Programming Microsoft Visual Basic .NET/Programming Microsoft Visual Basic .NET (Microsoft Press)(X08-78517)(2002).bin/setup/vbnet/13 threading/threadingdemo/module1.vb

Text File | 2002-03-20 | 24.2 KB | 737 lines

Imports System.Threading

Module MainModule

    Sub Main()
        ' Run one of the Textxxxx procedures below by uncommenting only one statement

        'TestThread()
        'TestSuspendResume()
        'TestJoin()
        'TestInterrupt()
        'TestThreadStatic()
        'TestThreadLocalStorage()
        'TestThreadData()
        'TestEventNotifications()
        'TestWrapperClass()
        'TestSynchronizationProblem()
        'TestSyncLock()
        'TestSyncRoot()
        'TestMonitorEnter()
        'TestMonitorTryEnter()
        'TestInterlocked()
        'TestMutex()
        'TestReaderWriterLock()
        'TestAutoResetEvent()
        'TestThreadPool()
        'TestServerTimer()
        'TestThreadingTimer()
        'TestSynchronizationAttribute()

        ' You need these statements when running inside Visual Studio, so that
        ' the Console window doesn't disappear
        Console.WriteLine("")
        Console.WriteLine(">>> Press Enter to terminate the program <<<")
        Console.ReadLine()
    End Sub

    ' this procedure tests basic thread capabilities

    Sub TestThread()
        ' Create a new thread and define its starting point.
        Dim t As New Thread(New ThreadStart(AddressOf DoTheTask))
        ' Run the new thread.
        t.Start()

        ' Print some messages to the Console window.
        Dim i As Integer
        For i = 1 To 10
            Console.WriteLine("Msg #{0} from main thread (ID={1})", i, AppDomain.GetCurrentThreadId)
            ' Wait for .2 seconds.
            Thread.CurrentThread.Sleep(200)
        Next
    End Sub

    Sub DoTheTask()
        Dim i As Integer
        For i = 1 To 10
            Console.WriteLine("Msg #{0} from secondary thread (ID={1})", i, AppDomain.GetCurrentThreadId)
            ' wait for .2 seconds.
            Thread.CurrentThread.Sleep(200)
        Next
    End Sub

    ' this procedure tests suspending and resuming threads

    Sub TestSuspendResume()
        ' Define and start a new thread.
        Dim t As New Thread(AddressOf DoTheTask)
        t.Start()
        Thread.Sleep(500)

        ' Suspend the thread.
        Console.WriteLine("Suspending secondary thread.")
        t.Suspend()
        Thread.Sleep(500)

        ' Resume the thread.
        Console.WriteLine("Resuming secondary thread.")
        t.Resume()
        Thread.Sleep(500)
        ' ...
        ' Abort the thread.
        Console.WriteLine("Aborting secondary thread.")
        t.Abort()
    End Sub

    ' this procecure tests the Join method

    Sub TestJoin()
        Dim t As New Thread(AddressOf DoTheTask)
        t.Start()
        Console.WriteLine("Waiting for the secondary thread to terminate")

        ' Wait for the other thread to die.
        t.Join()
        Console.WriteLine("Resuming the main thread")
        Console.WriteLine("")

        t = New Thread(AddressOf DoTheTask)
        t.Start()
        Console.WriteLine("Starting another thread, again")

        ' Wait for the other thread to die, but print a message every second.
        Do Until t.Join(1000)
            Console.WriteLine("Waiting for the other thread to die...")
        Loop
        Console.WriteLine("Resuming the main thread")
    End Sub

    ' this procedure tests the Interrupt method

    Sub TestInterrupt()
        Dim t As New Thread(AddressOf DoTheTask2)
        t.Start()
        ' let it do some work, then interrupt it
        Thread.Sleep(500)

        Console.WriteLine("Interrupting the secondary thread")
        t.Interrupt()
    End Sub

