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 * Copyright 2014 Red Hat, Inc., and individual contributors
 * as indicated by the @author tags.
 *
 * 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 io.undertow.util;

import java.lang.reflect.Constructor;
import java.util.AbstractCollection;
import java.util.Deque;

A concurrent deque that allows direct item removal without traversal.
Author:
Jason T. Greene/**
 * A concurrent deque that allows direct item removal without traversal.
 *
 * @author Jason T. Greene
 */
public abstract  class ConcurrentDirectDeque<E> extends AbstractCollection<E> implements Deque<E>, java.io.Serializable {
    private static final Constructor<? extends ConcurrentDirectDeque> CONSTRUCTOR;

    static {
        boolean fast = false;
        try {
            new FastConcurrentDirectDeque();
            fast = true;
        } catch (Throwable t) {
        }

        Class<? extends ConcurrentDirectDeque> klazz = fast ? FastConcurrentDirectDeque.class : PortableConcurrentDirectDeque.class;
        try {
            CONSTRUCTOR = klazz.getConstructor();
        } catch (NoSuchMethodException e) {
            throw new NoSuchMethodError(e.getMessage());
        }
    }

    public static <K> ConcurrentDirectDeque<K> newInstance() {
        try {
            return CONSTRUCTOR.newInstance();
        } catch (Exception e) {
            throw new IllegalStateException(e);
        }
    }

    public abstract Object offerFirstAndReturnToken(E e);

    public abstract Object offerLastAndReturnToken(E e);

    public abstract void removeToken(Object token);
}