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  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

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 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP

 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP

 #include "gc_implementation/g1/collectionSetChooser.hpp"

 #include "gc_implementation/g1/g1MMUTracker.hpp"

 #include "memory/collectorPolicy.hpp"

 // A G1CollectorPolicy makes policy decisions that determine the

 // characteristics of the collector.  Examples include:

 //   * choice of collection set.

 //   * when to collect.

 class HeapRegion;

 class CollectionSetChooser;

 class G1GCPhaseTimes;

 // TraceGen0Time collects data on _both_ young and mixed evacuation pauses

 // (the latter may contain non-young regions - i.e. regions that are

 // technically in Gen1) while TraceGen1Time collects data about full GCs.

 class TraceGen0TimeData : public CHeapObj<mtGC> {

  private:

   unsigned  _young_pause_num;

   unsigned  _mixed_pause_num;

   NumberSeq _all_stop_world_times_ms;

   NumberSeq _all_yield_times_ms;

   NumberSeq _total;

   NumberSeq _other;

   NumberSeq _root_region_scan_wait;

   NumberSeq _parallel;

   NumberSeq _ext_root_scan;

   NumberSeq _satb_filtering;

   NumberSeq _update_rs;

   NumberSeq _scan_rs;

   NumberSeq _obj_copy;

   NumberSeq _termination;

   NumberSeq _parallel_other;

   NumberSeq _clear_ct;

   void print_summary(const char* str, const NumberSeq* seq) const;

   void print_summary_sd(const char* str, const NumberSeq* seq) const;

 public:

    TraceGen0TimeData() : _young_pause_num(0), _mixed_pause_num(0) {};

   void record_start_collection(double time_to_stop_the_world_ms);

   void record_yield_time(double yield_time_ms);

   void record_end_collection(double pause_time_ms, G1GCPhaseTimes* phase_times);

   void increment_young_collection_count();

   void increment_mixed_collection_count();

   void print() const;

 };

 class TraceGen1TimeData : public CHeapObj<mtGC> {

  private:

   NumberSeq _all_full_gc_times;

  public:

   void record_full_collection(double full_gc_time_ms);

   void print() const;

 };

 // There are three command line options related to the young gen size:

 // NewSize, MaxNewSize and NewRatio (There is also -Xmn, but that is

 // just a short form for NewSize==MaxNewSize). G1 will use its internal

 // heuristics to calculate the actual young gen size, so these options

 // basically only limit the range within which G1 can pick a young gen

 // size. Also, these are general options taking byte sizes. G1 will

 // internally work with a number of regions instead. So, some rounding

 // will occur.

 //

 // If nothing related to the the young gen size is set on the command

 // line we should allow the young gen to be between

 // G1DefaultMinNewGenPercent and G1DefaultMaxNewGenPercent of the

 // heap size. This means that every time the heap size changes the

 // limits for the young gen size will be updated.

 //

 // If only -XX:NewSize is set we should use the specified value as the

 // minimum size for young gen. Still using G1DefaultMaxNewGenPercent

 // of the heap as maximum.

 //

 // If only -XX:MaxNewSize is set we should use the specified value as the

 // maximum size for young gen. Still using G1DefaultMinNewGenPercent

 // of the heap as minimum.

 //

 // If -XX:NewSize and -XX:MaxNewSize are both specified we use these values.

 // No updates when the heap size changes. There is a special case when

 // NewSize==MaxNewSize. This is interpreted as "fixed" and will use a

 // different heuristic for calculating the collection set when we do mixed

 // collection.

 //

 // If only -XX:NewRatio is set we should use the specified ratio of the heap

 // as both min and max. This will be interpreted as "fixed" just like the

 // NewSize==MaxNewSize case above. But we will update the min and max

 // everytime the heap size changes.

