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.*;
import java.nio.charset.*;


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

public class ThreadLocalCoders {

    private static final int CACHE_SIZE = 3;

    private static abstract class Cache {

	// Thread-local reference to array of cached objects, in LRU order
	private ThreadLocal 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 = (Object[])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 String)
		    return (((CharsetDecoder)ob).charset().name().equals(name));
		if (name instanceof Charset)
		    return ((CharsetDecoder)ob).charset().equals(name);
		return false;
	    }
	    Object create(Object name) {
		if (name instanceof String)
		    return Charset.forName((String)name).newDecoder();
		if (name instanceof Charset)
		    return ((Charset)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 String)
		    return (((CharsetEncoder)ob).charset().name().equals(name));
		if (name instanceof Charset)
		    return ((CharsetEncoder)ob).charset().equals(name);
		return false;
	    }
	    Object create(Object name) {
		if (name instanceof String)
		    return Charset.forName((String)name).newEncoder();
		if (name instanceof Charset)
		    return ((Charset)name).newEncoder();
		assert false;
		return null;
	    }
	};

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

}