realtime_buffer.h

// Copyright (c) 2013, hiDOF, Inc.
//
// 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 the hiDOF, Inc. 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 HOLDER 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.
 
/*
 * Publishing ROS messages is difficult, as the publish function is
 * not realtime safe.  This class provides the proper locking so that
 * you can call publish in realtime and a separate (non-realtime)
 * thread will ensure that the message gets published over ROS.
 *
 * Author: Wim Meeussen
 */
 
#ifndef REALTIME_TOOLS__REALTIME_BUFFER_H_
#define REALTIME_TOOLS__REALTIME_BUFFER_H_
 
#include <chrono>
#include <mutex>
#include <thread>
 
namespace realtime_tools
{
template <class T>
class RealtimeBuffer
{
public:
  RealtimeBuffer() : new_data_available_(false)
  {
    // allocate memory
    non_realtime_data_ = new T();
    realtime_data_ = new T();
  }
 
  explicit RealtimeBuffer(const T & data) : new_data_available_(false)
  {
    // allocate memory
    non_realtime_data_ = new T(data);
    realtime_data_ = new T(data);
  }
 
  ~RealtimeBuffer()
  {
    if (non_realtime_data_) {
      delete non_realtime_data_;
    }
    if (realtime_data_) {
      delete realtime_data_;
    }
  }
 
  RealtimeBuffer(const RealtimeBuffer & source)
  {
    // allocate memory
    non_realtime_data_ = new T();
    realtime_data_ = new T();
 
    // Copy the data from old RTB to new RTB
    writeFromNonRT(*source.readFromNonRT());
  }
 
  RealtimeBuffer & operator=(const RealtimeBuffer & source)
  {
    if (this == &source) {
      return *this;
    }
 
    // Copy the data from old RTB to new RTB
    writeFromNonRT(*source.readFromNonRT());
 
    return *this;
  }
 
  T * readFromRT()
  {
    // Check if the data is currently being written to (is locked)
    std::unique_lock<std::mutex> guard(mutex_, std::try_to_lock);
    if (guard.owns_lock()) {
      // swap pointers
      if (new_data_available_) {
        T * tmp = realtime_data_;
        realtime_data_ = non_realtime_data_;
        non_realtime_data_ = tmp;
        new_data_available_ = false;
      }
    }
    return realtime_data_;
  }
 
  T * readFromNonRT() const
  {
    std::lock_guard<std::mutex> guard(mutex_);
 
    if (new_data_available_) {
      return non_realtime_data_;
    } else {
      return realtime_data_;
    }
  }
 
  void writeFromNonRT(const T & data)
  {
#ifdef NON_POLLING
    std::lock_guard<std::mutex> guard(mutex_);
#else
    std::unique_lock<std::mutex> guard(mutex_, std::defer_lock);
    while (!guard.try_lock()) {
      std::this_thread::sleep_for(std::chrono::microseconds(500));
    }
#endif
 
    // copy data into non-realtime buffer
    *non_realtime_data_ = data;
    new_data_available_ = true;
  }
 
  void initRT(const T & data)
  {
    *non_realtime_data_ = data;
    *realtime_data_ = data;
  }
 
  void reset()
  {
    // delete the old memory
    if (non_realtime_data_) {
      delete non_realtime_data_;
    }
    if (realtime_data_) {
      delete realtime_data_;
    }
 
    // allocate memory
    non_realtime_data_ = new T();
    realtime_data_ = new T();
  }
 
private:
  T * realtime_data_;
  T * non_realtime_data_;
  bool new_data_available_;
 
  // Set as mutable so that readFromNonRT() can be performed on a const buffer
  mutable std::mutex mutex_;
};  // class
 
}  // namespace realtime_tools
#endif  // REALTIME_TOOLS__REALTIME_BUFFER_H_