 //

 // NewSize and MaxNewSize override NewRatio. So, NewRatio is ignored if it is

 // combined with either NewSize or MaxNewSize. (A warning message is printed.)

 class G1YoungGenSizer : public CHeapObj<mtGC> {

 private:

   enum SizerKind {

     SizerDefaults,

     SizerNewSizeOnly,

     SizerMaxNewSizeOnly,

     SizerMaxAndNewSize,

     SizerNewRatio

   };

   SizerKind _sizer_kind;

   uint _min_desired_young_length;

   uint _max_desired_young_length;

   bool _adaptive_size;

   uint calculate_default_min_length(uint new_number_of_heap_regions);

   uint calculate_default_max_length(uint new_number_of_heap_regions);

 public:

   G1YoungGenSizer();

   void heap_size_changed(uint new_number_of_heap_regions);

   uint min_desired_young_length() {

     return _min_desired_young_length;

   }

   uint max_desired_young_length() {

     return _max_desired_young_length;

   }

   bool adaptive_young_list_length() {

     return _adaptive_size;

   }

 };

 class G1CollectorPolicy: public CollectorPolicy {

 private:

   // either equal to the number of parallel threads, if ParallelGCThreads

   // has been set, or 1 otherwise

   int _parallel_gc_threads;

   // The number of GC threads currently active.

   uintx _no_of_gc_threads;

   enum SomePrivateConstants {

     NumPrevPausesForHeuristics = 10

   };

   G1MMUTracker* _mmu_tracker;

   void initialize_flags();

   void initialize_all() {

     initialize_flags();

     initialize_size_info();

     initialize_perm_generation(PermGen::MarkSweepCompact);

   }

   CollectionSetChooser* _collectionSetChooser;

   double _full_collection_start_sec;

   size_t _cur_collection_pause_used_at_start_bytes;

   uint   _cur_collection_pause_used_regions_at_start;

   // These exclude marking times.

   TruncatedSeq* _recent_gc_times_ms;

   TruncatedSeq* _concurrent_mark_remark_times_ms;

   TruncatedSeq* _concurrent_mark_cleanup_times_ms;

   TraceGen0TimeData _trace_gen0_time_data;

   TraceGen1TimeData _trace_gen1_time_data;

   double _stop_world_start;

   // indicates whether we are in young or mixed GC mode

   bool _gcs_are_young;

   uint _young_list_target_length;

   uint _young_list_fixed_length;

   size_t _prev_eden_capacity; // used for logging

   // The max number of regions we can extend the eden by while the GC

   // locker is active. This should be >= _young_list_target_length;

   uint _young_list_max_length;

   bool                  _last_gc_was_young;

   bool                  _during_marking;

   bool                  _in_marking_window;

   bool                  _in_marking_window_im;

   SurvRateGroup*        _short_lived_surv_rate_group;

   SurvRateGroup*        _survivor_surv_rate_group;

   // add here any more surv rate groups

   double                _gc_overhead_perc;

   double _reserve_factor;

   uint _reserve_regions;

   bool during_marking() {

     return _during_marking;

   }

 private:

   enum PredictionConstants {

     TruncatedSeqLength = 10

   };

   TruncatedSeq* _alloc_rate_ms_seq;

   double        _prev_collection_pause_end_ms;

   TruncatedSeq* _rs_length_diff_seq;

   TruncatedSeq* _cost_per_card_ms_seq;

   TruncatedSeq* _young_cards_per_entry_ratio_seq;

   TruncatedSeq* _mixed_cards_per_entry_ratio_seq;

   TruncatedSeq* _cost_per_entry_ms_seq;

   TruncatedSeq* _mixed_cost_per_entry_ms_seq;

   TruncatedSeq* _cost_per_byte_ms_seq;

   TruncatedSeq* _constant_other_time_ms_seq;

   TruncatedSeq* _young_other_cost_per_region_ms_seq;

   TruncatedSeq* _non_young_other_cost_per_region_ms_seq;

   TruncatedSeq* _pending_cards_seq;

   TruncatedSeq* _rs_lengths_seq;

   TruncatedSeq* _cost_per_byte_ms_during_cm_seq;

