C# - Catch Events In Multi-threaded Application That Can Be Watched By Main Thread?
Dec 4, 2009
I have a console application (VB.NET). When it is started, it spawns worker threads to find work in the database and do the task, then look for the next task (A workflow basically).
The problem that I have is that I have my Event Handler in the main thread that spawns the worker threads. Those workers, if they error, raise an event to a public delegate. However my main thread is not detecting these events, and I cannot figure out how to make it. My intention is to do all logging (text/database), email alerts, and restarting the worker to find another task that is not errored. (This will be expanded in the LogErrorMessage routine and such, for now I am just keeping it a simple Console.Writeline so that I can see if the method is being fired or not)
Here is the code around what I am trying to do:
Logger Class:
Public Delegate Sub LogDelegateError(ByVal Ex As Exception)
Public Class EventLogger
Public Event EventError As LogDelegateError
[Code].....
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Aug 27, 2009
Raising events in multithreaded classes?
I am running a class(gamepad handler) that uses many child threads to check for key input and the like then it raises events to my form to sort out the needed reaction, Is there a way to make the event raises on the same thread as the class itself.
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May 17, 2011
I am usng a multi threaded process to fire off a task, but when it is completed I want to make a label visible on the main form (form 1), eg "process completed", however the code I have in place comes up with the following error message;
Cross-thread operation not valid: Control 'lblCompleted' accessed from a thread other than the thread it was created on.
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Jul 23, 2009
how to re-write my application (http:[url]....) to be multi-threaded using the background worker. The use case is something like:
1. User opens a binary file, it can be several Gbytes in size so reading it into memory isn't practical.
2. User can then navigate through the file in 188byte chunks, data is read from disk, decoded, and displayed for each chunk in turn.
3. User may want to search for some data or build a report. This will involve repeating the read, decode, display, function multiple times. During this looping the GUI stops responding and there is no option to cancel so I want to make it multi-threaded. So, is it safe to open the file in the GUI thread and then read from the file in the background thread? I currently use something like this to open the file once:
Dim fi As New FileInfo(filepath)
fs = fi.OpenRead()
and then in a separate sub multiple calls to:[code]..........
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Jul 26, 2010
I have a thread in an application which calls a sub routine Main(). The Main sub routine in turn call several sub routines/functions from with the same module,several different classes in the same application. Also some sub routines/functions call routines from a class library. Now say the routine/function in class library goes into a infinite loop and never returns. I would like my thread in the application to raise a event and display message to the users about the infinite loop. I am giving some sample code for the application.
Imports System.Threading
Module VMain
Public gbSuspend As Boolean
[CODE]...
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May 21, 2010
I have 2 classes, one is frmMain a windows form and the other is a class in vb.NET 2003.
frmMain contains a start button which executes the monitor function in the other class. My question is, I am manually adding the event handlers -- when the events are executed how do I get them to excute on the "main thread". Because when the tooltip balloon pops up at the tray icon it displays a second tray icon instead of popping up at the existing tray icon. I can confirm that this is because the events are firing on new threads because if I try to display a balloon tooltip from frmMain it will display on the existing tray icon.
Here is a part of the second class (not the entire thing):
Friend Class monitorFolders
Private _watchFolder As System.IO.FileSystemWatcher = New System.IO.FileSystemWatcher
[Code].....
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Jan 21, 2012
this is my first post and my knowledge of Visual Basic is still in its infancy (this is my first real attempt at app that is any use) however I am trying to develop an application to delete user profile and home directory folders.
I have the application working but the problem is with the application hanging (I understand this to be due to it running as a single thread and the main form gets ignored while the deletion is occuring) during the deletion process, I have tried various ways to resolve this such as starting the delete procedure as a new thread but cant get it to work without the hang.
[Code]...
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Feb 10, 2012
I have two applications. For performing certain functions, i run a second exe, via a process, and wait till it is complete (exited) to continue with my main application. I run through many repetitive functions on different files.Everything runs fine however, when i am doing a run and it is on the x loop number, the main application seems to halt the secondary process exe. I can only assume this is what is happening as, if i close/stop (not pause) my main application in VB, the second exe continues from where it was halted until it completes.
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Jul 21, 2011
I'm trying to run a multi-threaded console app in VB and am having thread cross-over. Basically I want to run 5 threads, have them continually access a queue, process, and repeat until there's nothing left. When all threads have processed I want them to do something else.I'm attempting to use SyncLock to prevent multiple threads from accessing but it does not seem to be working.[code]
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Jul 14, 2010
This is my attempt to create a ObservableCollection in VB that is WPF thread-safe. Can you think of any problems it may have?
[Code]...
