Home > 3rd Party Software, Desarrollo > Enhanced memory leak detection prevention from Tomcat7 available in Tomcat6

Enhanced memory leak detection prevention from Tomcat7 available in Tomcat6

Announced in a post here on Tomcat Expert last year, the new memory leak detection and prevention feature has been a widely anticipated new feature that addresses how Tomcat can cause memory leaks in the permanent generation (PermGen) that lead to OutOfMemoryErrors when re-loading web applications.

This feature exists in two parts. First, it prevents memory leaks through a new life-cycle listener, the JreMemoryLeakPreventionListener that calls various parts of the Java API. Its common that if the web application is the first code to call the Java APIs, the web application class loader will be pinned in memory, causing leaks. The listener ensures that Tomcat is the first to make a call, and therefore prevents the class loader from being pinned in memory. For more details on what this listener actually does, the source code is pretty well commented.

Second, it handles detection by executing code when a web application is stopped, undeployed or reloaded. It scans the code for standard causes of memory leaks, and where it can, fixes the leaks. Implemented in the WebappClassLoader, there are a series of expandable, standard API calls and some reflection tricks that help this detection feature do its job. For more on what these checks do, check out the explanation by Sylvain Laurent on the Tomcat Wiki, or of course, you can look at the source code. Start with the clearReferences() method.

Updates to these features are spread over several 6.0 versions, with 6.0.30 having the latest version of the feature.

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