    ' a secondary thread that protects itself from the interrupt method

    Sub DoTheTask2()
        Dim interrupted As Boolean

        ' emclose the entire working code in a Try block
        Try
            Dim i As Integer
            For i = 1 To 10
                Console.WriteLine("Msg #" & i.ToString & " from secondary thread")
                ' wait for .2 seconds.
                Thread.CurrentThread.Sleep(200)
            Next
            ' We get here if the timeout elapsed and no exception is thrown.
            ' (Not really necessary, because the variable is already False.)
            interrupted = False
        Catch ex As Exception
            interrupted = True
        Finally
            ' print a suitable message
            If interrupted Then
                Console.WriteLine("The thread was interrupted")
            Else
                Console.WriteLine("The thread terminated normally.")
            End If
        End Try
    End Sub

    ' this procedure tests the ThreadStatic attribute

    Sub TestThreadStatic()
        Dim threads(10) As Thread
        Dim i As Integer

        For i = 1 To 10
            ' Create a new thread
            threads(i) = New Thread(AddressOf DoTheTask3)
            ' set its Name property
            threads(i).Name = "thread #" & i.ToString
            ' run it
            threads(i).Start()
        Next

        ' wait until all threads end
        For i = 1 To 10
            threads(i).Join()
        Next
    End Sub

    ' a variable that isn't shared among thread
    <ThreadStatic()> Dim m_ThreadId As String

    Sub DoTheTask3()
        ' Initialize the m_ThreadId variable with thread name
        m_ThreadId = Thread.CurrentThread.Name

        ' signal that the thread has started
        Console.WriteLine(Thread.CurrentThread.Name & " has started")
        ' just wait for a while
        Thread.CurrentThread.Sleep(2000)

        ' check that the m_ThreadID property hasn't been changed by other threads
        If m_ThreadId = Thread.CurrentThread.Name Then
            Console.WriteLine("m_ThreadID hasn't changed for " & Thread.CurrentThread.Name)
        Else
            Console.WriteLine("m_ThreadID *has* changed for " & Thread.CurrentThread.Name)
        End If
    End Sub

    ' this procedure tests Thread Local Storage

    Sub TestThreadLocalStorage()
        ' Allocate a new unnamed TLS slot.
        Dim slot As LocalDataStoreSlot = Thread.AllocateDataSlot()

        ' The AllocateNamedDataSlot method fails if the slot exists already.
        Dim namedSlot As LocalDataStoreSlot = Thread.AllocateNamedDataSlot("id")

        ' The GetNamedDataSlot method returns a reference to an existing named slot
        ' or creates a new slot if necessary.
        Dim namedSlot2 As LocalDataStoreSlot = Thread.GetNamedDataSlot("id")

        ' Store a value in the slot created previously.
        Thread.SetData(slot, 123)
        ' ...
        ' Read the value back.
        Console.Write(Thread.GetData(slot))     ' => 123

        ' Destroys the slot named ID from all the threads in the current application.
        Thread.FreeNamedDataSlot("id")
    End Sub

    ' this procedure tests sharing data with a thread with DataClass

    Sub TestThreadData()
        Dim i As Integer
        Dim dc(9) As ThreadData
        Dim t As Thread
        Dim allDone As Boolean

        ' Create multiple threads.
        For i = 0 To 9
            ' Create a new data object and initialize its property
            dc(i) = New ThreadData()
            dc(i).Id = i + 1
            dc(i).Msg = "A message"
            ' Create a new thread and define its starting point.
            t = New Thread(AddressOf dc(i).DoTheTask)
            t.Start()
        Next

        ' Poll until all threads have completed.
        ' (Just an example that retrieves values from threads.)
        Do Until allDone
            Console.WriteLine("Waiting...")
            Thread.CurrentThread.Sleep(200)
            ' Check that all threads have set Done=True.
            allDone = True
            For i = 0 To 9
                allDone = allDone And dc(i).Done
            Next
        Loop
    End Sub

