/*
 * Copyright (C) 2009 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 * copyright notice, this list of conditions and the following disclaimer
 * in the documentation and/or other materials provided with the
 * distribution.
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 * contributors may be used to endorse or promote products derived from
 * this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef PlatformMessagePortChannel_h
#define PlatformMessagePortChannel_h

#include "MessagePortChannel.h"

#include <wtf/MessageQueue.h>
#include <wtf/PassRefPtr.h>
#include <wtf/Threading.h>

namespace WebCore {

    class MessagePort;

    // PlatformMessagePortChannel is a platform-dependent interface to the remote side of a message channel.
    // This default implementation supports multiple threads running within a single process. Implementations for multi-process platforms should define these public APIs in their own platform-specific PlatformMessagePortChannel file.
    // The goal of this implementation is to eliminate contention except when cloning or closing the port, so each side of the channel has its own separate mutex.
    class PlatformMessagePortChannel : public ThreadSafeShared<PlatformMessagePortChannel> {
    public:
        static void createChannel(PassRefPtr<MessagePort>, PassRefPtr<MessagePort>);

        // APIs delegated from MessagePortChannel.h
        bool entangleIfOpen(MessagePort*);
        void disentangle();
        void postMessageToRemote(PassOwnPtr<MessagePortChannel::EventData>);
        bool tryGetMessageFromRemote(OwnPtr<MessagePortChannel::EventData>&);
        void close();
        bool isConnectedTo(MessagePort*);
        bool hasPendingActivity();
        MessagePort* locallyEntangledPort(const ScriptExecutionContext*);

        // Wrapper for MessageQueue that allows us to do thread safe sharing by two proxies.
        class MessagePortQueue : public ThreadSafeShared<MessagePortQueue> {
        public:
            static PassRefPtr<MessagePortQueue> create() { return adoptRef(new MessagePortQueue()); }

            bool tryGetMessage(OwnPtr<MessagePortChannel::EventData>& message)
            {
                MessagePortChannel::EventData* holder = 0;
                bool messageAvailable = m_queue.tryGetMessage(holder);
                if (messageAvailable)
                    message.set(holder);
                return messageAvailable;
            }

            bool appendAndCheckEmpty(PassOwnPtr<MessagePortChannel::EventData> message)
            {
                return m_queue.appendAndCheckEmpty(message.release());
            }

            bool isEmpty()
            {
                return m_queue.isEmpty();
            }

            ~MessagePortQueue()
            {
                // Manually free any items left in the queue, since we can't use OwnPtr internally.
                MessagePortChannel::EventData* data = 0;
                while (m_queue.tryGetMessage(data))
                    delete data;
            }
        private:
            MessagePortQueue() { }

            // OwnPtr is Noncopyable, so we can't use it as the template type in a MessageQueue. So we just store a pointer to EventData and manually free it in the destructor.
            // FIXME: Use a lock-free queue implementation to completely eliminate contention when sending/receiving messages.
            MessageQueue<MessagePortChannel::EventData*> m_queue;
        };

        ~PlatformMessagePortChannel();

    private:
        static PassRefPtr<PlatformMessagePortChannel> create(PassRefPtr<MessagePortQueue> incoming, PassRefPtr<MessagePortQueue> outgoing);
        PlatformMessagePortChannel(PassRefPtr<MessagePortQueue> incoming, PassRefPtr<MessagePortQueue> outgoing);

        PassRefPtr<PlatformMessagePortChannel> entangledChannel();
        void setEntangledChannel(PassRefPtr<PlatformMessagePortChannel>);

        void setRemotePort(MessagePort*);
        MessagePort* remotePort();
        void closeInternal();

        // Mutex used to ensure exclusive access to the object internals.
        Mutex m_mutex;

        // Pointer to our entangled pair - cleared when close() is called.
        RefPtr<PlatformMessagePortChannel> m_entangledChannel;

        // Reference to the message queue for the (local) entangled port.
        RefPtr<MessagePortQueue> m_incomingQueue;
        RefPtr<MessagePortQueue> m_outgoingQueue;

        // The port we are connected to (the remote port) - this is the port that is notified when new messages arrive.
        MessagePort* m_remotePort;
    };

} // namespace WebCore

#endif // PlatformMessagePortChannel_h
