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//                        Kokkos v. 2.0
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#ifndef KOKKOS_SHARED_ALLOC_HPP_
#define KOKKOS_SHARED_ALLOC_HPP_

namespace Kokkos {
namespace Experimental {
namespace Impl {

template< class MemorySpace = void , class DestroyFunctor = void >
class SharedAllocationRecord ;

class SharedAllocationHeader {
private:

  typedef SharedAllocationRecord<void,void>  Record ;

  static constexpr unsigned maximum_label_length = ( 1u << 7 /* 128 */ ) - sizeof(Record*);

  template< class , class > friend class SharedAllocationRecord ;

  Record * m_record ;
  char     m_label[ maximum_label_length ];

public:

  /* Given user memory get pointer to the header */
  KOKKOS_INLINE_FUNCTION static
  const SharedAllocationHeader * get_header( void * alloc_ptr )
    { return reinterpret_cast<SharedAllocationHeader*>( reinterpret_cast<char*>(alloc_ptr) - sizeof(SharedAllocationHeader) ); }
};

template<>
class SharedAllocationRecord< void , void > {
protected:

  static_assert( sizeof(SharedAllocationHeader) == ( 1u << 7 /* 128 */ ) , "sizeof(SharedAllocationHeader) != 128" );

  template< class , class > friend class SharedAllocationRecord ;

  typedef void (* function_type )( SharedAllocationRecord<void,void> * );

  static int s_tracking_enabled ;

  SharedAllocationHeader * const m_alloc_ptr ;
  size_t                   const m_alloc_size ;
  function_type            const m_dealloc ;
  SharedAllocationRecord * const m_root ;
  SharedAllocationRecord *       m_prev ;
  SharedAllocationRecord *       m_next ;
  int                            m_count ;

  SharedAllocationRecord( const SharedAllocationRecord & ) = delete ;
  SharedAllocationRecord & operator = ( const SharedAllocationRecord & ) = delete ;

  /**\brief  Construct and insert into 'arg_root' tracking set.
   *         use_count is zero.
   */
  SharedAllocationRecord( SharedAllocationRecord * arg_root
                        , SharedAllocationHeader * arg_alloc_ptr
                        , size_t                   arg_alloc_size
                        , function_type            arg_dealloc
                        );

public:

  static int tracking_enabled() { return s_tracking_enabled ; }

  /**\brief A host process thread claims and disables the 
   *        shared allocation tracking flag.
   */
  static void tracking_claim_and_disable();

  /**\brief A host process thread releases and enables the 
   *        shared allocation tracking flag.
   */
  static void tracking_release_and_enable();

  ~SharedAllocationRecord() = default ;

  constexpr SharedAllocationRecord()
    : m_alloc_ptr( 0 )
    , m_alloc_size( 0 )
    , m_dealloc( 0 )
    , m_root( this )
    , m_prev( this )
    , m_next( this )
    , m_count( 0 )
    {}

  static constexpr unsigned maximum_label_length = SharedAllocationHeader::maximum_label_length ;

  KOKKOS_INLINE_FUNCTION
  const SharedAllocationHeader * head() const { return m_alloc_ptr ; }

  /* User's memory begins at the end of the header */
  KOKKOS_INLINE_FUNCTION
  void * data() const { return reinterpret_cast<void*>( m_alloc_ptr + 1 ); }

  /* User's memory begins at the end of the header */
  constexpr size_t size() const { return m_alloc_size - sizeof(SharedAllocationHeader) ; }

  /* Cannot be 'constexpr' because 'm_count' is volatile */
  int use_count() const { return m_count ; }

  /* Increment use count */
  static void increment( SharedAllocationRecord * );

  /* Decrement use count. If 1->0 then remove from the tracking list and invoke m_dealloc */
  static SharedAllocationRecord * decrement( SharedAllocationRecord * );

  /* Given a root record and data pointer find the record */
  static SharedAllocationRecord * find( SharedAllocationRecord * const , void * const );

  /*  Sanity check for the whole set of records to which the input record belongs.
   *  Locks the set's insert/erase operations until the sanity check is complete.
   */
  static bool is_sane( SharedAllocationRecord * );