   G1YoungGenSizer* _young_gen_sizer;

   uint _eden_cset_region_length;

   uint _survivor_cset_region_length;

   uint _old_cset_region_length;

   void init_cset_region_lengths(uint eden_cset_region_length,

                                 uint survivor_cset_region_length);

   uint eden_cset_region_length()     { return _eden_cset_region_length;     }

   uint survivor_cset_region_length() { return _survivor_cset_region_length; }

   uint old_cset_region_length()      { return _old_cset_region_length;      }

   uint _free_regions_at_end_of_collection;

   size_t _recorded_rs_lengths;

   size_t _max_rs_lengths;

   double _sigma;

   size_t _rs_lengths_prediction;

   double sigma() { return _sigma; }

   // A function that prevents us putting too much stock in small sample

   // sets.  Returns a number between 2.0 and 1.0, depending on the number

   // of samples.  5 or more samples yields one; fewer scales linearly from

   // 2.0 at 1 sample to 1.0 at 5.

   double confidence_factor(int samples) {

     if (samples > 4) return 1.0;

     else return  1.0 + sigma() * ((double)(5 - samples))/2.0;

   }

   double get_new_neg_prediction(TruncatedSeq* seq) {

     return seq->davg() - sigma() * seq->dsd();

   }

 #ifndef PRODUCT

   bool verify_young_ages(HeapRegion* head, SurvRateGroup *surv_rate_group);

 #endif // PRODUCT

   void adjust_concurrent_refinement(double update_rs_time,

                                     double update_rs_processed_buffers,

                                     double goal_ms);

   uintx no_of_gc_threads() { return _no_of_gc_threads; }

   void set_no_of_gc_threads(uintx v) { _no_of_gc_threads = v; }

   double _pause_time_target_ms;

   size_t _pending_cards;

 public:

   // Accessors

   void set_region_eden(HeapRegion* hr, int young_index_in_cset) {

     hr->set_young();

     hr->install_surv_rate_group(_short_lived_surv_rate_group);

     hr->set_young_index_in_cset(young_index_in_cset);

   }

   void set_region_survivor(HeapRegion* hr, int young_index_in_cset) {

     assert(hr->is_young() && hr->is_survivor(), "pre-condition");

     hr->install_surv_rate_group(_survivor_surv_rate_group);

     hr->set_young_index_in_cset(young_index_in_cset);

   }

 #ifndef PRODUCT

   bool verify_young_ages();

 #endif // PRODUCT

   double get_new_prediction(TruncatedSeq* seq) {

     return MAX2(seq->davg() + sigma() * seq->dsd(),

                 seq->davg() * confidence_factor(seq->num()));

   }

   void record_max_rs_lengths(size_t rs_lengths) {

     _max_rs_lengths = rs_lengths;

   }

   size_t predict_rs_length_diff() {

     return (size_t) get_new_prediction(_rs_length_diff_seq);

   }

   double predict_alloc_rate_ms() {

     return get_new_prediction(_alloc_rate_ms_seq);

   }

   double predict_cost_per_card_ms() {

     return get_new_prediction(_cost_per_card_ms_seq);

   }

   double predict_rs_update_time_ms(size_t pending_cards) {

     return (double) pending_cards * predict_cost_per_card_ms();

   }

   double predict_young_cards_per_entry_ratio() {

     return get_new_prediction(_young_cards_per_entry_ratio_seq);

   }

   double predict_mixed_cards_per_entry_ratio() {

     if (_mixed_cards_per_entry_ratio_seq->num() < 2) {

       return predict_young_cards_per_entry_ratio();

     } else {

       return get_new_prediction(_mixed_cards_per_entry_ratio_seq);

     }

   }

   size_t predict_young_card_num(size_t rs_length) {

     return (size_t) ((double) rs_length *

                      predict_young_cards_per_entry_ratio());

   }

   size_t predict_non_young_card_num(size_t rs_length) {

     return (size_t) ((double) rs_length *

                      predict_mixed_cards_per_entry_ratio());

   }

   double predict_rs_scan_time_ms(size_t card_num) {

     if (gcs_are_young()) {

       return (double) card_num * get_new_prediction(_cost_per_entry_ms_seq);

