/***************************************************************************
 *                                                                         *
 *   Copyright (C) 2006 Andreas Persson                                    *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program 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 for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the Free Software           *
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,                *
 *   MA  02110-1301  USA                                                   *
 ***************************************************************************/

#ifndef __SYNCHRONIZEDCONFIG_H__
#define __SYNCHRONIZEDCONFIG_H__

#include "atomic.h"

namespace LinuxSampler {

    /**
     * Thread safe management of configuration data, where the data is
     * updated by a single non real time thread and read by a single
     * real time thread.
     *
     * The synchronization is achieved by using two instances of the
     * configuration data. The non real time thread gets access to the
     * instance not currently in use by the real time thread by
     * calling GetConfigForUpdate(). After the data is updated, the
     * non real time thread must call SwitchConfig() and redo the
     * update on the other instance. SwitchConfig() blocks until it is
     * safe to modify the other instance.
     *
     * The real time thread calls Lock() to get access to the data,
     * and Unlock() when it is finished reading the data. (Neither
     * Lock nor Unlock will block the real time thread, or use any
     * system calls.)
     */
    template<class T>
    class SynchronizedConfig {
        public:
            SynchronizedConfig();

            // methods for the real time thread

            /**
             * Gets the configuration object for use by the real time
             * thread. The object is safe to use (read only) until
             * Unlock() is called.
             *
             * @returns a reference to the configuration object to be
             *          read by the real time thread
             */
            const T& Lock() {
                atomic_set(&lock, 1);
                return config[atomic_read(&indexAtomic)];
            }

            /**
             * Unlock the configuration object. Unlock() must be
             * called by the real time thread after it has finished
             * reading the configuration object. If the non real time
             * thread is waiting in SwitchConfig() it will be awaken.
             */
            void Unlock() {
                atomic_set(&lock, 0);
            }


            // methods for the non real time thread

            /**
             * Gets the configuration object for use by the non real
             * time thread. The object returned is not in use by the
             * real time thread, so it can safely be updated. After
             * the update is done, the non real time thread must call
             * SwitchConfig() and the same update must be done again.
             *
             * @returns a reference to the configuration object to be
             *          updated by the non real time thread
             */
            T& GetConfigForUpdate();

            /**
             * Atomically switch the newly updated configuration
             * object with the one used by the real time thread, then
             * wait for the real time thread to finish working with
             * the old object before returning the old object.
             * SwitchConfig() must be called by the non real time
             * thread after an update has been done, and the object
             * returned must be updated in the same way as the first.
             *
             * @returns a reference to the configuration object to be
             *          updated by the non real time thread
             */
            T& SwitchConfig();

        private:
            atomic_t lock;
            atomic_t indexAtomic;
            int updateIndex;
            T config[2];
    };

    template<class T> SynchronizedConfig<T>::SynchronizedConfig() {
        atomic_set(&lock, 0);
        atomic_set(&indexAtomic, 0);
    }

    template<class T> T& SynchronizedConfig<T>::GetConfigForUpdate() {
        updateIndex = atomic_read(&indexAtomic) ^ 1;
        return config[updateIndex];
    }

    template<class T> T& SynchronizedConfig<T>::SwitchConfig() {
        atomic_set(&indexAtomic, updateIndex);
        while (atomic_read(&lock))
            usleep(50000);
        return config[updateIndex ^ 1];
    }

} // namespace LinuxSampler

#endif