Question Atomic Operations In .Net Or Checking File For Lock?
May 17, 2010
I would like to know if there is any opportunity in VB.Net to use atomic operations. Or Maybe there is an opportunity to check if a file is allready in use or opened.The reason why I ask is because I got a little application that I would like to log its actions. As the applications uses threads the method for writing the log file sometimes is trying to open the log-file more than once which leads to an exception.
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May 28, 2010
I'd like to write a small app to get the time from an "atomic" clock -- I believe the UTC time and then compare this against the system clock.
So far I've been able to get the system time details with the code below but just cannot figure out where to start on getting the atomic clock(s) time.
I did Google this for examples and have not found anything useful, I did find a list of atomic time servers @ the following URL and realise I have to connect to NIST Internet Time Service clock
Dim localDirect As Date = Date.Now
Dim utcDirect As Date = Date.UtcNow
Dim localFromUtc As Date = utcDirect.ToLocalTime()
[Code]....
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Apr 18, 2011
So I'm developing a program were, given some data by the user, the prorgam inserts some records into a database. To insert individual records in different tables I use either the standard INSERT method provided by the Table Data Adapter or a custom Insert Method when I want to insert something slightly differently.Sometimes the user would press a button and an operation where different records in different related tables are inserted. Since each Insert is handled individually for by the DataAdapters of each table, how can I manage to bring the whole thing to an atomic transaction way? I mean, let's say for example the User inserts a new Document in the system, the document has one or many Editions. How could i do something like: if the document was not created properly, then do not insert the editions.
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May 18, 2011
I want to perform two hashing operations concurrently on a single file, without reading the file twice. Is there some way to share the FileStream between two synchronized hashing threads? For example:
Dim Stream As New IO.FileStream("...", IO.FileMode.Open)
Dim HashA, HashB As Byte()
Dim A = New System.Threading.Thread(Sub()
[code]....
Maybe some way of caching a stream? Trouble is, I don't want the entire file in memory at once (it could be many gigabytes in size) and I don't want the file read more than once, due to speed issues. I want the file cached only sufficiently to ensure that both threads can work.For example, suppose at some point in time, thread A had read 100k of the file, but thread B had only read 20k of the file. The portion of the file between 20k and 100k should be cached; but then progressively forgotten as thread B catches up. Then again, if thread B is too slow, we might still end up with hundreds of megabytes being cached.Maybe thread A should be made to wait while thread B catches up. Maybe the ReadByte() function of the stream should block for a while if one of the threads is too far behind?
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Jun 5, 2011
The file operation calls are returning before they are actually complete, or the disk is being cached somehow. What is happening here is that a zipped file containing a number of files to be updated on the users machine has been unzipped and the filenames are returned in an array called 'newfiles'. Each actual file unzipped is temporarily preceded by a '~' character. We rename each existing file to <filename>.old, then delete all the old files. However, sometimes when the code runs, the old files are not deleted. The only explanation for this I can think of is that the second 'Fileexists' is not seeing the files because the filesystem has not caught up at that point. I've never seen this behaviour documented anywhere, though. It works fine when single-stepped.
For Each fn As String In newfiles
If .FileExists(fn) Then
'rename existing file to .old
delpath = Path.ChangeExtension(fn, "old")
.RenameFile(fn, delpath)
End If
'rename the new file to correct name i.e. remove "~"
[Code] .....
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Nov 28, 2011
I have a small code that can start multiple threads in numerous numbers and these threads will perform some calculations and file operations (read and/or write) that are private to themselves (each of the calculations and file operations are independent).But I can not figure out how to make the connection for threads to file operations.
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Sep 14, 2009
Say I have some code that does this:
Public Function AppendToLogFile(ByVal s As String) As Boolean
Dim success As Boolean = True
Dim fs As IO.FileStream = Nothing
[Code].....
First of all: is it a problem that I have that Try/Catch/Finally block inside of a SyncLock?
Second of all: suppose this code runs, on an event, potentially many times within a small timeframe--say, ten times in one second. Is it OK to have it SyncLock like this, or would it make more sense to have it add a line to a Queue, and then write all the lines from the Queue to the file on a timer that goes off, say, every second?
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Nov 29, 2010
I am currently working on an application which requires reading, writing and modifying data from a TEXT file. I have searched a lot but was not able to find a simple way to achieve this. I have to use a standard VB form with textboxes for ths text file opearations. s
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Nov 29, 2010
I am currently working on an application which requires reading, writing and modifying data from a TEXT file. I have searched a lot but was not able to find a simple way to achieve this. I have to use a standard VB form with textboxes for this text file operations.