     } else {

       return predict_mixed_rs_scan_time_ms(card_num);

     }

   }

   double predict_mixed_rs_scan_time_ms(size_t card_num) {

     if (_mixed_cost_per_entry_ms_seq->num() < 3) {

       return (double) card_num * get_new_prediction(_cost_per_entry_ms_seq);

     } else {

       return (double) (card_num *

                        get_new_prediction(_mixed_cost_per_entry_ms_seq));

     }

   }

   double predict_object_copy_time_ms_during_cm(size_t bytes_to_copy) {

     if (_cost_per_byte_ms_during_cm_seq->num() < 3) {

       return (1.1 * (double) bytes_to_copy) *

               get_new_prediction(_cost_per_byte_ms_seq);

     } else {

       return (double) bytes_to_copy *

              get_new_prediction(_cost_per_byte_ms_during_cm_seq);

     }

   }

   double predict_object_copy_time_ms(size_t bytes_to_copy) {

     if (_in_marking_window && !_in_marking_window_im) {

       return predict_object_copy_time_ms_during_cm(bytes_to_copy);

     } else {

       return (double) bytes_to_copy *

               get_new_prediction(_cost_per_byte_ms_seq);

     }

   }

   double predict_constant_other_time_ms() {

     return get_new_prediction(_constant_other_time_ms_seq);

   }

   double predict_young_other_time_ms(size_t young_num) {

     return (double) young_num *

            get_new_prediction(_young_other_cost_per_region_ms_seq);

   }

   double predict_non_young_other_time_ms(size_t non_young_num) {

     return (double) non_young_num *

            get_new_prediction(_non_young_other_cost_per_region_ms_seq);

   }

   double predict_base_elapsed_time_ms(size_t pending_cards);

   double predict_base_elapsed_time_ms(size_t pending_cards,

                                       size_t scanned_cards);

   size_t predict_bytes_to_copy(HeapRegion* hr);

   double predict_region_elapsed_time_ms(HeapRegion* hr, bool for_young_gc);

   void set_recorded_rs_lengths(size_t rs_lengths);

   uint cset_region_length()       { return young_cset_region_length() +

                                            old_cset_region_length(); }

   uint young_cset_region_length() { return eden_cset_region_length() +

                                            survivor_cset_region_length(); }

   double predict_survivor_regions_evac_time();

   void cset_regions_freed() {

     bool propagate = _last_gc_was_young && !_in_marking_window;

     _short_lived_surv_rate_group->all_surviving_words_recorded(propagate);

     _survivor_surv_rate_group->all_surviving_words_recorded(propagate);

     // also call it on any more surv rate groups

   }

   G1MMUTracker* mmu_tracker() {

     return _mmu_tracker;

   }

   double max_pause_time_ms() {

     return _mmu_tracker->max_gc_time() * 1000.0;

   }

   double predict_remark_time_ms() {

     return get_new_prediction(_concurrent_mark_remark_times_ms);

   }

   double predict_cleanup_time_ms() {

     return get_new_prediction(_concurrent_mark_cleanup_times_ms);

   }

   // Returns an estimate of the survival rate of the region at yg-age

   // "yg_age".

   double predict_yg_surv_rate(int age, SurvRateGroup* surv_rate_group) {

     TruncatedSeq* seq = surv_rate_group->get_seq(age);

     if (seq->num() == 0)

       gclog_or_tty->print("BARF! age is %d", age);

     guarantee( seq->num() > 0, "invariant" );

     double pred = get_new_prediction(seq);

     if (pred > 1.0)

       pred = 1.0;

     return pred;

   }

   double predict_yg_surv_rate(int age) {

     return predict_yg_surv_rate(age, _short_lived_surv_rate_group);

   }

   double accum_yg_surv_rate_pred(int age) {

     return _short_lived_surv_rate_group->accum_surv_rate_pred(age);

   }

 private:

   // Statistics kept per GC stoppage, pause or full.

