/*
 * JBoss, Home of Professional Open Source.
 * 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.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.atomic.AtomicIntegerFieldUpdater;
import java.util.function.Consumer;
import java.util.function.Supplier;

import io.undertow.UndertowMessages;

/**
 * Simple pool that attempts to maintain a specified number of objects in the pool. If more objects are created new ones
 * are created on the fly, and then destroyed once the pool is full.
 *
 * @author ckozak
 * @author Stuart Douglas
 */
public class SimpleObjectPool<T> implements ObjectPool {

    private final Supplier<T> supplier;
    private final Consumer<T> recycler;
    private final Consumer<T> consumer;
    private final LinkedBlockingDeque<T> pool;

    public SimpleObjectPool(int poolSize, Supplier<T> supplier, Consumer<T> recycler, Consumer<T> consumer) {
        this.supplier = supplier;
        this.recycler = recycler;
        this.consumer = consumer;
        pool = new LinkedBlockingDeque<T>(poolSize);
    }

    public SimpleObjectPool(int poolSize, Supplier<T> supplier, Consumer<T> consumer) {
        this(poolSize, supplier, object -> {}, consumer);
    }

    @Override
    public PooledObject<T> allocate() {
        T obj = pool.poll();
        if(obj == null) {
            obj = supplier.get();
        }
        return new SimplePooledObject<>(obj, this);
    }

    private static final class SimplePooledObject<T> implements PooledObject<T> {

        private static final AtomicIntegerFieldUpdater<SimplePooledObject> closedUpdater =
                AtomicIntegerFieldUpdater.newUpdater(SimplePooledObject.class, "closed");
        private volatile int closed;
        private final T object;
        private final SimpleObjectPool<T> objectPool;

        SimplePooledObject(T object, SimpleObjectPool<T> objectPool) {
            this.object = object;
            this.objectPool = objectPool;
        }

        @Override
        public T getObject() {
            if (closedUpdater.get(this) != 0) {
                throw UndertowMessages.MESSAGES.objectIsClosed();
            }
            return object;
        }

        @Override
        public void close() {
            if (closedUpdater.compareAndSet(this, 0, 1)) {
                objectPool.recycler.accept(object);
                if (!objectPool.pool.offer(object)) {
                    objectPool.consumer.accept(object);
                }
            }
        }
    }
}
