IBM User Guide for Java V7 on Windows > Troubleshooting and support > Using diagnostic tools

Shared classes diagnostic data

Understanding how to diagnose problems that might occur will help you to use shared classes mode.

For an introduction to shared classes, see Class data sharing.

• Deploying shared classes
  You cannot enable class sharing without considering how to deploy it sensibly for your application. This section looks at some of the important issues to consider.
• Dealing with runtime bytecode modification
  Modifying bytecode at run time is an increasingly popular way to engineer required function into classes. Sharing modified bytecode improves startup time, especially when the modification being used is expensive. You can safely cache modified bytecode and share it between JVMs, but there are many potential problems because of the added complexity. It is important to understand the features described in this section to avoid any potential problems.
• Understanding dynamic updates
  The shared class cache must respond to file system updates; otherwise, a JVM might load classes from the cache that are out of date or "stale". After a class has been marked stale, it is not returned by the cache if it is requested by a class loader. Instead, the class loader must reload the class from disk and store the updated version in the cache.
• Using the Java Helper API
  Classes are shared by the bootstrap class loader internally in the JVM. Any other Java class loader must use the Java Helper API to find and store classes in the shared class cache.
• Understanding shared classes diagnostics output
  When running in shared classes mode, a number of diagnostics tools can help you. The verbose options are used at run time to show cache activity and you can use the printStats and printAllStats utilities to analyze the contents of a shared class cache.
• Debugging problems with shared classes
  The following sections describe some of the situations you might encounter with shared classes and also the tools that are available to assist in diagnosing problems.
• Class sharing with OSGi ClassLoading framework
  Eclipse releases after 3.0 use the OSGi ClassLoading framework, which cannot automatically share classes. A Class Sharing adapter has been written specifically for use with OSGi, which allows OSGi class loaders to access the class cache.

Parent: Using diagnostic tools

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