   TruncatedSeq* _recent_prev_end_times_for_all_gcs_sec;

   // Add a new GC of the given duration and end time to the record.

   void update_recent_gc_times(double end_time_sec, double elapsed_ms);

   // The head of the list (via "next_in_collection_set()") representing the

   // current collection set. Set from the incrementally built collection

   // set at the start of the pause.

   HeapRegion* _collection_set;

   // The number of bytes in the collection set before the pause. Set from

   // the incrementally built collection set at the start of an evacuation

   // pause, and incremented in finalize_cset() when adding old regions

   // (if any) to the collection set.

   size_t _collection_set_bytes_used_before;

   // The number of bytes copied during the GC.

   size_t _bytes_copied_during_gc;

   // The associated information that is maintained while the incremental

   // collection set is being built with young regions. Used to populate

   // the recorded info for the evacuation pause.

   enum CSetBuildType {

     Active,             // We are actively building the collection set

     Inactive            // We are not actively building the collection set

   };

   CSetBuildType _inc_cset_build_state;

   // The head of the incrementally built collection set.

   HeapRegion* _inc_cset_head;

   // The tail of the incrementally built collection set.

   HeapRegion* _inc_cset_tail;

   // The number of bytes in the incrementally built collection set.

   // Used to set _collection_set_bytes_used_before at the start of

   // an evacuation pause.

   size_t _inc_cset_bytes_used_before;

   // Used to record the highest end of heap region in collection set

   HeapWord* _inc_cset_max_finger;

   // The RSet lengths recorded for regions in the CSet. It is updated

   // by the thread that adds a new region to the CSet. We assume that

   // only one thread can be allocating a new CSet region (currently,

   // it does so after taking the Heap_lock) hence no need to

   // synchronize updates to this field.

   size_t _inc_cset_recorded_rs_lengths;

   // A concurrent refinement thread periodcially samples the young

   // region RSets and needs to update _inc_cset_recorded_rs_lengths as

   // the RSets grow. Instead of having to syncronize updates to that

   // field we accumulate them in this field and add it to

   // _inc_cset_recorded_rs_lengths_diffs at the start of a GC.

   ssize_t _inc_cset_recorded_rs_lengths_diffs;

   // The predicted elapsed time it will take to collect the regions in

   // the CSet. This is updated by the thread that adds a new region to

   // the CSet. See the comment for _inc_cset_recorded_rs_lengths about

   // MT-safety assumptions.

   double _inc_cset_predicted_elapsed_time_ms;

   // See the comment for _inc_cset_recorded_rs_lengths_diffs.

   double _inc_cset_predicted_elapsed_time_ms_diffs;

   // Stash a pointer to the g1 heap.

   G1CollectedHeap* _g1;

   G1GCPhaseTimes* _phase_times;

   // The ratio of gc time to elapsed time, computed over recent pauses.

   double _recent_avg_pause_time_ratio;

   double recent_avg_pause_time_ratio() {

     return _recent_avg_pause_time_ratio;

   }

   // At the end of a pause we check the heap occupancy and we decide

   // whether we will start a marking cycle during the next pause. If

   // we decide that we want to do that, we will set this parameter to

   // true. So, this parameter will stay true between the end of a

   // pause and the beginning of a subsequent pause (not necessarily

   // the next one, see the comments on the next field) when we decide

   // that we will indeed start a marking cycle and do the initial-mark

   // work.

   volatile bool _initiate_conc_mark_if_possible;

   // If initiate_conc_mark_if_possible() is set at the beginning of a

   // pause, it is a suggestion that the pause should start a marking

   // cycle by doing the initial-mark work. However, it is possible

   // that the concurrent marking thread is still finishing up the

   // previous marking cycle (e.g., clearing the next marking

   // bitmap). If that is the case we cannot start a new cycle and

   // we'll have to wait for the concurrent marking thread to finish

   // what it is doing. In this case we will postpone the marking cycle

   // initiation decision for the next pause. When we eventually decide

   // to start a cycle, we will set _during_initial_mark_pause which

   // will stay true until the end of the initial-mark pause and it's

   // the condition that indicates that a pause is doing the

   // initial-mark work.