    ' this procedure tests using events for thread notifications

    ' NOTE: if you make this variable ThreadStatic, the program won't work any longer
    ' because each thread will decrement a different copy of the variable.
    '<ThreadStatic()> _
    Dim runningThreads As Integer

    Sub TestEventNotifications()
        Dim i As Integer
        Dim dc(4) As ThreadData2
        Dim t As Thread

        Thread.CurrentThread.Name = "Main thread"

        ' Create multiple threads.
        For i = 0 To 4
            ' Create a new data object and initialize its property
            dc(i) = New ThreadData2()
            dc(i).Id = i + 1
            dc(i).Msg = "A message"
            ' have this object's events point to the local event procedure
            AddHandler dc(i).TaskCompleted, AddressOf TaskCompleted
            ' Create a new thread and define its starting point.
            t = New Thread(AddressOf dc(i).DoTheTask)
            t.Name = "Thread #" & dc(i).Id.ToString
            t.Start()
            ' increment number of running threds
            runningThreads += 1
        Next

        ' Poll until all threads have completed.
        ' (Just an example that retrieves values from threads.)
        Do Until runningThreads = 0
            Console.WriteLine("Waiting...")
            Thread.CurrentThread.Sleep(200)
        Loop
    End Sub

    ' an event procedure that runs when another thread terminates

    Sub TaskCompleted(ByVal Sender As Object, ByVal endTime As Date)
        ' get the ID of the thread that terminated
        Dim id As Integer = CType(Sender, ThreadData2).Id
        ' display a message
        '        Console.WriteLine("Thread {0} terminated at {1}.", id, endTime)
        Console.WriteLine("Thread {0} terminated (Running on {1})", id, Thread.CurrentThread.Name)
        ' decrement counter of running threads.
        runningThreads -= 1
    End Sub

    ' this procedure tests the ThreadWrapperBase class

    Sub TestWrapperClass()
        Dim i As Integer
        Dim mytasks(10) As MyTask

        For i = 1 To 10
            ' Initialize thread data, then start the thread.
            mytasks(i) = New MyTask(i, "Message from thread")
            mytasks(i).Thread.Name = "Thread #" & CStr(i)
            mytasks(i).Start()
        Next

        ' Wait until all tasks have completed.
        For i = 1 To 10
            Do Until mytasks(i).Done
                Console.WriteLine("Waiting...  (Main thread)")
                Thread.Sleep(200)
            Loop
        Next
    End Sub

    ' this procedure shows problems caused by lack of synchronization

    Sub TestSynchronizationProblem()
        ' Create five auxiliary threads.
        Dim i As Integer
        For i = 1 To 5
            Dim t As New Thread(AddressOf DoTheTask4)
            ' Assign a name to this thread, so that we can track its output.
            t.Name = "Thread #" & i.ToString
            t.Start()
        Next
    End Sub

    Sub DoTheTask4()
        ' Print a lot of information to the console window.
        Dim i As Integer
        For i = 1 To 100
            ' Split the output line in pieces.
            Console.Write("Message ")
            Console.Write("from ")
            Console.WriteLine(Thread.CurrentThread.Name)
            'Thread.Sleep(20)
        Next
    End Sub

    ' this procedure shows the solution based on SyncLock

    Sub TestSyncLock()
        ' Create five auxiliary threads.
        Dim i As Integer
        For i = 1 To 5
            Dim t As New Thread(AddressOf DoTheTask5)
            ' Assign a name to this thread, so that we can track its output.
            t.Name = "Thread #" & i.ToString
            t.Start()
        Next
    End Sub

    ' The lock object (any non-Nothing value will do).
    Dim consoleLock As String = "lock me"

