src/hotspot/share/classfile/fieldLayoutBuilder.hpp

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#ifndef SHARE_CLASSFILE_FIELDLAYOUTBUILDER_HPP
#define SHARE_CLASSFILE_FIELDLAYOUTBUILDER_HPP

#include "classfile/classFileParser.hpp"
#include "classfile/classLoaderData.hpp"
#include "memory/allocation.hpp"
#include "oops/fieldStreams.hpp"
#include "utilities/growableArray.hpp"

// Classes below are used to compute the field layout of classes.


// A LayoutRawBlock describes an element of a layout.
// Each field is represented by a LayoutRawBlock.
// LayoutRawBlocks can also represent elements injected by the JVM:
// padding, empty blocks, inherited fields, etc.
// All LayoutRawBlocks must have a size and an alignment. The size is the
// exact size of the field expressed in bytes. The alignment is
// the alignment constraint of the field (1 for byte, 2 for short,
// 4 for int, 8 for long, etc.)
//
// LayoutRawBlock are designed to be used in two data structures:
//   - a linked list in a layout (using _next_block, _prev_block)
//   - a GrowableArray in field group (the growable array contains pointers to LayoutRawBlocks)
//
//  next/prev pointers are included in the LayoutRawBlock class to narrow
//  the number of allocation required during the computation of a layout.
//
class LayoutRawBlock : public ResourceObj {
 public:
  // Some code relies on the order of values below.
  enum Kind {
    EMPTY,         // empty slot, space is taken from this to allocate fields
    RESERVED,      // reserved for JVM usage (for instance object header)
    PADDING,       // padding (because of alignment constraints or @Contended)
    REGULAR,       // primitive or oop field (including non-flattened inline fields)
    FLATTENED,     // flattened field
    INHERITED      // field(s) inherited from super classes
  };

 private:
  LayoutRawBlock* _next_block;
  LayoutRawBlock* _prev_block;
  Kind _kind;
  int _offset;
  int _alignment;
  int _size;
  int _field_index;
  bool _is_reference;

 public:
  LayoutRawBlock(Kind kind, int size);
  LayoutRawBlock(int index, Kind kind, int size, int alignment, bool is_reference = false);
  LayoutRawBlock* next_block() const { return _next_block; }
  void set_next_block(LayoutRawBlock* next) { _next_block = next; }
  LayoutRawBlock* prev_block() const { return _prev_block; }
  void set_prev_block(LayoutRawBlock* prev) { _prev_block = prev; }
  Kind kind() const { return _kind; }
  int offset() const {
    assert(_offset >= 0, "Must be initialized");
    return _offset;
  }
  void set_offset(int offset) { _offset = offset; }
  int alignment() const { return _alignment; }
  int size() const { return _size; }
  void set_size(int size) { _size = size; }
  int field_index() const {
    assert(_field_index != -1, "Must be initialized");
    return _field_index;
  }
  bool is_reference() const { return _is_reference; }

  bool fit(int size, int alignment);

  static int compare_offset(LayoutRawBlock** x, LayoutRawBlock** y)  { return (*x)->offset() - (*y)->offset(); }
  // compare_size_inverted() returns the opposite of a regular compare method in order to
  // sort fields in decreasing order.
  // Note: with line types, the comparison should include alignment constraint if sizes are equals
  static int compare_size_inverted(LayoutRawBlock** x, LayoutRawBlock** y)  {
    int diff = (*y)->size() - (*x)->size();
    // qsort() may reverse the order of fields with the same size.
    // The extension is to ensure stable sort.
    if (diff == 0) {
      diff = (*x)->field_index() - (*y)->field_index();
    }
    return diff;
  }

};

// A Field group represents a set of fields that have to be allocated together,
// this is the way the @Contended annotation is supported.
// Inside a FieldGroup, fields are sorted based on their kind: primitive,
// oop, or flattened.
//
class FieldGroup : public ResourceObj {

 private:
  FieldGroup* _next;
  GrowableArray<LayoutRawBlock*>* _primitive_fields;
  GrowableArray<LayoutRawBlock*>* _oop_fields;
  int _contended_group;
  int _oop_count;
  static const int INITIAL_LIST_SIZE = 16;

 public:
  FieldGroup(int contended_group = -1);

  FieldGroup* next() const { return _next; }
  void set_next(FieldGroup* next) { _next = next; }
  GrowableArray<LayoutRawBlock*>* primitive_fields() const { return _primitive_fields; }
  GrowableArray<LayoutRawBlock*>* oop_fields() const { return _oop_fields; }
  int contended_group() const { return _contended_group; }
  int oop_count() const { return _oop_count; }

  void add_primitive_field(int idx, BasicType type);
  void add_oop_field(int idx);
  void sort_by_size();
};

