/*
 *
 * Copyright (c) 2006 The Apache Software Foundation
 *
 * Licensed 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.qpid.server.transport;

import org.apache.mina.common.*;
import org.apache.mina.util.*;
import org.apache.mina.util.Queue;
import org.apache.mina.util.Stack;

import java.util.*;

/**
 * A Thread-pooling filter.  This filter forwards {@link IoHandler} events
 * to its thread pool.
 * <p/>
 * This is an implementation of
 * <a href="http://deuce.doc.wustl.edu/doc/pspdfs/lf.pdf">Leader/Followers
 * thread pool</a> by Douglas C. Schmidt et al.
 */
public class ThreadPoolFilter extends IoFilterAdapter
{
    /**
     * Default maximum size of thread pool (2G).
     */
    public static final int DEFAULT_MAXIMUM_POOL_SIZE = Integer.MAX_VALUE;

    /**
     * Default keep-alive time of thread pool (1 min).
     */
    public static final int DEFAULT_KEEP_ALIVE_TIME = 60 * 1000;

    /**
     * A queue which contains {@link Integer}s which represents reusable
     * thread IDs.  {@link Worker} first checks this queue and then
     * uses {@link #threadId} when no reusable thread ID is available.
     */
    private static final Queue threadIdReuseQueue = new Queue();
    private static int threadId = 0;

    private static int acquireThreadId()
    {
        synchronized (threadIdReuseQueue)
        {
            Integer id = (Integer) threadIdReuseQueue.pop();
            if (id == null)
            {
                return ++ threadId;
            }
            else
            {
                return id.intValue();
            }
        }
    }

    private static void releaseThreadId(int id)
    {
        synchronized (threadIdReuseQueue)
        {
            threadIdReuseQueue.push(new Integer(id));
        }
    }

    private final String threadNamePrefix;
    private final Map buffers = new IdentityHashMap();
    private final BlockingQueue unfetchedSessionBuffers = new BlockingQueue();
    private final Set allSessionBuffers = new IdentityHashSet();

    private Worker leader;
    private final Stack followers = new Stack();
    private final Set allWorkers = new IdentityHashSet();

    private int maximumPoolSize = DEFAULT_MAXIMUM_POOL_SIZE;
    private int keepAliveTime = DEFAULT_KEEP_ALIVE_TIME;

    private boolean shuttingDown;

    private int poolSize;
    private final Object poolSizeLock = new Object();

    /**
     * Creates a new instance of this filter with default thread pool settings.
     */
    public ThreadPoolFilter()
    {
        this("IoThreadPool");
    }

    /**
     * Creates a new instance of this filter with the specified thread name prefix
     * and other default settings.
     *
     * @param threadNamePrefix the prefix of the thread names this pool will create.
     */
    public ThreadPoolFilter(String threadNamePrefix)
    {
        if (threadNamePrefix == null)
        {
            throw new NullPointerException("threadNamePrefix");
        }
        threadNamePrefix = threadNamePrefix.trim();
        if (threadNamePrefix.length() == 0)
        {
            throw new IllegalArgumentException("threadNamePrefix is empty.");
        }
        this.threadNamePrefix = threadNamePrefix;
    }

    public String getThreadNamePrefix()
    {
        return threadNamePrefix;
    }

    public int getPoolSize()
    {
        synchronized (poolSizeLock)
        {
            return poolSize;
        }
    }

    public int getMaximumPoolSize()
    {
        return maximumPoolSize;
    }

    public int getKeepAliveTime()
    {
        return keepAliveTime;
    }

    public void setMaximumPoolSize(int maximumPoolSize)
    {
        if (maximumPoolSize <= 0)
        {
            throw new IllegalArgumentException();
        }
        this.maximumPoolSize = maximumPoolSize;
    }

    public void setKeepAliveTime(int keepAliveTime)
    {
        this.keepAliveTime = keepAliveTime;
    }

    public void init()
    {
        shuttingDown = false;
        leader = new Worker();
        leader.start();
        leader.lead();
    }

    public void destroy()
    {
        shuttingDown = true;
        int expectedPoolSize = 0;
        while (getPoolSize() != expectedPoolSize)
        {
            List allWorkers;
            synchronized (poolSizeLock)
            {
                allWorkers = new ArrayList(this.allWorkers);
            }

