frmmorethreads.vb

清华大学出版社出版的 移动应用开发宝典 张大威（2008）的附书源代码

Imports Microsoft.VisualBasic
Imports System
Imports System.Windows.Forms
Imports System.Threading
Imports System.Diagnostics
Imports System.Collections.Generic

Namespace CodeForChapter11cs
  Public Partial Class frmMoreThreads
	  Inherits Form
	Public Sub New()
	  InitializeComponent()
	End Sub

	Private someCounter As Long = 0

	Private Sub button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles button1.Click
	  someCounter = 0
      Dim t1 As Thread = New Thread(AddressOf Me.ThreadBoth) ' Me.ThreadFirst1)
	  t1.Name = "Worker Thread 1 "
      Dim t2 As Thread = New Thread(AddressOf Me.ThreadBoth) ' Me.ThreadSecond2)
	  t2.Name = "Worker Thread 2 "

	  t1.Start()
	  t2.Start()

	  t1.Join()
	  t2.Join()

	  MessageBox.Show("Final result = " & someCounter.ToString())
	End Sub

	#Region "race condition 1"
	Private Sub ThreadFirst1()
	  For j As Long = 0 To 99999999
		Debug.WriteLine(Thread.CurrentThread.Name & "before inc")
		someCounter += 1
	  Next j
	  MessageBox.Show(Thread.CurrentThread.Name, "Done")
	End Sub

	Private Sub ThreadSecond2()
	  For j As Long = 0 To 99999999
		Debug.WriteLine(Thread.CurrentThread.Name & "before inc")
		someCounter -= 1
	  Next j
	  MessageBox.Show(Thread.CurrentThread.Name, "Done")
	End Sub
	#End Region

	Private Sub ThreadBoth()
	  Debug.WriteLine(Thread.CurrentThread.Name & "enters method")
	  Dim localVar As Integer = 0
	  localVar += 1

      'SyncLock (someLock) ' uncomment the lock region to achieve the undesired effects
      If someCounter = 0 Then
        Debug.WriteLine(Thread.CurrentThread.Name & "in if block")
        Thread.Sleep(1) 'simulate some longer activity
        someCounter += localVar
        Debug.WriteLine(Thread.CurrentThread.Name & "just incremented")
      Else
        Debug.WriteLine(Thread.CurrentThread.Name & "in else block")
        someCounter += 3
      End If
      'End SyncLock
      Return
    End Sub

	#Region "Not used in sample. Shows Monitor code"
	Private someLock As Object = New Object()
	Private Sub SomeMethod()
	  ' some code

	  Monitor.Enter(Me)
	  Try
		' critical region, only 1 thread at a time enters this

	  Finally
		Monitor.Exit(Me)
	  End Try

	  ' other code
	End Sub

	#End Region
  End Class
End Namespace