// The FieldLayout class represents a set of fields organized
// in a layout.
// An instance of FieldLayout can either represent the layout
// of non-static fields (used in an instance object) or the
// layout of static fields (to be included in the class mirror).
//
// _block is a pointer to a list of LayoutRawBlock ordered by increasing
// offsets.
// _start points to the LayoutRawBlock with the first offset that can
// be used to allocate fields of the current class
// _last points to the last LayoutRawBlock of the list. In order to
// simplify the code, the LayoutRawBlock list always ends with an
// EMPTY block (the kind of LayoutRawBlock from which space is taken
// to allocate fields) with a size big enough to satisfy all
// field allocations.
//
class FieldLayout : public ResourceObj {
 private:
  GrowableArray<FieldInfo>* _field_info;
  ConstantPool* _cp;
  LayoutRawBlock* _blocks;  // the layout being computed
  LayoutRawBlock* _start;   // points to the first block where a field can be inserted
  LayoutRawBlock* _last;    // points to the last block of the layout (big empty block)

 public:
  FieldLayout(GrowableArray<FieldInfo>* field_info, ConstantPool* cp);
  void initialize_static_layout();
  void initialize_instance_layout(const InstanceKlass* ik, bool& super_ends_with_oop);

  LayoutRawBlock* first_empty_block() {
    LayoutRawBlock* block = _start;
    while (block->kind() != LayoutRawBlock::EMPTY) {
      block = block->next_block();
    }
    return block;
  }

  LayoutRawBlock* start() { return _start; }
  void set_start(LayoutRawBlock* start) { _start = start; }
  LayoutRawBlock* last_block() { return _last; }

  LayoutRawBlock* first_field_block();
  void add(GrowableArray<LayoutRawBlock*>* list, LayoutRawBlock* start = nullptr);
  void add_field_at_offset(LayoutRawBlock* blocks, int offset, LayoutRawBlock* start = nullptr);
  void add_contiguously(GrowableArray<LayoutRawBlock*>* list, LayoutRawBlock* start = nullptr);
  LayoutRawBlock* insert_field_block(LayoutRawBlock* slot, LayoutRawBlock* block);
  void reconstruct_layout(const InstanceKlass* ik, bool& has_instance_fields, bool& ends_with_oop);
  void fill_holes(const InstanceKlass* ik);
  LayoutRawBlock* insert(LayoutRawBlock* slot, LayoutRawBlock* block);
  void remove(LayoutRawBlock* block);
  void print(outputStream* output, bool is_static, const InstanceKlass* super);
};


// FieldLayoutBuilder is the main entry point for layout computation.
// This class has three methods to generate layout: one for regular classes
// and two for classes with hard coded offsets (java,lang.ref.Reference
// and the boxing classes). The rationale for having multiple methods
// is that each kind of class has a different set goals regarding
// its layout, so instead of mixing several layout strategies into a
// single method, each kind has its own method (see comments below
// for more details about the allocation strategies).
//
// Computing the layout of a class always goes through 4 steps:
//   1 - Prologue: preparation of data structure and gathering of
//       layout information inherited from super classes
//   2 - Field sorting: fields are sorted according to their
//       kind (oop, primitive, inline class) and their contention
//       annotation (if any)
//   3 - Layout is computed from the set of lists generated during
//       step 2
//   4 - Epilogue: oopmaps are generated, layout information is
//       prepared so other VM components can use it (instance size,
//       static field size, non-static field size, etc.)
//
//  Steps 1 and 4 are common to all layout computations. Step 2 and 3
//  can vary with the allocation strategy.
//
class FieldLayoutBuilder : public ResourceObj {
 private:

  const Symbol* _classname;
  const InstanceKlass* _super_klass;
  ConstantPool* _constant_pool;
  GrowableArray<FieldInfo>* _field_info;
  FieldLayoutInfo* _info;
  FieldGroup* _root_group;
  GrowableArray<FieldGroup*> _contended_groups;
  FieldGroup* _static_fields;
  FieldLayout* _layout;
  FieldLayout* _static_layout;
  int _nonstatic_oopmap_count;
  int _alignment;
  bool _has_nonstatic_fields;
  bool _is_contended; // is a contended class?
  bool _super_ends_with_oop;

 public:
  FieldLayoutBuilder(const Symbol* classname, const InstanceKlass* super_klass, ConstantPool* constant_pool,
                     GrowableArray<FieldInfo>* field_info, bool is_contended, FieldLayoutInfo* info);

  int get_alignment() {
    assert(_alignment != -1, "Uninitialized");
    return _alignment;
  }

  void build_layout();
  void compute_regular_layout();
  void insert_contended_padding(LayoutRawBlock* slot);

 private:
  void prologue();
  void epilogue();
  void regular_field_sorting();
  FieldGroup* get_or_create_contended_group(int g);
};

#endif // SHARE_CLASSFILE_FIELDLAYOUTBUILDER_HPP