C# - Multithreaded Drawing In .NET?
Jul 24, 2010
(Edit: to clarify, my main goal is concurrency, but not necessarily for multi-core machines)
I'm fairly new to all concepts on concurrency, but I figured out I needed to have parallel drawing routines, for a number of reasons:
I wanted to draw different portions of a graphic separatedly (background refreshed less often than foreground, kept on a buffer). I wanted control about priority (More priority to UI responsiveness than drawing a complex graph). I wanted to have per-frame drawing calculations multithreaded. I wanted to offer cancelling for complex on-buffer drawing routines.
However, being such a beginner, my code soon looked like a mess and refactoring or bug-fixing became so awkward that I decided I need to play more with it before doing anything serious.
So, I'd like to know how to make clean, easy to mantain .NET multithreaded code that makes sense when I look at it after waking up the next day. The bigest issue I had was structuring the application so all parts talk to each other in a smart (as opposed to awkward and hacky) way.
I have a preference for sources that I can digest in my free time (e.g., not a 500+ pages treatise on concurrency) and for C#/VB.NET, up to the latest version (since I see there have been advances). Basically I want something straight to the point so I can get started by playing with the concepts on my toy projects.
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Jun 3, 2012
draw individual pixels, without resorting to drawing a line and setting it's length to 1. Is there an actual ability to draw a pixel that is just 1 pixel big?
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Feb 28, 2012
As the question states, can a shared method of an object be multithreaded? I don't quite having threading down in my skillset, otherwise I would test myself. On the other hand, I am involved in designing class that could be part of a multithreaded application in VB.Net.
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Mar 16, 2012
I don't want it to be MultiThreaded. i read some tutorials and have a good idea. but unfortuantely all the tutorials on the web write code without explaining. so is anyone here has a good knowledge with Chat application ? I know it's about sockets and stuff but i just need an explaination with code ;)
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Aug 20, 2009
I am using Visual Basic 2008 Express Edition and I want to create a multithreaded application.
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Oct 29, 2008
I have a background thread that waits for data to come in. When data arrives, it fires off a call to the GUI thread.All works just peachy, except if there's ever a run-time exception in the GUI thread. If that happens, the debugger always halts at the point in the worker thread that called the GUI thread. It never shows the proper line that the error occured on.How do I get the debugger to stop at the error in the GUI thread?
Here's the pertinent code from the worker thread:
Code:
Public NotInheritable Class UIThreadMarshal
Private Shared _MainForm As Form = Nothing
Public Shared WriteOnly Property MainForm() As Form
[code]....
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Oct 14, 2010
After trying to make an application multithreaded, almost towards the end of the processing of 10,000 records, I get a webexception - operation timeout.Now it seems to process around 8000 records just fine, for each record it is also doing some business logic and with it, performing a call to a webservice.
without threading, its fine - no problems. with threading, we hit the issue.so there are 10,000 records to go through. this is of course slow when done in sync mode (Single threading) but much faster when placing items in the threadpool and waiting until completion.
im not sure exactly why the problem happens. how should I debug this when multithreading? its just odd that for around 3/4 of records, the calls are doing very well, then on the last bit to go, it bombs out.
again - no issues when single threading.update: seems to be after around 1000 records that have been processed that it seems to happen.the application calls out to an internal webservice which then does the direct callout to the "outside world" webservice. The internal webservice does some caching but shouldnt have any effect really.
The outside service it is calling is httpBinding. ReceiveTimeout is set to 00:10:00 (10 minutes) and bypassProxyOnLocal="false"im still not quite understanding why it would timeout after 1000 records because it seems to process the others just fine and does come back (or so it seems) when its making a call to the service
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Dec 26, 2010
I'm trying to build a multithreaded app but I couldnt find anything on google on how to catch the value that the lambda function returns.
ThreadPool.QueueUserWorkItem(New WaitCallback(Function() As Integer
Value += 1
Return Value
End Function))
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Mar 8, 2010
In a multithreaded application. I have a bunch of function that loop through a collection to read the information. I also have a bunch of function that modifies that same collection.
I'm looking for a way to isolate all the read and the write together. I don't want a write to be done while a read is in progress. I was thinking of using SyncLock on the collection object but this will block multiple read trying to work in parallel.
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Mar 20, 2009
I started throwing exceptions on a multithreaded application, and got a mess.There is a good tutorial on managing exceptions in multithreaded applications?
