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本文主要研究一下Elasticsearch的EvictingQueue
EvictingQueue
elasticsearch-7.0.1/server/src/main/java/org/elasticsearch/common/collect/EvictingQueue.java
public class EvictingQueue<T> implements Queue<T> { private final int maximumSize; private final ArrayDeque<T> queue; /** * Construct a new {@code EvictingQueue} that holds {@code maximumSize} elements. * * @param maximumSize The maximum number of elements that the queue can hold * @throws IllegalArgumentException if {@code maximumSize} is less than zero */ public EvictingQueue(int maximumSize) { if (maximumSize < 0) { throw new IllegalArgumentException("maximumSize < 0"); } this.maximumSize = maximumSize; this.queue = new ArrayDeque<>(maximumSize); } /** * @return the number of additional elements that the queue can accommodate before evictions occur */ public int remainingCapacity() { return this.maximumSize - this.size(); } /** * Add the given element to the queue, possibly forcing an eviction from the head if {@link #remainingCapacity()} is * zero. * * @param t the element to add * @return true if the element was added (always the case for {@code EvictingQueue} */ @Override public boolean add(T t) { if (maximumSize == 0) { return true; } if (queue.size() == maximumSize) { queue.remove(); } queue.add(t); return true; } /** * @see #add(Object) */ @Override public boolean offer(T t) { return add(t); } @Override public T remove() { return queue.remove(); } @Override public T poll() { return queue.poll(); } @Override public T element() { return queue.element(); } @Override public T peek() { return queue.peek(); } @Override public int size() { return queue.size(); } @Override public boolean isEmpty() { return queue.isEmpty(); } @Override public boolean contains(Object o) { return queue.contains(o); } @Override public Iterator<T> iterator() { return queue.iterator(); } @Override public Object[] toArray() { return queue.toArray(); } @Override public <T1> T1[] toArray(T1[] a) { return queue.toArray(a); } @Override public boolean remove(Object o) { return queue.remove(o); } @Override public boolean containsAll(Collection<?> c) { return queue.containsAll(c); } /** * Add the given elements to the queue, possibly forcing evictions from the head if {@link #remainingCapacity()} is * zero or becomes zero during the execution of this method. * * @param c the collection of elements to add * @return true if any elements were added to the queue */ @Override public boolean addAll(Collection<? extends T> c) { boolean modified = false; for (T e : c) if (add(e)) modified = true; return modified; } @Override public boolean removeAll(Collection<?> c) { return queue.removeAll(c); } @Override public boolean retainAll(Collection<?> c) { return queue.retainAll(c); } @Override public void clear() { queue.clear(); }}- EvictingQueue实现了Queue接口，它的构造器要求输入maximumSize，然后根据maximumSize创建ArrayDeque；其add方法会判断当前队列大小是否等于maximumSize，等于则移除队首的元素然后再添加新元素
实例
elasticsearch-7.0.1/server/src/test/java/org/elasticsearch/search/aggregations/pipeline/MovFnWhitelistedFunctionTests.java
public void testWindowMax() { int numValues = randomIntBetween(1, 100); int windowSize = randomIntBetween(1, 50); EvictingQueue<Double> window = new EvictingQueue<>(windowSize); for (int i = 0; i < numValues; i++) { double randValue = randomDouble(); double expected = -Double.MAX_VALUE; if (i == 0) { window.offer(randValue); continue; } for (double value : window) { expected = Math.max(expected, value); } double actual = MovingFunctions.max(window.stream().mapToDouble(Double::doubleValue).toArray()); assertEquals(expected, actual, 0.01 * Math.abs(expected)); window.offer(randValue); } }- 这里使用EvictingQueue作为一个window的数据，不断根据numValues来offer数据，同时计算window中的最大值
小结
EvictingQueue实现了Queue接口，它的构造器要求输入maximumSize，然后根据maximumSize创建ArrayDeque；其add方法会判断当前队列大小是否等于maximumSize，等于则移除队首的元素然后再添加新元素
doc
- EvictingQueue