Java时间轮算法的实现代码示例

考虑这样一个场景，现在有5000个任务，要让这5000个任务每隔5分中触发某个操作，怎么去实现这个需求。大部分人首先想到的是使用定时器，但是5000个任务，你就要用5000个定时器，一个定时器就是一个线程，你懂了吧，这种方法肯定是不行的。

针对这个场景，催生了时间轮算法，时间轮到底是什么？我一贯的风格，自行谷歌去。大发慈悲，发个时间轮介绍你们看看，看文字和图就好了，代码不要看了，那个文章里的代码运行不起来，时间轮介绍。

看好了介绍，我们就开始动手吧。

开发环境：idea + jdk1.8 + maven

新建一个maven工程

创建如下的目录结构

不要忘了pom.xml中添加netty库

<dependencies>
    <dependency>
      <groupid>io.netty</groupid>
      <artifactid>netty-all</artifactid>
      <version>4.1.5.final</version>
    </dependency>
  </dependencies>

代码如下

timeout.java

package com.tanghuachun.timer;
public interface timeout {
  timer timer();
  timertask task();
  boolean isexpired();
  boolean iscancelled();
  boolean cancel();
}

timer.java

package com.tanghuachun.timer;
import java.util.set;
import java.util.concurrent.timeunit;

public interface timer {
  timeout newtimeout(timertask task, long delay, timeunit unit, string argv);
  set<timeout> stop();
}

timertask.java

package com.tanghuachun.timer;
public interface timertask {
  void run(timeout timeout, string argv) throws exception;
}

timerwheel.java

/*
 * 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 com.tanghuachun.timer;
import io.netty.util.*;
import io.netty.util.internal.platformdependent;
import io.netty.util.internal.stringutil;
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.threadfactory;
import java.util.concurrent.timeunit;
import java.util.concurrent.atomic.atomicintegerfieldupdater;

public class timerwheel implements timer {

  static final internallogger logger =
      internalloggerfactory.getinstance(timerwheel.class);

  private static final resourceleakdetector<timerwheel> leakdetector = resourceleakdetectorfactory.instance()
      .newresourceleakdetector(timerwheel.class, 1, runtime.getruntime().availableprocessors() * 4l);

  private static final atomicintegerfieldupdater<timerwheel> worker_state_updater;
  static {
    atomicintegerfieldupdater<timerwheel> workerstateupdater =
        platformdependent.newatomicintegerfieldupdater(timerwheel.class, "workerstate");
    if (workerstateupdater == null) {
      workerstateupdater = atomicintegerfieldupdater.newupdater(timerwheel.class, "workerstate");
    }
    worker_state_updater = workerstateupdater;
  }

  private final resourceleak 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", "redundantfieldinitialization" })
  private volatile int workerstate = worker_state_init; // 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 volatile long starttime;

  /**
   * creates a new timer with the default thread factory
   * ({@link executors#defaultthreadfactory()}), default tick duration, and
   * default number of ticks per wheel.
   */
  public timerwheel() {
    this(executors.defaultthreadfactory());
  }

  /**
   * 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 <= 0
   */
  public timerwheel(long tickduration, timeunit unit) {
    this(executors.defaultthreadfactory(), tickduration, unit);
  }

  /**
   * 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 <= 0
   */
  public timerwheel(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.
   *
   * @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 timerwheel(threadfactory threadfactory) {
    this(threadfactory, 100, timeunit.milliseconds);
  }

  /**
   * 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 <= 0
   */
  public timerwheel(
      threadfactory threadfactory, long tickduration, timeunit unit) {
    this(threadfactory, tickduration, unit, 512);
  }

  /**
   * 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 <= 0
   */
  public timerwheel(
      threadfactory threadfactory,
      long tickduration, timeunit unit, int ticksperwheel) {
    this(threadfactory, tickduration, unit, ticksperwheel, true);
  }

  /**
   * 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 <= 0
   */
  public timerwheel(
      threadfactory threadfactory,
      long tickduration, timeunit unit, int ticksperwheel, boolean leakdetection) {

    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.open(this) : null;
  }

  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
   *                {@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(
          timerwheel.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.
      worker_state_updater.set(this, worker_state_shutdown);

      if (leak != null) {
        leak.close();
      }

      return collections.emptyset();
    }

    boolean interrupted = false;
    while (workerthread.isalive()) {
      workerthread.interrupt();
      try {
        workerthread.join(100);
      } catch (interruptedexception ignored) {
        interrupted = true;
      }
    }

    if (interrupted) {
      thread.currentthread().interrupt();
    }

    if (leak != null) {
      leak.close();
    }
    return worker.unprocessedtimeouts();
  }

  @override
  public timeout newtimeout(timertask task, long delay, timeunit unit, string argv) {
    if (task == null) {
      throw new nullpointerexception("task");
    }
    if (unit == null) {
      throw new nullpointerexception("unit");
    }
    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;
    hashedwheeltimeout timeout = new hashedwheeltimeout(this, task, deadline, argv);
    timeouts.add(timeout);
    return timeout;
  }

  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(timerwheel.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.
     * @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(timerwheel.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;

    static {
      atomicintegerfieldupdater<hashedwheeltimeout> updater =
          platformdependent.newatomicintegerfieldupdater(hashedwheeltimeout.class, "state");
      if (updater == null) {
        updater = atomicintegerfieldupdater.newupdater(hashedwheeltimeout.class, "state");
      }
      state_updater = updater;
    }

    private final timerwheel 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;
    string argv;

    // 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(timerwheel timer, timertask task, long deadline, string argv) {
      this.timer = timer;
      this.task = task;
      this.deadline = deadline;
      this.argv = argv;

    }

    @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);
      }
    }

    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, argv);
      } 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(stringutil.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.
   */
  private static final class hashedwheelbucket {
    // used for the linked-list datastructure
    private hashedwheeltimeout head;
    private hashedwheeltimeout tail;

    /**
     * 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 {@link hashedwheeltimeout}s for the given {@code deadline}.
     */
    public void expiretimeouts(long deadline) {
      hashedwheeltimeout timeout = head;

      // process all timeouts
      while (timeout != null) {
        boolean remove = false;
        if (timeout.remainingrounds <= 0) {
          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));
          }
          remove = true;
        } else if (timeout.iscancelled()) {
          remove = true;
        } else {
          timeout.remainingrounds --;
        }
        // store reference to next as we may null out timeout.next in the remove block.
        hashedwheeltimeout next = timeout.next;
        if (remove) {
          remove(timeout);
        }
        timeout = next;
      }
    }

    public void 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;
    }

    /**
     * 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;
    }
  }
}

编写测试类main.java

package com.tanghuachun.timer;
import java.util.concurrent.timeunit;

/**
 * created by darren on 2016/11/17.
 */
public class main implements timertask{
  final static timer timer = new timerwheel();


  public static void main(string[] args) {
    timertask timertask = new main();
    for (int i = 0; i < 10; i++) {
      timer.newtimeout(timertask, 5, timeunit.seconds, "" + i );
    }
  }
  @override
  public void run(timeout timeout, string argv) throws exception {
    system.out.println("timeout, argv = " + argv );
  }
}

然后就可以看到运行结果啦。

工程代码下载（以maven的方式导入）。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。

原文链接：http://blog.csdn.net/tanghuachun/article/details/53208492