  /*  Print host-accessible records */
  static void print_host_accessible_records( std::ostream &
                                           , const char * const space_name
                                           , const SharedAllocationRecord * const root
                                           , const bool detail );
};

namespace {

/* Taking the address of this function so make sure it is unique */
template < class MemorySpace , class DestroyFunctor >
void deallocate( SharedAllocationRecord<void,void> * record_ptr )
{
  typedef SharedAllocationRecord< MemorySpace , void > base_type ;
  typedef SharedAllocationRecord< MemorySpace , DestroyFunctor > this_type ;

  this_type * const ptr = static_cast< this_type * >(
                          static_cast< base_type * >( record_ptr ) );

  ptr->m_destroy.destroy_shared_allocation();

  delete ptr ;
}

}

/*
 *  Memory space specialization of SharedAllocationRecord< Space , void > requires :
 *
 *  SharedAllocationRecord< Space , void > : public SharedAllocationRecord< void , void >
 *  {
 *    // delete allocated user memory via static_cast to this type.
 *    static void deallocate( const SharedAllocationRecord<void,void> * );
 *    Space m_space ;
 *  }
 */
template< class MemorySpace , class DestroyFunctor >
class SharedAllocationRecord : public SharedAllocationRecord< MemorySpace , void >
{
private:

  SharedAllocationRecord( const MemorySpace & arg_space
                        , const std::string & arg_label
                        , const size_t        arg_alloc
                        )
    /*  Allocate user memory as [ SharedAllocationHeader , user_memory ] */
    : SharedAllocationRecord< MemorySpace , void >( arg_space , arg_label , arg_alloc , & Kokkos::Experimental::Impl::deallocate< MemorySpace , DestroyFunctor > )
    , m_destroy()
    {}

  SharedAllocationRecord() = delete ;
  SharedAllocationRecord( const SharedAllocationRecord & ) = delete ;
  SharedAllocationRecord & operator = ( const SharedAllocationRecord & ) = delete ;

public:

  DestroyFunctor  m_destroy ;

  // Allocate with a zero use count.  Incrementing the use count from zero to one
  // inserts the record into the tracking list.  Decrementing the count from one to zero
  // removes from the trakcing list and deallocates.
  KOKKOS_INLINE_FUNCTION static
  SharedAllocationRecord * allocate( const MemorySpace & arg_space 
                                   , const std::string & arg_label
                                   , const size_t        arg_alloc
                                   )
    {
#if defined( KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST )
      return new SharedAllocationRecord( arg_space , arg_label , arg_alloc );
#else
      return (SharedAllocationRecord *) 0 ;
#endif
    }
};

union SharedAllocationTracker {
private:

  typedef SharedAllocationRecord<void,void>  Record ;

  enum : uintptr_t { DO_NOT_DEREF_FLAG = 0x01ul };

  // The allocation record resides in Host memory space
  Record  * m_record ;
  uintptr_t m_record_bits ;

public:

  // Use macros instead of inline functions to reduce
  // pressure on compiler optimization by reducing
  // number of symbols and inline functons.

#if defined( KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST )

#define KOKKOS_SHARED_ALLOCATION_TRACKER_ENABLED	\
  Record::tracking_enabled()

#define KOKKOS_SHARED_ALLOCATION_TRACKER_INCREMENT	\
  if ( ! ( m_record_bits & DO_NOT_DEREF_FLAG ) ) Record::increment( m_record );

#define KOKKOS_SHARED_ALLOCATION_TRACKER_DECREMENT	\
  if ( ! ( m_record_bits & DO_NOT_DEREF_FLAG ) ) Record::decrement( m_record );

#else

#define KOKKOS_SHARED_ALLOCATION_TRACKER_ENABLED  0

#define KOKKOS_SHARED_ALLOCATION_TRACKER_INCREMENT /* */

#define KOKKOS_SHARED_ALLOCATION_TRACKER_DECREMENT /* */

#endif

  /** \brief  Assign a specialized record */
  inline
  void assign_allocated_record_to_uninitialized( Record * arg_record )
    { Record::increment( m_record = arg_record ); }

  template< class MemorySpace >
  constexpr
  SharedAllocationRecord< MemorySpace , void > &
  get_record() const
    { return * static_cast< SharedAllocationRecord< MemorySpace , void > * >( m_record ); }

  template< class MemorySpace >
  std::string get_label() const
    {
      return ( m_record_bits & DO_NOT_DEREF_FLAG )
             ? std::string()
             : static_cast< SharedAllocationRecord< MemorySpace , void > * >( m_record )->get_label()
             ;
    }

