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ManualResetEvent类用法小结

编辑:dnawo 日期:2014-08-18

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假设有一个程序中调用了三个异步方法，代码如下：

复制内容到剪贴板程序代码 程序代码
public class Test
{
    public void Todo(string message)
    {
        Console.WriteLine("{0} {1}", DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss"), message);
    }

    private Action<string> _todo = null;

    public Test()
    {
        _todo = Todo;
    }

    public IAsyncResult BeginTodo(string message, AsyncCallback callback, object state)
    {
        return _todo.BeginInvoke(message, callback, state);
    }

    public void EndTodo(IAsyncResult ar)
    {
        _todo.EndInvoke(ar);
    }
}

public class Program
{
    static void callback1(IAsyncResult ar)
    {
        Test test = (Test)ar.AsyncState;
        test.EndTodo(ar);
    }

    static void callback2(IAsyncResult ar)
    {
        Test test = (Test)ar.AsyncState;
        test.EndTodo(ar);
    }

    static void callback3(IAsyncResult ar)
    {
        Test test = (Test)ar.AsyncState;
        test.EndTodo(ar);
    }

    static public void Main(string[] args)
    {
        Test test1 = new Test();
        test1.BeginTodo("test1", callback1, test1);

        Test test2 = new Test();
        test2.BeginTodo("test2", callback2, test2);

        Test test3 = new Test();
        test3.BeginTodo("test3", callback3, test3);

        Console.ReadKey();
    }
}

执行结果如下图所示：



也就是说，异步方法的执行顺序是不固定的，但有时我们希望它们能按顺序执行，修改代码如下：

复制内容到剪贴板程序代码 程序代码
public class Program
{
    static void callback1(IAsyncResult ar)
    {
        Test test = (Test)ar.AsyncState;
        test.EndTodo(ar);

        Test test2 = new Test();
        test2.BeginTodo("test2", callback2, test2);
    }

    static void callback2(IAsyncResult ar)
    {
        Test test = (Test)ar.AsyncState;
        test.EndTodo(ar);

        Test test3 = new Test();
        test3.BeginTodo("test3", callback3, test3);
    }

    static void callback3(IAsyncResult ar)
    {
        Test test = (Test)ar.AsyncState;
        test.EndTodo(ar);
    }

    static public void Main(string[] args)
    {
        Test test1 = new Test();
        test1.BeginTodo("test1", callback1, test1);        

        Console.ReadKey();
    }
}

看着有没有感觉很乱？能不能让代码既像开始那样有条理，又能按顺序执行呢？ManualResetEvent类出场了：

复制内容到剪贴板程序代码 程序代码
public class Program
{
    static ManualResetEvent done1 = new ManualResetEvent(false);
    static ManualResetEvent done2 = new ManualResetEvent(false);
    static ManualResetEvent done3 = new ManualResetEvent(false);

    static void callback1(IAsyncResult ar)
    {
        Test test = (Test)ar.AsyncState;
        test.EndTodo(ar);
        done1.Set();
    }

    static void callback2(IAsyncResult ar)
    {
        Test test = (Test)ar.AsyncState;
        test.EndTodo(ar);
        done2.Set();
    }

    static void callback3(IAsyncResult ar)
    {
        Test test = (Test)ar.AsyncState;
        test.EndTodo(ar);
        done3.Set();
    }

    static public void Main(string[] args)
    {
        Test test1 = new Test();
        test1.BeginTodo("test1", callback1, test1);
        done1.WaitOne(); //阻塞当前线程，待Set后继续执行

        Test test2 = new Test();
        test2.BeginTodo("test2", callback2, test2);
        done2.WaitOne(); //阻塞当前线程，待Set后继续执行

        Test test3 = new Test();
        test3.BeginTodo("test3", callback3, test3);
        done3.WaitOne(); //阻塞当前线程，待Set后继续执行

        Console.ReadKey();
    }
}


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