    Sub DoTheTask5()
        ' Print a lot of information to the console window.
        Dim i As Integer
        For i = 1 To 100
            SyncLock consoleLock
                ' Split the output line in pieces.
                Console.Write("Message ")
                Console.Write("from ")
                Console.WriteLine(Thread.CurrentThread.Name)
            End SyncLock
        Next
    End Sub

    ' this procedure tests the SyncRoot property

    Dim dblArr() As Double = {1.24, 456.9, 1.11, 99.34, 543.56}

    Sub TestSyncRoot()
        Dim t As New Thread(AddressOf DoTheTask6)
        t.Start()
        t.Join()
    End Sub

    Sub DoTheTask6()
        Dim sum As Double
        SyncLock dblArr.SyncRoot
            ' Inside this block access to the ArrayList is thread-safe.
            Dim d As Double
            For Each d In dblArr
                sum += d
            Next
            Console.WriteLine("sum is {0}", sum)     ' => sum is 1102.15
        End SyncLock
    End Sub

    ' this procedure tests the Monitor.Enter / Exit methods

    Sub TestMonitorEnter()
        ' Create five auxiliary threads.
        Dim threads(5) As Thread

        Dim i As Integer
        For i = 1 To 5
            threads(i) = New Thread(AddressOf DoTheTask7)
            ' Assign a name to this thread, so that we can track its output.
            threads(i).Name = "Thread #" & i.ToString
            threads(i).Start()
        Next

        ' wait until all threads terminate
        For i = 1 To UBound(threads)
            threads(i).Join()
        Next
    End Sub

    Sub DoTheTask7()
        ' Print a lot of information to the console window.
        Dim i As Integer
        For i = 1 To 100
            Monitor.Enter(consoleLock)
            ' Split the output line in pieces.
            Console.Write("Message ")
            Console.Write("from ")
            Console.WriteLine(Thread.CurrentThread.Name)
            Monitor.Exit(consoleLock)
        Next
    End Sub

    ' this procedure tests the Monitor.Enter / Exit methods

    Sub TestMonitorTryEnter()
        ' Create five auxiliary threads.
        Dim threads(5) As Thread

        Dim i As Integer
        For i = 1 To 5
            threads(i) = New Thread(AddressOf DoTheTask8)
            ' Assign a name to this thread, so that we can track its output.
            threads(i).Name = "Thread #" & i.ToString
            threads(i).Start()
        Next

        ' wait until all threads terminate
        For i = 1 To UBound(threads)
            threads(i).Join()
        Next
    End Sub

    Sub DoTheTask8()
        ' Print a lot of information to the console window.
        Dim i As Integer
        For i = 1 To 100
            Do Until Monitor.TryEnter(consoleLock, 10)
                Console.WriteLine("{0} failed to acquire the lock", Thread.CurrentThread.Name)
            Loop

            ' Split the output line in pieces.
            Console.Write("Message ")
            Console.Write("from ")
            Console.WriteLine(Thread.CurrentThread.Name)
            ' Release the lock.
            Monitor.Exit(consoleLock)
        Next
    End Sub

    ' this procedure tests the Interlocked class

    Sub TestInterlocked()
        ' Create ten auxiliary threads.
        Dim threads(10) As Thread

        Dim i As Integer
        For i = 1 To 10
            threads(i) = New Thread(AddressOf DoTheTask9)
            ' Assign a name to this thread, so that we can track its output.
            threads(i).Name = "Thread #" & i.ToString
            threads(i).Start()
        Next

        ' wait until all threads terminate
        For i = 1 To UBound(threads)
            threads(i).Join()
        Next
    End Sub

    ' Increment and Decrement methods work with 32-bit integers.
    Dim lockCounter As Integer

    Sub DoTheTask9()
        ' Print a lot of information to the console window.
        Dim i As Integer

