CircularBuffer.hpp

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// Copyright 2025 Intelligent Robotics Lab
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
 
#ifndef EASYNAV_COMMON__CIRCULARBUFFER_HPP_
#define EASYNAV_COMMON__CIRCULARBUFFER_HPP_
 
#include <vector>
#include <mutex>
#include <cstddef>
 
namespace easynav
{

template<typename T>
class CircularBuffer
{
public:
  explicit CircularBuffer(std::size_t capacity)
  : buffer_(capacity),
    capacity_(capacity),
    head_(0),
    tail_(0),
    size_(0)
  {
  }

  CircularBuffer(const CircularBuffer & other)
  : buffer_(other.capacity_),
    capacity_(other.capacity_),
    head_(0),
    tail_(0),
    size_(0)
  {
    std::lock_guard<std::mutex> lock(other.mutex_);
    buffer_ = other.buffer_;
    head_ = other.head_;
    tail_ = other.tail_;
    size_ = other.size_;
  }

  CircularBuffer & operator=(const CircularBuffer & other)
  {
    if (this == &other) {
      return *this;
    }
 
    // Lock both mutexes in a deadlock-safe way.
    std::scoped_lock<std::mutex, std::mutex> lock(mutex_, other.mutex_);
 
    capacity_ = other.capacity_;
    buffer_ = other.buffer_;
    head_ = other.head_;
    tail_ = other.tail_;
    size_ = other.size_;
    return *this;
  }

  CircularBuffer(CircularBuffer &&) = delete;
  CircularBuffer & operator=(CircularBuffer &&) = delete;

  std::size_t capacity() const noexcept
  {
    return capacity_;
  }

  std::size_t size() const noexcept
  {
    std::lock_guard<std::mutex> lock(mutex_);
    return size_;
  }

  bool empty() const noexcept
  {
    std::lock_guard<std::mutex> lock(mutex_);
    return size_ == 0;
  }

  bool full() const noexcept
  {
    std::lock_guard<std::mutex> lock(mutex_);
    return size_ == capacity_;
  }

  void clear() noexcept
  {
    std::lock_guard<std::mutex> lock(mutex_);
    head_ = 0;
    tail_ = 0;
    size_ = 0;
  }

  void push(const T & value)
  {
    std::lock_guard<std::mutex> lock(mutex_);
    buffer_[head_] = value;
    advance_head_();
  }

  void push(T && value)
  {
    std::lock_guard<std::mutex> lock(mutex_);
    buffer_[head_] = std::move(value);
    advance_head_();
  }

  bool pop(T & out)
  {
    std::lock_guard<std::mutex> lock(mutex_);
    if (size_ == 0) {
      return false;
    }
 
    out = buffer_[tail_];
    tail_ = (tail_ + 1) % capacity_;
    --size_;
    return true;
  }

  bool latest(T & out) const
  {
    std::lock_guard<std::mutex> lock(mutex_);
    if (size_ == 0) {
      return false;
    }
 
    const std::size_t newest_index =
      (head_ + capacity_ - 1) % capacity_;
    out = buffer_[newest_index];
    return true;
  }

  const T & latest_ref() const
  {
    std::lock_guard<std::mutex> lock(mutex_);
 
    const std::size_t newest_index =
      (head_ + capacity_ - 1) % capacity_;
    return buffer_[newest_index];
  }
 
  // DEBUG ONLY: raw access to slots
  struct DebugSlotView
  {
    bool has_value;
    const T & value;
  };
 
  DebugSlotView raw_slot(std::size_t idx) const
  {
    if (!buffer_[idx].engaged) {
      // dummy static empty
      static T dummy{};
      static const DebugSlotView empty{false, dummy};
      return empty;
    }
    return DebugSlotView{true, buffer_[idx].storage};
  }
 
private:
  void advance_head_()
  {
    head_ = (head_ + 1) % capacity_;
    if (size_ < capacity_) {
      ++size_;
    } else {
      // Buffer is full, we overwrite the oldest element.
      tail_ = (tail_ + 1) % capacity_;
    }
  }
 
  mutable std::mutex mutex_;
  std::vector<T> buffer_;
  std::size_t capacity_;
  std::size_t head_;   // next position to write
  std::size_t tail_;   // next position to read
  std::size_t size_;   // number of valid elements
};
 
}  // namespace easynav
 
#endif  // EASYNAV_COMMON__CIRCULARBUFFER_HPP_