如何确定ASP.NET应用程序域的生命周期

微软称Application_Start是：

Called when the first resource (such
as a page) in an ASP.NET application
is requested. The Application_Start
method is called only one time during
the life cycle of an application. You
can use this method to perform startup
tasks such as loading data into the
cache and initializing static values.

这就是我们目前的做法：

protected void Application_Start(object sender,EventArgs e)
{
    _counters.Get<AutoCounter>("TAS:RequestCount").Reset();
    _counters.Get<AutoCounter>("TAS:RequestTime").Reset();
    _counters.Get<AutoCounter>("TAS:TimeBetweenErrors").Reset();
    _counters.Get<AutoCounter>("TAS:ErrorCount").Reset();
}

但是,它们会以意外的间隔重置.什么决定应用程序域的生命周期何时结束,并在下一个请求中调用此方法？