VB.NET并行与分布式编程(六)-线程与内核同步[5]

VB.NET并行与分布式编程(6)-线程与内核同步[5]

在以前的示例中，主线程都是以join的方式等待3个工作线程一起完成连续减法运算，现在我们用上节所说的WaitHandle类，我们使用其中的一个方法WaitHandle.WaitAll，这个方法能同时等待多个线程，只至所有等待对象都完成

Imports SystemImports System.ThreadingImports System.DiagnosticsImports System.Diagnostics.ThreadStateModule Module1 <MTAThread()> _ Sub Main() Dim mythread1 As Thread Dim mythread2 As Thread Dim mythread3 As Thread '创建线程对象 mythread1 = New Thread(AddressOf mythreadrun) mythread2 = New Thread(AddressOf mythreadrun) mythread3 = New Thread(AddressOf mythreadrun) mythread1.Name = "thread_1" mythread2.Name = "thread_2" mythread3.Name = "thread_3" Console.WriteLine(Now.ToLongTimeString & "线程对象创建完毕,开始执行线程") Dim myprocess As Process = Process.GetCurrentProcess() Console.WriteLine("进程名称:" & myprocess.ProcessName) '分别给每个线程创建一个AutoResetEvent Dim threadevent(2) As AutoResetEvent threadevent(0) = New AutoResetEvent(False) threadevent(1) = New AutoResetEvent(False) threadevent(2) = New AutoResetEvent(False) '执行线程 mythread1.Start(threadevent(0)) mythread2.Start(threadevent(1)) mythread3.Start(threadevent(2)) '等待线程执行完毕 WaitHandle.WaitAll(threadevent) '线程执行完毕 Console.WriteLine(Now.ToLongTimeString & "线程执行完毕!") End Sub Public Sub mythreadrun(ByVal threadevent As Object) Dim mynum As Double Static Dim jg As Double = 1000 Static autoEvent As New AutoResetEvent(True) Try For mynum = 1 To 5 Step 0.1 autoEvent.WaitOne() jg -= mynum Console.WriteLine(Thread.CurrentThread.Name & "==>" & Now.ToLongTimeString & "=>" & (jg + mynum) & "-" & mynum & "，计算结果为：" & jg) autoEvent.Set() Next Catch Console.WriteLine(Thread.CurrentThread.Name & " " & Now.ToLongTimeString & "线程异常终止!") '终止线程 Thread.CurrentThread.Abort() Finally Console.WriteLine(Thread.CurrentThread.Name & "优先级: " & Thread.CurrentThread.Priority.ToString) Console.WriteLine(Thread.CurrentThread.Name & " " & Now.ToLongTimeString & "线程运行完毕!") autoEvent.Set() CType(threadevent, AutoResetEvent).Set() End Try End SubEnd Module

??上述代码中，有几个要点：

1）要使用多线程套间（MTAThread ），以前我们使用的是单线程套间（STAThread），但WaitHandle.WaitAll要求

运动在MTAThread下

将<MTAThread()> 标志加上
Module Module1

??? <MTAThread()> _
??? Sub Main()

2）定义一个AutoResetEvent数组，并初始化

??????? Dim threadevent(2) As AutoResetEvent
??????? threadevent(0) = New AutoResetEvent(False)
??????? threadevent(1) = New AutoResetEvent(False)
??????? threadevent(2) = New AutoResetEvent(False)

?

3)将数组中的元素分别传给3个线程

??????? mythread1.Start(threadevent(0))
??????? mythread2.Start(threadevent(1))
??????? mythread3.Start(threadevent(2))

然后主线程等待这数组中的3个元素都为终止状态，即所有运算完成才终止

????? Finally
??????????? Console.WriteLine(Thread.CurrentThread.Name & "优先级:? " & Thread.CurrentThread.Priority.ToString)
??????????? Console.WriteLine(Thread.CurrentThread.Name & "? " & Now.ToLongTimeString & "线程运行完毕!")
??????????? autoEvent.Set()
??????????? CType(threadevent, AutoResetEvent).Set()
最后在前面的例子中，如果一个线程计算发生错误，则可能会导致autoEvent.Set()没有执行，将会造成其它线程永久性等待。因此本节将autoEvent.Set()加入?? Finally中



?