        ' Note that not all threads will print all the 100 messages

        For i = 1 To 100
            ' Increment the lock counter and return the new value.
            ' (Up to 4 threads are allowed to run in the critical section.)
            If Interlocked.Increment(lockCounter) <= 4 Then
                ' display number of threads in the critical section
                Console.WriteLine("Message from {0}  ({1} threads running in critical section)", Thread.CurrentThread.Name, lockCounter)
                Thread.Sleep(10)
            End If
            ' Allow other threads to enter the critical section.
            Interlocked.Decrement(lockCounter)
        Next
    End Sub

    ' this procedure tests the Mutex object

    ' three mutex objects, representing three available resources
    Dim mutexes() As Mutex = {New Mutex(), New Mutex(), New Mutex()}

    Sub TestMutex()
        ' Create ten auxiliary threads.
        Dim threads(10) As Thread

        Dim i As Integer
        For i = 1 To 10
            threads(i) = New Thread(AddressOf DoTheTask10)
            ' Assign a name to this thread, so that we can track its output.
            threads(i).Name = "Thread #" & i.ToString
            threads(i).Start()
        Next

        ' wait until all threads terminate
        For i = 1 To UBound(threads)
            threads(i).Join()
        Next
    End Sub

    Sub DoTheTask10()
        ' Print a lot of information to the console window.
        Dim i As Integer
        For i = 1 To 100
            Dim mutexNdx As Integer = Mutex.WaitAny(mutexes)
            ' use only the resource representing the mutexNdx.
            Console.WriteLine("{0} is using Mutex #{1}", Thread.CurrentThread.Name, mutexNdx)
            mutexes(mutexNdx).ReleaseMutex()
        Next
    End Sub

    ' This procedure tests the ReaderWriterLock class

    Dim rwl As New ReaderWriterLock()
    Dim rnd As New Random()

    Sub TestReaderWriterLock()
        Dim i As Integer
        For i = 1 To 10
            Dim t As New Thread(AddressOf DoTheTask12)
            t.Name = i.ToString
            t.Start()
        Next
        Thread.Sleep(20000)
    End Sub

    Sub DoTheTask12()
        Dim i As Integer
        Dim tname As String = Thread.CurrentThread.Name()
        ' Perform 10 read or write operations. (Reads are more frequent.)
        For i = 1 To 10
            If rnd.NextDouble < 0.8 Then
                ' Attempt a read operation.
                rwl.AcquireReaderLock(Timeout.Infinite)
                Console.WriteLine("Thread {0} is reading", tname)
                Thread.Sleep(300)
                Console.WriteLine("Thread {0} completed the read operation", _
                    tname)
                rwl.ReleaseReaderLock()
            Else
                ' Attempt a write operation.
                rwl.AcquireWriterLock(Timeout.Infinite)
                Console.WriteLine("Thread {0} is writing", tname)
                Thread.Sleep(300)
                Console.WriteLine("Thread {0} completed the write operation", _
                    tname)
                rwl.ReleaseWriterLock()
            End If
        Next
    End Sub

    ' This procedure tests the AutoResetEvent class

    ' The shared AutoResetEvent object
    Public are As New AutoResetEvent(False)
    ' The ArrayList where matching filenames should be added
    Public filesAl As New ArrayList()
    ' The number of running threads
    Public searchingThreads As Integer

    Sub TestAutoResetEvent()
        ' Search the file in all the subdirectories of C:
        Dim dirname As String
        For Each dirname In System.IO.Directory.GetDirectories("C:\")
            Interlocked.Increment(searchingThreads)
            ' Create a new wrapper class, pointing to a subdirectory.
            Dim sf As New FileFinder(dirname, "*.zip")
            ' Create a new thread for that subdirectory only, and run it.
            Dim t As New Thread(AddressOf sf.StartSearch)
            t.Start()
        Next

        ' Remember how many results we have so far.
        Dim resCount As Integer = 0
        Do While searchingThreads > 0
            ' Wait until there are new results.
            are.WaitOne()

