/*!
 *  Copyright (c) 2017 by Contributors
 * @file dgl/runtime/ndarray.h
 * @brief shared memory management.
 */
#ifndef DGL_RUNTIME_SHARED_MEM_H_
#define DGL_RUNTIME_SHARED_MEM_H_

#ifdef _WIN32
#include <windows.h>
#endif  // _WIN32
#include <string>

namespace dgl {
namespace runtime {

/*
 * @brief This class owns shared memory.
 *
 * When the object is gone, the shared memory will also be destroyed.
 * When the shared memory is destroyed, the file corresponding to
 * the shared memory is removed.
 */
class SharedMemory {
  /*
   * @brief whether the shared memory is owned by the object.
   *
   * If shared memory is created in the object, it'll be owned by the object
   * and will be responsible for deleting it when the object is destroyed.
   */
  bool own_;

  /* @brief the file descripter of the shared memory. */
#ifndef _WIN32
  int fd_;
#else   // !_WIN32
  HANDLE handle_;
#endif  // _WIN32
  /* @brief the address of the shared memory. */
  void *ptr_;
  /* @brief the size of the shared memory. */
  size_t size_;

  /*
   * @brief the name of the object.
   *
   * In Unix, shared memory is identified by a file. Thus, `name` is actually
   * the file name that identifies the shared memory.
   */
  std::string name;

 public:
  /* @brief Get the filename of shared memory file
   */
  std::string GetName() const { return name; }

  /*
   * @brief constructor of the shared memory.
   * @param name The file corresponding to the shared memory.
   */
  explicit SharedMemory(const std::string &name);
  /*
   * @brief destructor of the shared memory.
   * It deallocates the shared memory and removes the corresponding file.
   */
  ~SharedMemory();
  /*
   * @brief create shared memory.
   * It creates the file and shared memory.
   * @param sz the size of the shared memory.
   * @return the address of the shared memory
   */
  void *CreateNew(size_t sz);
  /*
   * @brief allocate shared memory that has been created.
   * @param sz the size of the shared memory.
   * @return the address of the shared memory
   */
  void *Open(size_t sz);

  /*
   * @brief check if the shared memory exist.
   * @param name the name of the shared memory.
   * @return a boolean value to indicate if the shared memory exists.
   */
  static bool Exist(const std::string &name);
};

}  // namespace runtime
}  // namespace dgl
#endif  // DGL_RUNTIME_SHARED_MEM_H_
