src/Pure/PIDE/xml.scala

 
   class Cache(initial_size: Int = 131071, max_string: Int = 100)
   {
     private val table =
       Collections.synchronizedMap(new WeakHashMap[Any, WeakReference[Any]](initial_size))
+
+    def size: Int = table.size
 
     private def lookup[A](x: A): Option[A] =
     {
       val ref = table.get(x)
       if (ref == null) None