CyclicBuffer.java

/**
 * Logback: the reliable, generic, fast and flexible logging framework.
 * Copyright (C) 1999-2013, QOS.ch. All rights reserved.
 *
 * This program and the accompanying materials are dual-licensed under
 * either the terms of the Eclipse Public License v1.0 as published by
 * the Eclipse Foundation
 *
 *   or (per the licensee's choosing)
 *
 * under the terms of the GNU Lesser General Public License version 2.1
 * as published by the Free Software Foundation.
 */
package ch.qos.logback.core.helpers;

import java.util.ArrayList;
import java.util.List;

/**
 * CyclicBuffer holds values in a cyclic array.
 *
 * <p>It allows read access to any element in the buffer not just the first or
 * last element.
 *
 * @author Ceki Gülcü
 */
public class CyclicBuffer<E> {

  E[] ea;
  int first;
  int last;
  int numElems;
  int maxSize;

  /**
   * Instantiate a new CyclicBuffer of at most <code>maxSize</code> events.
   *
   * The <code>maxSize</code> argument must a positive integer.
   *
   * @param maxSize
   *                The maximum number of elements in the buffer.
   */
  public CyclicBuffer(int maxSize) throws IllegalArgumentException {
    if (maxSize < 1) {
      throw new IllegalArgumentException("The maxSize argument (" + maxSize
          + ") is not a positive integer.");
    }
    init(maxSize);
  }

  public CyclicBuffer(CyclicBuffer<E> other) {
   this.maxSize = other.maxSize;
   ea = (E[]) new Object[maxSize];
   System.arraycopy(other.ea, 0, this.ea, 0, maxSize);
   this.last = other.last;
   this.first = other.first;
   this.numElems = other.numElems;
  }

  @SuppressWarnings("unchecked")
  private void init(int maxSize) {
    this.maxSize = maxSize;
    ea = (E[]) new Object[maxSize];
    first = 0;
    last = 0;
    numElems = 0;
  }

  /**
   * Clears the buffer and resets all attributes.
   */
  public void clear() {
    init(this.maxSize);
  }

  /**
   * Add an <code>event</code> as the last event in the buffer.
   * @param event the log event
   */
  public void add(E event) {
    ea[last] = event;
    if (++last == maxSize)
      last = 0;

    if (numElems < maxSize)
      numElems++;
    else if (++first == maxSize)
      first = 0;
  }

  /**
   * Get the <i>i</i>th oldest event currently in the buffer. If <em>i</em>
   * is outside the range 0 to the number of elements currently in the buffer,
   * then <code>null</code> is returned.
   * @param i the index of the oldest event to fetch
   * @return the event
   */
  public E get(int i) {
    if (i < 0 || i >= numElems)
      return null;

    return ea[(first + i) % maxSize];
  }

  public int getMaxSize() {
    return maxSize;
  }

  /**
   * Get the oldest (first) element in the buffer. The oldest element is removed
   * from the buffer.
   * @return the element
   */
  public E get() {
    E r = null;
    if (numElems > 0) {
      numElems--;
      r = ea[first];
      ea[first] = null;
      if (++first == maxSize)
        first = 0;
    }
    return r;
  }

  public List<E> asList() {
    List<E> tList = new ArrayList<E>();
    for(int i = 0; i < length(); i++) {
      tList.add(get(i));
    }
    return tList;
  }

  /**
   * Get the number of elements in the buffer. This number is guaranteed to be
   * in the range 0 to <code>maxSize</code> (inclusive).
   * @return the element count
   */
  public int length() {
    return numElems;
  }

  /**
   * Resize the cyclic buffer to <code>newSize</code>.
   *
   * @param newSize the desired size
   * @throws IllegalArgumentException
   *                 if <code>newSize</code> is negative.
   */
  @SuppressWarnings("unchecked")
  public void resize(int newSize) {
    if (newSize < 0) {
      throw new IllegalArgumentException("Negative array size [" + newSize
          + "] not allowed.");
    }
    if (newSize == numElems)
      return; // nothing to do

    //
    E[] temp = (E[]) new Object[newSize];

    int loopLen = newSize < numElems ? newSize : numElems;

    for (int i = 0; i < loopLen; i++) {
      temp[i] = ea[first];
      ea[first] = null;
      if (++first == numElems)
        first = 0;
    }
    ea = temp;
    first = 0;
    numElems = loopLen;
    maxSize = newSize;
    if (loopLen == newSize) {
      last = 0;
    } else {
      last = loopLen;
    }
  }
}