            ' Note that you should always use the SyncRoot property when using
            ' an ArrayList and other collectionlike objects as lock objects.
            SyncLock filesAl.SyncRoot
                ' Display names of all new results.
                Dim i As Integer
                For i = resCount To filesAl.Count - 1
                    Console.WriteLine(filesAl(i))
                Next
                ' Remember that you've displayed these filenames.
                resCount = filesAl.Count
            End SyncLock
        Loop
        Console.WriteLine("")
        Console.WriteLine("Found {0} files", resCount)
    End Sub

    ' this procedure tests the ThreadPool class

    Sub TestThreadPool()
        Dim i As Integer
        For i = 1 To 20
            Try
                ' Create a new object for the next lightweight task.
                Dim task As New LightweightTask()
                ' Pass additional information to that object
                ' (Not used in this demo).
                task.SomeData = "other data"
                ' Run the task with a thread from the pool
                ' (Pass the counter as an argument).
                ThreadPool.QueueUserWorkItem( _
                   New WaitCallback(AddressOf task.DoTheTask), i)
            Catch e As NotSupportedException
                Console.WriteLine("Failed (maybe a non-Windows 2000 system)")
                Exit Sub
            End Try
        Next

        ' Give all lightweight threads a chance to complete.
        Thread.Sleep(4000)
    End Sub

    ' this procedure tests the System.Timers.Timer class

    Dim WithEvents Timer As System.Timers.Timer
    Dim eventCount As Integer

    Sub TestServerTimer()
        ' Initialize the time to fire every  second.
        ' (You can change it later through the Interval property.)
        Timer = New System.Timers.Timer(1000)
        ' True means it fires repeatedly, False means it fires only once.
        Timer.AutoReset = True
        ' Ensure the timer is enabled. (Same as Start method.)
        Timer.Enabled = True

        ' Pause here until 5 events fire.
        Do
            Console.WriteLine("Message from main thread")
            Thread.Sleep(100)
        Loop Until eventCount = 5

        ' Stop the timer (not really necessary in this example).
        Timer.Stop()        ' Same as Timer.Enabled = False.
        ' Release all resources.
        Timer.Close()
    End Sub

    ' The Elapsed event
    Public Sub Timer_Elapsed(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs) Handles Timer.Elapsed
        ' Display current system time in Output window.
        Console.WriteLine("Event raised at {0}", e.SignalTime)
        ' Remember how many events fired so far.
        eventCount += 1
    End Sub

    ' this procedure tests the System.Threading.Timer

    Sub TestThreadingTimer()
        ' Get the first callback after 1 second
        Dim dueTime As New TimeSpan(0, 0, 1)
        ' get additional callbacks every half a second
        Dim period As New TimeSpan(0, 0, 0, 0, 500)
        ' create the timer
        Dim t As New System.Threading.Timer(New TimerCallback(AddressOf TimerProc), Nothing, dueTime, period)

        ' wait for 5 seconds in this demo.
        Thread.Sleep(5000)

        ' destroy the timer
        t.Dispose()
    End Sub

    ' the callback procedure

    Sub TimerProc(ByVal state As Object)
        ' Display current system time in Output window.
        Console.WriteLine("Callback proc called at {0}", Date.Now)
    End Sub

    ' this procedure tests the Synchronization attribute

    Dim disp As New Display()

    Sub TestSynchronizationAttribute()
        Dim i As Integer
        Dim threads(10) As Thread
        Dim o As New Object()

        For i = 1 To 10
            threads(i) = New Thread(AddressOf DoTheTask11)
            threads(i).Name = "Thread #" & i.ToString
            threads(i).Start()
        Next

        ' wait for all threads to terminate.
        For i = 1 To UBound(threads)
            threads(i).Join()
        Next
    End Sub

    Sub DoTheTask11()
        ' Print a lot of information to the Output window.
        Dim i As Integer
        For i = 1 To 20
            disp.DisplayData()
        Next
    End Sub

End Module