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// Contains two generations that both use an AdjoiningVirtualSpaces.

// The two generations are adjacent in the reserved space for the

// heap.  Each generation has a virtual space and shrinking and

// expanding of the generations can still be down with that

// virtual space as was previously done.  If expanding of reserved

// size of a generation is required, the adjacent generation

// must be shrunk.  Adjusting the boundary between the generations

// is called for in this class.

class AdjoiningGenerations : public CHeapObj<mtGC> {

  friend class VMStructs;

 private:

  // The young generation and old generation, respectively

  PSYoungGen* _young_gen;

  PSOldGen* _old_gen;

  // The spaces used by the two generations.

  AdjoiningVirtualSpaces _virtual_spaces;

  // Move boundary up to expand old gen.  Checks are made to

  // determine if the move can be done with specified limits.

  void request_old_gen_expansion(size_t desired_change_in_bytes);

  // Move boundary down to expand young gen.

  bool request_young_gen_expansion(size_t desired_change_in_bytes);

 public:

  AdjoiningGenerations(ReservedSpace rs, GenerationSizer* policy, size_t alignment);

  // Accessors

  PSYoungGen* young_gen() { return _young_gen; }

  PSOldGen* old_gen() { return _old_gen; }

  AdjoiningVirtualSpaces* virtual_spaces() { return &_virtual_spaces; }

  // Additional space is needed in the old generation.  Check

  // the available space and attempt to move the boundary if more space

  // is needed.  The growth is not guaranteed to occur.

  void adjust_boundary_for_old_gen_needs(size_t desired_change_in_bytes);

  // Similarly for a growth of the young generation.

  void adjust_boundary_for_young_gen_needs(size_t eden_size, size_t survivor_size);

  // Return the total byte size of the reserved space

  // for the adjoining generations.

  size_t reserved_byte_size();

};