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Nov 16, 2009
I have developed a multithread Windows Application that requires to print various Docss/rpt's off. The problem is I get a "Load Report Failed" error message when creating a new instance of my embedded crystal report.
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Aug 2, 2010
Given the code, ss there a way to propagate messages send from any of the multithreaded chat client to all the other chat client:
First the main will call startClient:
Public Sub startClient(ByVal inClientSocket As TcpClient, _
ByVal clineNo As String)
[code]......
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Jul 5, 2011
I have an application using taskfactory that creates multiple tasks which insert records into the same table in a database. I have jobs that cleanup the table when it gets too large and have the execution time-out set to 0 in options in sql server management studio. I keep getting the following error on the tasks when trying to do an insert using a stored procedure and set an exception handling process to sleep and try again. This does not help as it seems it timeouts on almost every attempt.Not sure how to handle this and ensure the table handles all these inserts. Tried including connect timeout = 600 in one of the processes connectionstring but this did not help.Also set sqlquerytimeout value in registry to 90 but still not helping.
ERROR: timeout expired the timeout period elapsed prior to completion of the operation or the server is not responding...
could not see the details of the error since visual studio 2010 debug options had to be set that way, but I will set a responsestream and capture but I rebooted sql server and somehow everything is fine now...not sure why.
Errors have reoccurred.
at System.Data.SqlClient.SqlConnection.OnError(SqlException exception,
Boolean breakConnection)
[code]....
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May 16, 2010
I have been reading through lots of sample code and explainations regaurding the uses of Sync lock in multithreaded programs but still am a little fuzzy on this.
Am I correct in assuming that if I have two or more threads running the same procedure which has a sync lock on a shared resource that the first thread to call the lock will complete its update of the resource and any of the other threads to try and lock this object would just wait in line until it is released by the first object?
I am also a bit fuzzy on what is actually locked by the sync lock.
Lets say I have code that uses sync lock and the object specified is the current thread. Does that also lock the shared resources that are referenced within the sync lock block or would I need to use another method to do this?
What if my shared resourses were all in another class and I issue a sync lock on that class before I try to modify the resources would that be the proper way to go about it?
And last but not least is there any need to use sync lock when the shared resource is in effect read only [meaning the program will read the value but will not change it during runtime]
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Apr 17, 2011
I've finally gotten multi-threading working on my application, but now I'm having trouble showing forms when I need to. I currently have three threads in my program: one for updating a textbox, one for transferring files, and one for displaying forms. Here's a snippet of code from my program:
[code]...
I'm getting the error: Control 'frmXCopy' accessed from a thread other than the thread it was created on. I know what this means, but I can't find a way to make the ShowForm Sub run off of the main application thread.
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Jul 11, 2011
I have a multi threaded app that writes log to file. occasionally, saving fails using this code:
Friend Sub SaveToText(ByVal FileName As String, ByVal Text As String)
'// create a writer and open the file
Dim objLock As New Object
SyncLock objLock
Dim tw As TextWriter = Nothing
[Code] .....
The error message I get:
The process cannot access the file 'error.log' because it is being used by another process.
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Feb 18, 2012
I need some code to draw a resizable, draggable rectangular cursor (or selection box) on a picturebox. I found some excellent code (albeit rather old) that does just that, but on a form rather than a picturebox. I have tried converting the code - basically moving things to the picturebox events (Paint, MouseDown, MouseMove etc). It nearly works but leaves a trail behind it when you move or resize the cursor. In other words, the selection rectangle is not being erased before being drawn in the new position.
Is there some fundamental difference between drawing graphics on a form and drawing on a picturebox that would cause this behaviour? Something like, when you invalidate a form and cause a redraw it erases what you did last? If not, then I just need to dig a bit further and work out how the cursor is being erased from the previous position.
Here's the original code that works fine on a form:
Private DragRect As New RectangleF(20, 20, 100, 80)
Private Adornments(7) As RectangleF
Private MouseInRect As Boolean = False
[Code]....
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Oct 31, 2011
I have a linq query which loads approx. 1000 lines into a variable, during that process I want to display a progressbar, not necessarily stating the percentage, can be marquee style, doesnt matter.
This progressbar is on a modal form to precent the user from interacting with the app for the time the query's running.
[Code]...
