sdrtrunk/src/main/java/io/github/dsheirer/sample/OverflowableTransferQueue.java

/*******************************************************************************
 * sdrtrunk
 * Copyright (C) 2014-2017 Dennis Sheirer
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 *
 ******************************************************************************/
package io.github.dsheirer.sample;

import io.github.dsheirer.sample.real.IOverflowListener;
import io.github.dsheirer.source.Source;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Collection;
import java.util.concurrent.LinkedTransferQueue;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;

public class OverflowableTransferQueue<E>
{
    private final static Logger mLog = LoggerFactory.getLogger(OverflowableTransferQueue.class);

    public enum State {NORMAL, OVERFLOW};
    private IOverflowListener mOverflowListener;
    private Source mSourceOverflowListener;

    protected LinkedTransferQueue<E> mQueue = new LinkedTransferQueue<E>();
    protected AtomicInteger mCounter = new AtomicInteger();
    protected AtomicBoolean mOverflow = new AtomicBoolean();
    private int mMaximumSize;
    private int mResetThreshold;

    /**
     * Concurrent transfer queue that couples a higher-throughput linked transfer queue with an atomic integer for
     * monitoring queue size.  When the queue size exceeds maximum size (overflow), all inbound elements are ignored
     * until the queue size is reduced to or below the reset threshold.
     *
     * @param maximumSize of the queue.  Overflow state will occur once queue size exceeds this value.
     * @param resetThreshold for resetting overflow state to normal, once queue size is at or below this value.
     */
    public OverflowableTransferQueue(int maximumSize, int resetThreshold)
    {
        mMaximumSize = maximumSize;
        mResetThreshold = resetThreshold;
    }

    /**
     * Adds the element to the queue if able to do so without exceeding maximum queue size.  Otherwise, ignores
     * the element.
     */
    public void offer(E e)
    {
        if(!mOverflow.get())
        {
            mQueue.offer(e);

            int size = mCounter.incrementAndGet();

            if(size > mMaximumSize)
            {
                setOverflow(true);
            }
        }
        else
        {
            overflow(e);
        }
    }

    /**
     * Invoked when the buffer is in an overflow state.  The element argument is thrown away.  Override this method
     * in subclasses to perform any necessary cleanup action(s).
     *
     * @param e element that is being thrown away due to an overflow condition
     */
    protected void overflow(E e)
    {
        //No-op.  Override in subclass to perform any cleanup actions during overflow
    }

    /**
     * Removes and returns a single element from the head of the queue or null if the queue is empty
     */
    public E poll()
    {
        return mQueue.poll();
    }

    /**
     * Retrieves elements from the queue into the collection up to the maximum number of elements specified
     */
    public int drainTo(Collection<? super E> collection, int maxElements)
    {
        int drainCount = mQueue.drainTo(collection, maxElements);

        int size = mCounter.addAndGet(-drainCount);

        if(mOverflow.get() && size <= mResetThreshold)
        {
            setOverflow(false);
        }

        return drainCount;
    }

    /**
     * Sets a listener to receive overflow state change events.
     */
    public void setOverflowListener(IOverflowListener listener)
    {
        mOverflowListener = listener;
    }

    /**
     * Sets the source to receive overflow state change events (in addition to an IOverflow listener)
     */
    public void setSourceOverflowListener(Source source)
    {
        mSourceOverflowListener = source;
    }


    /**
     * Toggles the overflow state and broadcast state change to listener
     */
    private void setOverflow(boolean overflow)
    {
        if(mOverflow.compareAndSet(!overflow, overflow))
        {
            if(mOverflowListener != null)
            {
                mOverflowListener.sourceOverflow(overflow);
            }

            if(mSourceOverflowListener != null)
            {
                mSourceOverflowListener.broadcastOverflowState(overflow);
            }
        }
    }

    /**
     * Clears all elements from the queue and resets the internal counter to 0
     */
    public void clear()
    {
        synchronized(mQueue)
        {
            mQueue.clear();
            mCounter.set(0);
            mOverflow.set(false);
        }
    }
}