   volatile bool _during_initial_mark_pause;

   bool _last_young_gc;

   // This set of variables tracks the collector efficiency, in order to

   // determine whether we should initiate a new marking.

   double _cur_mark_stop_world_time_ms;

   double _mark_remark_start_sec;

   double _mark_cleanup_start_sec;

   // Update the young list target length either by setting it to the

   // desired fixed value or by calculating it using G1's pause

   // prediction model. If no rs_lengths parameter is passed, predict

   // the RS lengths using the prediction model, otherwise use the

   // given rs_lengths as the prediction.

   void update_young_list_target_length(size_t rs_lengths = (size_t) -1);

   // Calculate and return the minimum desired young list target

   // length. This is the minimum desired young list length according

   // to the user's inputs.

   uint calculate_young_list_desired_min_length(uint base_min_length);

   // Calculate and return the maximum desired young list target

   // length. This is the maximum desired young list length according

   // to the user's inputs.

   uint calculate_young_list_desired_max_length();

   // Calculate and return the maximum young list target length that

   // can fit into the pause time goal. The parameters are: rs_lengths

   // represent the prediction of how large the young RSet lengths will

   // be, base_min_length is the alreay existing number of regions in

   // the young list, min_length and max_length are the desired min and

   // max young list length according to the user's inputs.

   uint calculate_young_list_target_length(size_t rs_lengths,

                                           uint base_min_length,

                                           uint desired_min_length,

                                           uint desired_max_length);

   // Check whether a given young length (young_length) fits into the

   // given target pause time and whether the prediction for the amount

   // of objects to be copied for the given length will fit into the

   // given free space (expressed by base_free_regions).  It is used by

   // calculate_young_list_target_length().

   bool predict_will_fit(uint young_length, double base_time_ms,

                         uint base_free_regions, double target_pause_time_ms);

 public:

   G1CollectorPolicy();

   virtual G1CollectorPolicy* as_g1_policy() { return this; }

   virtual CollectorPolicy::Name kind() {

     return CollectorPolicy::G1CollectorPolicyKind;

   }

   G1GCPhaseTimes* phase_times() const { return _phase_times; }

   // Check the current value of the young list RSet lengths and

   // compare it against the last prediction. If the current value is

   // higher, recalculate the young list target length prediction.

   void revise_young_list_target_length_if_necessary();

   // This should be called after the heap is resized.

   void record_new_heap_size(uint new_number_of_regions);

   void init();

   // Create jstat counters for the policy.

   virtual void initialize_gc_policy_counters();

   virtual HeapWord* mem_allocate_work(size_t size,

                                       bool is_tlab,

                                       bool* gc_overhead_limit_was_exceeded);

   // This method controls how a collector handles one or more

   // of its generations being fully allocated.

   virtual HeapWord* satisfy_failed_allocation(size_t size,

                                               bool is_tlab);

   BarrierSet::Name barrier_set_name() { return BarrierSet::G1SATBCTLogging; }

   GenRemSet::Name  rem_set_name()     { return GenRemSet::CardTable; }

   bool need_to_start_conc_mark(const char* source, size_t alloc_word_size = 0);

   // Update the heuristic info to record a collection pause of the given

   // start time, where the given number of bytes were used at the start.

   // This may involve changing the desired size of a collection set.

   void record_stop_world_start();

   void record_collection_pause_start(double start_time_sec, size_t start_used);

   // Must currently be called while the world is stopped.

   void record_concurrent_mark_init_end(double

                                            mark_init_elapsed_time_ms);

   void record_concurrent_mark_remark_start();

   void record_concurrent_mark_remark_end();

   void record_concurrent_mark_cleanup_start();

   void record_concurrent_mark_cleanup_end(int no_of_gc_threads);

   void record_concurrent_mark_cleanup_completed();

   void record_concurrent_pause();

   void record_collection_pause_end(double pause_time);

   void print_heap_transition();

   void print_detailed_heap_transition();

