Android Open Source - azilink Timer Queue

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License

The source code is released under:

GNU General Public License

Java Source Code

/* AziLink: USB tethering for Android
 * Copyright (C) 2009 by James Perry/*  www.j  a  va 2 s.  c om*/
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) version 3 of the License.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

package org.lfx.azilink.net;

import java.util.Iterator;
import java.util.LinkedList;
import java.util.Map;
import java.util.TreeMap;

import android.os.SystemClock;

/**
 * Queue of timers that the select thread will automatically dispatch.  When a timer expires, the OnTimer
 * callback will be called.
 * 
 * @author Jim Perry
 *
 */
public class TimerQueue {
  /**
   * Map of all timers, indexed by the expiration time.
   */
  TreeMap< Long, LinkedList< TimerCallback > > mTimers = new TreeMap< Long, LinkedList< TimerCallback > >();  
  
  /**
   * Add a timer to the queue.
   * 
   * @param ms ms until timer expires.
   * @param cb callback to issue when timer expires
   * @return key that can be used to quickly alter the timer
   */
  long addTimer( int ms, TimerCallback cb ) {
    long fullTime = ms + SystemClock.elapsedRealtime();
    LinkedList< TimerCallback > entries = mTimers.get( fullTime );
    if( entries == null ) {
      entries = new LinkedList< TimerCallback >();
      entries.add( cb );
      mTimers.put( fullTime, entries );
    } else {
      entries.add( cb );
    }
    return fullTime;
  }
  
  /**
   * Change when a timer entry expires.
   * 
   * @param oldKey key for old timer
   * @param ms ms until timer expires
   * @param cb callback for this timer
   * @return new key for the timer
   */
  long changeTimer( long oldKey, int ms, TimerCallback cb ) {
    killTimer( oldKey, cb );
    return addTimer( ms, cb );
  }
  
  /**
   * Remove a timer from the queue.
   * 
   * @param key key for the timer
   * @param cb callback that was associated w/ this timer
   */
  void killTimer( long key, TimerCallback cb ) {
    LinkedList< TimerCallback > entries = mTimers.get( key );
    if( entries == null ) return;    
    Iterator< TimerCallback > i = entries.iterator();
    while( i.hasNext() ) {
      TimerCallback tcb = i.next();
      if( tcb == cb ) {
        i.remove();
        if( entries.isEmpty() ) {
          mTimers.remove( key );
        }
        return;
      }
    }
  }
  
  /**
   * Run all timers that have expired.
   */
  void runTimers() {
    // Read the timers off into a linked list first since the callback could start a new timer and 
    // we don't want to recurse.
    LinkedList< TimerCallback > cb = new LinkedList< TimerCallback >();
    Iterator<Map.Entry<Long, LinkedList<TimerCallback>>> i = mTimers.entrySet().iterator();
    long now = SystemClock.elapsedRealtime();
    
    while( i.hasNext() ) {
      Map.Entry<Long, LinkedList<TimerCallback>> entry = i.next();
      if( entry.getKey() > now ) break;
      Iterator< TimerCallback > j = entry.getValue().iterator();
      while( j.hasNext() ) {
        cb.add( j.next() );
      }
      i.remove();
    }
    
    Iterator< TimerCallback > k = cb.iterator();
    while( k.hasNext() ) {
      k.next().onTimer();
    }
  }
  
  /**
   * Return the elapsedTime when the next timer will expire.
   * @return time of next timer expiration
   */
  long nextTimer() {
    if( mTimers.isEmpty() ) return -1;
    return mTimers.firstKey();
  }
}

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