/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project 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 io.netty.util;

import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

import java.util.Collections;
import java.util.HashSet;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executors;
import java.util.concurrent.RejectedExecutionException;
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.atomic.AtomicIntegerFieldUpdater;
import java.util.concurrent.atomic.AtomicLong;

import static io.netty.util.internal.StringUtil.simpleClassName;

A Timer optimized for approximated I/O timeout scheduling. 
Tick Duration
 As described with 'approximated', this timer does not execute the scheduled TimerTask on time. HashedWheelTimer, on every tick, will check if there are any TimerTasks behind the schedule and execute them. 

You can increase or decrease the accuracy of the execution timing by
specifying smaller or larger tick duration in the constructor.  In most
network applications, I/O timeout does not need to be accurate.  Therefore,
the default tick duration is 100 milliseconds and you will not need to try
different configurations in most cases.
Ticks per Wheel (Wheel Size)
 HashedWheelTimer maintains a data structure called 'wheel'. To put simply, a wheel is a hash table of TimerTasks whose hash function is 'dead line of the task'. The default number of ticks per wheel (i.e. the size of the wheel) is 512. You could specify a larger value if you are going to schedule a lot of timeouts. 
Do not create many instances.
 HashedWheelTimer creates a new thread whenever it is instantiated and started. Therefore, you should make sure to create only one instance and share it across your application. One of the common mistakes, that makes your application unresponsive, is to create a new instance for every connection. 
Implementation Details
 HashedWheelTimer is based on George Varghese and
Tony Lauck's paper,
'Hashed
and Hierarchical Timing Wheels: data structures to efficiently implement a
timer facility'.  More comprehensive slides are located
here.
/**
 * A {@link Timer} optimized for approximated I/O timeout scheduling.
 *
 * <h3>Tick Duration</h3>
 *
 * As described with 'approximated', this timer does not execute the scheduled
 * {@link TimerTask} on time.  {@link HashedWheelTimer}, on every tick, will
 * check if there are any {@link TimerTask}s behind the schedule and execute
 * them.
 * <p>
 * You can increase or decrease the accuracy of the execution timing by
 * specifying smaller or larger tick duration in the constructor.  In most
 * network applications, I/O timeout does not need to be accurate.  Therefore,
 * the default tick duration is 100 milliseconds and you will not need to try
 * different configurations in most cases.
 *
 * <h3>Ticks per Wheel (Wheel Size)</h3>
 *
 * {@link HashedWheelTimer} maintains a data structure called 'wheel'.
 * To put simply, a wheel is a hash table of {@link TimerTask}s whose hash
 * function is 'dead line of the task'.  The default number of ticks per wheel
 * (i.e. the size of the wheel) is 512.  You could specify a larger value
 * if you are going to schedule a lot of timeouts.
 *
 * <h3>Do not create many instances.</h3>
 *
 * {@link HashedWheelTimer} creates a new thread whenever it is instantiated and
 * started.  Therefore, you should make sure to create only one instance and
 * share it across your application.  One of the common mistakes, that makes
 * your application unresponsive, is to create a new instance for every connection.
 *
 * <h3>Implementation Details</h3>
 *
 * {@link HashedWheelTimer} is based on
 * <a href="http://cseweb.ucsd.edu/users/varghese/">George Varghese</a> and
 * Tony Lauck's paper,
 * <a href="http://cseweb.ucsd.edu/users/varghese/PAPERS/twheel.ps.Z">'Hashed
 * and Hierarchical Timing Wheels: data structures to efficiently implement a
 * timer facility'</a>.  More comprehensive slides are located
 * <a href="http://www.cse.wustl.edu/~cdgill/courses/cs6874/TimingWheels.ppt">here</a>.
 */
public class HashedWheelTimer implements Timer {

    static final InternalLogger logger =
            InternalLoggerFactory.getInstance(HashedWheelTimer.class);

