InflaterCache.java

/*
 * Copyright (C) 2008, Google Inc.
 * Copyright (C) 2006-2008, Shawn O. Pearce <spearce@spearce.org> and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

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 static synchronized 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(Inflater i) {
        if (i != null) {
            i.reset();
            if (releaseImpl(i))
                i.end();
        }
    }

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

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