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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
正文完
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2019-06-05