    private static final AtomicInteger INSTANCE_COUNTER = new AtomicInteger();
    private static final AtomicBoolean WARNED_TOO_MANY_INSTANCES = new AtomicBoolean();
    private static final int INSTANCE_COUNT_LIMIT = 64;
    private static final ResourceLeakDetector<HashedWheelTimer> leakDetector = ResourceLeakDetectorFactory.instance()
            .newResourceLeakDetector(HashedWheelTimer.class, 1);

    private static final AtomicIntegerFieldUpdater<HashedWheelTimer> WORKER_STATE_UPDATER =
            AtomicIntegerFieldUpdater.newUpdater(HashedWheelTimer.class, "workerState");

    private final ResourceLeakTracker<HashedWheelTimer> leak;
    private final Worker worker = new Worker();
    private final Thread workerThread;

    public static final int WORKER_STATE_INIT = 0;
    public static final int WORKER_STATE_STARTED = 1;
    public static final int WORKER_STATE_SHUTDOWN = 2;
    @SuppressWarnings({ "unused", "FieldMayBeFinal" })
    private volatile int workerState; // 0 - init, 1 - started, 2 - shut down

    private final long tickDuration;
    private final HashedWheelBucket[] wheel;
    private final int mask;
    private final CountDownLatch startTimeInitialized = new CountDownLatch(1);
    private final Queue<HashedWheelTimeout> timeouts = PlatformDependent.newMpscQueue();
    private final Queue<HashedWheelTimeout> cancelledTimeouts = PlatformDependent.newMpscQueue();
    private final AtomicLong pendingTimeouts = new AtomicLong(0);
    private final long maxPendingTimeouts;

    private volatile long startTime;

    
Creates a new timer with the default thread factory (Executors.defaultThreadFactory()), default tick duration, and default number of ticks per wheel. /**
     * Creates a new timer with the default thread factory
     * ({@link Executors#defaultThreadFactory()}), default tick duration, and
     * default number of ticks per wheel.
     */
    public HashedWheelTimer() {
        this(Executors.defaultThreadFactory());
    }

    
Creates a new timer with the default thread factory (Executors.defaultThreadFactory()) and default number of ticks per wheel. 
Params:
tickDuration –   the duration between tick
unit –  the time unit of the tickDuration
Throws:
NullPointerException –  if unit is null
IllegalArgumentException – if tickDuration is <= 0/**
     * Creates a new timer with the default thread factory
     * ({@link Executors#defaultThreadFactory()}) and default number of ticks
     * per wheel.
     *
     * @param tickDuration   the duration between tick
     * @param unit           the time unit of the {@code tickDuration}
     * @throws NullPointerException     if {@code unit} is {@code null}
     * @throws IllegalArgumentException if {@code tickDuration} is &lt;= 0
     */
    public HashedWheelTimer(long tickDuration, TimeUnit unit) {
        this(Executors.defaultThreadFactory(), tickDuration, unit);
    }

    
Creates a new timer with the default thread factory (Executors.defaultThreadFactory()). 
Params:
tickDuration –   the duration between tick
unit –  the time unit of the tickDuration
ticksPerWheel –  the size of the wheel
Throws:
NullPointerException –  if unit is null
IllegalArgumentException – if either of tickDuration and ticksPerWheel is <= 0/**
     * Creates a new timer with the default thread factory
     * ({@link Executors#defaultThreadFactory()}).
     *
     * @param tickDuration   the duration between tick
     * @param unit           the time unit of the {@code tickDuration}
     * @param ticksPerWheel  the size of the wheel
     * @throws NullPointerException     if {@code unit} is {@code null}
     * @throws IllegalArgumentException if either of {@code tickDuration} and {@code ticksPerWheel} is &lt;= 0
     */
    public HashedWheelTimer(long tickDuration, TimeUnit unit, int ticksPerWheel) {
        this(Executors.defaultThreadFactory(), tickDuration, unit, ticksPerWheel);
    }

