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TrueZIP is a Java based Virtual File System (VFS) to enable transparent, multi-threaded read/write access to archive files (ZIP, TAR etc.) as if they were directories. Archive files may be arbitrarily nested and the nesting level is only limited by heap and file system size.

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/*
 * Copyright (C) 2010 Schlichtherle IT Services
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package de.schlichtherle.util.zip;

import java.lang.ref.Reference;
import java.lang.ref.SoftReference;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;
import java.util.zip.Inflater;

/**
 * Provides utility methods for pooling {@link Inflater}s.
 * Inflater objects are expensive to allocate, so pooling them improves
 * performance.
 *
 * @author Christian Schlichtherle
 * @version $Id$
 */
class InflaterPool {
    private static final Set allocated = new HashSet();
    private static final List released = new LinkedList();

    private InflaterPool() {
    }

    static Inflater fetch() {
        Inflater inflater = null;

        synchronized (released) {
            for (Iterator i = released.iterator(); i.hasNext(); ) {
                inflater = (Inflater) ((Reference) i.next()).get();
                i.remove();
                if (inflater != null) {
                    //inflater.reset();
                    break;
                }
            }
            if (inflater == null)
                inflater = new Inflater(true);

            // We MUST make sure that we keep a strong reference to the
            // inflater in order to retain it from being released again and
            // then finalized when the close() method of the InputStream
            // returned by getInputStream(...) is called from within another
            // finalizer.
            // The finalizer of the inflater calls end() and leaves the object
            // in a state so that the subsequent call to reset() throws an NPE.
            // The ZipFile class in Sun's JSE 5 shows this bug.
            allocated.add(inflater);
        }

        return inflater;
    }

    static void release(Inflater inflater) {
        inflater.reset();
        synchronized (released) {
            released.add(new SoftReference(inflater));
            allocated.remove(inflater);
        }
    }
}