src/java.base/share/classes/sun/nio/cs/ThreadLocalCoders.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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package sun.nio.cs;

import java.nio.charset.*;


/**
 * Utility class for caching per-thread decoders and encoders.
 */

public class ThreadLocalCoders {

    private static final int CACHE_SIZE = 3;

    private abstract static class Cache {

        // Thread-local reference to array of cached objects, in LRU order
        private ThreadLocal<Object[]> cache = new ThreadLocal<>();
        private final int size;

        Cache(int size) {
            this.size = size;
        }

        abstract Object create(Object name);

        private void moveToFront(Object[] oa, int i) {
            Object ob = oa[i];
            for (int j = i; j > 0; j--)
                oa[j] = oa[j - 1];
            oa[0] = ob;
        }

        abstract boolean hasName(Object ob, Object name);

        Object forName(Object name) {
            Object[] oa = cache.get();
            if (oa == null) {
                oa = new Object[size];
                cache.set(oa);
            } else {
                for (int i = 0; i < oa.length; i++) {
                    Object ob = oa[i];
                    if (ob == null)
                        continue;
                    if (hasName(ob, name)) {
                        if (i > 0)
                            moveToFront(oa, i);
                        return ob;
                    }
                }
            }

            // Create a new object
            Object ob = create(name);
            oa[oa.length - 1] = ob;
            moveToFront(oa, oa.length - 1);
            return ob;
        }

    }

    private static Cache decoderCache = new Cache(CACHE_SIZE) {
            boolean hasName(Object ob, Object name) {
                if (name instanceof Charset)
                    return ((CharsetDecoder)ob).charset().equals(name);
                if (name instanceof String)
                    return (((CharsetDecoder)ob).charset().name().equals(name));
                return false;
            }
            Object create(Object name) {
                if (name instanceof Charset)
                    return ((Charset)name).newDecoder();
                if (name instanceof String)
                    return Charset.forName((String)name).newDecoder();
                assert false;
                return null;
            }
        };

    public static CharsetDecoder decoderFor(Object name) {
        CharsetDecoder cd = (CharsetDecoder)decoderCache.forName(name);
        cd.reset();
        return cd;
    }

    private static Cache encoderCache = new Cache(CACHE_SIZE) {
            boolean hasName(Object ob, Object name) {
                if (name instanceof Charset)
                    return ((CharsetEncoder)ob).charset().equals(name);
                if (name instanceof String)
                    return (((CharsetEncoder)ob).charset().name().equals(name));
                return false;
            }
            Object create(Object name) {
                if (name instanceof Charset)
                    return ((Charset)name).newEncoder();
                if (name instanceof String)
                    return Charset.forName((String)name).newEncoder();
                assert false;
                return null;
            }
        };

    public static CharsetEncoder encoderFor(Object name) {
        CharsetEncoder ce = (CharsetEncoder)encoderCache.forName(name);
        ce.reset();
        return ce;
    }

}