ring_buffer.h

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#ifndef CVMFS_RING_BUFFER_H_
#define CVMFS_RING_BUFFER_H_

#include <cstddef>

#include "util/single_copy.h"

class RingBuffer : SingleCopy {
 public:
  typedef size_t ObjectHandle_t;
  static const ObjectHandle_t kInvalidObjectHandle;

  explicit RingBuffer(size_t total_size);
  ~RingBuffer();

  ObjectHandle_t PushFront(const void *obj, size_t size);

  ObjectHandle_t RemoveBack();

  size_t GetObjectSize(ObjectHandle_t handle) const;

  void CopyObject(ObjectHandle_t handle, void *to) const;

  void CopySlice(ObjectHandle_t handle, size_t size, size_t offset,
                 void *to) const;

  // All objects are prepended by a size tag, so we can store objects only
  // up to the available space minus the size of the size tag
  size_t GetMaxObjectSize() const { return total_size_ - sizeof(size_t); }
  bool HasSpaceFor(size_t size) const {
    return free_space_ >= size + sizeof(size_t);
  }

  size_t free_space() const { return free_space_; }

 private:
  void Put(const void *data, size_t size);
  void Get(size_t from, size_t size, void *to) const;
  void Shrink(size_t by);

  const size_t total_size_;
  size_t free_space_;
  size_t front_;
  size_t back_;
  unsigned char *buffer_;
};  // class RingBuffer

#endif  // CVMFS_RING_H_