netty5/src/main/java/org/jboss/netty/handler/timeout/HashedWheelTimer.java

/*
 * JBoss, Home of Professional Open Source
 *
 * Copyright 2009, Red Hat Middleware LLC, and individual contributors
 * by the @author tags. See the COPYRIGHT.txt in the distribution for a
 * full listing of individual contributors.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.jboss.netty.handler.timeout;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import org.jboss.netty.logging.InternalLogger;
import org.jboss.netty.logging.InternalLoggerFactory;
import org.jboss.netty.util.ConcurrentIdentityHashMap;
import org.jboss.netty.util.MapBackedSet;
import org.jboss.netty.util.ReusableIterator;
import org.jboss.netty.util.ThreadRenamingRunnable;

/**
 * @author The Netty Project (netty-dev@lists.jboss.org)
 * @author Trustin Lee (tlee@redhat.com)
 * @version $Rev$, $Date$
 */
public class HashedWheelTimer implements Timer {

    static final InternalLogger logger =
        InternalLoggerFactory.getInstance(HashedWheelTimer.class);
    private static final AtomicInteger id = new AtomicInteger();

    private final Worker worker = new Worker();
    final Thread workerThread;
    final AtomicBoolean shutdown = new AtomicBoolean();

    private final long roundDuration;
    final long tickDuration;
    final Set<HashedWheelTimeout>[] wheel;
    final ReusableIterator<HashedWheelTimeout>[] iterators;
    final int mask;
    final ReadWriteLock lock = new ReentrantReadWriteLock();
    volatile int wheelCursor;

    public HashedWheelTimer() {
        this(Executors.defaultThreadFactory());
    }

    public HashedWheelTimer(
            long tickDuration, TimeUnit unit, int ticksPerWheel) {
        this(Executors.defaultThreadFactory(), tickDuration, unit, ticksPerWheel);
    }

    public HashedWheelTimer(ThreadFactory threadFactory) {
        this(threadFactory, 100, TimeUnit.MILLISECONDS, 512); // about 50 sec
    }

    public HashedWheelTimer(
            ThreadFactory threadFactory,
            long tickDuration, TimeUnit unit, int ticksPerWheel) {

        if (threadFactory == null) {
            throw new NullPointerException("threadFactory");
        }
        if (unit == null) {
            throw new NullPointerException("unit");
        }
        if (tickDuration <= 0) {
            throw new IllegalArgumentException(
                    "tickDuration must be greater than 0: " + tickDuration);
        }
        if (ticksPerWheel <= 0) {
            throw new IllegalArgumentException(
                    "ticksPerWheel must be greater than 0: " + ticksPerWheel);
        }

        // Normalize ticksPerWheel to power of two and initialize the wheel.
        wheel = createWheel(ticksPerWheel);
        iterators = createIterators(wheel);
        mask = wheel.length - 1;

        // Convert tickDuration to milliseconds.
        this.tickDuration = tickDuration = unit.toMillis(tickDuration);

        // Prevent overflow.
        if (tickDuration == Long.MAX_VALUE ||
                tickDuration >= Long.MAX_VALUE / wheel.length) {
            throw new IllegalArgumentException(
                    "tickDuration is too long: " +
                    tickDuration +  ' ' + unit);
        }

        roundDuration = tickDuration * wheel.length;

        workerThread = threadFactory.newThread(new ThreadRenamingRunnable(
                        worker, "Hashed wheel timer #" + id.incrementAndGet()));
    }

    @SuppressWarnings("unchecked")
    private static Set<HashedWheelTimeout>[] createWheel(int ticksPerWheel) {
        if (ticksPerWheel <= 0) {
            throw new IllegalArgumentException(
                    "ticksPerWheel must be greater than 0: " + ticksPerWheel);
        }
        if (ticksPerWheel > 1073741824) {
            throw new IllegalArgumentException(
                    "ticksPerWheel may not be greater than 2^30: " + ticksPerWheel);
        }

        ticksPerWheel = normalizeTicksPerWheel(ticksPerWheel);
        Set<HashedWheelTimeout>[] wheel = new Set[ticksPerWheel];
        for (int i = 0; i < wheel.length; i ++) {
            wheel[i] = new MapBackedSet<HashedWheelTimeout>(
                    new ConcurrentIdentityHashMap<HashedWheelTimeout, Boolean>(16, 0.95f, 4));
        }
        return wheel;
    }

