Threading

'Start a Threading
 
'There're 3 Threadings in this application
Imports System.Threading
 
Public Class Form1
 
    Private trd1 As Thread
 
    Private trd2 As Thread
 
    Private p1 As Integer
 
    Private p2 As Integer
 
    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
 
        '时时输出p1,p2的值
 
        Label1.Text = Str(p1)
 
        Label2.Text = Str(p2)
 
        Timer1.Stop()
 
        Timer1.Start()
   End Sub
 
 
 
一般而言,如果您想终止一个线程,您可以使用System.Threading.Thread类的Abort方法. 例如:
      Dim worker As ThreadStart = New ThreadStart(AddressOf workerthreadmethod)
      Dim t As Thread = New Thread(worker)
      t.Start()
      MessageBox.Show("Wait for a while for the thread to start.")
      MessageBox.Show(t.ThreadState.ToString())
      t.Abort()
      MessageBox.Show(t.ThreadState.ToString())
      t.Join()
      MessageBox.Show(t.ThreadState.ToString()) 
 
  当然,在调用Abort方法后,线程并不是立刻终止,要等线程的所有finally快中的代码完成后才会完全终止. 所以在主线程中可以用Join方法来同步,当线程还未完全终止时,t.Join()将处于等待,直到t线程完全结束后再继续执行后面的语句。
  Abort方法是会导致线程跳出一个异常错误的，你需要在代码中捕获该异常。下面是一个比较完整的VB.NET线程例子：
 
  Imports System
  Imports System.Threading
  Public Class MyTestApp
 
    Public Shared Sub Main()
      Dim t As New Thread(New ThreadStart(AddressOf MyThreadMethod))
 
      'Start the thread
      t.Start()
      MsgBox("Are you ready to kill the thread?")
 
      'Kill the child thread and this will cause the thread raise an exception
      t.Abort()
      ' Wait for the thread to exit
      t.Join()
      MsgBox("The secondary thread has terminated.")
 
    End Sub
    Shared Sub MyThreadMethod()
      Dim i As Integer
      Try
          Do While True
            Thread.CurrentThread.Sleep(1000)
            Console.WriteLine("This is the secondary thread running.")
          Loop
      Catch e As ThreadAbortException
          MsgBox("This thread is going to be terminated by the Abort method in the Main function")
      End Try
    End Sub
  End Class
 
  ************************************************************************************************
 
    Thread.Abort()方法用来永久销毁一个线程，而且将抛出ThreadAbortException异常。使终结的线程可以捕获到异常但是很难控制恢复，仅有的办法是调用Thread.ResetAbort()来取消刚才的调用，而且只有当这个异常是由于被调用线程引起的异常。因此，A线程可以正确的使用Thread.Abort()方法作用于B线程，但是B线程却不能调用Thread.ResetAbort()来取消Thread.Abort()操作。
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
 
        MessageBox.Show("this is the main thread")
 
    End Sub
 
 
 
 
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Timer1.Start()
 
        trd1 = New Thread(AddressOf ThreadTask1)
 
        trd1.IsBackground = True
 
        trd1.Start()
 
        trd2 = New Thread(AddressOf ThreadTask2)
 
        trd2.IsBackground = True
 
        trd2.Start()
 
    End Sub
 
 
 
 
    Private Sub ThreadTask1()
 
        Dim i, j As Integer
 
        Dim f As Boolean
 
        i = 1
 
        j = 1
 
        p1 = 1
 
        Do
 
            f = True
 
            For j = 2 To i - 1
 
                If i Mod j = 0 Then
 
                    f = False
 
                End If
 
            Next
 
            If f Then
 
                p1 = i
 
            End If
 
            i = i + 1
 
            MessageBox.Show(p1)
 
        Loop
    End Sub
 
    Private Sub ThreadTask2()
 
        Dim i, j As Integer
 
        Dim f As Boolean
 
        i = 1
 
        j = 1
 
        p2 = 1
 
        Do
 
            f = True
 
            For j = 2 To i - 1
 
                If i Mod j = 0 Then
 
                    f = False
                End If
 
            Next
 
            If f Then
 
                p2 = i
            End If
 
            i = i + 1
        Loop
    End Sub
 
 
    Private Sub btnTrd1Stop_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnTrd1Stop.Click
 
        '完全停止一个Threading
 
        trd1.Abort()
 
    End Sub
 
    Private Sub btnTrd2Stop_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnTrd2Stop.Click
 
        trd2.Abort()
 
    End Sub
 
End Class