Programming Microsoft Visual Basic .NET/Programming Microsoft Visual Basic .NET (Microsoft Press)(X08-78517)(2002).bin/setup/vbnet/13 threading/threadingdemo/classes.vb

Text File | 2002-03-16 | 5.3 KB | 184 lines

Imports System.Threading

' a class that lets you share data with another thread

Class ThreadData
    Public Id As Integer
    Public Msg As String
    Public Done As Boolean

    ' The entry point for the thread
    Sub DoTheTask()
        Dim i As Integer
        For i = 1 To 10
            ' just show that the thread got the correct values
            Console.WriteLine("{0} (Thread ID = {1})", Msg, Id)
            ' Wait for .2 seconds.
            Thread.CurrentThread.Sleep(200)
        Next
        ' Signal that this thread has completed.
        Done = True
    End Sub
End Class

' a class that lets you share data with another thread
' and that raises an event when the tasks has completed

Class ThreadData2
    Event TaskCompleted(ByVal sender As Object, ByVal endTime As Date)

    Public Id As Integer
    Public Msg As String
    Public Done As Boolean

    ' The entry point for the thread
    Sub DoTheTask()
        Dim i As Integer
        For i = 1 To 10
            ' just show that the thread got the correct values
            Console.WriteLine("{0} (Thread ID = {1})", Msg, Id)
            ' Wait for .2 seconds.
            Thread.CurrentThread.Sleep(200)
        Next
        ' Signal that this thread has completed.
        Done = True

        ' raise an event
        RaiseEvent TaskCompleted(Me, Date.Now)
    End Sub
End Class

' this class is a base class for a thread wrapper

MustInherit Class ThreadWrapperBase
    ' This public member exposes the Thread object.
    Public ReadOnly Thread As System.Threading.Thread

    ' The constructor creates the thread object and runs the code
    Sub New()
        Me.Thread = New System.Threading.Thread(AddressOf Me.RunThread)
    End Sub

    ' This starts the thread
    Overridable Sub Start()
        Me.Thread.Start()
    End Sub

    ' This private procedure is where the thread starts its execution;
    ' when the thread terminates, the Done flag is set to
    Private Sub RunThread()
        m_Done = False
        OnStart()
        m_Done = True
    End Sub

    Dim m_Done As Boolean

    ' This property returns True if the thread has completed its task.
    ReadOnly Property Done() As Boolean
        Get
            Return m_Done
        End Get
    End Property

    ' Derived classes must override this to provide the actual code for the thread.
    Protected MustOverride Sub OnStart()
End Class

' an example of a thread wrapper

Class MyTask
    Inherits ThreadWrapperBase

    ' Instance data
    Public Id As Integer
    Public Msg As String

    Sub New(ByVal id As Integer, ByVal msg As String)
        Me.Id = id
        Me.Msg = msg
    End Sub

    ' The code that the thread must execute
    Protected Overrides Sub OnStart()
        Dim i As Integer
        For i = 1 To 10
            ' just show that the thread got the correct values.
            Console.WriteLine("{0} (Thread ID = {1})", Msg, Id)
            ' Wait for .2 seconds.
            Thread.CurrentThread.Sleep(200)
        Next
    End Sub

End Class

' this class is used to demonstrate the ThreadPool

Class LightweightTask
    Public SomeData As String

    ' The method that contains the interesting code
    ' (Not really interesting in this example).
    Sub DoTheTask(ByVal state As Object)
        Console.WriteLine("Message from thread #" & state.ToString)
    End Sub
End Class

' this class demonstrates the Synchronization attribute

<System.Runtime.Remoting.Contexts.Synchronization()> _
Class Display
    ' Synchronized classes must inherit from ContextBoundObject.
    Inherits ContextBoundObject

    Sub DisplayData()
        Console.Write("Message ")
        Console.Write("from ")
        Console.WriteLine(Thread.CurrentThread.Name)
    End Sub
End Class

' this class is used to test the AutoResetEvent class

Class FileFinder
    Dim StartPath As String       ' The starting search path
    Dim SearchedPattern As String ' The search pattern (can contain wildcards)

    Sub New(ByVal path As String, ByVal search As String)
        Me.StartPath = path
        Me.SearchedPattern = search
    End Sub

    ' This is the method with which thread execution starts.
    Sub StartSearch()
        Search(Me.StartPath)
        ' Decrease the number of running threads before exiting.
        Interlocked.Decrement(searchingThreads)
        are.Set()
    End Sub

    ' This recursive procedure does the actual job.
    Sub Search(ByVal path As String)
        Dim files() As String
        ' Get all the files that match the search pattern.
        files = System.IO.Directory.GetFiles(path, SearchedPattern)
        ' If there is at least one file, let the main thread know about it.
        If Not files Is Nothing Then
            ' Get a lock on the result ArrayList.
            SyncLock filesAl.SyncRoot
                ' Add all found files.
                filesAl.AddRange(files)
                ' Let the consumer thread know about the new filenames.
                are.Set()
            End SyncLock
        End If

        ' Repeat the search on all subdirectories.
        Dim dirname As String
        For Each dirname In System.IO.Directory.GetDirectories(path)
            Search(dirname)
        Next
    End Sub
End Class