.net - How To SyncLock A Shared Integer
May 28, 2012
I am pretty new to multi-threading in general and I would like to know how can I lock a shared integer variable to not be accessed by other threads while it is read/updated by an other thread.When I try do do SyncLock myInteger, I get that error : Error 6 'SyncLock' operand cannot be of type 'Integer' because 'Integer' is not a reference type.
Here a simplified example of what I mean
Private Shared myInteger As Integer
Private Sub MySub()
SyncLock myInteger ' This does not work
' read/write a new value to myInteger
End SyncLock
End Sub
MySub is called by multiple instances of the class, and running in multiple threads?
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Feb 11, 2009
I am trying to get a handle on SyncLock and multithreading, but I am having some trouble wrapping my head around exactly how it should be implemented. I have a Public Class Utilities with a many Shared Functions. I want to make sure that each function can only be executed when there are no other concurrent calls to the same function. So If I have 2 functions, A and B in a Public Class Utilities, what is the syntax so that a function "locks" while it is being executed, preventing any subsequent calls until the "locking" thread has completed?
CODE
Public Class Utilities
Public Shared Function A (ByRef i As Integer) As Integer
[CODE].............................
I know I need to wrap the statements of execution in a SyncLock block, but I am unsure of the scope of the parameter used with SyncLock...is it private to the function, class, etc? Can the same object be used to lock both functions if they are independent?
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Aug 25, 2011
I have a class like this:
[Code]...
It works, when I make getBar methods public, but I don't want to expose these unneccessarily. Why I can't call private shared methods from a public one in the same class is over my head. I'm using .net framework 4.0 in a web application.
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Sep 15, 2010
I was just wondering if mixing SyncLock blocks and Monitor.Enter/Exit statements is dangerous. I know SyncLock uses Monitor and a Try block in the background, but are there any problems with using the two together for thread synchronization?
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Mar 30, 2012
I've taken over the maintenance of the website (ASP.NET VB) and on one particular page I noticed the below code
Inherits System.Web.UI.Page
Public Shared UserNumber As String
Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Init
[Code]....
My question is whether the variable UserNumber can be accessed or changed by any other user than the current one?
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Aug 12, 2009
Given in the following language specification, for me at least, calling Db.Foobar() [In the following code] does not indeed call off to the Shared Constructors of the base classes. I am curious as to a) is this my own fault for doing something wrong or b) is this an error in the language specification[code]...
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Mar 25, 2011
Is there simple way to SyncLock an object that can be null? And before you ask for it, yes, I know that it isn't logical to perform a SyncLock on a null variable. However, that would simplify my code because right now, I have no choice but to perform a null check all over the place before calling a SyncLock.
[Code]...
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Sep 7, 2010
If I have two Synclocks
synclock a
synclock b
end synclock
[code].....
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Apr 13, 2011
I was wondering if this is known / expected behavior. By design?Is it documented somewhere?
My 'real' code does need something to keep one thread from accessing a listview while another is busy clearing and refreshing the Items collection, so it's not as easy as omitting the synclock section in the example below (The SyncLock in my case is on the ListView).
This code, which can be pasted over a new empty form's user code class, deadlocks during the Invoke call. It doesn't reach the entry point of SetText (setting a brakpoint there, the deadlock occurs before the breakpoint is hit).[cod]e...
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Aug 3, 2009
I have an application that requires several threads, otherwise the main UI thread would end up frozen.i am after a little advice as i have not really don alot of threaded applications.
First Question;
I have a thread which handles data coming in from the serial port( this wil become much more complicated), is it safe to use a synclock on the serialport object : -
[code]...
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Jan 7, 2011
Suppose I have a byte array, Private Data as Byte(). This array is private within a class. The class provides public functions for reading and writing to Data. This class can be accessed by multiple threads, so I want to avoid a situation where reading from it and writing from it don't happen at the same time.
For now, I am using SyncLock to avoid issues. Can I put SyncLock Data in just the write functions, or does it need to be in the read functions? Or, both? I don't have a specific code example in mind. I am just curious if there is any benefit to locking for both read and write functions if the writing functions' SyncLock will make writing have exclusive access to it in the first place.
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Oct 24, 2009
I'm trying to SyncLock my DataTable, to avoid problems with multithreading and stuff. But it doesn't seems to work. I'm trying to lock a DataTable wich is acceseed inside a nested for-loop:
vb.net
SyncLock radiolopere
For Each row As DataRowView In tableview
[code].....
