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int val = (int) Application["MyValue"];

Application.UnLock();

You should always use Lock and UnLock together. However, if you omit the call to UnLock, the likelihood of incurring a deadlock is not high because the Microsoft .NET Framework automatically removes the lock when the request completes or times out, or when an unhandled error occurs. For this reason, if you handle the exception, consider using a finally block to clear the lock or expect to face some delay while ASP.NET clears the lock for you when the request ends.

Tradeoffs of Application State

Instead of writing global data to the HttpApplicationState object, you can use public members within the global.asax file. Compared to entries in the HttpApplicationState collection, a global member is preferable because it is strongly typed and does not require a hashtable access to locate the value. On the other hand, a global variable is not synchronized per se and must be manually protected. You have to use language constructs to protect access to these members—for example, the C# lock operator or, in Microsoft Visual Basic .NET, the SyncLock operator.

Whatever form you choose for storing the global state of an application, some general considerations apply regarding the opportunity to store data globally. For one thing, global data storage results in permanent memory occupation. Unless explicitly removed by the code, any data stored in the application global state is removed only when the application shuts down. On one end, putting a few megabytes of data in the application’s memory speeds up access; on the other hand, doing this occupies valuable memory for the entire duration of the application.

For this reason, it is extremely important that you consider using the Cache object (which is discussed further in the next chapter) whenever you have a need for globally shared data. Unlike data stored with Application and global members, data stored in the ASP.NET Cache is subject to an automatic scavenging mechanism that ensures the data is removed when a too-high percentage of virtual memory is being consumed. In addition, the Cache object has a lot of other beneficial features that we’ll explore in the next chapter. The bottom line is that the Cache object was introduced specifically to mitigate the problem of memory occupation and to replace the Application object.

To put it down even clearer, today writing to the Application object is bad practice and is supported only to help with migration from classic ASP, where it was the common and easiest way of storing global data. In ASP.NET, Cache is the recommended solution for a single worker process and distributed caches (for example, Microsoft AppFabric Caching Services) if you’re in a Web farm context.

The Session’s State

The HttpSessionState class provides a dictionary-based model of storing and retrieving session-state values. Unlike HttpApplicationState, this class doesn’t expose its contents to all users operating on the virtual directory at a given time. Only the requests that originate in the context of the same session—that is, those generated across multiple page requests made by the same user—can access the session state. The session state can be stored and published in a variety of ways, including in a Web farm or Web garden scenario. By default, though, the session state is held within the ASP.NET worker process.

The ASP.NET implementation of session state provides some extremely handy facilities—such as support for cookieless browsers, Web farms, and Web gardens—and the capability of being hosted by external processes, including Microsoft SQL Server. In this way, ASP. NET session management can provide an unprecedented level of robustness and reliability. Developers can also create custom data stores for session state. For example, if you need the robustness that a database-oriented solution can guarantee but you work with Oracle databases, you need not install SQL Server as well. By writing a piece of additional code, you can support an Oracle session data store while using the same