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/*
 * Licensed to Elasticsearch under one or more contributor
 * license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright
 * ownership. Elasticsearch 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.elasticsearch.common.util.concurrent;


import java.util.AbstractQueue;
import java.util.Collection;
import java.util.Iterator;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * A size based queue wrapping another blocking queue to provide (somewhat relaxed) capacity checks.
 * Mainly makes sense to use with blocking queues that are unbounded to provide the ability to do
 * capacity verification.
 */
public class SizeBlockingQueue extends AbstractQueue implements BlockingQueue {

    private final BlockingQueue queue;
    private final int capacity;

    private final AtomicInteger size = new AtomicInteger();

    public SizeBlockingQueue(BlockingQueue queue, int capacity) {
        assert capacity >= 0;
        this.queue = queue;
        this.capacity = capacity;
    }

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

    public int capacity() {
        return this.capacity;
    }

    @Override
    public Iterator iterator() {
        final Iterator it = queue.iterator();
        return new Iterator() {
            E current;

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

            @Override
            public E next() {
                current = it.next();
                return current;
            }

            @Override
            public void remove() {
                // note, we can't call #remove on the iterator because we need to know
                // if it was removed or not
                if (queue.remove(current)) {
                    size.decrementAndGet();
                }
            }
        };
    }

    @Override
    public E peek() {
        return queue.peek();
    }

    @Override
    public E poll() {
        E e = queue.poll();
        if (e != null) {
            size.decrementAndGet();
        }
        return e;
    }

    @Override
    public E poll(long timeout, TimeUnit unit) throws InterruptedException {
        E e = queue.poll(timeout, unit);
        if (e != null) {
            size.decrementAndGet();
        }
        return e;
    }

    @Override
    public boolean remove(Object o) {
        boolean v = queue.remove(o);
        if (v) {
            size.decrementAndGet();
        }
        return v;
    }

    /**
     * Forces adding an element to the queue, without doing size checks.
     */
    public void forcePut(E e) throws InterruptedException {
        size.incrementAndGet();
        try {
            queue.put(e);
        } catch (InterruptedException ie) {
            size.decrementAndGet();
            throw ie;
        }
    }


    @Override
    public boolean offer(E e) {
        while (true) {
            final int current = size.get();
            if (current >= capacity()) {
                return false;
            }
            if (size.compareAndSet(current, 1 + current)) {
                break;
            }
        }
        boolean offered = queue.offer(e);
        if (!offered) {
            size.decrementAndGet();
        }
        return offered;
    }

    @Override
    public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException {
        // note, not used in ThreadPoolExecutor
        throw new IllegalStateException("offer with timeout not allowed on size queue");
    }

    @Override
    public void put(E e) throws InterruptedException {
        // note, not used in ThreadPoolExecutor
        throw new IllegalStateException("put not allowed on size queue");
    }

    @Override
    public E take() throws InterruptedException {
        E e;
        try {
            e = queue.take();
            size.decrementAndGet();
        } catch (InterruptedException ie) {
            throw ie;
        }
        return e;
    }

    @Override
    public int remainingCapacity() {
        return capacity() - size.get();
    }

    @Override
    public int drainTo(Collection c) {
        int v = queue.drainTo(c);
        size.addAndGet(-v);
        return v;
    }

    @Override
    public int drainTo(Collection c, int maxElements) {
        int v = queue.drainTo(c, maxElements);
        size.addAndGet(-v);
        return v;
    }

    @Override
    public Object[] toArray() {
        return queue.toArray();
    }

    @Override
    public  T[] toArray(T[] a) {
        return (T[]) queue.toArray(a);
    }

    @Override
    public boolean contains(Object o) {
        return queue.contains(o);
    }

    @Override
    public boolean containsAll(Collection c) {
        return queue.containsAll(c);
    }
}