.net - Events Raised By BackgroundWorker Not Executed On Expected Thread
Mar 22, 2010
A winforms dialog is using BackgroundWorker to perform some asynchronous operations with significant success. On occasion, the async process being run by the background worker will need to raise events to the winforms app for user response (a message that asks the user if they wish to cancel), the response of which captured in an CancelEventArgs type of the event.
Being an implementation of threading, I would have expected the RaiseEvent of the worker to fire, and then the worker would continue, hence requiring me to pause the worker until the response is received. Instead however, the worker is held to wait for the code executed by the raise event to complete.
It seems like method I am calling via the event call is actually on the worker thread used by the background worker, and I am surprised, since I expected to see it on the Main Thread which is where the mainform is running. Also surprisingly, there are no cross thread exceptions thrown.
I implemented the communication between two classes by using events in VB.Net.Now I want to store (record) all events that occure and to re-raise (replay) them again later.
Here is what I have already:
Class1: Public Event Button1Pressed(ByVal sender As Object) Private Sub btnButton_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnButton.Click RaiseEvent Button1Pressed(Me) End Sub
[Code]...
I could add another handler to the event I want to record, but then in the handler I only get the parameters that are passed to the event and not the event itself.Another thing I don't know how to solve is, that I can't raise an event from an extern class.
I'm currently designing an assembly that will be used by third parties. One of the classes has a long process of TCP connections and it informs about its process using events. For example
''# Do stuff that takes some time RaiseEvent CompletedFirstPartEvent() ''# Do stuff that takes some time
[Code].....
What I've seen if that if the handler of one of those events takes too long (or even worse, it blocks) I can have timeouts and it's hard for the developer to see that one class is not working fine because his handler is taking too long.
I was going to fire the events in a new Thread to avoid this issue but this looks strange to me because I've never seen something like that, what I've seen until now is the developer spawning a new Thread if his handler was going to be timeconsuming. So the question is:
What would you do? Create a new thread or force the user to create his own thread? (Or is -there a better approach that I don't know?)
I want to raise an event from a non-UI thread where the event will be handled by the UI. Currently, I have to use .Invoke in my methods (which updates UI) called from the event.
How can I raise the event, similar to Background Worker's progress update event, where I don't have to specifically do an .Invoke for UI updates?
Do I wrap the event with a delegate or something? Sample code will be fine though, if the explanation was tedious.
A BackgroundWorker thread can pass data to the primary thread. It does it via the RunWorkerCompleted and ProgressChanged events, which I believe run in the primary thread. I would like to encapsulate the BackgroundWorker control in a class so that I can instantiate it more than once. But I don't know how the BGW can then communicate with the primary thread. If the BGW control is within a class, it does not have access to the properties outside the class. In that case, how can the BGW pass data to the thread that instantiated it?
I'm working with BackgroundWorker, I want the BackgroundWorker do the retrieval process of data from database while the user can still do another task on the form. The problem is, after retrieving the data, I can't seem to access the ListView in my Form from the DoWork event of BackgroundWorker, I will populate that ListView using the data I've retrieved.
Consider this example, this is how I'm doing it:
Public Class Test Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
How do run processes synchronously from a thread or backgroundworker thread? Is it even possible?We have program that allows the user to download several files from a remote server, compress them, and then email the files.It has several long running processes that must run in order. We want these to run on a separate thread so as not to make the form unresponsive. Does a way exist to do this? We attempted a rather clumsy way of approaching this problem by using background worker threads. When each thread is completed and returned back to RunWorkerCompleted, we start another background worker thread and repeat the the next process. It works somewhat but seems to take a lot of resources to run.
I'm working with vb.net 3.5SP1 /VS2008. I'm familiar with windows threads from C++ but I didn't do it since the 90s.I have 5 threadpool calls (ThreadPool.QueueUserWorkItem) that do some complex work (they read info from different web pages, regular expressions, etc) and each updates different columns in a data-grid view. They pause for 1 second between each web read with thread.sleep (not to overload the server). My issue is that some of the threads do not complete. I get for example 3 results when I should have 8. Sometimes it works fine. This is an older 3.0Ghz HT machine, I want to test it on the lowest common denominator(and that is all I have ). I tried using Monitor.Enter(ListView1)it seems to help but it is hard to tell. I tried using the thread debug window but it is not really helpful, it seems do disappear during execution. If I remove the threads I always get my data. I'm wondering if something is being blocked? Is there a way to debug this?
Also, does thread.sleep(x) stop all threads or just the thread that the statement is executed in?
im sorry if this has been asked before.but i couldent find it in my first look i have a form that runs a query on a mysql database but as it runs the query the form stops responding till it finishes sooo i had the smart idea of putting it in a back ground worker..
GREAT i thot i had it working it all seemed to go greeat then i noticed when i try to change the label text on the form to corispond to the info it got... it wont work it give me a cross threading error....
how to cross thread between the back ground worker and the origial form..
I have some classes right now that I have that I reuse for Client/Server programming. I'm using Thread in these classes though for monitoring for things being written to the network streams and stuff like that. I'm just not sure if I should be using the background worker class instead. I'm also using TCPClient and Listener classes, should I be using sockets directly? I guess it would all depend on the flexibility I would need in a given application's specs.
