聊聊flink的DualKeyMap

序

本文主要研究一下flink的DualKeyMap

实例

	@Test
	public void testKeySets() {
		final Random random = new Random();
		final int capacity = 10;
		final Set<Tuple2<Integer, Integer>> keys = new HashSet<>(capacity);

		for (int i = 0; i < capacity; i++) {
			int keyA = random.nextInt();
			int keyB = random.nextInt();
			keys.add(Tuple2.of(keyA, keyB));
		}

		final DualKeyMap<Integer, Integer, String> dualKeyMap = new DualKeyMap<>(capacity);

		for (Tuple2<Integer, Integer> key : keys) {
			dualKeyMap.put(key.f0, key.f1, "foobar");
		}

		assertThat(dualKeyMap.keySetA(), Matchers.equalTo(keys.stream().map(t -> t.f0).collect(Collectors.toSet())));
		assertThat(dualKeyMap.keySetB(), Matchers.equalTo(keys.stream().map(t -> t.f1).collect(Collectors.toSet())));
	}

• DualKeyMap有两个key，put值的时候，需要指定keyA及keyB

DualKeyMap

flink-1.7.2/flink-runtime/src/main/java/org/apache/flink/runtime/jobmaster/slotpool/DualKeyMap.java

public class DualKeyMap<A, B, V> {

	private final HashMap<A, Tuple2<B, V>> aMap;

	private final HashMap<B, A> bMap;

	private transient Collection<V> values;

	public DualKeyMap(int initialCapacity) {
		this.aMap = new HashMap<>(initialCapacity);
		this.bMap = new HashMap<>(initialCapacity);
	}

	public int size() {
		return aMap.size();
	}

	public V getKeyA(A aKey) {
		final Tuple2<B, V> value = aMap.get(aKey);

		if (value != null) {
			return value.f1;
		} else {
			return null;
		}
	}

	public V getKeyB(B bKey) {
		final A aKey = bMap.get(bKey);

		if (aKey != null) {
			return aMap.get(aKey).f1;
		} else {
			return null;
		}
	}

	public V put(A aKey, B bKey, V value) {
		Tuple2<B, V> aValue = aMap.put(aKey, Tuple2.of(bKey, value));
		bMap.put(bKey, aKey);

		if (aValue != null) {
			return aValue.f1;
		} else {
			return null;
		}
	}

	public boolean containsKeyA(A aKey) {
		return aMap.containsKey(aKey);
	}

	public boolean containsKeyB(B bKey) {
		return bMap.containsKey(bKey);
	}

	public V removeKeyA(A aKey) {
		Tuple2<B, V> aValue = aMap.remove(aKey);

		if (aValue != null) {
			bMap.remove(aValue.f0);
			return aValue.f1;
		} else {
			return null;
		}
	}

	public V removeKeyB(B bKey) {
		A aKey = bMap.remove(bKey);

		if (aKey != null) {
			Tuple2<B, V> aValue = aMap.remove(aKey);
			if (aValue != null) {
				return aValue.f1;
			} else {
				return null;
			}
		} else {
			return null;
		}
	}

	public Collection<V> values() {
		Collection<V> vs = values;

		if (vs == null) {
			vs = new Values();
			values = vs;
		}

		return vs;
	}

	public Set<A> keySetA() {
		return aMap.keySet();
	}

	public Set<B> keySetB() {
		return bMap.keySet();
	}

	public void clear() {
		aMap.clear();
		bMap.clear();
	}

	// -----------------------------------------------------------------------
	// Inner classes
	// -----------------------------------------------------------------------

	/**
	 * Collection which contains the values of the dual key map.
	 */
	private final class Values extends AbstractCollection<V> {

		@Override
		public Iterator<V> iterator() {
			return new ValueIterator();
		}

		@Override
		public int size() {
			return aMap.size();
		}
	}

	/**
	 * Iterator which iterates over the values of the dual key map.
	 */
	private final class ValueIterator implements Iterator<V> {

		private final Iterator<Tuple2<B, V>> iterator = aMap.values().iterator();

		@Override
		public boolean hasNext() {
			return iterator.hasNext();
		}

		@Override
		public V next() {
			Tuple2<B, V> value = iterator.next();

			return value.f1;
		}
	}
}

• DualKeyMap定义了三个泛型，分别是A，B，V，即keyA，keyB，value的泛型；它维护了两个HashMap，其中aMap的key为keyA，value为Tuple2<B, V>；bMap的key为keyB，value为keyA
• DualKeyMap提供了getKeyA、getKeyB、containsKeyA、containsKeyB、removeKeyA、removeKeyB、keySetA、keySetB、size、put、values、clear方法
• values方法返回的是Values，它继承了AbstractCollection，它的iterator方法返回的是ValueIterator；ValueIterator实现了Iterator接口，其内部使用的是aMap.values().iterator()

小结

• DualKeyMap定义了三个泛型，分别是A，B，V，即keyA，keyB，value的泛型；它维护了两个HashMap，其中aMap的key为keyA，value为Tuple2<B, V>；bMap的key为keyB，value为keyA
• DualKeyMap提供了getKeyA、getKeyB、containsKeyA、containsKeyB、removeKeyA、removeKeyB、keySetA、keySetB、size、put、values、clear方法；put值的时候，需要指定keyA及keyB
• values方法返回的是Values，它继承了AbstractCollection，它的iterator方法返回的是ValueIterator；ValueIterator实现了Iterator接口，其内部使用的是aMap.values().iterator()

doc

• DualKeyMap