Added comments only.

git-svn-id: https://svn.apache.org/repos/asf/jakarta/commons/proper/logging/trunk@370738 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/commons/logging/impl/ServletContextCleaner.java

@@ -68,6 +68,33 @@ public class ServletContextCleaner implements ServletContextListener {
         // Walk up the tree of classloaders, finding all the available
         // LogFactory classes and releasing any objects associated with
         // the tccl (ie the webapp).
+        //
+        // When there is only one LogFactory in the classpath, and it
+        // is within the webapp being undeployed then there is no problem;
+        // garbage collection works fine.
+        //
+        // When there are multiple LogFactory classes in the classpath but
+        // parent-first classloading is used everywhere, this loop is really
+        // short. The first instance of LogFactory found will
+        // be the highest in the classpath, and then no more will be found.
+        // This is ok, as with this setup this will be the only LogFactory
+        // holding any data associated with the tccl being released.
+        //
+        // When there are multiple LogFactory classes in the classpath and
+        // child-first classloading is used in any classloader, then multiple
+        // LogFactory instances may hold info about this TCCL; whenever the
+        // webapp makes a call into a class loaded via an ancestor classloader
+        // and that class calls LogFactory the tccl gets registered in
+        // the LogFactory instance that is visible from the ancestor
+        // classloader. However the concrete logging library it points
+        // to is expected to have been loaded via the TCCL, so the 
+        // underlying logging lib is only initialised/configured once.
+        // These references from ancestor LogFactory classes down to
+        // TCCL classloaders are held via weak references and so should
+        // be released but there are circumstances where they may not.
+        // Walking up the classloader ancestry ladder releasing
+        // the current tccl at each level tree, though, will definitely
+        // clear any problem references.
         ClassLoader loader = tccl;
         while (loader != null) {
             // Load via the current loader. Note that if the class is not accessable