VB.NET并行与分布式编程(6)-线程与内核同步[12]

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我们还可以使用信号量来完成同步

?Semaphore 类限制可同时访问某一资源或资源池的线程数，即信号量。

?线程通常使用 WaitOne 方法进入信号量，并且通常使用此方法重载以退出

Imports SystemImports System.ThreadingImports System.DiagnosticsImports System.Diagnostics.ThreadStateModule Module1 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 Dim mycount 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，并返回调用Release之前的信号量 mycount = semaphore.Release() Console.WriteLine("{0}号生产者线程运行,上次线号量为：{1}", Thread.CurrentThread.ManagedThreadId, mycount) 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() Console.WriteLine("{0}号消费者线程运行", Thread.CurrentThread.ManagedThreadId) 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 SubEnd Module

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?上述代码有几个地方需要注意：

1、信号量的增加

Release()方法释放信号量，实质是增加一个信号量

Release()方法可以带参数，其参数可以指定增加几个信号量

2、信号量关闭

用完信号量后，需要关闭,close()

3、信号量的减少

WaitOne()方法实现等待信号量，如果还有信号量可以供使用，则减1

4、信号量对象的初始化

Dim mysemaphore As New Semaphore(0, 5)
0为初始值，5为最大值

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