/*

 * Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General  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  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  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.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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package java.net.http;

import java.nio.Buffer;

import java.util.concurrent.BlockingQueue;

import java.util.concurrent.LinkedBlockingQueue;

import java.util.concurrent.atomic.AtomicInteger;

import java.util.function.Supplier;

import static java.lang.System.Logger.Level.TRACE;

import static java.net.http.WSShared.duplicate;

import static java.net.http.WSUtils.logger;

import static java.util.Objects.requireNonNull;

final class WSSharedPool<T extends Buffer> implements Supplier<WSShared<T>> {

    private final Supplier<T> factory;

    private final BlockingQueue<T> queue;

    WSSharedPool(Supplier<T> factory, int maxPoolSize) {

        this.factory = requireNonNull(factory);

        this.queue = new LinkedBlockingQueue<>(maxPoolSize);

    }

    @Override

    public Pooled get() {

        T b = queue.poll();

        if (b == null) {

            logger.log(TRACE, "Pool {0} contains no free buffers", this);

            b = requireNonNull(factory.get());

        }

        Pooled buf = new Pooled(new AtomicInteger(1), b, duplicate(b));

        logger.log(TRACE, "Pool {0} created new buffer {1}", this, buf);

        return buf;

    }

    private void put(Pooled b) {

        assert b.disposed.get() && b.refCount.get() == 0

                : WSUtils.dump(b.disposed, b.refCount, b);

        b.shared.clear();

        boolean accepted = queue.offer(b.getShared());

        if (logger.isLoggable(TRACE)) {

            if (accepted) {

                logger.log(TRACE, "Pool {0} accepted {1}", this, b);

            } else {

                logger.log(TRACE, "Pool {0} discarded {1}", this, b);

            }

        }

    }

    @Override

    public String toString() {

        return super.toString() + "[queue.size=" + queue.size() + "]";

    }

    private final class Pooled extends WSShared<T> {

        private final AtomicInteger refCount;

        private final T shared;

        private Pooled(AtomicInteger refCount, T shared, T region) {

            super(region);

            this.refCount = refCount;

            this.shared = shared;

        }

        private T getShared() {

            return shared;

        }

        @Override

        @SuppressWarnings("unchecked")

        public Pooled share(final int pos, final int limit) {

            synchronized (this) {

                T buffer = buffer();

                checkRegion(pos, limit, buffer);

                final int oldPos = buffer.position();

                final int oldLimit = buffer.limit();

                select(pos, limit, buffer);

                T slice = WSShared.slice(buffer);

                select(oldPos, oldLimit, buffer);

                referenceAndGetCount();

                Pooled buf = new Pooled(refCount, shared, slice);

                logger.log(TRACE, "Shared {0} from {1}", buf, this);

                return buf;

            }

        }

        @Override

        public void dispose() {

            logger.log(TRACE, "Disposed {0}", this);

            super.dispose();

            if (dereferenceAndGetCount() == 0) {

                WSSharedPool.this.put(this);

            }

        }

        private int referenceAndGetCount() {

            return refCount.updateAndGet(n -> {

                if (n != Integer.MAX_VALUE) {

                    return n + 1;

                } else {

                    throw new IllegalArgumentException

                            ("Too many references: " + this);

                }

            });

        }

        private int dereferenceAndGetCount() {

            return refCount.updateAndGet(n -> {

                if (n > 0) {

                    return n - 1;

                } else {

                    throw new InternalError();

                }

            });

        }

        @Override

        public String toString() {

            return WSUtils.toStringSimple(this) + "[" + WSUtils.toString(buffer)

                    + "[refCount=" + refCount + ", disposed=" + disposed + "]]";

        }

    }

}