Executes {@link ASTRunnable#runOnAST(ILanguage, IASTTranslationUnit)} with the AST
	 * provided by this cache for the given translation unit. Handles acquiring
	 * and releasing the index read-lock for the client.
Executes {@link ASTRunnable#runOnAST(ILanguage, IASTTranslationUnit)} with the AST
	 * provided by this cache for the given translation unit. Handles acquiring
	 * and releasing the index read-lock for the client. | ASTCache.java