   // Record the fact that a full collection occurred.

   void record_full_collection_start();

   void record_full_collection_end();

   // Record how much space we copied during a GC. This is typically

   // called when a GC alloc region is being retired.

   void record_bytes_copied_during_gc(size_t bytes) {

     _bytes_copied_during_gc += bytes;

   }

   // The amount of space we copied during a GC.

   size_t bytes_copied_during_gc() {

     return _bytes_copied_during_gc;

   }

   // Determine whether there are candidate regions so that the

   // next GC should be mixed. The two action strings are used

   // in the ergo output when the method returns true or false.

   bool next_gc_should_be_mixed(const char* true_action_str,

                                const char* false_action_str);

   // Choose a new collection set.  Marks the chosen regions as being

   // "in_collection_set", and links them together.  The head and number of

   // the collection set are available via access methods.

   void finalize_cset(double target_pause_time_ms);

   // The head of the list (via "next_in_collection_set()") representing the

   // current collection set.

   HeapRegion* collection_set() { return _collection_set; }

   void clear_collection_set() { _collection_set = NULL; }

   // Add old region "hr" to the CSet.

   void add_old_region_to_cset(HeapRegion* hr);

   // Incremental CSet Support

   // The head of the incrementally built collection set.

   HeapRegion* inc_cset_head() { return _inc_cset_head; }

   // The tail of the incrementally built collection set.

   HeapRegion* inc_set_tail() { return _inc_cset_tail; }

   // Initialize incremental collection set info.

   void start_incremental_cset_building();

   // Perform any final calculations on the incremental CSet fields

   // before we can use them.

   void finalize_incremental_cset_building();

   void clear_incremental_cset() {

     _inc_cset_head = NULL;

     _inc_cset_tail = NULL;

   }

   // Stop adding regions to the incremental collection set

   void stop_incremental_cset_building() { _inc_cset_build_state = Inactive; }

   // Add information about hr to the aggregated information for the

   // incrementally built collection set.

   void add_to_incremental_cset_info(HeapRegion* hr, size_t rs_length);

   // Update information about hr in the aggregated information for

   // the incrementally built collection set.

   void update_incremental_cset_info(HeapRegion* hr, size_t new_rs_length);

 private:

   // Update the incremental cset information when adding a region

   // (should not be called directly).

   void add_region_to_incremental_cset_common(HeapRegion* hr);

 public:

   // Add hr to the LHS of the incremental collection set.

   void add_region_to_incremental_cset_lhs(HeapRegion* hr);

   // Add hr to the RHS of the incremental collection set.

   void add_region_to_incremental_cset_rhs(HeapRegion* hr);

 #ifndef PRODUCT

   void print_collection_set(HeapRegion* list_head, outputStream* st);

 #endif // !PRODUCT

   bool initiate_conc_mark_if_possible()       { return _initiate_conc_mark_if_possible;  }

   void set_initiate_conc_mark_if_possible()   { _initiate_conc_mark_if_possible = true;  }

   void clear_initiate_conc_mark_if_possible() { _initiate_conc_mark_if_possible = false; }

   bool during_initial_mark_pause()      { return _during_initial_mark_pause;  }

   void set_during_initial_mark_pause()  { _during_initial_mark_pause = true;  }

   void clear_during_initial_mark_pause(){ _during_initial_mark_pause = false; }

   // This sets the initiate_conc_mark_if_possible() flag to start a

   // new cycle, as long as we are not already in one. It's best if it

   // is called during a safepoint when the test whether a cycle is in

   // progress or not is stable.

   bool force_initial_mark_if_outside_cycle(GCCause::Cause gc_cause);

   // This is called at the very beginning of an evacuation pause (it

   // has to be the first thing that the pause does). If

   // initiate_conc_mark_if_possible() is true, and the concurrent

   // marking thread has completed its work during the previous cycle,

   // it will set during_initial_mark_pause() to so that the pause does

   // the initial-mark work and start a marking cycle.

   void decide_on_conc_mark_initiation();

