由于asp2.0提供了异步页的支持使异步调用webservice的性能有了真正的提升。
使用异步页，首先要设置async="true"，异步页是在prerender和prerendercomplete事件间加入begin，end异步方法实现的，begin和end方法属于不同的线程。
ws异步页的实现有两种方式：
1、使用等待方法实现异步
通用类，封装了ws
/**//// <summary>
        /// 使用等待方法实现异步
        /// </summary>
        /// <param name="name"></param>
        /// <returns></returns>
        private account account;
        private string username;
        public account account
        {
            get { return account; }
            set { account = value; }
        }
        public string username
        {
            get { return username; }
            set { username = value; }
        }
        public iasyncresult beginasyncgetaccount(object sender, eventargs e, asynccallback cb, object state)
        {
          
            return vb.begingetaccountbyname(username,cb,state);
        }
        public void endasyncgetaccount(iasyncresult ar)
        {
            account = vb.endgetaccountbyname(ar);
        }

          /**//// <summary>
        /// 使用事件驱动的异步
        /// </summary>
        /// <param name="username"></param>
        public void getaccountcompleted(object source, vb.getaccountbynamecompletedeventargs e)
        {
            account = e.result;
        }
        public void asgetaccount(string username)
        {
                      vb.getaccountbynamecompleted += new getaccountbynamecompletedeventhandler(getaccountcompleted);
            vb.getaccountbynameasync(username）
           
        }调用方法
 protected void page_load(object sender, eventargs e)
    {
        this.prerendercomplete += new eventhandler(page_prerendercomplete);
        b.username = "dinghao";
      
        addonprerendercompleteasync(b.beginasyncgetaccount, b.endasyncgetaccount);
    }
    protected void page_prerendercomplete(object sender, eventargs e)
    {
        //异步调用结束
        vb.account a = b.account;
        accountif ai = new accountif(a);
        ais[0] = ai;
        gridview1.datasource = ais;
        gridview1.databind();
    }由于addonprerendercompleteasync的两个委托都是void类型，所以在通用类中要加入有返回值的属性如：account供主调方法使用，另外委托中没有异步方法的参数信息，要加入参数的属性如：username
2、事件驱动的异步（2.0新增）
调用方法：
protected void page_load(object sender, eventargs e)
    {
        this.prerendercomplete += new eventhandler(page_prerendercomplete);
        b.asgetaccount("dinghao");
    
    }
    protected void page_prerendercomplete(object sender, eventargs e)
    {
        //异步调用结束
        vb.account a = b.account;
        accountif ai = new accountif(a);
        ais[0] = ai;
        gridview1.datasource = ais;
        gridview1.databind();
    }这种调用方式，用的是*completed事件，在*async完成时触发，这种调用方式可以
省去account，username属性，用起来比较简单

http://bluewater.cnblogs.com/archive/2006/06/20/430758.html