org.apache.zookeeper.util.CircularBlockingQueue Maven / Gradle / Ivy
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.zookeeper.util;
import java.util.ArrayDeque;
import java.util.Collection;
import java.util.Iterator;
import java.util.Objects;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* A bounded blocking queue backed by an array. This queue orders elements FIFO
* (first-in-first-out). The head of the queue is that element that has been on
* the queue the longest time. The tail of the queue is that element that has
* been on the queue the shortest time. New elements are inserted at the tail of
* the queue, and the queue retrieval operations obtain elements at the head of
* the queue. If the queue is full, the head of the queue (the oldest element)
* will be removed to make room for the newest element.
*/
public class CircularBlockingQueue implements BlockingQueue {
private static final Logger LOG = LoggerFactory.getLogger(CircularBlockingQueue.class);
/** Main lock guarding all access */
private final ReentrantLock lock;
/** Condition for waiting takes */
private final Condition notEmpty;
/** The array-backed queue */
private final ArrayDeque queue;
private final int maxSize;
private long droppedCount;
public CircularBlockingQueue(int queueSize) {
this.queue = new ArrayDeque<>(queueSize);
this.maxSize = queueSize;
this.lock = new ReentrantLock();
this.notEmpty = this.lock.newCondition();
this.droppedCount = 0L;
}
/**
* This method differs from {@link BlockingQueue#offer(Object)} in that it
* will remove the oldest queued element (the element at the front of the
* queue) in order to make room for any new elements if the queue is full.
*
* @param e the element to add
* @return true since it will make room for any new elements if required
*/
@Override
public boolean offer(E e) {
Objects.requireNonNull(e);
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (this.queue.size() == this.maxSize) {
final E discard = this.queue.remove();
this.droppedCount++;
LOG.debug("Queue is full. Discarding oldest element [count={}]: {}",
this.droppedCount, discard);
}
this.queue.add(e);
this.notEmpty.signal();
} finally {
lock.unlock();
}
return true;
}
@Override
public E poll(long timeout, TimeUnit unit) throws InterruptedException {
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (this.queue.isEmpty()) {
if (nanos <= 0) {
return null;
}
nanos = this.notEmpty.awaitNanos(nanos);
}
return this.queue.poll();
} finally {
lock.unlock();
}
}
@Override
public E take() throws InterruptedException {
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
while (this.queue.isEmpty()) {
this.notEmpty.await();
}
return this.queue.poll();
} finally {
lock.unlock();
}
}
@Override
public boolean isEmpty() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return this.queue.isEmpty();
} finally {
lock.unlock();
}
}
@Override
public int size() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return this.queue.size();
} finally {
lock.unlock();
}
}
/**
* Returns the number of elements that were dropped from the queue because the
* queue was full when a new element was offered.
*
* @return The number of elements dropped (lost) from the queue
*/
public long getDroppedCount() {
return this.droppedCount;
}
/**
* For testing purposes only.
*
* @return True if a thread is blocked waiting for a new element to be offered
* to the queue
*/
boolean isConsumerThreadBlocked() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return lock.getWaitQueueLength(this.notEmpty) > 0;
} finally {
lock.unlock();
}
}
@Override
public int drainTo(Collection c) {
throw new UnsupportedOperationException();
}
@Override
public E poll() {
throw new UnsupportedOperationException();
}
@Override
public E element() {
throw new UnsupportedOperationException();
}
@Override
public E peek() {
throw new UnsupportedOperationException();
}
@Override
public E remove() {
throw new UnsupportedOperationException();
}
@Override
public boolean addAll(Collection arg0) {
throw new UnsupportedOperationException();
}
@Override
public void clear() {
throw new UnsupportedOperationException();
}
@Override
public boolean containsAll(Collection arg0) {
throw new UnsupportedOperationException();
}
@Override
public Iterator iterator() {
throw new UnsupportedOperationException();
}
@Override
public boolean removeAll(Collection arg0) {
throw new UnsupportedOperationException();
}
@Override
public boolean retainAll(Collection arg0) {
throw new UnsupportedOperationException();
}
@Override
public Object[] toArray() {
throw new UnsupportedOperationException();
}
@Override
public T[] toArray(T[] arg0) {
throw new UnsupportedOperationException();
}
@Override
public boolean add(E e) {
throw new UnsupportedOperationException();
}
@Override
public boolean contains(Object o) {
throw new UnsupportedOperationException();
}
@Override
public int drainTo(Collection c, int maxElements) {
throw new UnsupportedOperationException();
}
@Override
public boolean offer(E e, long timeout, TimeUnit unit)
throws InterruptedException {
throw new UnsupportedOperationException();
}
@Override
public void put(E e) throws InterruptedException {
throw new UnsupportedOperationException();
}
@Override
public int remainingCapacity() {
throw new UnsupportedOperationException();
}
@Override
public boolean remove(Object o) {
throw new UnsupportedOperationException();
}
}