Threading and get data

Question

User-1271631458 posted

Hi everybody,

I have a problem with threads,this is my demo.I want to get _data at result,I need a demo,thanks.

Imports System.Threading.Thread
Public Class Form1

Private _data As New List(Of String)

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
       Dim thread As Threading.Thread
       Dim str As ArrayList = New ArrayList
       str.Add(1)
       str.Add(2)
       str.Add(3)
       str.Add(4)

For Each item In str
thread = New Threading.Thread(AddressOf GetData)
thread.Start()
Next
'result = _data
End Sub

Private Sub GetData()
For i As Integer = 0 To 1000
_data.Add(i)
Next
End Sub

End Class

Answer 1

User753101303 posted

Hi,

Try maybe to find a desktop development forum at https://social.msdn.microsoft.com/Forums/en-US/home Maybe start there by explaining a real (or realistic at least) use case you would like to handle in your desktop app.

For now having multiple threads doing nothing more than always working on the same data is not a good use case as access needs to be synchronized : http://www.albahari.com/threading/part2.aspx#_Synchronization

And so yo would use a lock statement resulting in each thread updating the list one after the other (or always competing to add a single element at a time).

You could have also a look at https://docs.microsoft.com/en-us/dotnet/standard/parallel-programming/task-parallel-library-tpl 

Answer 2

User-719153870 posted

Hi Klaus Shen,

Private Sub GetData()
For i As Integer = 0 To 1000
_data.Add(i)
Next
End Sub

We can see in your GetData() method, nothing is returned?

Please try below code:

Public Class Form1
    Private _data As List(Of String) = New List(Of String)()

 

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)
        Dim thread As System.Threading.Thread
        Dim str As ArrayList = New ArrayList()
        str.Add(1)
        str.Add(2)
        str.Add(3)
        str.Add(4)

 

        For Each item In str
            thread = New System.Threading.Thread(GetData(_data))
            thread.Start()
        Next

 

        Dim result As List(Of String) = _data
    End Sub

 

    Private Function GetData(ByVal list As List(Of String)) As List(Of String)
        For i As Integer = 0 To 1000
            list.Add(i)
        Next

        Return list
    End Function
End Class

Best Regard,

Yang Shen