            // You may not interrupt the current thread.
            if (allWorkers.remove(Thread.currentThread()))
            {
                expectedPoolSize = 1;
            }

            for (Iterator i = allWorkers.iterator(); i.hasNext();)
            {
                Worker worker = (Worker) i.next();
                while (worker.isAlive())
                {
                    worker.interrupt();
                    try
                    {
                        // This timeout will help us from
                        // infinite lock-up and interrupt workers again.
                        worker.join(100);
                    }
                    catch (InterruptedException e)
                    {
                    }
                }
            }
        }

        this.allSessionBuffers.clear();
        this.unfetchedSessionBuffers.clear();
        this.buffers.clear();
        this.followers.clear();
        this.leader = null;
    }

    private void increasePoolSize(Worker worker)
    {
        synchronized (poolSizeLock)
        {
            poolSize++;
            allWorkers.add(worker);
        }
    }

    private void decreasePoolSize(Worker worker)
    {
        synchronized (poolSizeLock)
        {
            poolSize--;
            allWorkers.remove(worker);
        }
    }

    private void fireEvent(NextFilter nextFilter, IoSession session,
                           EventType type, Object data)
    {
        final BlockingQueue unfetchedSessionBuffers = this.unfetchedSessionBuffers;
        final Set allSessionBuffers = this.allSessionBuffers;
        final Event event = new Event(type, nextFilter, data);

        synchronized (unfetchedSessionBuffers)
        {
            final SessionBuffer buf = getSessionBuffer(session);
            final Queue eventQueue = buf.eventQueue;

            synchronized (buf)
            {
                eventQueue.push(event);
            }

            if (!allSessionBuffers.contains(buf))
            {
                allSessionBuffers.add(buf);
                unfetchedSessionBuffers.push(buf);
            }
        }
    }

    /**
     * Implement this method to fetch (or pop) a {@link SessionBuffer} from
     * the given <tt>unfetchedSessionBuffers</tt>.  The default implementation
     * simply pops the buffer from it.  You could prioritize the fetch order.
     *
     * @return A non-null {@link SessionBuffer}
     */
    protected SessionBuffer fetchSessionBuffer(Queue unfetchedSessionBuffers)
    {
        return (SessionBuffer) unfetchedSessionBuffers.pop();
    }

    private SessionBuffer getSessionBuffer(IoSession session)
    {
        final Map buffers = this.buffers;
        SessionBuffer buf = (SessionBuffer) buffers.get(session);
        if (buf == null)
        {
            synchronized (buffers)
            {
                buf = (SessionBuffer) buffers.get(session);
                if (buf == null)
                {
                    buf = new SessionBuffer(session);
                    buffers.put(session, buf);
                }
            }
        }
        return buf;
    }

    private void removeSessionBuffer(SessionBuffer buf)
    {
        final Map buffers = this.buffers;
        final IoSession session = buf.session;
        synchronized (buffers)
        {
            buffers.remove(session);
        }
    }

    protected static class SessionBuffer
    {
        private final IoSession session;

        private final Queue eventQueue = new Queue();

        private SessionBuffer(IoSession session)
        {
            this.session = session;
        }

        public IoSession getSession()
        {
            return session;
        }

        public Queue getEventQueue()
        {
            return eventQueue;
        }
    }

    private class Worker extends Thread
    {
        private final int id;
        private final Object promotionLock = new Object();
        private boolean dead;

        private Worker()
        {
            int id = acquireThreadId();
            this.id = id;
            this.setName(threadNamePrefix + '-' + id);
            increasePoolSize(this);
        }

        public boolean lead()
        {
            final Object promotionLock = this.promotionLock;
            synchronized (promotionLock)
            {
                if (dead)
                {
                    return false;
                }

                leader = this;
                promotionLock.notify();
            }

            return true;
        }

        public void run()
        {
            for (; ;)
            {
                if (!waitForPromotion())
                {
                    break;
                }