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Aug 10, 2011
I'm trying to teach myself how to create multi-threaded applications in Visual Basic Express 2008. I found a page headed "Creating Threads and Passing Data at Start Time" in the Library here -
[url]
However, I can't get any of the examples on that page to run. I pasted the code from an example into a new Project in my IDE but pressing F5 just gives me build errors which I have no idea how to resolve. It's probably something trivial but I can't progress with these examples. Please can somebody tell me what I need to add to get them to run
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Apr 5, 2011
I am drawing five images in a row. The five are the same thing at five different zoom levels. Therefore, only one of the five will be displayed at any one time, but the others have to be there because there can be over 100 images being displayed on the screen at any one time, and each drawing is quite complicated. If I were to draw them all on the fly, then zooming would require that all 115 images be recreated and redrawn with each zoom. That's painful. To avoid that, I draw all five zoom levels of each image. When the user iteracts with the form, they will be interacting with, at most, two of the images, so when they interact with the form, only two of the 115 have to be redrawn, though those two have to have all five zoom levels drawn, for a total of 10 images.
[Code].....
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Nov 11, 2010
I've just completed my first multi-threaded task under windows. Historically I am a VMS Engineer. You could multithread in drivers in VMS but VMS never had formalized threads. Which means it never had applications threads. Threads will become increasing important in the future. I thought this maybe a good time to discuss them. Not having access to sources hurts in terms of the amount of depth one can achieve in Windows. Some of the topics for this thread might be...compute resource regulation, how to do multi-threading and of course things to watch out for.
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Mar 12, 2011
I have written a rather complex dll for processing a large volume of data (~4,000,000 records) from an Oracle database. It works well, but takes about 23 hours to run.Since I wrote the code fairly compartmentalized I realized that there are 6 routines that should be able to run concurrently, and I have a multi core processor,I decided to try my first multi-threaded implementation.
In the routine I am working on I am doing no I/O everything is in memory in variables. My data is already in dataTables and hashTables. Most of the data is defined as private in the class scope, but no conflicting updates should happen because the code segments works very distinct portions of the dataTables.The concept is simple, I have 2 routines that need to complete before launching my threads, and one routine that needs to run after all of the threads have completed. Here is what I am trying;
ProcessDXDate()
ProcessHistology()
aryThreads(0) = New Threading.Thread(AddressOf ProcessLaterality)[code].....
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Oct 22, 2009
I'm using VB.NET. I want to build a large List (Of MyClassOrStructure) that becomes static after its initial population.I'm going to have multiple threads that need to iterate through this list to read data (no writing, inserting, or deleting)
Are there any very bad things that I need to keep an eye out for?
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Feb 1, 2011
I am trying to create a proxy checker. This is my first attempt at multithreading and it's not going so well, the threads seem to be waiting for one to complete before initializing the next.
[Code]...
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Nov 14, 2009
I'm having some trouble creating a multi-client server / client thingy.So far, I've used Atheist's example and allowed the clients to successfully transmit information.However, whenever I send more than 1 message to the server at the same time, the server bugs up and does not receive the message at all. I suspect it has something to do with the DoRead method reading from both clients and stuffing it up or something.
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Mar 19, 2012
I've got a multi-threaded app - that is using a global COLLECTION of objects.I'm starting to think that objects - when copied to objects - are really just reference pointers to the "single object" in memory - as they would be in JAVASCRIPT (too many languages At any rate - this code - when taking the object from the collection to work with is it making a new object to play with or is it working the single object that actually resides in the collection?
[Code]...
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Sep 30, 2009
I'm trying to get a VB2008 multi thread application working that connects to a local server program using sockets. Server requests for this particular system can be more quickly handled by a number of connections, so I've written some code to run any number of data request threads that I choose. The problem that I'm having is that the data returned from the server is getting mixed up and is often returned to a different thread/socket than the one that requested it. Other than that, it seems to work okay. If I use just one thread, then the system works as it should. Pls. see incuded code, which is heavily edited to remove all the other fruit salad. Is there any way to set up the sockets so that data returned to the socket/thread that requested it?
Module StaticDeclarations
Public WithEvents g_SD As New SocketDataClass(New MainThread.MTCallback(AddressOf MainThread.MTResultCallbackSub))
Public WithEvents g_MT As New MainThread(New SocketDataClass.SDCallback(AddressOf SocketDataClass.SDThreadResultCallbackSub))
[code]....
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Jul 25, 2009
I have an application with 4 threads. (GUI, Controller, Producer, Consumer) The GUI is self-explanatory. The controller starts the producer and consumer threads after some intial setup. The producer creates items and places them in a free slot in a "ring buffer". The consumer takes items from the "ring buffer" and writes them to disk. The producer creates items at a much higher rate than the consumer. The consumer is IO heavy and IO bound. Currently I am checking a variable in each ring buffer slot to determine if it can be written to.
if Slot.Free then
Write Slot.Data To Disk
end if
I am not using lock/synclock instead I'm just reading / writing the value of the slot's "free" variable. I don't believe that is correct even though it is a volatile read/write. Is there a better method to read/write this variable? The variable is of type "integer" and is either 0 or 1.
