Why Do My Static Variables Reset in ASP.NET WebMethods?

ASP.NET Static Variables: Understanding Their Behavior

ASP.NET developers frequently utilize static variables to maintain shared data within classes or modules. However, their lifespan can be unpredictable, particularly within page classes and WebMethods.

The Mystery of Static Variable Resets in WebMethods

A common issue is the unexpected clearing of static variables in page classes, even when the session remains active. This behavior is often confusing.

App Domain Recycling and Class Replacement: The Root Cause

The key to understanding these resets lies in ASP.NET's app domain recycling and class replacement mechanisms. Static variables exist only for the lifetime of an app domain. Recycling the app domain or using a new class instance will cause these variables to be reset. ASP.NET might recompile a page class, effectively replacing the old class with a new one, resulting in the loss of static variable data.

Best Practices: Avoiding Static Variable Loss

To prevent data loss, avoid using static variables directly within page classes. Instead, use a separate class (outside the App_Code folder) to store persistent data. For example:

public static class GlobalData
{
    public static int GlobalCounter;
    public static string GlobalSetting;
}

This approach ensures data persistence across requests and class recompilations.

Important Considerations:

• Pool-Specific Variables: Static variables are shared within an application pool; each pool has its own set.
• App Domain Restarts: App domain restarts always reset static variables, regardless of their location.
• Thread Safety: Static variables are not inherently thread-safe; use the lock keyword for concurrent access.
• True Persistence: For data that needs to survive app domain restarts, use a database, dedicated storage classes, or database-backed session state.

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