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Nov 16, 2010
I have a class that contains a List(of T) used in a multithreaded application. I have three methods Get, Add and Remove where these access and modify the List(of T). I was using SyncLock to lock m_List any time I queried it for the desired object as well as when I added or removed objects. However I'm curious as to if there is a performance gain by simply locking m_List when I add an object or remove an object as opposed to when I'm searching for a desired object?
[Code]...
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Apr 22, 2011
I have a List of objects shared by multiple threads, it sometimes generate IndexOutOfRangeException when trying to Clear. While searching for solution I found that I should use SyncLock while accessing the List. But my question if what is the importance of lockObject in SyncLock block
E.g. while clearing myList
Can I use
Synclock myList
myList.Clear
End SyncLock
or lockObject should be different from myList?
What I think about sysnclock is "lock is obtained for object specified as lockObject". What if I specify list to be cleared as lockObject, shouldn't the compiler supposed to obtain the exclusive access to list before clearing it ?
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Mar 5, 2009
Once again Invoke has come back to haunt me! I have an application that has some background threads, serial communications and obviously a GUI. Now, the serial ports received incoming messages as events and these get processed and incoming data is logged both to a file and also appended to a RTB in the GUI (done using Invoke if InvokeRequired is true).Now, under normal circumstances everything is super happy and runs quite nicely but when stressed I reach some sort of deadlock.
What happens is I have two methods AddOutput and RemoveOutput. These both sync over an object SyncOutput As Object. When messages are received on the serial port they are processed and depending on whether or not a response is required AddOutput is called. This adds out going messages to a dictionary which is then accessed by a thread and the messages are sent out. If an acknowledgement message is received then the corresponding message in the dictionary is removed.
[Code]...
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Oct 2, 2009
If completedOrders.Count <> 0 Then
For i = 0 To completedOrders.Count - 1
SyncLock completedOrders
'Do some work, for example this:
Dim text As String = completedOrders(0).getCN & " " & completedOrders(0).getDeviceName & " "
End SyncLock
Next
End If
Is a synclock needed before the if statement or for loop? In other words. When you call methods like .length or .count is it necessary to synclock them or can another thread be writing to it at the same time. CompletedOrders is a generic list of a class.
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Sep 8, 2011
Ok so I coded this app that generates a number/word and it will upload to my database. Speed wasn't the issue when my db was under 1million entry. Now that I got about 100million entry it takes a few mins to upload.I worked with threading before but now I want all my threads to access this function that will give them a string. Now here is the problem, if 2 or more thread access the function at the same time, it will crash.How can I by pass that?I read about SyncLock. Can I use SyncLock on my function on each thread?
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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 3, 2009
Is it possible to skip a code block when a synclock is active?
For instance:
A object of class Bicycle is used by thread 1 and has a synclock on it.
Then thread 2 comes along and needs to know if the lights of the bike are working. But if there is a synclock active then thread 2 just forgets about checking the lights and goes to make a delicious chocolate pie.
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Jun 30, 2011
Can someone who is using a 64 bit machine help me pintpoint this crash to either the VS2010 IDE itself or one of the plugins I have installed?
It's the code fragment below. When I copy & paste it into the Main() function of a new VB.Net console app on my Win7 64 bit machine, the VS IDE crashes and dies onthe spot, every time I try it.
Doing exactly the same on a 32 bit XP machine, nothing abnormal happens.
The 64 bit machine does have some IDE plug-ins installed, the biggest of which is DevExpress (the free version), so i think either one of those or the fact that the IDE is running on 64 bit must be the culprit.
This is the code. The static variable can also be made a module-level variable, with the same result.
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Jun 1, 2010
I'm having trouble working out how to lock my application out of a section of code while it waits for a response from an external program've used Synclock on a section of code with the Me object in the expression. In this Synclock I call an overridden ShowDialog method of a dialog box, which has a timeout parameter, but does return the value from the underlying ShowDialog function call ,once the timer is setup. Works like this.
SyncLock Me
Dim frmDlgWithTimeout As New frmDlgWithTimeout ' dialog box with overridden ShowDialog '
Dim res As DialogResult = frmDlgWithTimeout.ShowDialog(10 * 1000) ' 10 sec timeout '
[code]....
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Jan 31, 2011
i have some test code which i run at every load of a page in my asp.net website [Code] the "dotrace" simply add a record to a log table in the db. now the right result would be that i should have the entries in the db in order "entered","exiting","exited" but actually when i look in the db i see first 2 "entered" then 2 "exiting" etc. meaning that the multi-threading is working ok, but not the synclock. is that correct?
and how can this be fixed? the real code will be adding records to the db and might be called from several pages of different sessions, but the same code must not run twice concurrently. if i open multiple pages at once, they still clash some times. but if i'm correct, the issue is now not with the synclock as much as with the httpruntime.cache, because when using a standard property, on one page, the code works 100%. so how can i make sure that 2 threads, even from totally different sessions never run the trylock simultaneously?
