src/hotspot/share/memory/memRegion.hpp

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#ifndef SHARE_MEMORY_MEMREGION_HPP
#define SHARE_MEMORY_MEMREGION_HPP

#include "memory/allocation.hpp"
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"

// A very simple data structure representing a contiguous region
// region of address space.

// Note that MemRegions are typically passed by value, not by reference.
// The intent is that they remain very small and contain no
// objects. The copy constructor and destructor must be trivial,
// to support optimization for pass-by-value.
// These should almost never be allocated in heap but we do
// create MemRegions (in CardTable and G1CMRootMemRegions) on the heap so operator
// new and operator new [] were added for these special cases.

class MemRegion {
  friend class VMStructs;
private:
  HeapWord* _start;
  size_t    _word_size;

public:
  MemRegion() : _start(nullptr), _word_size(0) {};
  MemRegion(HeapWord* start, size_t word_size) :
    _start(start), _word_size(word_size) {};
  MemRegion(HeapWord* start, HeapWord* end) :
    _start(start), _word_size(pointer_delta(end, start)) {
    assert(end >= start, "incorrect constructor arguments");
  }

  MemRegion intersection(const MemRegion mr2) const;
  // regions must overlap or be adjacent
  MemRegion _union(const MemRegion mr2) const;
  // minus will fail a guarantee if mr2 is interior to this,
  // since there's no way to return 2 disjoint regions.
  MemRegion minus(const MemRegion mr2) const;

  HeapWord* start() const { return _start; }
  HeapWord* end() const   { return _start + _word_size; }
  HeapWord* last() const  { return _start + _word_size - 1; }

  void set_start(HeapWord* start) { _start = start; }
  void set_end(HeapWord* end)     { _word_size = pointer_delta(end, _start); }
  void set_word_size(size_t word_size) {
    _word_size = word_size;
  }

  bool contains(const MemRegion mr2) const {
    return _start <= mr2._start && end() >= mr2.end();
  }
  bool contains(const void* addr) const {
    return addr >= (void*)_start && addr < (void*)end();
  }
  bool equals(const MemRegion mr2) const {
    // first disjunct since we do not have a canonical empty set
    return ((is_empty() && mr2.is_empty()) ||
            (start() == mr2.start() && end() == mr2.end()));
  }

  size_t byte_size() const { return _word_size * sizeof(HeapWord); }
  size_t word_size() const { return _word_size; }

  bool is_empty() const { return word_size() == 0; }

  // Creates and initializes an array of MemRegions of the given length.
  static MemRegion* create_array(size_t length, MemTag mem_tag);
  static void destroy_array(MemRegion* array, size_t length);
};

// For iteration over MemRegion's.

class MemRegionClosure : public StackObj {
public:
  virtual void do_MemRegion(MemRegion mr) = 0;
};

#endif // SHARE_MEMORY_MEMREGION_HPP