    
Creates a new timer with the default tick duration and default number of
ticks per wheel.
Params:
threadFactory –  a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.
Throws:
NullPointerException – if threadFactory is null/**
     * Creates a new timer with the default tick duration and default number of
     * ticks per wheel.
     *
     * @param threadFactory  a {@link ThreadFactory} that creates a
     *                       background {@link Thread} which is dedicated to
     *                       {@link TimerTask} execution.
     * @throws NullPointerException if {@code threadFactory} is {@code null}
     */
    public HashedWheelTimer(ThreadFactory threadFactory) {
        this(threadFactory, 100, TimeUnit.MILLISECONDS);
    }

    
Creates a new timer with the default number of ticks per wheel.
Params:
threadFactory –  a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.
tickDuration –   the duration between tick
unit –  the time unit of the tickDuration
Throws:
NullPointerException –  if either of threadFactory and unit is null
IllegalArgumentException – if tickDuration is <= 0/**
     * Creates a new timer with the default number of ticks per wheel.
     *
     * @param threadFactory  a {@link ThreadFactory} that creates a
     *                       background {@link Thread} which is dedicated to
     *                       {@link TimerTask} execution.
     * @param tickDuration   the duration between tick
     * @param unit           the time unit of the {@code tickDuration}
     * @throws NullPointerException     if either of {@code threadFactory} and {@code unit} is {@code null}
     * @throws IllegalArgumentException if {@code tickDuration} is &lt;= 0
     */
    public HashedWheelTimer(
            ThreadFactory threadFactory, long tickDuration, TimeUnit unit) {
        this(threadFactory, tickDuration, unit, 512);
    }

    
Creates a new timer.
Params:
threadFactory –  a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.
tickDuration –   the duration between tick
unit –  the time unit of the tickDuration
ticksPerWheel –  the size of the wheel
Throws:
NullPointerException –  if either of threadFactory and unit is null
IllegalArgumentException – if either of tickDuration and ticksPerWheel is <= 0/**
     * Creates a new timer.
     *
     * @param threadFactory  a {@link ThreadFactory} that creates a
     *                       background {@link Thread} which is dedicated to
     *                       {@link TimerTask} execution.
     * @param tickDuration   the duration between tick
     * @param unit           the time unit of the {@code tickDuration}
     * @param ticksPerWheel  the size of the wheel
     * @throws NullPointerException     if either of {@code threadFactory} and {@code unit} is {@code null}
     * @throws IllegalArgumentException if either of {@code tickDuration} and {@code ticksPerWheel} is &lt;= 0
     */
    public HashedWheelTimer(
            ThreadFactory threadFactory,
            long tickDuration, TimeUnit unit, int ticksPerWheel) {
        this(threadFactory, tickDuration, unit, ticksPerWheel, true);
    }

    
Creates a new timer.
Params:
threadFactory –  a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.
tickDuration –         the duration between tick
unit –  the time unit of the tickDuration
ticksPerWheel –        the size of the wheel
leakDetection –  true if leak detection should be enabled always, if false it will only be enabled if the worker thread is not a daemon thread.
Throws:
NullPointerException –  if either of threadFactory and unit is null
IllegalArgumentException – if either of tickDuration and ticksPerWheel is <= 0/**
     * Creates a new timer.
     *
     * @param threadFactory        a {@link ThreadFactory} that creates a
     *                             background {@link Thread} which is dedicated to
     *                             {@link TimerTask} execution.
     * @param tickDuration         the duration between tick
     * @param unit                 the time unit of the {@code tickDuration}
     * @param ticksPerWheel        the size of the wheel
     * @param leakDetection        {@code true} if leak detection should be enabled always,
     *                             if false it will only be enabled if the worker thread is not
     *                             a daemon thread.
     * @throws NullPointerException     if either of {@code threadFactory} and {@code unit} is {@code null}
     * @throws IllegalArgumentException if either of {@code tickDuration} and {@code ticksPerWheel} is &lt;= 0
     */
    public HashedWheelTimer(
        ThreadFactory threadFactory,
        long tickDuration, TimeUnit unit, int ticksPerWheel, boolean leakDetection) {
        this(threadFactory, tickDuration, unit, ticksPerWheel, leakDetection, -1);
    }

