[FLINK-1005] Add non-object reusing variants of key-grouped iterator.

Clean minor javadoc errors.

flink-runtime/src/main/java/org/apache/flink/runtime/operators/GroupReduceDriver.java

@@ -51,6 +51,8 @@ public class GroupReduceDriver<IT, OT> implements PactDriver<GroupReduceFunction
 
 	private TypeComparator<IT> comparator;
 	
+	private boolean mutableObjectMode = false;
+	
 	private volatile boolean running;
 
 	// ------------------------------------------------------------------------

stratosphere-runtime/src/main/java/eu/stratosphere/pact/runtime/util/KeyGroupedIteratorImmutable.java

+/***********************************************************************************************************************
+ * Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu)
+ *
+ * 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 eu.stratosphere.pact.runtime.util;
+
+import java.io.IOException;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+import eu.stratosphere.api.common.typeutils.TypeComparator;
+import eu.stratosphere.api.common.typeutils.TypeSerializer;
+import eu.stratosphere.util.MutableObjectIterator;
+
+/**
+ * The KeyValueIterator returns a key and all values that belong to the key (share the same key).
+ * 
+ */
+public final class KeyGroupedIteratorImmutable<E> {
+	
+	private final MutableObjectIterator<E> iterator;
+
+	private final TypeSerializer<E> serializer;
+	
+	private final TypeComparator<E> comparator;
+	
+	private ValuesIterator valuesIterator;
+	
+	private E lastKeyRecord;
+	
+	private E lookahead;
+	
+	private boolean done;
+
+	/**
+	 * Initializes the KeyGroupedIterator. It requires an iterator which returns its result
+	 * sorted by the key fields.
+	 * 
+	 * @param iterator An iterator over records, which are sorted by the key fields, in any order.
+	 * @param serializer The serializer for the data type iterated over.
+	 * @param comparator The comparator for the data type iterated over.
+	 */
+	public KeyGroupedIteratorImmutable(MutableObjectIterator<E> iterator,
+			TypeSerializer<E> serializer, TypeComparator<E> comparator)
+	{
+		if (iterator == null || serializer == null || comparator == null) {
+			throw new NullPointerException();
+		}
+		
+		this.iterator = iterator;
+		this.serializer = serializer;
+		this.comparator = comparator;
+	}
+
+	/**
+	 * Moves the iterator to the next key. This method may skip any values that have not yet been returned by the
+	 * iterator created by the {@link #getValues()} method. Hence, if called multiple times it "removes" key groups.
+	 * 
+	 * @return true, if the input iterator has an other group of records with the same key.
+	 */
+	public boolean nextKey() throws IOException {
+		
+		if (lookahead != null) {
+			// common case: whole value-iterator was consumed and a new key group is available.
+			this.comparator.setReference(this.lookahead);
+			this.valuesIterator.next = this.lookahead;
+			this.lastKeyRecord = this.lookahead;
+			this.lookahead = null;
+			return true;
+		}
+		
+		// first element, empty/done, or the values iterator was not entirely consumed
+		if (this.done) {
+			return false;
+		}
+			
+		if (this.valuesIterator != null) {
+			// values was not entirely consumed. move to the next key
+			// Required if user code / reduce() method did not read the whole value iterator.
+			E next = this.serializer.createInstance();
+			while (true) {
+				if ((next = this.iterator.next(next)) != null) {
+					if (!this.comparator.equalToReference(next)) {
+						// the keys do not match, so we have a new group. store the current key
+						this.comparator.setReference(next);
+						this.valuesIterator.next = next;
+						this.lastKeyRecord = next;
+						return true;
+					}
+				}
+				else {
+					// input exhausted
+					this.valuesIterator.next = null;
+					this.valuesIterator = null;
+					this.lastKeyRecord = null;
+					this.done = true;
+					return false;
+				}
+			}
+		}
+		else {
+			// first element
+			// get the next element
+			E first = this.iterator.next(this.serializer.createInstance());
+			if (first != null) {
+				this.comparator.setReference(first);
+				this.valuesIterator = new ValuesIterator(first);
+				this.lastKeyRecord = first;
+				return true;
+			}
+			else {
+				// empty input, set everything null
+				this.done = true;
+				return false;
+			}
+		}
+	}
+	
+	private E advanceToNext() {
+		try {
+			E next = this.iterator.next(serializer.createInstance());
+			if (next != null) {
+				if (comparator.equalToReference(next)) {
+					// same key
+					return next;
+				} else {
+					// moved to the next key, no more values here
+					this.lookahead = next;
+					return null;
+				}
+			}
+			else {
+				// backing iterator is consumed
+				this.done = true;
+				return null;
+			}
+		}
+		catch (IOException e) {
+			throw new RuntimeException("An error occurred while reading the next record.", e);
+		}
+	}
+	
+	public E getCurrent() {
+		return lastKeyRecord;
+	}
+	
+	public TypeComparator<E> getComparatorWithCurrentReference() {
+		return this.comparator;
+	}
+
+	/**
+	 * Returns an iterator over all values that belong to the current key. The iterator is initially <code>null</code>
+	 * (before the first call to {@link #nextKey()} and after all keys are consumed. In general, this method returns
+	 * always a non-null value, if a previous call to {@link #nextKey()} return <code>true</code>.
+	 * 
+	 * @return Iterator over all values that belong to the current key.
+	 */
+	public ValuesIterator getValues() {
+		return this.valuesIterator;
+	}
+
+	// --------------------------------------------------------------------------------------------
+	
+	public final class ValuesIterator implements Iterator<E> {
+		
+		private E next;
+		
+		private ValuesIterator(E first) {
+			this.next = first;
+		}
+
+		@Override
+		public boolean hasNext() {
+			return next != null;
+		}
+
+		@Override
+		public E next() {
+			if (this.next != null) {
+				E current = this.next;
+				this.next = KeyGroupedIteratorImmutable.this.advanceToNext();
+				return current;
+			} else {
+				throw new NoSuchElementException();
+			}
+		}
+
+		@Override
+		public void remove() {
+			throw new UnsupportedOperationException();
+		}
+	}
+}