text: /*********************************************************************************
   *  OKVIS - Open Keyframe-based Visual-Inertial SLAM
   *  Copyright (c) 2015, Autonomous Systems Lab / ETH Zurich
   *
   *  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.
   *   * Neither the name of Autonomous Systems Lab / ETH Zurich nor the names of
   *     its 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 OWNER OR CONTRIBUTORS BE
   *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   *  POSSIBILITY OF SUCH DAMAGE.
   *
   *  Created on: Sep 13, 2014
   *      Author: Pascal Gohl
   *    Modified: Stefan Leutenegger (s.leutenegger@imperial.ac.uk)
   *    Modified: Andreas Forster (an.forster@gmail.com)
   *********************************************************************************/
  
  /**
   * @file ImuFrameSynchronizer.hpp
   * @brief Header file for the ImuFrameSynchronizer class.
   * @author Pascal Gohl
   * @author Stefan Leutenegger
   * @author Andreas Forster
   */
  
  #ifndef INCLUDE_OKVIS_IMUFRAMESYNCHRONIZER_H_
  #define INCLUDE_OKVIS_IMUFRAMESYNCHRONIZER_H_
  
  #include <atomic>
  #include <mutex>
  #include <condition_variable>
  
  #include <okvis/Time.hpp>
  
  /// \brief okvis Main namespace of this package.
  namespace okvis {
  
  /**
   * @brief This class is to safely notify different threads whether IMU measurements
   *        up to a timestamp (e.g. the one of a camera frame) have already been registered.
   */
  class ImuFrameSynchronizer {
   public:
    /// @brief Constructor.
    ImuFrameSynchronizer();
    /// @brief Destructor.
    ~ImuFrameSynchronizer();
  
    /**
     * @brief Tell the synchronizer that a new IMU measurement has been registered.
     * @param stamp Timestamp of the new IMU mewasurement.
     */
    void gotImuData(const okvis::Time& stamp);
  
    /**
     * @brief Wait until a IMU measurement with a timestamp equal or newer to the supplied one is registered.
     * @param frame_stamp Timestamp until you want to have IMU measurements for.
     * @return False if a shutdown signal has been received. Otherwise true.
     */
    bool waitForUpToDateImuData(const okvis::Time& frame_stamp);
  
    /// @brief Tell the synchronizer to shutdown. This will notify all waiting threads to wake up.
    void shutdown();
  
   private:
    okvis::Time newestImuDataStamp_;           ///< Newest IMU data timestamp.
    okvis::Time imuDataNeededUntil_;           ///< A thread is waiting for IMU data newer or equal to this timestamp.
    std::condition_variable gotNeededImuData_; ///< Condition variable for waiting and notyfing.
    std::mutex mutex_;                         ///< Mutex.
    std::atomic_bool shutdown_;                ///< True if shutdown() was called.
  };
  
  } /* namespace okvis */
  
  #endif /* INCLUDE_OKVIS_IMUFRAMESYNCHRONIZER_H_ */
  