Local Variables Are Automatically Shared
Mar 13, 2012
I was reviewing the MSDN documentation on VB.Net's little-used Static keyword for local variables. My question is not about how Static works (I personally plan to avoid using it as it seems like it could cause grief to future programmers who don't notice the side-effects.) My question is about this statement in the docs:[code]So can anyone interpret the above statement for me in a way that makes sense? Or is this a bug in the documentation? It's been there since the VS 2005 version of the docs and is still present in the Visual Studio 11 version.
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Jun 8, 2009
I came across a number of new Private Shared variables (of type Hashtables(Of String), initialized in the declaration) added to a partial class for a very large (DataContext-derived) class. This seems sensible to me in one sense because they never change, and making these shared variables ensures that they won't get re-initialized every time a function is called. However, these variables are only used within the scope of one function in the class, and I fear the private namespace of this DataContext-derived class is getting rather polluted, and having these sorts of things exposed at such a high level might be confusing to others reading the code in the future.
Would there be negative performance impact to making these local variables within the function where they are used, or is there some better way to handle this? Basically we are using these 3 hashtables to determine whether anything within particular subsets of properties changed (using GetModifiedMembers and then using the Overlaps function of the hashset to see if any of the modified members correspond to members we care about).
Edit: I caved and took the time to write my own test program, which confirmed that there is a cost to using local variables (which I assume applies generally to all cases -- I doubt there's any case where a shared variable would be slower unless using the shared variable requires some additional logic to do so properly): [Code]
So in this particular case, using the local variable costs about 200%. But in most cases (including my own), the time is probably negligible compared to the overall task. So I guess the question now becomes, how do people generally feel about improving code maintainability at the cost of negligible but known performance impacts?
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Aug 23, 2011
Will the list in this shared method keep its state throughout the life of the method? Or will a new list be created every time this method is called?
[Code]...
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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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Apr 12, 2010
I see several posts about getting the UNC of a remote drive, anyone have any ideas how I get the name of a shared directory on a local machine?
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Jan 18, 2011
I have a problem with inherited classes. Have a look at the following VB.NET 2.0 / VS 2005 code:
MustInherit Class templateclass
Public Shared x As String
End Class
Class child1
[code]....
The templateclass has a shared variable x which is of course inherited by the child classes. But I wonder that all child classes share only one x! Until now I thought that shared variables are only shared among the instances of a class, not among all childs. This is very annoying because I have a base class which I need in two slightly different versions and they should not "share the shared" variables. And because the classes have a lot of shared variables, shadowing each in the childs would be very..
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Oct 20, 2011
I'm trying to split some prior crafted code into a DLL. It's a simple logger system.There are a few things that need to be shared with the main form in the project, so I set them up as a shared variable, but I don't use shared stuff often, and I worry it will cause variable conflicts regarding scope. I figured I would make a post here about it and see if someone can explain what I don't fully understand.Since this is a logger it will be used a couple of places. Other DLLs that need logging may reference it through a instanced object and project reference. My main form will also have an instanced object and a reference to the logger libary.Since one of my properties is a connection string and it's shared, does this mean that a instance of my logger class inside a DLL will have the same shared values as a instance on my main UI form? Or will the fact that the instance is inside of a DLL provide the scope boundary I need?
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Jul 23, 2009
I am making a small application in which i have added a class module and a window forms in vb.net. i want to acess the shared variables and mathods of class without making any object.
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Jun 22, 2009
exact diff b/t Static v/s Shared variables in VB.NET?
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Nov 29, 2009
basically i was wondering if we could inherit shared variables but restrict its scope to only that of the class itself.
Class A
Public Shared shared_variable as Boolean = true
End Class
[code]....
when i do this A.shared_variable = False, B's shared_variable also becomes false. how do i stop this?i cannot remove the Shared keyword because shared_variable should be able to be accessed without an instance of the class?
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Feb 21, 2012
I've been doing some reading on garbage collection in .NET and I was hoping for some clarification. So, as I understand it if I declare a public shared class variable, the GC will never get rid of it. Is this correct?Also, what then of private variables? Take the following example:
public class myClass
private shared myString As String
public sub ChangeString(newString As String)
[code].....
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Mar 12, 2012
So I am currently attempting to wrap my head around create multi-threaded programs and I am currently running into an issue when using a Shared variable across multiple threads.The program is structured as follows: Public Shared IsActive as Boolean
Main Thread = GUISets the Value of IsActive through a Button ControlTwo Worker ThreadsBoth threads are while loops that read the IsActive Boolean Ex:While IsActive = True Do Work End WhileHowever when I change the value of IsActive from the Main Thread it causes the worker threads to stop (ThreadState = 16).
I have been reading that I have to synchronize/lock shared resources and have tried SyncLock and Monitor methods without success (it is entirely possible I am not using the above correctly, so If someone could provide proper examples for the above situation using the mentioned methods please share them).
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Feb 15, 2009
I have created a public shared subroutine in a class file in asp.net 2 (vb.net) web site app_folder.The subroutine retrives some values from a sql database via an sql query and assigns the datareader field values to several variables The problem is I can't seem to assign the variables from the subroutine to the variables and textbox controls in the asp.net page I am calling the subroutine from. The textbox text value just appear blank.By the way, if I response.write the variables in the subroutine they appear populated by the sql data reader.
