gc/shared/spaceDecorator.hpp

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#ifndef SHARE_GC_SHARED_SPACEDECORATOR_HPP
#define SHARE_GC_SHARED_SPACEDECORATOR_HPP

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

class SpaceDecorator: public AllStatic {
 public:
  // Initialization flags.
  static const bool Clear               = true;
  static const bool DontClear           = false;
  static const bool Mangle              = true;
  static const bool DontMangle          = false;
};

// Functionality for use with class Space and class MutableSpace.
//   The approach taken with the mangling is to mangle all
// the space initially and then to mangle areas that have
// been allocated since the last collection.  Mangling is
// done in the context of a generation and in the context
// of a space.
//   The space in a generation is mangled when it is first
// initialized and when the generation grows.  The spaces
// are not necessarily up-to-date when this mangling occurs
// and the method mangle_region() is used.
//   After allocations have been done in a space, the space generally
// need to be remangled.  Remangling is only done on the
// recently allocated regions in the space.  Typically, that is
// the region between the new top and the top just before a
// garbage collection.
//   An exception to the usual mangling in a space is done when the
// space is used for an extraordinary purpose.  Specifically, when
// to-space is used as scratch space for a mark-sweep-compact
// collection.
//   Spaces are mangled after a collection.  If the generation
// grows after a collection, the added space is mangled as part of
// the growth of the generation.  No additional mangling is needed when the
// spaces are resized after an expansion.
//   The class SpaceMangler keeps a pointer to the top of the allocated
// area and provides the methods for doing the piece meal mangling.
// Methods for doing sparces and full checking of the mangling are
// included.  The full checking is done if DEBUG_MANGLING is defined.
//   GenSpaceMangler is used with the GenCollectedHeap collectors and
// MutableSpaceMangler is used with the ParallelScavengeHeap collectors.
// These subclasses abstract the differences in the types of spaces used
// by each heap.

class SpaceMangler: public CHeapObj<mtGC> {
  friend class VMStructs;

  // High water mark for allocations.  Typically, the space above
  // this point have been mangle previously and don't need to be
  // touched again.  Space below this point has been allocated
  // and remangling is needed between the current top and this
  // high water mark.
  HeapWord* _top_for_allocations;
  HeapWord* top_for_allocations() { return _top_for_allocations; }

 public:

  // Setting _top_for_allocations to NULL at initialization
  // makes it always below top so that mangling done as part
  // of the initialize() call of a space does nothing (as it
  // should since the mangling is done as part of the constructor
  // for the space.
  SpaceMangler() : _top_for_allocations(NULL) {}

  // Methods for top and end that delegate to the specific
  // space type.
  virtual HeapWord* top() const = 0;
  virtual HeapWord* end() const = 0;

  // Return true if q matches the mangled pattern.
  static bool is_mangled(HeapWord* q) PRODUCT_RETURN0;

  // Used to save the an address in a space for later use during mangling.
  void set_top_for_allocations(HeapWord* v);

  // Overwrites the unused portion of this space.
  // Mangle only the region not previously mangled [top, top_previously_mangled)
  void mangle_unused_area();
  // Mangle all the unused region [top, end)
  void mangle_unused_area_complete();
  // Do some sparse checking on the area that should have been mangled.
  void check_mangled_unused_area(HeapWord* limit) PRODUCT_RETURN;
  // Do a complete check of the area that should be mangled.
  void check_mangled_unused_area_complete() PRODUCT_RETURN;

  // Mangle the MemRegion.  This is a non-space specific mangler.  It
  // is used during the initial mangling of a space before the space
  // is fully constructed.  Also is used when a generation is expanded
  // and possibly before the spaces have been reshaped to to the new
  // size of the generation.
  static void mangle_region(MemRegion mr) PRODUCT_RETURN;
};

class ContiguousSpace;
class MutableSpace;

// For use with GenCollectedHeap's
class GenSpaceMangler: public SpaceMangler {
  ContiguousSpace* _sp;

  ContiguousSpace* sp() { return _sp; }

  HeapWord* top() const;
  HeapWord* end() const;

 public:
  GenSpaceMangler(ContiguousSpace* sp) : SpaceMangler(), _sp(sp) {}
};

// For use with ParallelScavengeHeap's.
class MutableSpaceMangler: public SpaceMangler {
  MutableSpace* _sp;

  MutableSpace* sp() { return _sp; }

  HeapWord* top() const;
  HeapWord* end() const;

 public:
  MutableSpaceMangler(MutableSpace* sp) : SpaceMangler(), _sp(sp) {}
};

#endif // SHARE_GC_SHARED_SPACEDECORATOR_HPP