    @SuppressWarnings("unchecked")
    private static ReusableIterator<HashedWheelTimeout>[] createIterators(Set<HashedWheelTimeout>[] wheel) {
        ReusableIterator<HashedWheelTimeout>[] iterators = new ReusableIterator[wheel.length];
        for (int i = 0; i < wheel.length; i ++) {
            iterators[i] = (ReusableIterator<HashedWheelTimeout>) wheel[i].iterator();
        }
        return iterators;
    }

    private static int normalizeTicksPerWheel(int ticksPerWheel) {
        int normalizedTicksPerWheel = 1;
        while (normalizedTicksPerWheel < ticksPerWheel) {
            normalizedTicksPerWheel <<= 1;
        }
        return normalizedTicksPerWheel;
    }

    public void start() {
        workerThread.start();
    }

    public Set<Timeout> stop() {
        if (!shutdown.compareAndSet(false, true)) {
            return Collections.emptySet();
        }

        while (workerThread.isAlive()) {
            workerThread.interrupt();
            try {
                workerThread.join(100);
            } catch (InterruptedException e) {
                // Ignore
            }
        }

        Set<Timeout> unprocessedTimeouts = new HashSet<Timeout>();
        for (Set<HashedWheelTimeout> bucket: wheel) {
            unprocessedTimeouts.addAll(bucket);
            bucket.clear();
        }

        return Collections.unmodifiableSet(unprocessedTimeouts);
    }

    public Timeout newTimeout(TimerTask task, long delay, TimeUnit unit) {
        final long currentTime = System.currentTimeMillis();

        if (task == null) {
            throw new NullPointerException("task");
        }
        if (unit == null) {
            throw new NullPointerException("unit");
        }

        delay = unit.toMillis(delay);
        if (delay < tickDuration) {
            delay = tickDuration;
        }

        if (!workerThread.isAlive()) {
            start();
        }

        // Prepare the required parameters to create the timeout object.
        HashedWheelTimeout timeout;
        final long lastRoundDelay = delay % roundDuration;
        final long lastTickDelay = delay % tickDuration;
        final long relativeIndex =
            lastRoundDelay / tickDuration + (lastTickDelay != 0? 1 : 0);
        final long deadline = currentTime + delay;

        final long remainingRounds =
            delay / roundDuration - (delay % roundDuration == 0? 1 : 0);

        // Add the timeout to the wheel.
        lock.readLock().lock();
        try {
            timeout =
                new HashedWheelTimeout(
                        task, deadline,
                        (int) (wheelCursor + relativeIndex & mask),
                        remainingRounds);

            wheel[timeout.stopIndex].add(timeout);
        } finally {
            lock.readLock().unlock();
        }

        return timeout;
    }

    private final class Worker implements Runnable {

        private long startTime;
        private long tick;

        Worker() {
            super();
        }

        public void run() {
            List<HashedWheelTimeout> expiredTimeouts =
                new ArrayList<HashedWheelTimeout>();

            startTime = System.currentTimeMillis();
            tick = 1;

            while (!shutdown.get()) {
                waitForNextTick();
                fetchExpiredTimeouts(expiredTimeouts);
                notifyExpiredTimeouts(expiredTimeouts);
            }
        }

        private void fetchExpiredTimeouts(
                List<HashedWheelTimeout> expiredTimeouts) {