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Jul 31, 2010
Are the following three the same upon compilation
dim x as new assigningfunction
dim x as new assigningfunction()
dim x as assigningfunction = new assigningfunction()
[code].....
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Apr 23, 2012
Public Shared _formRef As frmMain
Public Shared f As frmMain
Class Server[code].....
but once firing off the code i get the error you see in my image attached.
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Feb 3, 2010
When you declare a local variable (inside a method), is it automatically disposed when the method ends? Or should I still use variable.Dispose() ?
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Feb 6, 2010
I am using a lot of variables in my code and like to have them listed or printed. How can I do that?
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Feb 7, 2010
I am a Visual Basic 2008 user (under Visual Studio 2008) and I have numerous local variables in my project. How can I list them to a file or to a printer?
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Feb 13, 2009
Is it possible to get the name of a local variable from a reference to the variable? For example, I can get the names and values of a calling function's parameters like this:
Dim frame As New StackFrame(1)
Dim pInfos() As ParameterInfo = frame.GetMethod().GetParameters()
Is there some way to get the same information for a calling function's local variables? This is kind of what I have in mind:
Sub SomeSub()
Dim count As Integer = 10
Dim average As Single = 45.67
[Code]......
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May 19, 2011
Well I am a new to VB.NET, converting a legacy system to .NET world. Recently I have been reviewing the already existing code since I joined the project quite late in the team. I find that there are many shared functions (not shared class) inside many classes. I doubt this may create some problem if two requests ( i.e two different HTTP request to the same method as it's a WCF application, of course exposed methods are not shared but internally called methods are shared) comes to the same shared method and both the calls to the method may have different method parameters/arguments, overwriting each other's arguments. In short, if shared method has a list of arguments which is going to be processed, is there any chance of inconsistencies in the light of multiple access to the shared method via two http requests.
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Jul 22, 2009
give me a good resource that explains the difference between a Private, Public, Shared Functions/Sub/Variables? I normally use Public for Subs/Functions inside of Modules I call from other parts of the program. But I'd like to get more of an understanding of how and when to use them. I want as little as impact to a system that is running my programs as possible, so i guess the key here is I'm trying to just get more proficient in my coding.
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Sep 30, 2011
I am writing some code that uses fixed regexs to search strings and pattern match. Its simple stuff, but I want to improve regex performance with compiling (its a high traffic website). I was thinking of compiling the regex and putting it in a Shared (static) variable inside a class. Something like this:
[Code]...
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Dec 8, 2011
I have the following class which I want to serialize to XML:
[Code]...
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Apr 18, 2012
I am wondering if you have a class and in the class you have a function which executes a sqlcommand. Which would u use ? the local variable declaration or the private member command variable.Assuming that the class has a private field called m_Cmd as OracleCommand..i am using oracle db so i use oraclecommand , if sql server then it should be sqlCommand.[code]
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May 13, 2010
when an exception occures, I want to save the data available on the stack and log it. how can I serialize all the available local variables and save them?
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Oct 26, 2011
For my application, I have a page that redirects to another page (within the same application) via Server.Transfer. I need to do this because the original page has an object that I need to access by using the Page.PreviousPage property.
Once my "destination" page has been fully loaded, a local deep clone that I made of the source page's object is suddenly released from memory once I perform a postback? Is this by design--something to do with the Server.Transfer?
Page1.aspx:
Public Structure myCustomObject
Implements ICloneable
Dim someField as String = "default value" ' Default value
[code]....
At this point, EVERYTHING works as it should. Stuff got cloned over correctly and all is well.(Let's say this is on a button click event) Debug.Write(newObj.someField) ' Output: "default value"<- This is NOT "changed value from source page" for some reason when it was working literally a few lines ago! My guess is that the Server.Transfer stops any association with the source page after the new page loads.
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Jan 12, 2012
When I want to maintain code readability and keep things neat. I would create temp variables . Below is one of my functions that uses it. Is it a bad practice? I would create temp variables cost more memory ?
Private sub test(byref transac as transaction , byref txntime as string )
Dim cmd as OracleCommand = nothing
Dim Adapter As OracleDataAdapter = nothing
Dim SQLStr As New StringBuilder
[Code] .....
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May 24, 2010
I have a page that redirects to another page (within the same application) via Server.Transfer. I need to do this because the original page has an object that I need to access by using the Page.PreviousPage property
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Dec 28, 2009
I've found out that if two instances of an SSRS report run at the same time, any Code variables declared at the class level (not inside a function) can collide. I suspect this may be the cause of our report failures and I'm working up a potential fix.The reason we're using the Code portion of SSRS at all is for things like custom group and page header calculation. The code is called from expressions in TextBoxes and returns what the current label should be. The code needs to maintain state to remember what the last header value was in order return it when unknown or to store the new header value for reuse
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Apr 20, 2010
I as part of the support VB code for a larger ASP project, I need to read back the existing data from an Access database, to see if user has changed a value.
I'm reading the existing data back into a DataView using the following function:
Public Shared Function GetPolicyStatus(ByVal intPolicyID As Integer) As DataView
Dim strConString As String
Dim conMyData As OleDbConnection
[Code]....
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