001/*
002 * Copyright 2012-2016 UnboundID Corp.
003 *
004 * This program is free software; you can redistribute it and/or modify
005 * it under the terms of the GNU General Public License (GPLv2 only)
006 * or the terms of the GNU Lesser General Public License (LGPLv2.1 only)
007 * as published by the Free Software Foundation.
008 *
009 * This program is distributed in the hope that it will be useful,
010 * but WITHOUT ANY WARRANTY; without even the implied warranty of
011 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
012 * GNU General Public License for more details.
013 *
014 * You should have received a copy of the GNU General Public License
015 * along with this program; if not, see <http://www.gnu.org/licenses>.
016 */
017
018package com.unboundid.scim.wink;
019
020
021
022import java.util.concurrent.Semaphore;
023
024
025
026/**
027 * A semaphore that can be dynamically resized.
028 */
029public final class AdjustableSemaphore extends Semaphore
030{
031  private static final long serialVersionUID = -2211345506986838529L;
032
033
034
035  /**
036   * The maximum number of permits provided by this semaphore.
037   */
038  private int maxPermits;
039
040
041
042  /**
043   * Create a new instance of this semaphore.
044   *
045   * @param maxPermits The initial number of permits.
046   */
047  public AdjustableSemaphore(final int maxPermits)
048  {
049    super(maxPermits);
050    this.maxPermits = maxPermits;
051  }
052
053
054
055  /**
056   * Retrieves the maximum number of permits.
057   * @return  The maximum number of permits.
058   */
059  public int getMaxPermits()
060  {
061    return maxPermits;
062  }
063
064
065
066  /**
067   * {@inheritDoc}
068   */
069  @Override
070  public int availablePermits()
071  {
072    // Do not return a negative number of permits. This could happen if
073    // there are threads waiting to acquire a permit and the maximum number
074    // of permits is reduced.
075    final int availablePermits = super.availablePermits();
076    return availablePermits >= 0 ? availablePermits : 0;
077  }
078
079
080
081  /**
082   * Set the maximum number of permits.
083   *
084   * @param maxPermits The maximum number of permits. Must be greater than zero.
085   */
086  public synchronized void setMaxPermits(final int maxPermits)
087  {
088    if (maxPermits < 1)
089    {
090      throw new IllegalArgumentException();
091    }
092
093    int delta = maxPermits - this.maxPermits;
094    if (delta == 0)
095    {
096      return;
097    }
098    else if (delta > 0)
099    {
100      release(delta);
101    }
102    else
103    {
104      reducePermits(-delta);
105    }
106
107    this.maxPermits = maxPermits;
108  }
109}