    
Creates a new timer.
Params:
threadFactory –  a ThreadFactory that creates a background Thread which is dedicated to TimerTask execution.
tickDuration –         the duration between tick
unit –  the time unit of the tickDuration
ticksPerWheel –        the size of the wheel
leakDetection –  true if leak detection should be enabled always, if false it will only be enabled if the worker thread is not a daemon thread.
maxPendingTimeouts –  The maximum number of pending timeouts after which call to newTimeout will result in RejectedExecutionException being thrown. No maximum pending timeouts limit is assumed if this value is 0 or negative.
Throws:
NullPointerException –  if either of threadFactory and unit is null
IllegalArgumentException – if either of tickDuration and ticksPerWheel is <= 0/**
     * Creates a new timer.
     *
     * @param threadFactory        a {@link ThreadFactory} that creates a
     *                             background {@link Thread} which is dedicated to
     *                             {@link TimerTask} execution.
     * @param tickDuration         the duration between tick
     * @param unit                 the time unit of the {@code tickDuration}
     * @param ticksPerWheel        the size of the wheel
     * @param leakDetection        {@code true} if leak detection should be enabled always,
     *                             if false it will only be enabled if the worker thread is not
     *                             a daemon thread.
     * @param  maxPendingTimeouts  The maximum number of pending timeouts after which call to
     *                             {@code newTimeout} will result in
     *                             {@link java.util.concurrent.RejectedExecutionException}
     *                             being thrown. No maximum pending timeouts limit is assumed if
     *                             this value is 0 or negative.
     * @throws NullPointerException     if either of {@code threadFactory} and {@code unit} is {@code null}
     * @throws IllegalArgumentException if either of {@code tickDuration} and {@code ticksPerWheel} is &lt;= 0
     */
    public HashedWheelTimer(
            ThreadFactory threadFactory,
            long tickDuration, TimeUnit unit, int ticksPerWheel, boolean leakDetection,
            long maxPendingTimeouts) {

        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);
        mask = wheel.length - 1;

        // Convert tickDuration to nanos.
        this.tickDuration = unit.toNanos(tickDuration);

        // Prevent overflow.
        if (this.tickDuration >= Long.MAX_VALUE / wheel.length) {
            throw new IllegalArgumentException(String.format(
                    "tickDuration: %d (expected: 0 < tickDuration in nanos < %d",
                    tickDuration, Long.MAX_VALUE / wheel.length));
        }
        workerThread = threadFactory.newThread(worker);

        leak = leakDetection || !workerThread.isDaemon() ? leakDetector.track(this) : null;

        this.maxPendingTimeouts = maxPendingTimeouts;

        if (INSTANCE_COUNTER.incrementAndGet() > INSTANCE_COUNT_LIMIT &&
            WARNED_TOO_MANY_INSTANCES.compareAndSet(false, true)) {
            reportTooManyInstances();
        }
    }

    @Override
    protected void finalize() throws Throwable {
        try {
            super.finalize();
        } finally {
            // This object is going to be GCed and it is assumed the ship has sailed to do a proper shutdown. If
            // we have not yet shutdown then we want to make sure we decrement the active instance count.
            if (WORKER_STATE_UPDATER.getAndSet(this, WORKER_STATE_SHUTDOWN) != WORKER_STATE_SHUTDOWN) {
                INSTANCE_COUNTER.decrementAndGet();
            }
        }
    }

    private static HashedWheelBucket[] 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);
        HashedWheelBucket[] wheel = new HashedWheelBucket[ticksPerWheel];
        for (int i = 0; i < wheel.length; i ++) {
            wheel[i] = new HashedWheelBucket();
        }
        return wheel;
    }

