jgit/org.eclipse.jgit/src/org/eclipse/jgit/lib/InflaterCache.java

/*
 * Copyright (C) 2008, Google Inc.
 * Copyright (C) 2006-2008, Shawn O. Pearce <spearce@spearce.org>
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
 *
 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
 *   written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
 * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.eclipse.jgit.lib;

import java.util.zip.Inflater;

/** Creates zlib based inflaters as necessary for object decompression. */
public class InflaterCache {
	private static final int SZ = 4;

	private static final Inflater[] inflaterCache;

	private static int openInflaterCount;

	static {
		inflaterCache = new Inflater[SZ];
	}

	/**
	 * Obtain an Inflater for decompression.
	 * <p>
	 * Inflaters obtained through this cache should be returned (if possible) by
	 * {@link #release(Inflater)} to avoid garbage collection and reallocation.
	 *
	 * @return an available inflater. Never null.
	 */
	public static Inflater get() {
		final Inflater r = getImpl();
		return r != null ? r : new Inflater(false);
	}

	private synchronized static Inflater getImpl() {
		if (openInflaterCount > 0) {
			final Inflater r = inflaterCache[--openInflaterCount];
			inflaterCache[openInflaterCount] = null;
			return r;
		}
		return null;
	}

	/**
	 * Release an inflater previously obtained from this cache.
	 *
	 * @param i
	 *            the inflater to return. May be null, in which case this method
	 *            does nothing.
	 */
	public static void release(final Inflater i) {
		if (i != null) {
			i.reset();
			if (releaseImpl(i))
				i.end();
		}
	}

	private static synchronized boolean releaseImpl(final Inflater i) {
		if (openInflaterCount < SZ) {
			inflaterCache[openInflaterCount++] = i;
			return false;
		}
		return true;
	}

	private InflaterCache() {
		throw new UnsupportedOperationException();
	}
}