--- /dev/null
+/*
+ * Copyright (c) 2003-2005 The BISON Project
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ *
+ */
+
+package peersim.core;
+
+/**
+ * This interface must be implemented by protocols that need to release
+ * some references when the fail state of their host node is set to
+ * {@link Fallible#DEAD}. Recall that this fail state means that the node
+ * will never get back online. However, other nodes and protocols might
+ * still have references to these dead nodes and protocols, and this fact
+ * is not always a bug. So implementing this interface allows for removing
+ * stuff that we know is no longer necessary. Especially for linkable
+ * protocols in the presence of churn, this is essential: they typically
+ * have to release their links to other nodes to prevent the formation of
+ * trees of removed nodes with a live reference to the root.
+ */
+public interface Cleanable
+{
+
+/**
+ * Performs cleanup when removed from the network. This is called by the
+ * host node when its fail state is set to {@link Fallible#DEAD}.
+ * It is very important that after calling this method, NONE of the methods
+ * of the implementing object are guaranteed to work any longer.
+ * They might throw arbitrary exceptions, etc. The idea is that after
+ * calling this, typically no one should access this object.
+ * However, as a recommendation, at least toString should be guaranteed to
+ * execute normally, to aid debugging.
+ */
+public void onKill();
+
+}