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Feb 28, 2010
I'm trying to figure out some Excel automation. I have a form set up so the user can click on a label to open an Excel file (as a background process I guess) so the file isn't actually visible. Once they click on the "Convert to Count" button it will multiply all the values in Column B by 1,250 and put the output in Column C. Once it has finished this action, it makes the file visible so the user can choose to save it or not. Also, some users have Excel 2003 and some have 2007. Would it be possible to be able to load both xls and xlsx?[URL]..I must say I am very new with .NET and have a little bit of knowledge with VB6. I'm not sure where to even begin. I've looked up some ways to load an excel file but couldn't get it to work the way I need it to. Most of the ways I found were loading the file into a DataGridView. I don't want to use a DataGridView if I don't have to. Some of the files the users might be loading could have 10,000+ rows and that would take too long I think.
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Dec 6, 2006
I am using XML files to store some iformation that are to be processed. I use this code to interact with the XML file:
Dim xmlDoc As New XmlDocumentxmlDoc.Load("theXMLFile")
Do XML stuff such as add elements...
xmlDoc.DocumentElement.AppendChild(oAlarm)xmlDoc.Save("theXMLFile")
What I want to do is to lock the file so that no other process can use the file. If a process wants to use the file, I also want it to wait and try again until file is available.
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Aug 22, 2006
.NET 1.1VB 2003i have create a program where the program will dynamically create a mdb file, create a table, then populate the table via ADOX.dll using com interop.After populating the table i would like to FTP the said file to some FTP folder, to my dismay everytime i try to upload the mdb file i always get 0 kb, then i found out that the mdb file is "FILE-LOCKED" by some unknown process, but i dont know why because i have manually released all the resources that has been used, here is my code
[Code]...
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Jun 21, 2011
Dim bmi As New BitmapImage(New Uri(fiInfo.FullName, UriKind.Absolute))
bmi.CacheOption = BitmapCacheOption.OnLoad
this does not Use OnLoad
[code].....
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Jan 20, 2010
I've searched high and low for an answer so I'm hoping someone can help me out and I hope I explain what is happening ok. I have a number of people testing an application and one of them in particular is running into this error repeatedly. The error does not happen on my machine or almost any other. I know it is in relation to database usage but what I can't figure out is why the user only gets the error after the database has been called x number of times (and closed each time its done being used) as opposed to why the program doesn't crash the first time the database file is accessed.
The database is in MS Access and here's some pertinent info from the code - and the error is not subject to any particular database call...it just seems that after so many hits to the database its had enough and it crashes.
[Code]...
Like I said, why would the code work on almost all other machines (he's got a newer machine too and has tried both XP and Vista machines) and if there is something about his system why does is successfully call and use the database for awhile but then crashes out seemingly after a certain number of uses of the database file? I know it is not a specific call to the database because the area the application typically crashes for him at can be bypassed by changing some of the options available to the user - when he cuts back on the options used the program simply crashes at a later point in the process.
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May 21, 2010
Is there a way to lock a file without having to actually open the file and maintain a "connection" to it from my VB app? This should then prevent other users from writing/deleting/renaming the file. But I also want to allow only my app to write/delete/rename if need be.
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May 20, 2010
I am using Ms Access 2000 on a Windows Server 2008 and I have four users connected on a network to the server accessing the databases through a VB6 application which is loaded on all of the users' computers.While using the VB6 program i receive the error "Error 3050 Could not lock file".I know it has to do with the .ldb file.I have checked the permission and all users have full read/write/modify rights on the drive and the folder that the databases are stored in.I checked the MaxLocksPerFile and it is set to 9500.I even tried compacting and repairing and still this error persists.
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Dec 21, 2011
I have a .Net 4 WinForms app that generates a DLL, calls CreateObject on the generated DLL then calls one of several methods that the DLL contains. The DLL is eventually used by a separate app. This WinForms app is just to generate and test the DLL hence why it can generate the DLL multiple times.The problem lies in the fact that calling CreateObject on the DLL locks the file to the process. The next time the DLL is generated it can't overwrite the previous DLL file on disk without closing the app completely and starting it again.
I've tried Marshal.ReleaseComObject, executing the CreateObject in a separate AppDomain, even setting the variable holding the COM object to a different COM object via CreateObject, manually calling GC.Collect() and a whole host of other things but none result in unlocking the file.The code flow is basically (simplified and generic names, etc.):
...
' Compile and generate DLL that is COM enabled and works fine
...
Dim foo As Object = CreateObject("Bar.Foo")
[code]....
is there a way to release a file lock on a COM DLL that has been instantiated via CreateObject without killing the process?
Note: this is a continuation of this original issue. I now have the DLL registering without locking the file but now the issue is with the CreateObject call not the DLL registration.
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Feb 8, 2009
How would I Create a New .txt File & Lock it with a Password with VB8....?
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Mar 30, 2009
i'm getting this error: "File sharing lock count exceeded. Increase MaxLocksPerFile registry entry." i know i can manually go into the registry and edit this, but is there a way to do this in code?
