src/hotspot/share/gc/shenandoah/shenandoahGeneration.hpp

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#ifndef SHARE_VM_GC_SHENANDOAH_SHENANDOAHGENERATION_HPP
#define SHARE_VM_GC_SHENANDOAH_SHENANDOAHGENERATION_HPP

#include "gc/shenandoah/heuristics/shenandoahSpaceInfo.hpp"
#include "gc/shenandoah/shenandoahAffiliation.hpp"
#include "gc/shenandoah/shenandoahGenerationType.hpp"
#include "gc/shenandoah/shenandoahLock.hpp"
#include "gc/shenandoah/shenandoahMarkingContext.hpp"
#include "memory/allocation.hpp"

class ShenandoahCollectionSet;
class ShenandoahHeap;
class ShenandoahHeapRegion;
class ShenandoahHeapRegionClosure;
class ShenandoahHeuristics;
class ShenandoahMode;
class ShenandoahReferenceProcessor;


class ShenandoahGeneration : public CHeapObj<mtGC>, public ShenandoahSpaceInfo {
  friend class VMStructs;
private:
  ShenandoahGenerationType const _type;

  // Marking task queues and completeness
  ShenandoahObjToScanQueueSet* _task_queues;
  ShenandoahSharedFlag _is_marking_complete;

  ShenandoahReferenceProcessor* const _ref_processor;

  volatile size_t _affiliated_region_count;

  // How much free memory is left in the last region of humongous objects.
  // This is _not_ included in used, but it _is_ deducted from available,
  // which gives the heuristics a more accurate view of how much memory remains
  // for allocation. This figure is also included the heap status logging.
  // The units are bytes. The value is only changed on a safepoint or under the
  // heap lock.
  size_t _humongous_waste;

  // Bytes reserved within this generation to hold evacuated objects from the collection set
  size_t _evacuation_reserve;

protected:
  // Usage

  volatile size_t _used;
  volatile size_t _bytes_allocated_since_gc_start;
  size_t _max_capacity;
  size_t _soft_max_capacity;

  ShenandoahHeuristics* _heuristics;

private:
  // Compute evacuation budgets prior to choosing collection set.
  void compute_evacuation_budgets(ShenandoahHeap* heap);

  // Adjust evacuation budgets after choosing collection set.
  void adjust_evacuation_budgets(ShenandoahHeap* heap,
                                 ShenandoahCollectionSet* collection_set);

  // Preselect for possible inclusion into the collection set exactly the most
  // garbage-dense regions, including those that satisfy criteria 1 & 2 below,
  // and whose live bytes will fit within old_available budget:
  // Criterion 1. region age >= tenuring threshold
  // Criterion 2. region garbage percentage > ShenandoahOldGarbageThreshold
  //
  // Identifies regions eligible for promotion in place,
  // being those of at least tenuring_threshold age that have lower garbage
  // density.
  //
  // Updates promotion_potential and pad_for_promote_in_place fields
  // of the heap. Returns bytes of live object memory in the preselected
  // regions, which are marked in the preselected_regions() indicator
  // array of the heap's collection set, which should be initialized
  // to false.
  size_t select_aged_regions(size_t old_available);

  size_t available(size_t capacity) const;

 public:
  ShenandoahGeneration(ShenandoahGenerationType type,
                       uint max_workers,
                       size_t max_capacity,
                       size_t soft_max_capacity);
  ~ShenandoahGeneration();

  bool is_young() const  { return _type == YOUNG; }
  bool is_old() const    { return _type == OLD; }
  bool is_global() const { return _type == GLOBAL || _type == NON_GEN; }

