VB.NET并行与分布式编程(6)-线程与内核同步[13]

Imports System
Imports System.Threading
Imports System.Diagnostics
Imports System.Diagnostics.ThreadState











Module Module1
    '生产者线程和消费者线程共同操作的数
    Dim mycounts As Integer = 0
    '定义一个互斥对象，用于解决生产线程和消费线程操作mycounts变量的同步问题
    Dim mymutex As New Mutex

    Sub Main()

        Dim mythread1 As Thread
        Dim mythread2 As Thread
        Dim mythread3 As Thread
        Dim mymakethread As Thread






        '创建线程对象
        mythread1 = New Thread(AddressOf mythreadrun)
        mythread2 = New Thread(AddressOf mythreadrun)
        mythread3 = New Thread(AddressOf mythreadrun)
        mymakethread = New Thread(AddressOf mymake)









        Console.WriteLine(Now.ToLongTimeString & "线程对象创建完毕,开始执行线程")

        '定义一个信号量
        Dim mysemaphore As New Semaphore(0, 5)

        '执行线程
        mymakethread.Start(mysemaphore)
        mythread1.Start(mysemaphore)
        mythread2.Start(mysemaphore)
        mythread3.Start(mysemaphore)





        '等待线程完成
        mymakethread.Join()
        mythread1.Join()
        mythread2.Join()
        mythread3.Join()


        '线程执行完毕
        Console.WriteLine(Now.ToLongTimeString & "主线程执行完毕!")
        mysemaphore.Close()


    End Sub
    Public Sub mymake(ByVal semaphore As Semaphore)
        '生产者线程
        Dim i As Integer
        '生产者完成生产5次就退出生产者线程，这里假定就输出一行
        For i = 1 To 5
            Console.WriteLine("{0}号生产者线程等待运行", Thread.CurrentThread.ManagedThreadId)
            '增加1个信号量
            semaphore.Release()
            mymutex.WaitOne()
            mycounts += 1
            Console.WriteLine("{0}号生产者线程运行,目前数量为：{1}", Thread.CurrentThread.ManagedThreadId, mycounts)
            mymutex.ReleaseMutex()
            Thread.Sleep(1)
        Next
    End Sub
    Public Sub mythreadrun(ByVal semaphore As Semaphore)
        '消费者线程,这里假定就输出一行
        Try
            Console.WriteLine("{0}号消费者线程等待运行", Thread.CurrentThread.ManagedThreadId)
            '将信号量的计数减1，如果此时信号量为0，则等待
            semaphore.WaitOne()
            mymutex.WaitOne()
            mycounts -= 1
            Console.WriteLine("{0}号消费者线程运行,目前数量为：{1}", Thread.CurrentThread.ManagedThreadId, mycounts)
            mymutex.ReleaseMutex()
            Thread.Sleep(15)
        Catch
            Console.WriteLine("{0}，{1}号线程异常终止!", Now.ToLongTimeString, Thread.CurrentThread.ManagedThreadId)
            '终止线程
            Thread.CurrentThread.Abort()
        Finally
            Console.WriteLine("{0}，{1}消费者线程运行完成!", Now.ToLongTimeString, Thread.CurrentThread.ManagedThreadId)
        End Try
    End Sub
End Module

为了更直观地体验信号量的功能，我们加入一个mycounts变量，生产线程负责这个变量每次增加1，而消费者线程负责这个变量每次减少1，为了解决同步问题，我们必须要引入互斥，用互斥来保护变量只能同时被一个线程操作 ,代码如上。

这个代码有几个地方需要注意

1、定义一个互斥对象，用于解决生产线程和消费线程操作mycounts变量的同步问题
Dim mymutex As New Mutex

2、主线程执行完毕，关闭信号量
Console.WriteLine(Now.ToLongTimeString & "主线程执行完毕!")
mysemaphore.Close()

3、将对mycounts变量的操作放在互斥体的保护下

            mymutex.WaitOne()
            mycounts += 1
            Console.WriteLine("{0}号生产者线程运行,目前数量为：{1}", Thread.CurrentThread.ManagedThreadId, mycounts)
            mymutex.ReleaseMutex()

其中， mymutex.WaitOne()等待，而 mymutex.ReleaseMutex()释放

此外，WaitHandle.SignalAndWait 方法在解决复杂的同步问题，尤其是防止死锁很有帮助，对于同时操作信号量和互斥体，可以使以原子方式释放互斥体并在事件上等待。WaitHandle.SignalAndWait 方法向一个WaitHandle 发出信号并等待另一个，如果信号和等待都成功完成，则为 true；如果等待没有完成，则此方法不返回,第一个参数为信号，第二个参数为等待

VB.NET并行与分布式编程(6)-线程与内核同步[13]

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