_CallBack(bool Active, _
void (*Entity_Callback)(int Site, int Application, int ID, _
[Code].....
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Feb 29, 2012
I am doing one web scraper which loops user set list of urls. Lists can be huge and that's why I need Threadpool for it.
My code so far (Scrape code missing)
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim ThreadingEvents(20) As ManualResetEvent
Dim iCounter As Integer = 0
For Each item As Object In ListBox1.Items
[Code] .....
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Jan 16, 2012
I have a code which adds each line of a textfile to a List(Of String).I have around 1.5 million entries in the textfile. It adds it to the list in like 1 second. However, I'm trying to add all the users to a threadpool to do a certain function. So I try:
For i as integer = 0 to list.count - 1
The list has like 1.5 million entries so the GUI freezes untill it all finishes in like 5 minutes. How can I make it go faster and not freeze the GUI?
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Aug 17, 2009
I have this code obtaining data from a sensor that is sending a string that contains 4 numbers separated by a tab and terminated by an end of line/ I am trying to use an asynchronous callback to get the data over TCP. That problem is that the callback function is not grabbing the complete string. Sometimes it will, other times it gets half in one retrieve and half in another. I need the callback to hold off until it gets a newline character.
Code:
Public Sub readVaisala()
Dim ip As String = "192.168.1.30"
Dim portNumber As Integer = 23
Dim time As Int32 = Now.Second * 1000 + Now.Millisecond
[code].....
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Mar 3, 2011
I have a C++ dll that contains a callback. The callback has one parameter that is passed in and one parameter that is passed out. The parameter that is passed from C++ is a variant. So, we are going from a variant in C++ to an object in VB.NET. The function works. However, It seems that there is a memory leak on the VB.Net side. This must be a Marshaling issue. I have tried to use the MarshalAs Functions, but to no avail.
VB.NET
Declare
Function EnableWriteNotification
Lib
[code]....
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Jan 4, 2011
there is error when i use callback function A callback was made on a garbage collected delegate of type 'skynet1!skynet1.Form1+myCallBack::Invoke'. This may cause application crashes, corruption and data loss. When passing delegates to unmanaged code, they must be kept alive by the managed application until it is guaranteed that they will never be called.
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