  KOKKOS_INLINE_FUNCTION
  int use_count() const
    {
#if defined( KOKKOS_ACTIVE_EXECUTION_MEMORY_SPACE_HOST )
      Record * const tmp = reinterpret_cast<Record*>( m_record_bits & ~DO_NOT_DEREF_FLAG );
      return ( tmp ? tmp->use_count() : 0 );
#else
      return 0 ;
#endif
    }

  KOKKOS_FORCEINLINE_FUNCTION
  ~SharedAllocationTracker()
    { KOKKOS_SHARED_ALLOCATION_TRACKER_DECREMENT }

  KOKKOS_FORCEINLINE_FUNCTION
  constexpr SharedAllocationTracker()
    : m_record_bits( DO_NOT_DEREF_FLAG ) {}

  // Move:

  KOKKOS_FORCEINLINE_FUNCTION
  SharedAllocationTracker( SharedAllocationTracker && rhs )
    : m_record_bits( rhs.m_record_bits )
    { rhs.m_record_bits = DO_NOT_DEREF_FLAG ; }

  KOKKOS_FORCEINLINE_FUNCTION
  SharedAllocationTracker & operator = ( SharedAllocationTracker && rhs )
    {
      // If this is tracking then must decrement
      KOKKOS_SHARED_ALLOCATION_TRACKER_DECREMENT
      // Move and reset RHS to default constructed value.
      m_record_bits = rhs.m_record_bits ;
      rhs.m_record_bits = DO_NOT_DEREF_FLAG ;
      return *this ;
    }

  // Copy:

  KOKKOS_FORCEINLINE_FUNCTION
  SharedAllocationTracker( const SharedAllocationTracker & rhs )
    : m_record_bits( KOKKOS_SHARED_ALLOCATION_TRACKER_ENABLED
                   ? rhs.m_record_bits
                   : rhs.m_record_bits | DO_NOT_DEREF_FLAG )
    {
      KOKKOS_SHARED_ALLOCATION_TRACKER_INCREMENT
    }

  /** \brief  Copy construction may disable tracking. */
  KOKKOS_FORCEINLINE_FUNCTION
  SharedAllocationTracker( const SharedAllocationTracker & rhs
                         , const bool enable_tracking )
    : m_record_bits( KOKKOS_SHARED_ALLOCATION_TRACKER_ENABLED
                     && enable_tracking
                   ? rhs.m_record_bits
                   : rhs.m_record_bits | DO_NOT_DEREF_FLAG )
    { KOKKOS_SHARED_ALLOCATION_TRACKER_INCREMENT }

  KOKKOS_FORCEINLINE_FUNCTION
  SharedAllocationTracker & operator = ( const SharedAllocationTracker & rhs )
    {
      // If this is tracking then must decrement
      KOKKOS_SHARED_ALLOCATION_TRACKER_DECREMENT
      m_record_bits = KOKKOS_SHARED_ALLOCATION_TRACKER_ENABLED
                    ? rhs.m_record_bits
                    : rhs.m_record_bits | DO_NOT_DEREF_FLAG ;
      KOKKOS_SHARED_ALLOCATION_TRACKER_INCREMENT
      return *this ;
    }

  /** \brief  Copy assignment may disable tracking */
  KOKKOS_FORCEINLINE_FUNCTION
  void assign( const SharedAllocationTracker & rhs
             , const bool enable_tracking )
    {
      KOKKOS_SHARED_ALLOCATION_TRACKER_DECREMENT
      m_record_bits = KOKKOS_SHARED_ALLOCATION_TRACKER_ENABLED
                      && enable_tracking
                    ? rhs.m_record_bits
                    : rhs.m_record_bits | DO_NOT_DEREF_FLAG ;
      KOKKOS_SHARED_ALLOCATION_TRACKER_INCREMENT
    }

#undef KOKKOS_SHARED_ALLOCATION_TRACKER_ENABLED
#undef KOKKOS_SHARED_ALLOCATION_TRACKER_INCREMENT
#undef KOKKOS_SHARED_ALLOCATION_TRACKER_DECREMENT

};


} /* namespace Impl */
} /* namespace Experimental */
} /* namespace Kokkos */

#endif