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Oct 1, 2011
I've been writing multi-threaded applications for a couple of years and have started reading about the Task class. It looks like it handles mutex and synchronous/asynchronous threading in an easier to follow fashion. I was just wondering if you the community likes writing threads the old way or the 4.0 tasking applications. Lastly, I thought multi-threading was parallel computing. But I was reading that there are special task etc. parallel functions.
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Feb 23, 2009
My application takes the currently logged-in user and uses an a DirectoryServices.DirectorySearcher to pull a few additional detail about them (some properties we have stored in a few custom AD fields, as well as their email address). This works great, though I've always though it was a little slow - my single-threaded code could only make about 2-3 requests/second to AD.
The real problem came when I moved this code to a web server. With multiple simultaneous users, the number of requests/second jumps greatly, and the LSASS.EXE process pegs on my server. I've checked the domain controllers, and they're just fine - the bottleneck is clearly on the application side. I suspect that what's slowing my down is the NTLM/Kerberos challenge/response, and the number of simultaneous requests pegs even the multi-core processor.
Our network policy doesn't allow anonymous reads from AD, so that choice is out. Also, I've tried every member of "AuthenticationTypes" (in the example, I'm using .FastBind), but they all seem to have about the same throughput rate with the same load on the processor.how I might work around this restriction and lower my demands on the processor? Here is the code I'm using - pretty straightforward:
Dim sPath As String = "LDAP://" & stringUserDN
Dim entry As New DirectoryEntry(sPath)
entry.AuthenticationType = AuthenticationTypes.FastBind[code]......
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Oct 12, 2009
I have written a small GUI based vb.net program that speaks to embedded devices via the com port. The GUI code contains a class which all communication to the embedded device is handled through (com port device, communication protocol, parsing info, holding device related info after each read).That class is called EDComms.
I wanted to add a thread so that the EDComms object could run in the background and report back as it downloads logs files and such (It can take a while to get log files from the device sometimes).So. Should I have EDComms inherit from backgroundworker thread? Or should I have a background worker thread as a member of EDComms?Right now I am going with the second choice. The only thing I have to do now is write a func for registering two delegates from the GUI for notifying task progress, and notifying task complete.Or is there a better choice than these two I have presented Perhaps have the thread as a member of the GUI?
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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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Jun 22, 2010
I have an Excel based algo-trading app that needs to take in lots of real-time data, and make trading decisions based on the calculations driven by the data. It is not one of those "read-only" stock ticker kinda spreadsheets.I created a COM object with VB.NET that runs in its own thread space which collects data from a socket, and when the data is read it raises an Event with data attached. In Excel VBA, the event handler parses the data, puts them to the right places on the spreadsheet to feed calculations (so far it sounds like a stock ticker app), and then, based on the results of the various calculations it does something.The problem is that when the user starts to click around the spreadsheet while there is large amount of data coming, the event handler's cell updating breaks apart. If the app is left alone without user action, it stands well. My frustration comes from not understanding what happens to the main thread when a user clicks around. Either the event handler blocks the user action, or the user action blocks the event handler (under which case I will put in some queuing facility). But I just don't see how user action can break the code (like causing VBA to stop executing)
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Mar 5, 2009
I'm using the MAPI code by Dave Brooks.I am attempting to programatically send out a Crystal Report that is generated.When I run through the code without threading everything runs fine. The problem is when I use threading I get the return error "General MAPI failure [2]".I have never used threading before and understand that there are dangers involved. Can anyone provide any insight into this issue? NOTE: I've removed exception handling to make the code clearer.[code]
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Mar 4, 2009
I'm creating a Client Server application which involves theServer running some scripts in clients and getting back results in an automated way. In Server, other than Main thread, i have 2 worker threads, a) one monitoring response from clients and b) the other scheduling next available job to respective client which executes that job. The issue here is ,I want these worker threads to write the status of their work in the UI(which comes under Main Thread). Also i need to write things in worker thread in a Data table and Rich Text Box in Main thread. But, I can't do so, since it has been blocked to access one thread's function or property directly from others. Is there any work around to do this?
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Jun 5, 2011
I'm having a small issue; I start a process and when that process exits, I raise an event which removes a control from my form.It all works perfectly until the part where I want to remove a control from my form. Visual Studio gives me a cross-thread exception even though I'm programming single threaded.
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Nov 12, 2009
Preface: I know this is an unusual/improper way to do this. I can do this with a "real" ShowDialog(), background worker/thread, and so on. I am trying to do specifically what I describe here, even if it is ugly. If this is impossible for X reason, I have created a fancy progress dialog for some of our long running operations. I need to have this dialog shown on a new thread while having processing continue on the calling (UI in most cases) thread.
[Code]...
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Aug 4, 2011
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
[Code].....
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