            // Find the expired timeouts and decrease the round counter
            // if necessary.  Note that we don't send the notification
            // immediately to make sure the listeners are called without
            // an exclusive lock.
            lock.writeLock().lock();
            try {
                int oldBucketHead = wheelCursor;
                int newBucketHead = oldBucketHead + 1 & mask;
                wheelCursor = newBucketHead;

                ReusableIterator<HashedWheelTimeout> i = iterators[oldBucketHead];
                fetchExpiredTimeouts(expiredTimeouts, i);
            } finally {
                lock.writeLock().unlock();
            }
        }

        private void fetchExpiredTimeouts(
                List<HashedWheelTimeout> expiredTimeouts,
                ReusableIterator<HashedWheelTimeout> i) {

            long currentTime = System.currentTimeMillis();
            i.rewind();
            while (i.hasNext()) {
                HashedWheelTimeout timeout = i.next();
                synchronized (timeout) {
                    if (timeout.remainingRounds <= 0) {
                        if (timeout.deadline <= currentTime) {
                            i.remove();
                            expiredTimeouts.add(timeout);
                        } else {
                            // A rare case where a timeout is put for the next
                            // round: just wait for the next round.
                        }
                    } else {
                        timeout.remainingRounds --;
                    }
                }
            }
        }

        private void notifyExpiredTimeouts(
                List<HashedWheelTimeout> expiredTimeouts) {
            // Notify the expired timeouts.
            for (int i = expiredTimeouts.size() - 1; i >= 0; i --) {
                expiredTimeouts.get(i).expire();
            }

            // Clean up the temporary list.
            expiredTimeouts.clear();
        }

        private void waitForNextTick() {
            for (;;) {
                final long currentTime = System.currentTimeMillis();
                final long sleepTime = tickDuration * tick - (currentTime - startTime);

                if (sleepTime <= 0) {
                    break;
                }

                try {
                    Thread.sleep(sleepTime);
                } catch (InterruptedException e) {
                    if (shutdown.get()) {
                        return;
                    }
                }
            }

            // Reset the tick if overflow is expected.
            if (tickDuration * tick > Long.MAX_VALUE - tickDuration) {
                startTime = System.currentTimeMillis();
                tick = 1;
            } else {
                // Increase the tick if overflow is not likely to happen.
                tick ++;
            }
        }
    }

    private final class HashedWheelTimeout implements Timeout {

        private final TimerTask task;
        final int stopIndex;
        final long deadline;
        volatile long remainingRounds;
        private volatile boolean cancelled;

        HashedWheelTimeout(
                TimerTask task, long deadline, int stopIndex, long remainingRounds) {
            this.task = task;
            this.deadline = deadline;
            this.stopIndex = stopIndex;
            this.remainingRounds = remainingRounds;
        }

        public TimerTask getTask() {
            return task;
        }

        public void cancel() {
            if (isExpired()) {
                return;
            }

            cancelled = true;

            // Might be called more than once, but doesn't matter.
            wheel[stopIndex].remove(this);
        }

        public boolean isCancelled() {
            return cancelled;
        }

        public boolean isExpired() {
            return cancelled || System.currentTimeMillis() > deadline;
        }

        public void expire() {
            if (cancelled) {
                return;
            }

            try {
                task.run(this);
            } catch (Throwable t) {
                logger.warn(
                        "An exception was thrown by " +
                        TimerTask.class.getSimpleName() + ".", t);
            }
        }

        @Override
        public String toString() {
            long currentTime = System.currentTimeMillis();
            long remaining = deadline - currentTime;

            StringBuilder buf = new StringBuilder(192);
            buf.append(getClass().getSimpleName());
            buf.append('(');

            buf.append("deadline: ");
            if (remaining > 0) {
                buf.append(remaining);
                buf.append(" ms later, ");
            } else if (remaining < 0) {
                buf.append(-remaining);
                buf.append(" ms ago, ");
            } else {
                buf.append("now, ");
            }

            if (isCancelled()) {
                buf.append (", cancelled");
            }

            return buf.append(')').toString();
        }
    }
}