                SessionBuffer buf = fetchBuffer();
                giveUpLead();
                if (buf == null)
                {
                    break;
                }

                processEvents(buf);
                follow();
                releaseBuffer(buf);
            }

            decreasePoolSize(this);
            releaseThreadId(id);
        }

        private SessionBuffer fetchBuffer()
        {
            BlockingQueue unfetchedSessionBuffers = ThreadPoolFilter.this.unfetchedSessionBuffers;
            synchronized (unfetchedSessionBuffers)
            {
                while (!shuttingDown)
                {
                    try
                    {
                        unfetchedSessionBuffers.waitForNewItem();
                    }
                    catch (InterruptedException e)
                    {
                        continue;
                    }

                    return ThreadPoolFilter.this.fetchSessionBuffer(unfetchedSessionBuffers);
                }
            }

            return null;
        }

        private void processEvents(SessionBuffer buf)
        {
            final IoSession session = buf.session;
            final Queue eventQueue = buf.eventQueue;
            for (; ;)
            {
                Event event;
                synchronized (buf)
                {
                    event = (Event) eventQueue.pop();
                    if (event == null)
                    {
                        break;
                    }
                }
                processEvent(event.getNextFilter(), session,
                             event.getType(), event.getData());
            }
        }

        private void follow()
        {
            final Object promotionLock = this.promotionLock;
            final Stack followers = ThreadPoolFilter.this.followers;
            synchronized (promotionLock)
            {
                if (this != leader)
                {
                    synchronized (followers)
                    {
                        followers.push(this);
                    }
                }
            }
        }

        private void releaseBuffer(SessionBuffer buf)
        {
            final BlockingQueue unfetchedSessionBuffers = ThreadPoolFilter.this.unfetchedSessionBuffers;
            final Set allSessionBuffers = ThreadPoolFilter.this.allSessionBuffers;
            final Queue eventQueue = buf.eventQueue;

            synchronized (unfetchedSessionBuffers)
            {
                if (eventQueue.isEmpty())
                {
                    allSessionBuffers.remove(buf);
                    removeSessionBuffer(buf);
                }
                else
                {
                    unfetchedSessionBuffers.push(buf);
                }
            }
        }

        private boolean waitForPromotion()
        {
            final Object promotionLock = this.promotionLock;

            long startTime = System.currentTimeMillis();
            long currentTime = System.currentTimeMillis();

            synchronized (promotionLock)
            {
                while (this != leader && !shuttingDown)
                {
                    // Calculate remaining keep-alive time
                    int keepAliveTime = getKeepAliveTime();
                    if (keepAliveTime > 0)
                    {
                        keepAliveTime -= (currentTime - startTime);
                    }
                    else
                    {
                        keepAliveTime = Integer.MAX_VALUE;
                    }

                    // Break the loop if there's no remaining keep-alive time.
                    if (keepAliveTime <= 0)
                    {
                        break;
                    }

                    // Wait for promotion
                    try
                    {
                        promotionLock.wait(keepAliveTime);
                    }
                    catch (InterruptedException e)
                    {
                    }

                    // Update currentTime for the next iteration
                    currentTime = System.currentTimeMillis();
                }

                boolean timeToLead = this == leader && !shuttingDown;

                if (!timeToLead)
                {
                    // time to die
                    synchronized (followers)
                    {
                        followers.remove(this);
                    }

                    // Mark as dead explicitly when we've got promotionLock.
                    dead = true;
                }

                return timeToLead;
            }
        }

        private void giveUpLead()
        {
            final Stack followers = ThreadPoolFilter.this.followers;
            Worker worker;
            do
            {
                synchronized (followers)
                {
                    worker = (Worker) followers.pop();
                }

                if (worker == null)
                {
                    // Increase the number of threads if we
                    // are not shutting down and we can increase the number.
                    if (!shuttingDown
                            && getPoolSize() < getMaximumPoolSize())
                    {
                        worker = new Worker();
                        worker.lead();
                        worker.start();
                    }

