variables of a function not colliding

Question

User2146470223 posted

Hi,

In a former thread about parallel functions/async tasks JBetancourt gave me this answer as a partial answer to many problems I had there:

if you extract your logic to a function and declare the variables inside the function the variables wont collide with each other, their scope will be limited to inside that function, so no need to duplicate variable declaration; think about extracting the functionality to a class instead of a function

I decided to open an own thread for this specific answer as the other thread is solved but this is still interesting.

Are there any references where I can get more information about this topic. I did not really find any on Google, so I guess I might have been using the wrong (order of) key words.

Does this also apply to/work with TPL and parallel.invoke?

Thanks in advance,

Pascal

Answer 1

User-335504541 posted

Hi Translating-IT,

Do you want to know how do variables work in multithread?

If so, I think you could refer to the links below:

https://docs.microsoft.com/en-us/dotnet/visual-basic/programming-guide/concepts/threading/parameters-and-return-values-for-multithreaded-procedures

https://stackoverflow.com/questions/1182423/net-multi-threaded-variable-access

https://docs.microsoft.com/en-us/dotnet/visual-basic/programming-guide/concepts/threading/multithreaded-applications

https://docs.microsoft.com/en-us/dotnet/standard/threading/synchronizing-data-for-multithreading

Best Regards,

Billy

 

Answer 2

User2146470223 posted

Hi Billy,

Yes, might be what I'm looking for but I dont get it for my problem:

Let's say I have:

    Async Function thread1() As Task
        Dim axsqlCon30 As New SqlConnection(ConStr2)
        SQL30.Connection = axsqlCon30
        Dim axsqlCon1 As New SqlConnection(ConStr2)
        SQL1.Connection = axsqlCon1
        Dim axsqlCon2 As New SqlConnection(ConStr2)
        SQL2.Connection = axsqlCon2
        Dim axsqlCon5 As New SqlConnection(ConStr2)
        SQL5.Connection = axsqlCon5

        For Each Tempit In suche100
            lCounter = 0
            uebja = 0
            splitter2 = "pzsplit"

            suche1 = Regex.Split(Tempit, splitter2)
            For x = 0 To UBound(suche1) 'Wörter
                If x > 0 Then
                    itemxx = suche1(x - 1)
                End If
                If suche1(x).StartsWith("pztaggi") Then
                    Dim match As Match = Regex.Match(suche1(x), "pztaggi\d+pztaggi")
                    tagsvor.Append(match)
                    If suche1(x).EndsWith("pztaggi") Then
                        Dim match2 As Match = Regex.Match(Right(suche1(x), 20), "pztaggi\d+pztaggi")
                        tagsnach.Insert(0, match2)
                        Continue For
                    End If
                ElseIf suche1(x).StartsWith("pzmaili") Then
                    Dim match As Match = Regex.Match(suche1(x), "pzmaili\d+pzmaili")
                    tagsvor.Append(match)
                    If suche1(x).EndsWith("pzmaili") Then
                        Dim match2 As Match = Regex.Match(Right(suche1(x), 20), "pzmaili\d+pzmaili")
                        tagsnach.Insert(0, match2)
                        Continue For
                    End If
                ElseIf suche1(x).StartsWith("pzlinki") Then
                    Dim match As Match = Regex.Match(suche1(x), "pzlinki[\d]*pzlinki")
                    Continue For
                    tagsvor.Append(match)
                    If suche1(x).EndsWith("pzlinki") Then
                        Dim match2 As Match = Regex.Match(Right(suche1(x), 20), "pzlinki[\d]*pzlinki")
                        tagsnach.Insert(0, match2)
                        Continue For
                    End If
                Else
                    If ganzsatz.TryGetValue(Tempit, str_item10) Then
                        sb_proofed2.Append("pzsplit" & tagsvor.ToString & str_item10 & tagsnach.ToString)
                        tagsvor.Clear()
                        tagsnach.Clear()
                        Exit For
                    End If
                End If
                If int_wortcount > 0 Then
                    int_wortcount = int_wortcount - 1
                    Continue For
                End If
                int_ubounddiff = UBound(suche1) - x
                Tempit3 = Regex.Replace(Regex.Replace(Trim(suche1(x)), "pztaggi[\d]*pztaggi", ""), "pzsplit\?[\d]*\?pzsplit", "")
                If x < UBound(suche1) Then
                    item = Regex.Replace(Regex.Replace(Trim(suche1(x + 1)), "pztaggi[\d]*pztaggi", ""), "pzsplit\?[\d]*\?pzsplit", "")
                End If
                'Response.Write(Tempit3 & "-")
                Tempit3b = Tempit3
                If Tempit3 = Tempit3.ToUpper() Then
                    boo_wortup = 1
                Else
                    boo_wortup = 0
                End If
                Dim boo_spechar As Boolean

' ############## and many more lines in between #################'

            Next
            If ganzsatz.TryGetValue(Tempit, str_item10) Then
            Else
                ganzsatz.TryAdd(Tempit, satzneu.ToString)
            End If
            satzneu.Clear()
        Next 'Sätze Ende
    End Function

and I want to run this task (thread1) on 2 threads with:

		Parallel.Invoke(Function()
							Try
								thread1()
							Catch ex As Exception
								
								anz.Append("<strong>" & Resources.text.error & "</strong>")
							End Try
						End Function,
						Function()
							Try
								thread1()
							Catch ex As Exception
	
								anz.Append("<strong>" & Resources.text.error & "</strong>")
							End Try
						End Function)

whereas both get fed with different starting values (I know the way it is above does not work out like this right now, so no need to correct it for me).

The question to answer is: Will variables and arrays like suche1 or boo_spechar that are dimmed and set within function Thread1() not be replaced when my task is working on the second parallel thread1(), when this part gets to the same line where the variable is dimmed and set?

regards,

Pascal

Answer 3

User475983607 posted

The question to answer is: Will variables and arrays like suche1 or boo_spechar that are dimmed and set within function Thread1() not be replaced when my task is working on the second parallel thread1(), when this part gets to the same line where the variable is dimmed and set?

Variables created inside a method are scoped to the method.  Method arguments are also scoped to the method but are passed form outside the method.  Therefore passing a reference type to a method and invoking the method on multiple threads can cause data collisions as well.

Answer 4

User2146470223 posted

Hi mgebhard,

That was also what I found that far but I was not sure whether I might have missed something.

I guess in the last thread JBetancourt did not get that I used the very same function/method as parallel thread. So when I explained that I had cloned the function to Thread2() while changing all the variables to var1 -> var100, var2 -> var200 he said there is no need to do so as vars would not be colliding anyway.

Maybe he thought I was using some other multithreading like parallel.foreach. From what I understood, there the inbuilt logic prevents such collision.