首先来一个小的asp.net mvc 4的sample,代码如下:
HomeController:
using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.Mvc; using System.Web.SessionState; namespace MvcApplication2.Controllers { public class HomeController : Controller { // // GET: /Home/ public ActionResult Index() { return View(); } public ActionResult Test() { //这里为了测试执行了等待30秒的代码,实际项目中会遇到 //很多类似需要很长时间的情况,比如调用webservice,或者处理很大数据 System.Threading.Thread.Sleep(30000); return View(); } } }
Global.asax:
using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.Http; using System.Web.Mvc; using System.Web.Optimization; using System.Web.Routing; namespace MvcApplication2 { // Note: For instructions on enabling IIS6 or IIS7 classic mode, // visit http://go.microsoft.com/?LinkId=9394801 public class MvcApplication : System.Web.HttpApplication { protected void Application_Start() { AreaRegistration.RegisterAllAreas(); WebApiConfig.Register(GlobalConfiguration.Configuration); FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters); RouteConfig.RegisterRoutes(RouteTable.Routes); BundleConfig.RegisterBundles(BundleTable.Bundles); } protected void Session_Start(object sender, EventArgs e) { } } }
Views中的代码省略。
这么简单的程序如果我们运行会发现一个问题:当我打开浏览器打开两个tab,先在一个tab中打开/Home/Test,这时这个tab会等30秒才能呈现页面,在这期间我在另一个tab中打开 /Home/Index,只有等第一个tab30秒过后,第二个tab才能呈现/Home/Index。而这种情况如果在实际项目中会非常影响性能,比如我们如果需要访问webservice耗用大量时间获取一些数据,同时我们又要通过ajax发送请求去处理一个查询,这时如果按照上面的做法,只能等待webservice方法执行完毕后才能处理ajax请求。(Note:这种情况只有在同一个session下存在,如果上面的操作不打开两个tab而是换成两个浏览器,类似情况不会发生)
解决方案:
这里我们需要了解一下asp.net mvc 中的SessionState的作用:
在stackoverflow的一片文章记录到:
Session state is designed so that only one request from a particular user/session occurs at a time. So if you have a page that has multiple AJAX callbacks happening at once they will be processed in serial fashion on the server. Going session-less means that they would execute in parallel.
大意就是Session state是用来将同一个session的请求按顺序处理,如果需要并行处理则需要设置session-less。
如何设置SessionState呢?
mvc4中可以在controller上面加如下Attribute:(在System.Web.SessionState命名空间下)
[SessionState(SessionStateBehavior.ReadOnly)]
mvc3加如下Attribute:
[ControllerSessionState(SessionStateBehavior.ReadOnly)]
SessionStateBehavior四个选项中的区别:
- Default – Same as Required.
- Required – A full Session lock is taken, and requests to this controller are serialized. This is the normal MVC behavior.
- ReadOnly – A Session lock is not taken, and a controller can read values in Session, but it cannot modify the values in Session. Requests to this controller will be parallelized.
- Disabled – Session is unavailable within this controller, and attempts to use it will be met with an error. Requests to this controller will be parallelized
Asp.net mvc 中处理同一个session的并行请求的问题