How to send mails automatically after a time period????

We need something in ASP.NET that is continuously running and gives us a callback. The IIS web server is continuously running. So, we somehow need to get a frequent callback from it so that we can lookup a job queue and see if there's something that needs to be executed. Now, there are several ways a web server comes to us:

• When a page hits
• When an application starts
• When an application stops
• When a session starts and ends/timeouts
• When a cache item expires

The page hit is random. If nobody visits your website for hours, you can't do the pending jobs for hours. Besides, the execution of a request is very short and needs to finish as soon as possible. If you plan to execute scheduled jobs on page execution, then the page will take longer to execute, which will result in a poor user experience. So, clearly this is not an option.

When an application starts, we get a callback in the Application_Start method of Global.asax. So, this is a good place to start a background thread which runs forever and executes scheduled jobs. However, the thread can be killed anytime the web server decides to take a nap due to zero load.

When an application stops, we get a callback at Application_End. But we can't do anything here because the whole application is going to die soon.

Session_Start in Global.asax is triggered when a user visits a page that requires a new session to be initiated. So, this is also random. We need something that fires consistently and periodically.

A cache item expires on a given time or duration. In ASP.NET, you can add entries in the Cache and set an absolute expiry date time, or you can set a duration after which the item is removed from the cache. You can do this by utilizing the following method of the Cache class:

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public void Insert ( System.String key , System.Object value , 
                     System.Web.Caching.CacheDependency dependencies , 
                     System.DateTime absoluteExpiration , 
                     System.TimeSpan slidingExpiration , 
                     System.Web.Caching.CacheItemPriority priority , 
                     System.Web.Caching.CacheItemRemovedCallback onRemoveCallback )

The onRemoveCallback is a delegate to a method which is called whenever a cache item expires. In that method, we can do anything we like. So, this is a good candidate for running code periodically, consistently without requiring any page visit.

Thank You...