[ONOS-2809] Support a TransactionalSet data structure

Change-Id: Ia99bc2285b3fea39ee3845f5f6613a45a6a61626

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.store.service;
+
+/**
+ * Transactional Set data structure.
+ * <p>
+ * A TransactionalSet is implemented with the help of TransactionalMap data structure.
+ * All operations performed on this set within a transaction boundary are invisible externally
+ * until the point when the transaction commits. A commit usually succeeds in the absence of conflicts.
+ *
+ * @param <E> type of element.
+ */
+public interface TransactionalSet<E> {
+
+    /**
+     * Adds the specified element to this set if it is not already present
+     * (optional operation).  More formally, adds the specified element
+     * <tt>e</tt> to this set if the set contains no element <tt>e2</tt>
+     * such that
+     * <tt>(e==null&nbsp;?&nbsp;e2==null&nbsp;:&nbsp;e.equals(e2))</tt>.
+     * If this set already contains the element, the call leaves the set
+     * unchanged and returns <tt>false</tt>.  In combination with the
+     * restriction on constructors, this ensures that sets never contain
+     * duplicate elements.
+     *
+     * @param e element to be added to this set
+     * @return <tt>true</tt> if this set did not already contain the specified
+     *         element
+     */
+    boolean add(E e);
+
+    /**
+     * Removes the specified element from this set if it is present
+     * (optional operation).  More formally, removes an element <tt>e</tt>
+     * such that
+     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>, if
+     * this set contains such an element.  Returns <tt>true</tt> if this set
+     * contained the element (or equivalently, if this set changed as a
+     * result of the call).  (This set will not contain the element once the
+     * call returns.)
+     *
+     * @param e element to be removed to this set
+     * @return <tt>true</tt> if this set contained the specified element
+     */
+    boolean remove(E e);
+
+    /**
+     * Returns <tt>true</tt> if this set contains the specified element.
+     * More formally, returns <tt>true</tt> if and only if this set
+     * contains an element <tt>e</tt> such that
+     * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.
+     *
+     * @param e element whose presence in this set is to be tested
+     * @return <tt>true</tt> if this set contains the specified element
+     * @throws ClassCastException if the type of the specified element
+     *         is incompatible with this set
+     * @throws NullPointerException if the specified element is null and this
+     *         set does not permit null elements
+     */
+    boolean contains(E e);
+}

+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.store.consistent.impl;
+
+
+import org.onosproject.store.service.Serializer;
+import org.onosproject.store.service.TransactionContext;
+import org.onosproject.store.service.TransactionalMap;
+import org.onosproject.store.service.TransactionalSet;
+
+/**
+ * Default TransactionalSet implementation that provides a repeatable reads
+ * transaction isolation level.
+ *
+ * @param <E> element type.
+ */
+public class DefaultTransactionalSet<E> implements TransactionalSet<E> {
+
+    private TransactionalMap<E, Boolean> map;
+
+    // dummy value to associate with an Object in the backing map
+    private static final Boolean PRESENT = new Boolean(true);
+
+    public DefaultTransactionalSet(
+            String name,
+            TransactionContext txContext,
+            Serializer serializer) {
+        map = txContext.getTransactionalMap(name, serializer);
+    }
+
+    @Override
+    public boolean add(E e) {
+        return map.put(e, PRESENT) == null;
+    }
+
+    @Override
+    public boolean remove(E e) {
+        return map.remove(e) != null;
+    }
+
+    @Override
+    public boolean contains(E e) {
+        return map.get(e) != null;
+    }
+}