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

    
Starts the background thread explicitly.  The background thread will
start automatically on demand even if you did not call this method.
Throws:
IllegalStateException – if this timer has been stopped already/**
     * Starts the background thread explicitly.  The background thread will
     * start automatically on demand even if you did not call this method.
     *
     * @throws IllegalStateException if this timer has been
     *                               {@linkplain #stop() stopped} already
     */
    public void start() {
        switch (WORKER_STATE_UPDATER.get(this)) {
            case WORKER_STATE_INIT:
                if (WORKER_STATE_UPDATER.compareAndSet(this, WORKER_STATE_INIT, WORKER_STATE_STARTED)) {
                    workerThread.start();
                }
                break;
            case WORKER_STATE_STARTED:
                break;
            case WORKER_STATE_SHUTDOWN:
                throw new IllegalStateException("cannot be started once stopped");
            default:
                throw new Error("Invalid WorkerState");
        }

        // Wait until the startTime is initialized by the worker.
        while (startTime == 0) {
            try {
                startTimeInitialized.await();
            } catch (InterruptedException ignore) {
                // Ignore - it will be ready very soon.
            }
        }
    }

    @Override
    public Set<Timeout> stop() {
        if (Thread.currentThread() == workerThread) {
            throw new IllegalStateException(
                    HashedWheelTimer.class.getSimpleName() +
                            ".stop() cannot be called from " +
                            TimerTask.class.getSimpleName());
        }

        if (!WORKER_STATE_UPDATER.compareAndSet(this, WORKER_STATE_STARTED, WORKER_STATE_SHUTDOWN)) {
            // workerState can be 0 or 2 at this moment - let it always be 2.
            if (WORKER_STATE_UPDATER.getAndSet(this, WORKER_STATE_SHUTDOWN) != WORKER_STATE_SHUTDOWN) {
                INSTANCE_COUNTER.decrementAndGet();
                if (leak != null) {
                    boolean closed = leak.close(this);
                    assert closed;
                }
            }

            return Collections.emptySet();
        }

        try {
            boolean interrupted = false;
            while (workerThread.isAlive()) {
                workerThread.interrupt();
                try {
                    workerThread.join(100);
                } catch (InterruptedException ignored) {
                    interrupted = true;
                }
            }

            if (interrupted) {
                Thread.currentThread().interrupt();
            }
        } finally {
            INSTANCE_COUNTER.decrementAndGet();
            if (leak != null) {
                boolean closed = leak.close(this);
                assert closed;
            }
        }
        return worker.unprocessedTimeouts();
    }

    @Override
    public Timeout newTimeout(TimerTask task, long delay, TimeUnit unit) {
        if (task == null) {
            throw new NullPointerException("task");
        }
        if (unit == null) {
            throw new NullPointerException("unit");
        }

        long pendingTimeoutsCount = pendingTimeouts.incrementAndGet();

        if (maxPendingTimeouts > 0 && pendingTimeoutsCount > maxPendingTimeouts) {
            pendingTimeouts.decrementAndGet();
            throw new RejectedExecutionException("Number of pending timeouts ("
                + pendingTimeoutsCount + ") is greater than or equal to maximum allowed pending "
                + "timeouts (" + maxPendingTimeouts + ")");
        }

        start();

        // Add the timeout to the timeout queue which will be processed on the next tick.
        // During processing all the queued HashedWheelTimeouts will be added to the correct HashedWheelBucket.
        long deadline = System.nanoTime() + unit.toNanos(delay) - startTime;

        // Guard against overflow.
        if (delay > 0 && deadline < 0) {
            deadline = Long.MAX_VALUE;
        }
        HashedWheelTimeout timeout = new HashedWheelTimeout(this, task, deadline);
        timeouts.add(timeout);
        return timeout;
    }