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Feb 1, 2010
I would like to implement a mulithtreaded crawler using the single thread crawler code I have now. Basically I read the urls from a text file, take each one and crawl and parse it. I know how thread basics of creating a thread and assigning a process to it but not too sure how to implement in the following way:
I need at least 3 threads and need to assign a url to each thread from a list of urls, and then each needs to go and fetch it and parse it before adding contents to a database. [Code] Now the code maynot make sense but what I need to do is add a unique url to each thread to go process.
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Jun 21, 2010
Say I have 3 Buttons, labelled: Unit 1, Unit 2 and Unit 3. When I click on any button I want a drawing of that unit to appear on screen at a pre-specified starting point. Thereafter when I press any other one of the buttons the unit drawings appear alongside each other in a line. So I could end up with:
[Code]...
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Aug 17, 2009
With this line...
If PictureBox1.Image = My.Resources._2star Then
I get this error: Operator '=' is not defined for types 'System.Drawing.Image' and 'System.Drawing.Bitmap'.Is there another way to say = with images?
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Sep 11, 2011
I'm trying to make a program of mine into a multithreaded application, but I've hit a pair of snags that I documented in the following code. I can expand this stub into a more efficient version of my existing application.
[Code]...
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Jul 5, 2011
Id like to say that I have a disk to be searched. The same task was run was multithreaded on an extreme x6800 and a new Lenovo W520.
The filescan on the x6800 dual processor extreme searched 1788 files in 477 seconds. The same search on a new WS520 took 82 seconds to search 2149 files. Multithreading works and the X6800 has an ssd and the lenovo has a standard mechancal disk! The task was diskbound.
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Nov 23, 2011
I would like to make a multi-socket TCP server (to accept multiple clients at the same time).I'm working with Visual Studio 2005 Express, maybe that's why files on CodeBank don't work..I found on the web an example about MultiThreaded Server Socket programming, but this is done for "Console application" in this way:
[Code]...
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May 23, 2009
Is it possible to convert an object form System.Drawing.Graphics to System.Drawing.Image?
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Jan 21, 2010
Here is my favicon code
Dim oURL As Uri = New Uri(e.Uri.AbsoluteUri)
Dim favicon As Image
If oURL.HostNameType = UriHostNameType.Dns Then
[code]....
The error is Value of type System.Drawing.Image cannot be converted to System.Drawing.Icon Is it even possible to make the favicon be the icon of the form?
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Sep 19, 2010
I'm trying to work out how i can make my multithreaded app stop at a certain point and wait for the user to type something into a text box and click ok. It must then carry on and when a different thread gets to that point it stops again and waits for the user to input some text again.
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Apr 3, 2009
im using an MDI parent form and MDI Child. how can i print the image that's inside a picture box that's inside the Child from a button that's on the Parent?when i try to use print preview or print dialog, i can't get it to recognize that the document is the picure inside the picture box. i've looked up this error message:Value of type 'System.Drawing.Image' cannot be converted to 'System.Drawing.Printing.PrintDocument'.[code]
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Mar 18, 2010
I have written a multithreaded crawler and the process is simply creating threads and having them access a list of urls to crawl. They then access the urls and parse the html content. All this seems to work fine. Now when I need to write to tables in a database is when I experience issues. I have 2 declared arraylists that will contain the content each thread parse. The first arraylist is simply the rss feed links and the other arraylist contains the different posts. I then use a for each loop to iterate one while sequentially incrementing the other and writing to the database. My problem is that each time a new thread accesses one of the lists the content is changed and this affects the iteration. I tried using nested loops but it did not work before and this works fine using a single thread.
Here is my
SyncLock dlock
For Each rsslink As String In finallinks
postlink = finalposts.Item(i)
[CODE]...
Finallinks and finalposts are the two arraylists. I did not include the rest of the code which shows the threads working but this is the essential part where my error occurs which is basically here postlink = finalposts.Item(i) i = i + 1
ERROR: index was out of range. Must be non-negative and less than the size of the collection. Parameter name:index
I tried copying it to a new list but dosent work.
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Apr 9, 2012
I am making a web browser using geckofx. I have put the favicon in a picture box but I have changed my mind and now I want it as the form's icon. The code for the favicon is:[code...]
The favicon works fine in the picture box but i think it will look better as an icon. If i change the line Me.PictureBox1.Image = favicon to Form1.icon = favicon I get the error Value of type 'System.Drawing.Image' cannot be converted to 'System.Drawing.Icon'. How can I get this to work?
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