view src/hotspot/share/memory/memRegion.hpp @ 54281:6fb43030a1b4

8214363: HeapWord should not be a fake class Summary: Change HeapWord and MetaWord to be pointers to incomplete types. Reviewed-by: tschatzl, mikael, coleenp, pliden
author kbarrett
date Mon, 18 Feb 2019 16:34:46 -0500
parents 026e1ea616c8
children 755e82641224
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 * published by the Free Software Foundation.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit if you need additional information or have any
 * questions.


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

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

// Note that MemRegions are 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 never be allocated in heap but we do
// create MemRegions (in CardTableBarrierSet) in heap so operator
// new and operator new [] added for this special case.

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

  MemRegion() : _start(NULL), _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(MetaWord* start, MetaWord* end) :
    _start((HeapWord*)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; }
  void* operator new(size_t size) throw();
  void* operator new [](size_t size) throw();
  void  operator delete(void* p);
  void  operator delete [](void* p);

// For iteration over MemRegion's.

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

// A ResourceObj version of MemRegionClosure

class MemRegionClosureRO: public MemRegionClosure {
  void* operator new(size_t size, ResourceObj::allocation_type type, MEMFLAGS flags) throw() {
        return ResourceObj::operator new(size, type, flags);
  void* operator new(size_t size, Arena *arena) throw() {
        return ResourceObj::operator new(size, arena);
  void* operator new(size_t size) throw() {
        return ResourceObj::operator new(size);

  void  operator delete(void* p) {} // nothing to do