I am writing an 'Admin Console' that accesses hMailServer via its provided COM interface. I am using Visual Basic 2010 Express. In one procedure, it scans for the whole accounts. Because it's a lengthy procedure, I shove it into a set of BackgroundWorker threads.
First result: A maximum of 19 simultaneous threads, with 36 seconds total time.Then I rewrote a time consuming thread initialization code segment, and managed to reduce the time required to approximately 14 seconds... but the thread count now hit 330 threads!Will that huge amount of threads be detrimental? E.g., causing out-of-memory exceptions &c. ?
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?
I have a background worker that's checking the status of four services on a remote server.This is setup on a timer (5 Seconds) as below. For some reason it's hanging the UI thread causing the application to 'lock' for a second each tick, I cannot work out why?!
Private Sub ServiceTimer_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ServiceTimer.Tick _ServiceBGWorker = New System.ComponentModel.BackgroundWorker()
Well to simplify it, whenever I use sendkeys from a background thread it just doesn't work. I even created a textbox, button, and backgroundworker with the following code:
Public Class Form1 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
I'm running some tasks on a BackgroundWorker thread and needed to display the current tasks in a label.Before adding the label, the tasks were completing just fine and the UI was responsive.Once I added the labels, the UI has become unresponsive. The issue, I believe, is the Invoke property.I've declared all my tasks, including the updating, in a sub and am getting the Invoke property of the label each time, in order to set the information.The following is an example of what I'm doing:
VB.NET Private Sub Test()If lblTask.InvokeRequired = True Then Dim mi As New MethodInvoker(AddressOf Test) lblTask.Invoke(mi)
I have designed a class for posting data to server, which is a time consuming task so that i have used background worker in my application. instead of repeatedly using backgroundworker in my application, i decided to add it to my class and generate two events PostWorkerReportProgress, PostWorkerComplted for my application
i have lurked on these forums before and finally signed up..i have a situation that, after days of searching the web, i have not been able to come up with a solution for.i have to fire off a function that takes a large amount of time (writes to database, creates files, etc etc)this function is a non-shared function of a class. if need be i could make it Shared.[code]the code works great, but what i need to be able to do is update a form with a progress bar as the job is processing.all of the examples i have seen that do this are being called from within a Windows Form and they access the form directly - i cant do that in this case. my form needs to be 1 form for 1 job being executed - can process multiple jobs at one time and thus i need multiple forms.i have tried making the form part of my delegate class but since it runs in the same thread the effect is it "freezes" until the job is complete.i have just started looking into using a background worker but again, all examples i have seen use the component as part of a form - that wont work for me.
I'm using the following to check the state of checkboxes and then activate some public subs based on the checked state of the checkboxes:
vb.net Public Sub TestSub() If Me.CheckBox1.InvokeRequired Then Me. CheckBox1.Invoke(New MethodInvoker(AddressOf TestSub)) Else Begin() End If End Sub
Within the Begin sub, I have code that performs specific actions and then updates a ListView with that information.As far as I can tell, the actions are being performed, but the ListView isn't being updated with the info.I'm calling the Test sub from a seperate form, within the BackGroundWorker's DoWork event.Would I have to check the InvokeRequired property of the ListView as well?I'm looking more into the documentation of the BackGroundWorker.
I have an application that interacts with third party COM objects. A method of the COM object that I call will sometimes stop responding. I created a Backgroundworker thread to call the function and I am trying to monitor it from my main thread to kill it if it hangs. I have additional code (not supplied) that tracks the processing time using system.timer from the main thread and I raise an event if it exceeds my threshold (this part is fine). This is when I want to kill the thread and stop code execution. The problem is.. if I use the cancelasync method it will just pend since the code execution is stuck on the function call.
The particular function call in the code snippet that hangs is "objCOM.SendDataToServer()". It typically takes 1-3 seconds to return, but if it gets no response it will just hang indefinitely and won't return at all (no errors just hangs).. there is no timeout... and since I don't have access to the source function I cannot supply one. I tried the .dispose() method of the thread, but apparently that doesn't kill it and neither does cancelasync. I just need help figuring out how to KILL this thread so I can reset the server connection and call the function again.
Public Class COMobject Private objCOM as new acs.manager Public Sub CallComFunction()
Is it possible to create a WebBrowser control in a background thread in BackgroundWorker?
Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork Using web1 As New WebBrowser[code].....
Does anyone know a way to create a background WebBrowser? I would like to do it to extract info from websites then spit out the various HTML DOM arrays
I have a form with Check Boxes on it and a second form that holds functions and a Backgroundworker.When a button is pressed on the first form, the second form loads and then runs the functions that relate to the appropriate Check Boxes.Doing it this way causes the second form to become inaccessible. I decided to run my code in the Backgroundworker's DoWork event and then call the RunWorkerAsync method in my form's Activated event. Before using the Backgroundworker, everything worked fine and now it doesn't.I assume the issue is with the Backgroundworker not being able to access controls on another thread.In debug mode,it automatically throws an exception, but doesn't error out when using the Release version, making me assume it's a legal call. But, if it's a legal call, then why can't I access the controls?
I have a backgroundworker that is downloading data from different webpages and process them to a datagridview.I get the Cross-thread operation not valid error on the first For loop.
Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork dim i as integer tot = (numPostnrTo.Value - numPostnrFrom.Value) / 10
