VB.NET并行与分布式编程(6)-线程与内核同步[17]

ReaderWriterLockSlim.EnterUpgradeableReadLock 方法尝试进入可升级模式锁定状态。

 

此方法在调用线程进入锁定状态之前一直处于阻塞状态，因此可能永远都不返回。 使用 TryEnterUpgradeableReadLock 方法阻塞指定的间隔时间，如果调用线程在此间隔期间并未进入可升级模式，将返回。

如果线程在读取模式下经常访问受 ReaderWriterLockSlim 保护的资源，则使用可升级模式；但在满足特定条件时可能需要进入写入模式。 处于可升级模式的线程可以降级为读取模式或升级为写入模式。

任意给定时间都只有一个线程可以进入可升级模式。 如果某个线程处于可升级模式，而且没有线程正等待进入写入模式，则即使有线程等待进入可升级模式，任意数量的其他线程也都可以进入读取模式。

如果一个或多个线程正等待进入写入模式，调用 EnterUpgradeableReadLock 方法的线程在这些线程超时或进入写入模式然后又从中退出之前，将一直受阻。

 

 

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











Module Module1
    Dim myLock As New ReaderWriterLockSlim()
    Dim jg As Double = 300
    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 mythreadread)
        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)
        '执行线程
        mythread3.Start()
        mythread2.Start()
        mythread1.Start()





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


        '线程执行完毕
        Console.WriteLine(Now.ToLongTimeString & "线程执行完毕!")
    End Sub
    Public Sub mythreadrun()
        Dim mynum As Double





        Try
            For mynum = 1 To 100
                '等待升级锁
                Console.WriteLine(Thread.CurrentThread.Name & "===>" & Now.ToLongTimeString & "等待获得升级锁")
                If myLock.TryEnterUpgradeableReadLock(3) Then
                    '获得升级锁
                    Console.WriteLine(Thread.CurrentThread.Name & " 获得升级锁")
                    '获得写锁，执行升级处理
                    myLock.EnterWriteLock()
                    jg -= mynum
                    Console.WriteLine(Thread.CurrentThread.Name & "获得写锁==>" & Now.ToLongTimeString & "=>" & (jg + mynum) & "-" & mynum & "，计算结果为：" & jg)
                    Thread.Sleep(13)
                    '退出写锁
                    myLock.ExitWriteLock()
                    Console.WriteLine(Thread.CurrentThread.Name & "退出写锁==>" & Now.ToLongTimeString)
                    '退出升级锁
                    myLock.ExitUpgradeableReadLock()
                    Console.WriteLine(Thread.CurrentThread.Name & "退出升级锁==>" & Now.ToLongTimeString)
                    If jg < 0 Then
                        Exit For
                    End If
                Else
                    Console.WriteLine(Thread.CurrentThread.Name & "获得升级锁失败")
                End If
                Thread.Sleep(16)
            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!")
        End Try
    End Sub
    Public Sub mythreadread()
        While jg > 0
            '获得升级锁
            Console.WriteLine(Thread.CurrentThread.Name & "===>" & Now.ToLongTimeString & "等待获得升级锁...")
            If myLock.TryEnterUpgradeableReadLock(5) Then
                Console.WriteLine(Thread.CurrentThread.Name & " 获得升级锁" & Now.ToLongTimeString)
                '获得读锁，执行降级处理
                If myLock.TryEnterReadLock(5) Then
                    '退出升级锁
                    Console.WriteLine(Thread.CurrentThread.Name & " 退出升级锁" & Now.ToLongTimeString)
                    Console.WriteLine(Thread.CurrentThread.Name & "==>" & Now.ToLongTimeString & " 获得读锁，当前计算值为{0}", jg)
                    myLock.ExitUpgradeableReadLock()
                    Thread.Sleep(15)
                    myLock.ExitReadLock()
                    Console.WriteLine(Thread.CurrentThread.Name & " 退出读锁和升级锁" & Now.ToLongTimeString)
                Else
                    Console.WriteLine(Thread.CurrentThread.Name & " 获得读锁失败" & Now.ToLongTimeString)
                End If
            Else
                Console.WriteLine(Thread.CurrentThread.Name & " 获得升级锁失败" & Now.ToLongTimeString)
            End If
            Thread.Sleep(10)
        End While
    End Sub
End Module

 效果如下：