    
Returns the number of pending timeouts of this Timer. /**
     * Returns the number of pending timeouts of this {@link Timer}.
     */
    public long pendingTimeouts() {
        return pendingTimeouts.get();
    }

    private static void reportTooManyInstances() {
        String resourceType = simpleClassName(HashedWheelTimer.class);
        logger.error("You are creating too many " + resourceType + " instances. " +
                resourceType + " is a shared resource that must be reused across the JVM," +
                "so that only a few instances are created.");
    }

    private final class Worker implements Runnable {
        private final Set<Timeout> unprocessedTimeouts = new HashSet<Timeout>();

        private long tick;

        @Override
        public void run() {
            // Initialize the startTime.
            startTime = System.nanoTime();
            if (startTime == 0) {
                // We use 0 as an indicator for the uninitialized value here, so make sure it's not 0 when initialized.
                startTime = 1;
            }

            // Notify the other threads waiting for the initialization at start().
            startTimeInitialized.countDown();

            do {
                final long deadline = waitForNextTick();
                if (deadline > 0) {
                    int idx = (int) (tick & mask);
                    processCancelledTasks();
                    HashedWheelBucket bucket =
                            wheel[idx];
                    transferTimeoutsToBuckets();
                    bucket.expireTimeouts(deadline);
                    tick++;
                }
            } while (WORKER_STATE_UPDATER.get(HashedWheelTimer.this) == WORKER_STATE_STARTED);

            // Fill the unprocessedTimeouts so we can return them from stop() method.
            for (HashedWheelBucket bucket: wheel) {
                bucket.clearTimeouts(unprocessedTimeouts);
            }
            for (;;) {
                HashedWheelTimeout timeout = timeouts.poll();
                if (timeout == null) {
                    break;
                }
                if (!timeout.isCancelled()) {
                    unprocessedTimeouts.add(timeout);
                }
            }
            processCancelledTasks();
        }

        private void transferTimeoutsToBuckets() {
            // transfer only max. 100000 timeouts per tick to prevent a thread to stale the workerThread when it just
            // adds new timeouts in a loop.
            for (int i = 0; i < 100000; i++) {
                HashedWheelTimeout timeout = timeouts.poll();
                if (timeout == null) {
                    // all processed
                    break;
                }
                if (timeout.state() == HashedWheelTimeout.ST_CANCELLED) {
                    // Was cancelled in the meantime.
                    continue;
                }

                long calculated = timeout.deadline / tickDuration;
                timeout.remainingRounds = (calculated - tick) / wheel.length;

                final long ticks = Math.max(calculated, tick); // Ensure we don't schedule for past.
                int stopIndex = (int) (ticks & mask);

                HashedWheelBucket bucket = wheel[stopIndex];
                bucket.addTimeout(timeout);
            }
        }

        private void processCancelledTasks() {
            for (;;) {
                HashedWheelTimeout timeout = cancelledTimeouts.poll();
                if (timeout == null) {
                    // all processed
                    break;
                }
                try {
                    timeout.remove();
                } catch (Throwable t) {
                    if (logger.isWarnEnabled()) {
                        logger.warn("An exception was thrown while process a cancellation task", t);
                    }
                }
            }
        }

        
calculate goal nanoTime from startTime and current tick number,
then wait until that goal has been reached.
Returns:
Long.MIN_VALUE if received a shutdown request,
current time otherwise (with Long.MIN_VALUE changed by +1)/**
         * calculate goal nanoTime from startTime and current tick number,
         * then wait until that goal has been reached.
         * @return Long.MIN_VALUE if received a shutdown request,
         * current time otherwise (with Long.MIN_VALUE changed by +1)
         */
        private long waitForNextTick() {
            long deadline = tickDuration * (tick + 1);

            for (;;) {
                final long currentTime = System.nanoTime() - startTime;
                long sleepTimeMs = (deadline - currentTime + 999999) / 1000000;

                if (sleepTimeMs <= 0) {
                    if (currentTime == Long.MIN_VALUE) {
                        return -Long.MAX_VALUE;
                    } else {
                        return currentTime;
                    }
                }

