src/hotspot/share/gc/shared/space.hpp

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * version 2 for more details (a copy is included in the LICENSE file that
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#ifndef SHARE_GC_SHARED_SPACE_HPP
#define SHARE_GC_SHARED_SPACE_HPP

#include "gc/shared/blockOffsetTable.hpp"
#include "gc/shared/cardTable.hpp"
#include "gc/shared/workerThread.hpp"
#include "memory/allocation.hpp"
#include "memory/iterator.hpp"
#include "memory/memRegion.hpp"
#include "oops/markWord.hpp"
#include "runtime/mutexLocker.hpp"
#include "utilities/align.hpp"
#include "utilities/macros.hpp"

// A space is an abstraction for the "storage units" backing
// up the generation abstraction. It includes specific
// implementations for keeping track of free and used space,
// for iterating over objects and free blocks, etc.

// A space in which the free area is contiguous.  It therefore supports
// faster allocation, and compaction.
//
// Invariant: bottom() and end() are on page_size boundaries and
// bottom() <= top() <= end()
// top() is inclusive and end() is exclusive.
class ContiguousSpace: public CHeapObj<mtGC> {
  friend class VMStructs;

private:
  HeapWord* _bottom;
  HeapWord* _end;
  HeapWord* _top;

  // Allocation helpers (return null if full).
  inline HeapWord* allocate_impl(size_t word_size);
  inline HeapWord* par_allocate_impl(size_t word_size);

public:
  ContiguousSpace();

  // Accessors
  HeapWord* bottom() const         { return _bottom; }
  HeapWord* end() const            { return _end;    }
  HeapWord* top() const            { return _top;    }

  void set_bottom(HeapWord* value) { _bottom = value; }
  void set_end(HeapWord* value)    { _end = value; }
  void set_top(HeapWord* value)    { _top = value; }

  // Testers
  bool is_empty() const              { return used() == 0; }

  // Returns true iff the given the space contains the
  // given address as part of an allocated object. For
  // certain kinds of spaces, this might be a potentially
  // expensive operation. To prevent performance problems
  // on account of its inadvertent use in product jvm's,
  // we restrict its use to assertion checks only.
  bool is_in(const void* p) const {
    return used_region().contains(p);
  }

  // Returns true iff the given reserved memory of the space contains the
  // given address.
  bool is_in_reserved(const void* p) const { return _bottom <= p && p < _end; }

  // Size computations.  Sizes are in bytes.
  size_t capacity() const { return byte_size(bottom(), end()); }
  size_t used()     const { return byte_size(bottom(), top()); }
  size_t free()     const { return byte_size(top(),    end()); }

  void print() const;
  void print_on(outputStream* st, const char* prefix) const;

  // Initialization.
  // "initialize" should be called once on a space, before it is used for
  // any purpose.  The "mr" arguments gives the bounds of the space, and
  // the "clear_space" argument should be true unless the memory in "mr" is
  // known to be zeroed.
  void initialize(MemRegion mr, bool clear_space, bool mangle_space);

  // The "clear" method must be called on a region that may have
  // had allocation performed in it, but is now to be considered empty.
  void clear(bool mangle_space);

  void mangle_unused_area() PRODUCT_RETURN;
  void mangle_unused_area(MemRegion mr) PRODUCT_RETURN;

  MemRegion used_region() const { return MemRegion(bottom(), top()); }

  // Allocation (return null if full).  Assumes the caller has established
  // mutually exclusive access to the space.
  HeapWord* allocate(size_t word_size);
  // Allocation (return null if full).  Enforces mutual exclusion internally.
  HeapWord* par_allocate(size_t word_size);

  // Iteration
  void object_iterate(ObjectClosure* blk);

  // Addresses for inlined allocation
  HeapWord** top_addr() { return &_top; }

  // Debugging
  void verify() const;
};

#endif // SHARE_GC_SHARED_SPACE_HPP