使用异步调用，某些时候可以提高性能，比如说写日志，对数据库进行操作的时候就可以使用异步操作的方式。这种方式相当于多线程并发运行，所以性能会有所提升。我后面会发篇随笔来使用异步调用的方法写日志。code:
　　using System;
　　namespace Sandals.Demo.AsynchronousCall
　　{
　　public static class AsyncDemo
　　{
　　//声明委托
　　private delegate string AsyncMethodCalledEventHander(int duration, out int threadId);
　　//create an instance of the delegate
　　private static AsyncMethodCalledEventHander eventHandler = new AsyncMethodCalledEventHander(MethodForAsyncCall);
　　/// <summary>
　　/// The method to be executed asynchronously
　　/// </summary>
　　/// <param name="duration">sleep duration for thread</param>
　　/// <param name="threadId">current thread id</param>
　　/// <returns></returns>
　　private static string MethodForAsyncCall(int duration, out int threadId)
　　{
　　Console.WriteLine("MethodForAsyncCall begin execute... ");
　　System.Threading.Thread.Sleep(duration);
　　threadId = System.Threading.Thread.CurrentThread.ManagedThreadId;
　　return String.Format("my execute time was {0} ", duration);
　　}
　　/// <summary>
　　/// this method for executing asyc method
　　/// </summary>
　　/// <param name="duration"></param>
　　/// <returns></returns>
　　public static IAsyncResult BeingRun(int duration)
　　{
　　int dumy;
　　IAsyncResult result = eventHandler.BeginInvoke(duration, out dumy, null, null);
　　return result;
　　}
　　/// <summary>
　　/// this methiod end the asyc method
　　/// </summary>
　　/// <param name="threadId"></param>
　　/// <param name="ar"></param>
　　/// <returns></returns>
　　public static string EndRun(out int threadId, IAsyncResult ar)
　　{
　　if (ar == null)
　　throw new NullReferenceException("parameter ar can not be a null");
　　return eventHandler.EndInvoke(out threadId, ar);
　　}
　　}
　　class Program
　　{
　　static void Main(string[] args)
　　{
　　IAsyncResult result = AsyncDemo.BeingRun(10000);
　　Console.WriteLine("the thread {0} continue to execute", System.Threading.Thread.CurrentThread.ManagedThreadId);
　　Console.WriteLine("the thread {0} begin to sleep, date: {1}", System.Threading.Thread.CurrentThread.ManagedThreadId, DateTime.Now);
　　System.Threading.Thread.Sleep(3000);
　　Console.WriteLine("the thread {0} sleep end, date: {1}", System.Threading.Thread.CurrentThread.ManagedThreadId, DateTime.Now);
　　int threadId = 0;
　　Console.WriteLine("call the mothod to end the ansychronous method");
　　Console.WriteLine("asynchronous method return value: {0}. thread id: {1}", AsyncDemo.EndRun(out threadId, result), threadId);
　　}
　　}
　　}