                // Check if we run on windows, as if thats the case we will need
                // to round the sleepTime as workaround for a bug that only affect
                // the JVM if it runs on windows.
                //
                // See https://github.com/netty/netty/issues/356
                if (PlatformDependent.isWindows()) {
                    sleepTimeMs = sleepTimeMs / 10 * 10;
                }

                try {
                    Thread.sleep(sleepTimeMs);
                } catch (InterruptedException ignored) {
                    if (WORKER_STATE_UPDATER.get(HashedWheelTimer.this) == WORKER_STATE_SHUTDOWN) {
                        return Long.MIN_VALUE;
                    }
                }
            }
        }

        public Set<Timeout> unprocessedTimeouts() {
            return Collections.unmodifiableSet(unprocessedTimeouts);
        }
    }

    private static final class HashedWheelTimeout implements Timeout {

        private static final int ST_INIT = 0;
        private static final int ST_CANCELLED = 1;
        private static final int ST_EXPIRED = 2;
        private static final AtomicIntegerFieldUpdater<HashedWheelTimeout> STATE_UPDATER =
                AtomicIntegerFieldUpdater.newUpdater(HashedWheelTimeout.class, "state");

        private final HashedWheelTimer timer;
        private final TimerTask task;
        private final long deadline;

        @SuppressWarnings({"unused", "FieldMayBeFinal", "RedundantFieldInitialization" })
        private volatile int state = ST_INIT;

        // remainingRounds will be calculated and set by Worker.transferTimeoutsToBuckets() before the
        // HashedWheelTimeout will be added to the correct HashedWheelBucket.
        long remainingRounds;

        // This will be used to chain timeouts in HashedWheelTimerBucket via a double-linked-list.
        // As only the workerThread will act on it there is no need for synchronization / volatile.
        HashedWheelTimeout next;
        HashedWheelTimeout prev;

        // The bucket to which the timeout was added
        HashedWheelBucket bucket;

        HashedWheelTimeout(HashedWheelTimer timer, TimerTask task, long deadline) {
            this.timer = timer;
            this.task = task;
            this.deadline = deadline;
        }

        @Override
        public Timer timer() {
            return timer;
        }

        @Override
        public TimerTask task() {
            return task;
        }

        @Override
        public boolean cancel() {
            // only update the state it will be removed from HashedWheelBucket on next tick.
            if (!compareAndSetState(ST_INIT, ST_CANCELLED)) {
                return false;
            }
            // If a task should be canceled we put this to another queue which will be processed on each tick.
            // So this means that we will have a GC latency of max. 1 tick duration which is good enough. This way
            // we can make again use of our MpscLinkedQueue and so minimize the locking / overhead as much as possible.
            timer.cancelledTimeouts.add(this);
            return true;
        }

        void remove() {
            HashedWheelBucket bucket = this.bucket;
            if (bucket != null) {
                bucket.remove(this);
            } else {
                timer.pendingTimeouts.decrementAndGet();
            }
        }

        public boolean compareAndSetState(int expected, int state) {
            return STATE_UPDATER.compareAndSet(this, expected, state);
        }

        public int state() {
            return state;
        }

        @Override
        public boolean isCancelled() {
            return state() == ST_CANCELLED;
        }

        @Override
        public boolean isExpired() {
            return state() == ST_EXPIRED;
        }

        public void expire() {
            if (!compareAndSetState(ST_INIT, ST_EXPIRED)) {
                return;
            }

            try {
                task.run(this);
            } catch (Throwable t) {
                if (logger.isWarnEnabled()) {
                    logger.warn("An exception was thrown by " + TimerTask.class.getSimpleName() + '.', t);
                }
            }
        }

        @Override
        public String toString() {
            final long currentTime = System.nanoTime();
            long remaining = deadline - currentTime + timer.startTime;

            StringBuilder buf = new StringBuilder(192)
               .append(simpleClassName(this))
               .append('(')
               .append("deadline: ");
            if (remaining > 0) {
                buf.append(remaining)
                   .append(" ns later");
            } else if (remaining < 0) {
                buf.append(-remaining)
                   .append(" ns ago");
            } else {
                buf.append("now");
            }