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Apr 29, 2012
i have written a small app that:-Periodically captures a portion of a screen to jpeg file-Uploads this file to ftp serverAt first i used My.Computer.Network.UploadFileand it worked like a charm. Then i wanted to move to FtpWebRequest async. The reason was because i implemented a global keyboard hook and locking the main thread for upload, disabled my keyboard.I copied the example in MSDN regarding FtpWebRequest. the problem i have is that it seems that the file that is being uploaded is locke
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Mar 24, 2010
how I can lock a file so it will be completely written to by the first application, then unlocked for reading by my second web ticker app? My IDE is VB 2008. The second app has a ticker timer which I can modify accordingly. However, I'm still concerned whether the web app will encounter a situation where it competes for file access.
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Feb 17, 2012
I have difficulty in removing the LDB generated by the "CREATE" method of ADOX in the following code segment.Aims: Create (on the fly) a new access database and then export data (says Arena modules) to that newly created database.
Expected: The newly created access database should be able to be used by some external operations, say Access.exe, after the end of the subroutine and without exiting the current VB program.
1) I tested that the "Arena code" do nothing about the create/release of the ldb file.
2) I tested the "Exclusive Mode" in connection string, but the access file is still locked by the vb program.
3) I tested under both inside the VB environment, and directly invoke the generated from Explorer, and same results.
4) Other database formats is not the options to me. (due to Arena export limit)
5) It is not a web app.
Code:
Sub Method1()
Dim logs As New System.Collections.Generic.List(Of String)
Dim arenaApp As Arena.Application = Nothing
Try
[code]....
Platform:
Windows 7 64bit, Office 2010 (32)
VB 2010 express
Lib: MS ADO Ext. 2.8 for DDL and Security
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Oct 4, 2011
I am writing a program that acceses a file in VB/Visual Studio 2008 on Win7 and running it as a user who has admin credentials. I am opening the file with the following code:
Dim Input As New FileStream("C:FileTest est.txt", FileMode.Append, FileAccess.Write, FileShare.None) To test to make sure I can't access this file, I tried to open it with Notepad and I was able to and got no errors. I wrote a new value using Notepad and even saved it and I didn't get any errors form Notepad or my VB program.
I then went on and treid to open the same file twice from my VB program as:
Dim Input As New FileStream("C:FileTest est.txt", FileMode.Append, FileAccess.Write, FileShare.None)
Dim Input2 As New FileStream("C:FileTest est.txt", FileMode., FileAccess.Read, FileShare.None)
And I receivded an error in my VB program as expected. So the FileShare.None switch kind of works. Although I was still able to open the file with Notepad while my VB program had it open. I was aslo able to open Windows Explorer and reame it and even delte it while my VB program had it "open", in the write mode no less without my VB program knowing anything about it.
Why are other applications able to ignore the FileShare.None switch? Seems pretty useless if that's the case. And a huge secruity problem
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Jan 24, 2012
1. I have to create a file. 2. Then I want to write a string into the text file.
I can do part 1 no problem with: File.Create(strFilePath) But when I try part 2 to write to the file it won't allow this as it's still being used:
sw = File.AppendText(strFileName)
sw.WriteLine(strCode)
sw.Flush()
sw.Close()
My code in part 2 works fine on a file that hasn't just been created.
How do I release the file from the File object?
There doesn't seem to be a .close or .flush option.
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Dec 15, 2011
i want to create an exe in vb.net by packaging few perl files along with it. when i am packaging those files i am able to hide those files by making the hide option true. but if the 'show hidden files' is selected those files will be visible. I want to lock/prevent the user from opening the perl file/code. want to know if there is any way to do it.
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Jun 18, 2009
I wanna load XML file with XDocument.Load method and lock it. How to do it?
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May 8, 2009
We needed an inter-process reader/writer lock.We decided to use a file and lock the first byte using LockEx and UnlockEx. The class creates a file in the system temp folder when it is created. The file is created with readwrite access and share read|write|delete.We also specify DeleteOnClose so we don't leave loads of temp files laying around. Obviously AcquireReader and AcquireWriter call LockEx with appropriate flags and ReleaseLock calls UnlockEx.We have tested this class using a small application that you can run several instances of and it works perfectly. The application that uses it has a problem, which we have managed to re-produce in another small test app. In pseudo code it is
Create InterProcessReaderWriter
Dispose InterProcessReaderWriter without acquiring any locks
Launch a child process which takes a reader lock
The first time this runs, it works fine. If you attempt to run it again, while the child process from the first time is still holding the lock, we get an UnauthorisedAccessException when trying to open the file.This appears to be a permission issue, not a sharing violation but all the processes in this test case are running as the same user.
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Aug 1, 2011
lock from reading/writing/copying a loaded XML file with XDocument.Load [VB 2010]?
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Aug 4, 2010
Is there any better performance by checking for a true value like this:
[CODE]..............
Than like this:
[CODE]..............
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Oct 19, 2011
Is there anyway of searching for a file (shortcut file) on the desktop in VB? I've tried :
If My.Computer.FileSystem.FileExists("DesktopMYFILE.lnk")
doesnt return anything
If My.Computer.FileSystem.FileExists("DesktopMYFILE.exe")
doesnt return anything
[Code]...
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