--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/sun/nio/ch/MembershipRegistry.java	Tue Sep 12 19:03:39 2017 +0200
@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 2008, 2009, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code 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 General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package sun.nio.ch;
+
+import java.nio.channels.*;
+import java.net.InetAddress;
+import java.net.NetworkInterface;
+import java.util.*;
+
+/**
+ * Simple registry of membership keys for a MulticastChannel.
+ *
+ * Instances of this object are not safe by multiple concurrent threads.
+ */
+
+class MembershipRegistry {
+
+    // map multicast group to keys
+    private Map<InetAddress,List<MembershipKeyImpl>> groups = null;
+
+    MembershipRegistry() {
+    }
+
+    /**
+     * Checks registry for membership of the group on the given
+     * network interface.
+     */
+    MembershipKey checkMembership(InetAddress group, NetworkInterface interf,
+                                  InetAddress source)
+    {
+        if (groups != null) {
+            List<MembershipKeyImpl> keys = groups.get(group);
+            if (keys != null) {
+                for (MembershipKeyImpl key: keys) {
+                    if (key.networkInterface().equals(interf)) {
+                        // already a member to receive all packets so return
+                        // existing key or detect conflict
+                        if (source == null) {
+                            if (key.sourceAddress() == null)
+                                return key;
+                            throw new IllegalStateException("Already a member to receive all packets");
+                        }
+
+                        // already have source-specific membership so return key
+                        // or detect conflict
+                        if (key.sourceAddress() == null)
+                            throw new IllegalStateException("Already have source-specific membership");
+                        if (source.equals(key.sourceAddress()))
+                            return key;
+                    }
+                }
+            }
+        }
+        return null;
+    }
+
+    /**
+     * Add membership to the registry, returning a new membership key.
+     */
+    void add(MembershipKeyImpl key) {
+        InetAddress group = key.group();
+        List<MembershipKeyImpl> keys;
+        if (groups == null) {
+            groups = new HashMap<>();
+            keys = null;
+        } else {
+            keys = groups.get(group);
+        }
+        if (keys == null) {
+            keys = new LinkedList<>();
+            groups.put(group, keys);
+        }
+        keys.add(key);
+    }
+
+    /**
+     * Remove a key from the registry
+     */
+    void remove(MembershipKeyImpl key) {
+        InetAddress group = key.group();
+        List<MembershipKeyImpl> keys = groups.get(group);
+        if (keys != null) {
+            Iterator<MembershipKeyImpl> i = keys.iterator();
+            while (i.hasNext()) {
+                if (i.next() == key) {
+                    i.remove();
+                    break;
+                }
+            }
+            if (keys.isEmpty()) {
+                groups.remove(group);
+            }
+        }
+    }
+
+    /**
+     * Invalidate all keys in the registry
+     */
+    void invalidateAll() {
+        if (groups != null) {
+            for (InetAddress group: groups.keySet()) {
+                for (MembershipKeyImpl key: groups.get(group)) {
+                    key.invalidate();
+                }
+            }
+        }
+    }
+}