                    // This loop should end because:
                    // 1) lead() is called already,
                    // 2) or it is shutting down and there's no more threads left.
                    break;
                }
            }
            while (!worker.lead());
        }
    }

    protected static class EventType
    {
        public static final EventType OPENED = new EventType("OPENED");

        public static final EventType CLOSED = new EventType("CLOSED");

        public static final EventType READ = new EventType("READ");

        public static final EventType WRITTEN = new EventType("WRITTEN");

        public static final EventType RECEIVED = new EventType("RECEIVED");

        public static final EventType SENT = new EventType("SENT");

        public static final EventType IDLE = new EventType("IDLE");

        public static final EventType EXCEPTION = new EventType("EXCEPTION");

        private final String value;

        private EventType(String value)
        {
            this.value = value;
        }

        public String toString()
        {
            return value;
        }
    }

    protected static class Event
    {
        private final EventType type;
        private final NextFilter nextFilter;
        private final Object data;

        public Event(EventType type, NextFilter nextFilter, Object data)
        {
            this.type = type;
            this.nextFilter = nextFilter;
            this.data = data;
        }

        public Object getData()
        {
            return data;
        }


        public NextFilter getNextFilter()
        {
            return nextFilter;
        }


        public EventType getType()
        {
            return type;
        }
    }

    public void sessionCreated(NextFilter nextFilter, IoSession session)
    {
        nextFilter.sessionCreated(session);
    }

    public void sessionOpened(NextFilter nextFilter,
                              IoSession session)
    {
        fireEvent(nextFilter, session, EventType.OPENED, null);
    }

    public void sessionClosed(NextFilter nextFilter,
                              IoSession session)
    {
        fireEvent(nextFilter, session, EventType.CLOSED, null);
    }

    public void sessionIdle(NextFilter nextFilter,
                            IoSession session, IdleStatus status)
    {
        fireEvent(nextFilter, session, EventType.IDLE, status);
    }

    public void exceptionCaught(NextFilter nextFilter,
                                IoSession session, Throwable cause)
    {
        fireEvent(nextFilter, session, EventType.EXCEPTION, cause);
    }

    public void messageReceived(NextFilter nextFilter,
                                IoSession session, Object message)
    {
        ByteBufferUtil.acquireIfPossible(message);
        fireEvent(nextFilter, session, EventType.RECEIVED, message);
    }

    public void messageSent(NextFilter nextFilter,
                            IoSession session, Object message)
    {
        ByteBufferUtil.acquireIfPossible(message);
        fireEvent(nextFilter, session, EventType.SENT, message);
    }

    protected void processEvent(NextFilter nextFilter,
                                IoSession session, EventType type,
                                Object data)
    {
        if (type == EventType.RECEIVED)
        {
            nextFilter.messageReceived(session, data);
            ByteBufferUtil.releaseIfPossible(data);
        }
        else if (type == EventType.SENT)
        {
            nextFilter.messageSent(session, data);
            ByteBufferUtil.releaseIfPossible(data);
        }
        else if (type == EventType.EXCEPTION)
        {
            nextFilter.exceptionCaught(session, (Throwable) data);
        }
        else if (type == EventType.IDLE)
        {
            nextFilter.sessionIdle(session, (IdleStatus) data);
        }
        else if (type == EventType.OPENED)
        {
            nextFilter.sessionOpened(session);
        }
        else if (type == EventType.CLOSED)
        {
            nextFilter.sessionClosed(session);
        }
    }

    public void filterWrite(NextFilter nextFilter, IoSession session, WriteRequest writeRequest)
    {
        nextFilter.filterWrite(session, writeRequest);
    }

    public void filterClose(NextFilter nextFilter, IoSession session) throws Exception
    {
        nextFilter.filterClose(session);
    }
}