   // If an expansion would be appropriate, because recent GC overhead had

   // exceeded the desired limit, return an amount to expand by.

   size_t expansion_amount();

   // Print tracing information.

   void print_tracing_info() const;

   // Print stats on young survival ratio

   void print_yg_surv_rate_info() const;

   void finished_recalculating_age_indexes(bool is_survivors) {

     if (is_survivors) {

       _survivor_surv_rate_group->finished_recalculating_age_indexes();

     } else {

       _short_lived_surv_rate_group->finished_recalculating_age_indexes();

     }

     // do that for any other surv rate groups

   }

   bool is_young_list_full() {

     uint young_list_length = _g1->young_list()->length();

     uint young_list_target_length = _young_list_target_length;

     return young_list_length >= young_list_target_length;

   }

   bool can_expand_young_list() {

     uint young_list_length = _g1->young_list()->length();

     uint young_list_max_length = _young_list_max_length;

     return young_list_length < young_list_max_length;

   }

   uint young_list_max_length() {

     return _young_list_max_length;

   }

   bool gcs_are_young() {

     return _gcs_are_young;

   }

   void set_gcs_are_young(bool gcs_are_young) {

     _gcs_are_young = gcs_are_young;

   }

   bool adaptive_young_list_length() {

     return _young_gen_sizer->adaptive_young_list_length();

   }

 private:

   //

   // Survivor regions policy.

   //

   // Current tenuring threshold, set to 0 if the collector reaches the

   // maximum amount of suvivors regions.

   int _tenuring_threshold;

   // The limit on the number of regions allocated for survivors.

   uint _max_survivor_regions;

   // For reporting purposes.

   size_t _eden_bytes_before_gc;

   size_t _survivor_bytes_before_gc;

   size_t _capacity_before_gc;

   // The amount of survor regions after a collection.

   uint _recorded_survivor_regions;

   // List of survivor regions.

   HeapRegion* _recorded_survivor_head;

   HeapRegion* _recorded_survivor_tail;

   ageTable _survivors_age_table;

 public:

   inline GCAllocPurpose

     evacuation_destination(HeapRegion* src_region, int age, size_t word_sz) {

       if (age < _tenuring_threshold && src_region->is_young()) {

         return GCAllocForSurvived;

       } else {

         return GCAllocForTenured;

       }

   }

   inline bool track_object_age(GCAllocPurpose purpose) {

     return purpose == GCAllocForSurvived;

   }

   static const uint REGIONS_UNLIMITED = (uint) -1;

   uint max_regions(int purpose);

   // The limit on regions for a particular purpose is reached.

   void note_alloc_region_limit_reached(int purpose) {

     if (purpose == GCAllocForSurvived) {

       _tenuring_threshold = 0;

     }

   }

   void note_start_adding_survivor_regions() {

     _survivor_surv_rate_group->start_adding_regions();

   }

   void note_stop_adding_survivor_regions() {

     _survivor_surv_rate_group->stop_adding_regions();

   }

   void record_survivor_regions(uint regions,

                                HeapRegion* head,

                                HeapRegion* tail) {

     _recorded_survivor_regions = regions;

     _recorded_survivor_head    = head;

     _recorded_survivor_tail    = tail;

   }

   uint recorded_survivor_regions() {

     return _recorded_survivor_regions;

   }

   void record_thread_age_table(ageTable* age_table) {

     _survivors_age_table.merge_par(age_table);

   }

   void update_max_gc_locker_expansion();

   // Calculates survivor space parameters.

   void update_survivors_policy();

 };

 // This should move to some place more general...

 // If we have "n" measurements, and we've kept track of their "sum" and the

 // "sum_of_squares" of the measurements, this returns the variance of the

 // sequence.

 inline double variance(int n, double sum_of_squares, double sum) {

   double n_d = (double)n;

   double avg = sum/n_d;

   return (sum_of_squares - 2.0 * avg * sum + n_d * avg * avg) / n_d;

 }

 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1COLLECTORPOLICY_HPP