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

            return buf.append(", task: ")
                      .append(task())
                      .append(')')
                      .toString();
        }
    }

    
Bucket that stores HashedWheelTimeouts. These are stored in a linked-list like datastructure to allow easy
removal of HashedWheelTimeouts in the middle. Also the HashedWheelTimeout act as nodes themself and so no
extra object creation is needed.
/**
     * Bucket that stores HashedWheelTimeouts. These are stored in a linked-list like datastructure to allow easy
     * removal of HashedWheelTimeouts in the middle. Also the HashedWheelTimeout act as nodes themself and so no
     * extra object creation is needed.
     */
    private static final class HashedWheelBucket {
        // Used for the linked-list datastructure
        private HashedWheelTimeout head;
        private HashedWheelTimeout tail;

        
Add HashedWheelTimeout to this bucket. /**
         * Add {@link HashedWheelTimeout} to this bucket.
         */
        public void addTimeout(HashedWheelTimeout timeout) {
            assert timeout.bucket == null;
            timeout.bucket = this;
            if (head == null) {
                head = tail = timeout;
            } else {
                tail.next = timeout;
                timeout.prev = tail;
                tail = timeout;
            }
        }

        
Expire all HashedWheelTimeouts for the given deadline. /**
         * Expire all {@link HashedWheelTimeout}s for the given {@code deadline}.
         */
        public void expireTimeouts(long deadline) {
            HashedWheelTimeout timeout = head;

            // process all timeouts
            while (timeout != null) {
                HashedWheelTimeout next = timeout.next;
                if (timeout.remainingRounds <= 0) {
                    next = remove(timeout);
                    if (timeout.deadline <= deadline) {
                        timeout.expire();
                    } else {
                        // The timeout was placed into a wrong slot. This should never happen.
                        throw new IllegalStateException(String.format(
                                "timeout.deadline (%d) > deadline (%d)", timeout.deadline, deadline));
                    }
                } else if (timeout.isCancelled()) {
                    next = remove(timeout);
                } else {
                    timeout.remainingRounds --;
                }
                timeout = next;
            }
        }

        public HashedWheelTimeout remove(HashedWheelTimeout timeout) {
            HashedWheelTimeout next = timeout.next;
            // remove timeout that was either processed or cancelled by updating the linked-list
            if (timeout.prev != null) {
                timeout.prev.next = next;
            }
            if (timeout.next != null) {
                timeout.next.prev = timeout.prev;
            }

            if (timeout == head) {
                // if timeout is also the tail we need to adjust the entry too
                if (timeout == tail) {
                    tail = null;
                    head = null;
                } else {
                    head = next;
                }
            } else if (timeout == tail) {
                // if the timeout is the tail modify the tail to be the prev node.
                tail = timeout.prev;
            }
            // null out prev, next and bucket to allow for GC.
            timeout.prev = null;
            timeout.next = null;
            timeout.bucket = null;
            timeout.timer.pendingTimeouts.decrementAndGet();
            return next;
        }

        
Clear this bucket and return all not expired / cancelled Timeouts. /**
         * Clear this bucket and return all not expired / cancelled {@link Timeout}s.
         */
        public void clearTimeouts(Set<Timeout> set) {
            for (;;) {
                HashedWheelTimeout timeout = pollTimeout();
                if (timeout == null) {
                    return;
                }
                if (timeout.isExpired() || timeout.isCancelled()) {
                    continue;
                }
                set.add(timeout);
            }
        }

        private HashedWheelTimeout pollTimeout() {
            HashedWheelTimeout head = this.head;
            if (head == null) {
                return null;
            }
            HashedWheelTimeout next = head.next;
            if (next == null) {
                tail = this.head =  null;
            } else {
                this.head = next;
                next.prev = null;
            }

            // null out prev and next to allow for GC.
            head.next = null;
            head.prev = null;
            head.bucket = null;
            return head;
        }
    }
}