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Apr 14, 2010
I am using Synclock to prevent multiple threads from logging text messages to the same file at the same time, but this doesn't seem to work:I get frequent sharing errors on the logfile, within the synclock block.The Synclock is using the variable holding the filename, because it exists all the time and because it is always the same object, whatever class instance or thread I'm in.[code]Despite using Synclock and a Using block around the code, I keep getting this error in the sw.WriteLine(Msg) line:System.IO.IOException: The process cannot access the file '(filename)' because it is being used by another process.Should I use some other type of object than a string to synchronize on?I cannot use a user interface object (button or so) because it is a windows service project.It was written and compiled in Visual Studio 2008, but targeting the 2.0 framework because it has to be able to run on some old Win2000 machines.
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Jan 14, 2011
I seem to be drawing a blank. I'd like to create a "shared" variable that is shared with all instances of a class but not classes that inherit from it. For example.Class A: Shared list As New List(Of String): list.Add("A")
Class B Inherits A: list.Add("B")Class C Inherits B: list.Add("C")The end result I'd like is that any instance of A has just A in the list. Any instance of B has A and B in the list. Any instance of C has A, B, and C in the list. I can accomplish it by creating Instance variables, but I have to construct the list for each instance of a class. I'd like to construct it once for a specific point in the Hierarchy and then share it accross other instances of that class.
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Jun 4, 2010
I am trying to add shared members in derived classes and use that values in base classes...
I have base
class DBLayer
public shared function GetDetail(byval UIN as integer)
dim StrSql = string.format("select * from {0} where uin = {1}", tablename, uin)
end function
end class
[Code]..
currently there is error using the tablename variable of derived class in base class but i want to use it i dun know other techniques if other solutions are better then u can post it or u can say how can i make it work? confused...
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Sep 25, 2010
ive got some simple problem i cant understand how to solve.
str(1) is an array and integer(or double, tried both)
a(1) is an array and integer (or double, tried both)
a(1) = a(1) + 1
Label1.Text = str(1) + a
the big part is where i get: operator '+' is not defined for types 'integer' and '1-dimensional array of integer'.why do i get that message and what does it mean? how do i make the code do what i want?
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Aug 11, 2011
I faced an error when upgrading VB6 code to VB.NET. The error occurs at AddressOf WindowProc
AddressOf expression cannot be converted to 'Integer' because 'Integer' is not a delegate type
My declaration for SetWindowLong is:
Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA"(
ByVal hWnd As Integer,
ByVal nIndex As Integer,[code]....
What is the reason for the error I get?
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Apr 25, 2011
I'm trying to create a linked list of an array of integers. Why is the following implicit conversion required?
When I run the code that contains that conversion, I get the following error.
As a real-time data acquisition user control data (a packet of an array of bytes) arrives every second, is converted into an integer array and inserted into a linked list.
The most recently arrived data is painted as coordinates on a grid at the right of a PictureBox using Graphics.DrawLine (pen,X1,Y1,X2,Y2).
The oldest data (arriving 120 seconds ago) will be drawn at the leftmost portion of the Picturebox.
Why a linked list rather than a list? To display 120 views of time sequence data, the draw routine the most recently inserted node to a node that points to Nothing. How do I limit the length of the linked list to 120 nodes and always ensure that the last node points to Nothing?
Do While Not item Is Nothing
item = item.NextItem
Loop
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Aug 3, 2009
I am a newbie in VB and I got a piece of code which can display the current running program. I need to use that in VB2005 and I got the below error message. Can anyone help how to fix it?[code]
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May 13, 2009
I'm trying to convert a VB6 project to .NET, but I get problems with some callback functions, and the following message comes up: "AddressOf' expression cannot be converted to 'integer' because integer is not a delegate type" I've seen several solutions to similar problems like this, but I am not able to understand this issue with delegates.
After the conversion, the code look like this:
Declare Function vsmsgwSetDataPackageCB Lib "vsmsgwW.dll" (ByVal PACKAGE As Integer, ByRef arg As Integer) As Integer
Dim arginitP As Integer
[Code]...
Which gives the error: Method 'Public Function PackageCB(HisNodeID As Integer, ByRef data() As Byte, ByVal length As Integer, ByRef arg As Integer) As Integer' does not have the same signature as delegate 'Delegate Function DelegatePackageCallback(hwnd As Integer, lparam As Integer) As Integer
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