引言
对于使用VB6的开发者而言，要在程序中实现多线程（multi-thread）功能，一般就是使用Win32 API调用。但凡是进行过这种尝试的开发者都会感觉到实现过程非常困难，而且总是会发生些null terminated strings GPF的错误。可是有了VB.NET，一切烦恼都成为过去。
自由线程（free threaded）
在VB6中，我们只能对组件设置多线程模式，这通常就是单元模式的多线程。对于单元线程组件而言，组件中的每个可执行方法都将在一个和组件相联系的线程上运行。这样，我们就可以通过创建新的组件实例，使得每个实例都有一个相应的线程单元，从而达到每个正在运行的组件都有它自己的线程，多个组件可以在各自的单元中同时运行方法。
但是如果在程序的Session或Application控制范围内，我们不会使用单元线程组件，最佳的也是唯一的选择是自由线程组件。可是仅仅有VB6还不行，我们需要VC++或Java的帮助。
现在好了，VB.NET改善了这些功能，.NET SDK中包含的System.Threading名字空间专门负责实现多线程功能，而且操作相当简单：只需要利用System.Threading名字空间中的Thread类，就具有了实现自由线程的属性和方法。
一个创建自由线程的例子解析
我们来看看下面的VB.NET代码，它演示了实现自由线程的过程：
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| Imports System ’ Import the threading namespace Imports System.Threading Public Class clsMultiThreading ’ This is a simple method that runs a loop 5 times ’ This method is the one called by the HelloWorldThreadingInVB ’ class, on a separate thread. Public Sub OwnThread() Dim intCounter as integer For intCounter = 1 to 5 Console.WriteLine("Inside the class: " & intCounter.ToString()) Next End Sub End Class Public Class HelloWorldThreadingInVB ’ This method is executed when this EXE is run Public Shared Sub Main() Dim intCounter as integer ’ Declare an instance of the class clsMultithreading object Dim objMT as clsMultiThreading = new clsMultiThreading() ’ Declare an instance of the Thread object. This class ’ resides in the System.Threading namespace Dim objNewThread as Thread ’Create a New Thread with the Thread Class and pass ’ the address of OwnThread method of clsMultiThreading class objNewThread = new Thread(new ThreadStart(AddressOf objMT.OwnThread)) ’ Start a new Thread. This basically calls the OwnThread ’ method within the clsMultiThreading class ’ It is important to know that this method is called on another ’ Thread, as you will see from the output objNewThread.Start() ’ Run a loop and display count For intCounter = 10 to 15 Console.WriteLine("Inside the Sub Main: " & intCounter.ToString()) Next End Sub End Class |
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