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  *

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 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_HEAPREGIONSEQ_HPP

 #define SHARE_VM_GC_IMPLEMENTATION_G1_HEAPREGIONSEQ_HPP

 class HeapRegion;

 class HeapRegionClosure;

 class FreeRegionList;

 // This class keeps track of the region metadata (i.e., HeapRegion

 // instances). They are kept in the _regions array in address

 // order. A region's index in the array corresponds to its index in

 // the heap (i.e., 0 is the region at the bottom of the heap, 1 is

 // the one after it, etc.). Two regions that are consecutive in the

 // array should also be adjacent in the address space (i.e.,

 // region(i).end() == region(i+1).bottom().

 //

 // We create a HeapRegion when we commit the region's address space

 // for the first time. When we uncommit the address space of a

 // region we retain the HeapRegion to be able to re-use it in the

 // future (in case we recommit it).

 //

 // We keep track of three lengths:

 //

 // * _length (returned by length()) is the number of currently

 //   committed regions.

 // * _allocated_length (not exposed outside this class) is the

 //   number of regions for which we have HeapRegions.

 // * _max_length (returned by max_length()) is the maximum number of

 //   regions the heap can have.

 //

 // and maintain that: _length <= _allocated_length <= _max_length

 class HeapRegionSeq: public CHeapObj<mtGC> {

   friend class VMStructs;

   // The array that holds the HeapRegions.

   HeapRegion** _regions;

   // Version of _regions biased to address 0

   HeapRegion** _regions_biased;

   // The number of regions committed in the heap.

   uint _length;

   // The address of the first reserved word in the heap.

   HeapWord* _heap_bottom;

   // The address of the last reserved word in the heap - 1.

   HeapWord* _heap_end;

   // The log of the region byte size.

   uint _region_shift;

   // A hint for which index to start searching from for humongous

   // allocations.

   uint _next_search_index;

   // The number of regions for which we have allocated HeapRegions for.

   uint _allocated_length;

   // The maximum number of regions in the heap.

   uint _max_length;

   // Find a contiguous set of empty regions of length num, starting

   // from the given index.

   uint find_contiguous_from(uint from, uint num);

   // Map a heap address to a biased region index. Assume that the

   // address is valid.

   inline uintx addr_to_index_biased(HeapWord* addr) const;

   void increment_allocated_length() {

     assert(_allocated_length < _max_length, "pre-condition");

     _allocated_length++;

   }

   void increment_length() {

     assert(_length < _max_length, "pre-condition");

     _length++;

   }

   void decrement_length() {

     assert(_length > 0, "pre-condition");

     _length--;

   }

  public:

   // Empty contructor, we'll initialize it with the initialize() method.

   HeapRegionSeq() { }

   void initialize(HeapWord* bottom, HeapWord* end, uint max_length);

   // Return the HeapRegion at the given index. Assume that the index

   // is valid.

   inline HeapRegion* at(uint index) const;

   // If addr is within the committed space return its corresponding

   // HeapRegion, otherwise return NULL.

   inline HeapRegion* addr_to_region(HeapWord* addr) const;

   // Return the HeapRegion that corresponds to the given

   // address. Assume the address is valid.

   inline HeapRegion* addr_to_region_unsafe(HeapWord* addr) const;

   // Return the number of regions that have been committed in the heap.

   uint length() const { return _length; }

   // Return the maximum number of regions in the heap.

   uint max_length() const { return _max_length; }

   // Expand the sequence to reflect that the heap has grown from

   // old_end to new_end. Either create new HeapRegions, or re-use

   // existing ones, and return them in the given list. Returns the

   // memory region that covers the newly-created regions. If a

   // HeapRegion allocation fails, the result memory region might be

   // smaller than the desired one.

   MemRegion expand_by(HeapWord* old_end, HeapWord* new_end,

                       FreeRegionList* list);

   // Return the number of contiguous regions at the end of the sequence

   // that are available for allocation.

   uint free_suffix();

   // Find a contiguous set of empty regions of length num and return

   // the index of the first region or G1_NULL_HRS_INDEX if the

   // search was unsuccessful.

   uint find_contiguous(uint num);

   // Apply blk->doHeapRegion() on all committed regions in address order,

   // terminating the iteration early if doHeapRegion() returns true.

   void iterate(HeapRegionClosure* blk) const;

   // As above, but start the iteration from hr and loop around. If hr

   // is NULL, we start from the first region in the heap.

   void iterate_from(HeapRegion* hr, HeapRegionClosure* blk) const;

   // Tag as uncommitted as many regions that are completely free as

   // possible, up to num_regions_to_remove, from the suffix of the committed

   // sequence. Return the actual number of removed regions.

   uint shrink_by(uint num_regions_to_remove);

   // Do some sanity checking.

   void verify_optional() PRODUCT_RETURN;

 };

 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_HEAPREGIONSEQ_HPP