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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

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 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * 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.

 *

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#ifndef SHARE_VM_GC_IMPLEMENTATION_G1_COLLECTIONSETCHOOSER_HPP

#define SHARE_VM_GC_IMPLEMENTATION_G1_COLLECTIONSETCHOOSER_HPP

#include "gc_implementation/g1/heapRegion.hpp"

#include "utilities/growableArray.hpp"

// We need to sort heap regions by collection desirability.

// This sorting is currently done in two "stages". An initial sort is

// done following a cleanup pause as soon as all of the marked but

// non-empty regions have been identified and the completely empty

// ones reclaimed.

// This gives us a global sort on a GC efficiency metric

// based on predictive data available at that time. However,

// any of these regions that are collected will only be collected

// during a future GC pause, by which time it is possible that newer

// data might allow us to revise and/or refine the earlier

// pause predictions, leading to changes in expected gc efficiency

// order. To somewhat mitigate this obsolescence, more so in the

// case of regions towards the end of the list, which will be

// picked later, these pre-sorted regions from the _markedRegions

// array are not used as is, but a small prefix thereof is

// insertion-sorted again into a small cache, based on more

// recent remembered set information. Regions are then drawn

// from this cache to construct the collection set at each

// incremental GC.

// This scheme and/or its implementation may be subject to

// revision in the future.

class CSetChooserCache VALUE_OBJ_CLASS_SPEC {

private:

  enum {

    CacheLength = 16

  } PrivateConstants;

  HeapRegion*  _cache[CacheLength];

  int          _occupancy; // number of regions in cache

  int          _first;     // (index of) "first" region in the cache

  // adding CacheLength to deal with negative values

  inline int trim_index(int index) {

    return (index + CacheLength) % CacheLength;

  }

  inline int get_sort_index(int index) {

    return -index-2;

  }

  inline int get_index(int sort_index) {

    return -sort_index-2;

  }

public:

  CSetChooserCache(void);

  inline int occupancy(void) { return _occupancy; }

  inline bool is_full()      { return _occupancy == CacheLength; }

  inline bool is_empty()     { return _occupancy == 0; }

  void clear(void);

  void insert(HeapRegion *hr);

  HeapRegion *remove_first(void);

  inline HeapRegion *get_first(void) {

    return _cache[_first];

  }

#ifndef PRODUCT

  bool verify (void);

  bool region_in_cache(HeapRegion *hr) {

    int sort_index = hr->sort_index();

    if (sort_index < -1) {

      int index = get_index(sort_index);

      guarantee(index < CacheLength, "should be within bounds");

      return _cache[index] == hr;

    } else

      return 0;

  }

#endif // PRODUCT

};

class CollectionSetChooser: public CHeapObj {

  GrowableArray<HeapRegion*> _markedRegions;

  int _curMarkedIndex;

  int _numMarkedRegions;

  CSetChooserCache _cache;

  // True iff last collection pause ran of out new "age 0" regions, and

  // returned an "age 1" region.

  bool _unmarked_age_1_returned_as_new;

  jint _first_par_unreserved_idx;

public:

  HeapRegion* getNextMarkedRegion(double time_so_far, double avg_prediction);

  CollectionSetChooser();

  void sortMarkedHeapRegions();

  void fillCache();

  void addMarkedHeapRegion(HeapRegion *hr);

  // Must be called before calls to getParMarkedHeapRegionChunk.

  // "n_regions" is the number of regions, "chunkSize" the chunk size.

  void prepareForAddMarkedHeapRegionsPar(size_t n_regions, size_t chunkSize);

  // Returns the first index in a contiguous chunk of "n_regions" indexes

  // that the calling thread has reserved.  These must be set by the

  // calling thread using "setMarkedHeapRegion" (to NULL if necessary).

  jint getParMarkedHeapRegionChunk(jint n_regions);

  // Set the marked array entry at index to hr.  Careful to claim the index

  // first if in parallel.

  void setMarkedHeapRegion(jint index, HeapRegion* hr);

  // Atomically increment the number of claimed regions by "inc_by".

  void incNumMarkedHeapRegions(jint inc_by);

  void clearMarkedHeapRegions();

  void updateAfterFullCollection();

  bool unmarked_age_1_returned_as_new() { return _unmarked_age_1_returned_as_new; }

  // Returns true if the used portion of "_markedRegions" is properly

  // sorted, otherwise asserts false.

#ifndef PRODUCT

  bool verify(void);

  bool regionProperlyOrdered(HeapRegion* r) {

    int si = r->sort_index();

    return (si == -1) ||

      (si > -1 && _markedRegions.at(si) == r) ||

      (si < -1 && _cache.region_in_cache(r));

  }

#endif

};

#endif // SHARE_VM_GC_IMPLEMENTATION_G1_COLLECTIONSETCHOOSER_HPP