  // see description in field declaration
  void set_evacuation_reserve(size_t new_val);
  size_t get_evacuation_reserve() const;
  void augment_evacuation_reserve(size_t increment);

  inline ShenandoahGenerationType type() const { return _type; }

  virtual ShenandoahHeuristics* heuristics() const { return _heuristics; }

  ShenandoahReferenceProcessor* ref_processor() { return _ref_processor; }

  virtual ShenandoahHeuristics* initialize_heuristics(ShenandoahMode* gc_mode);

  size_t soft_max_capacity() const override { return _soft_max_capacity; }
  size_t max_capacity() const override      { return _max_capacity; }
  virtual size_t used_regions() const;
  virtual size_t used_regions_size() const;
  virtual size_t free_unaffiliated_regions() const;
  size_t used() const override { return Atomic::load(&_used); }
  size_t available() const override;
  size_t available_with_reserve() const;
  size_t used_including_humongous_waste() const {
    return used() + get_humongous_waste();
  }

  // Returns the memory available based on the _soft_ max heap capacity (soft_max_heap - used).
  // The soft max heap size may be adjusted lower than the max heap size to cause the trigger
  // to believe it has less memory available than is _really_ available. Lowering the soft
  // max heap size will cause the adaptive heuristic to run more frequent cycles.
  size_t soft_available() const override;

  size_t bytes_allocated_since_gc_start() const override;
  void reset_bytes_allocated_since_gc_start();
  void increase_allocated(size_t bytes);

  // These methods change the capacity of the generation by adding or subtracting the given number of bytes from the current
  // capacity, returning the capacity of the generation following the change.
  size_t increase_capacity(size_t increment);
  size_t decrease_capacity(size_t decrement);

  // Set the capacity of the generation, returning the value set
  size_t set_capacity(size_t byte_size);

  void log_status(const char* msg) const;

  // Used directly by FullGC
  template <bool FOR_CURRENT_CYCLE, bool FULL_GC = false>
  void reset_mark_bitmap();

  // Used by concurrent and degenerated GC to reset remembered set.
  void swap_card_tables();

  // Update the read cards with the state of the write table (write table is not cleared).
  void merge_write_table();

  // Called before init mark, expected to prepare regions for marking.
  virtual void prepare_gc();

  // Called during final mark, chooses collection set, rebuilds free set.
  virtual void prepare_regions_and_collection_set(bool concurrent);

  // Cancel marking (used by Full collect and when cancelling cycle).
  virtual void cancel_marking();

  virtual bool contains(ShenandoahAffiliation affiliation) const = 0;

  // Return true if this region is affiliated with this generation.
  virtual bool contains(ShenandoahHeapRegion* region) const = 0;

  // Return true if this object is affiliated with this generation.
  virtual bool contains(oop obj) const = 0;

  // Apply closure to all regions affiliated with this generation.
  virtual void parallel_heap_region_iterate(ShenandoahHeapRegionClosure* cl) = 0;

  // Apply closure to all regions affiliated with this generation (include free regions);
  virtual void parallel_heap_region_iterate_free(ShenandoahHeapRegionClosure* cl);

  // Apply closure to all regions affiliated with this generation (single threaded).
  virtual void heap_region_iterate(ShenandoahHeapRegionClosure* cl) = 0;

  // This is public to support cancellation of marking when a Full cycle is started.
  virtual void set_concurrent_mark_in_progress(bool in_progress) = 0;

  // Check the bitmap only for regions belong to this generation.
  bool is_bitmap_clear();

  // We need to track the status of marking for different generations.
  bool is_mark_complete() { return _is_marking_complete.is_set(); }
  virtual void set_mark_complete();
  virtual void set_mark_incomplete();

  ShenandoahMarkingContext* complete_marking_context();

  // Task queues
  ShenandoahObjToScanQueueSet* task_queues() const { return _task_queues; }
  virtual void reserve_task_queues(uint workers);
  virtual ShenandoahObjToScanQueueSet* old_gen_task_queues() const;

  // Scan remembered set at start of concurrent young-gen marking.
  void scan_remembered_set(bool is_concurrent);

  // Return the updated value of affiliated_region_count
  size_t increment_affiliated_region_count();

  // Return the updated value of affiliated_region_count
  size_t decrement_affiliated_region_count();
  // Same as decrement_affiliated_region_count, but w/o the need to hold heap lock before being called.
  size_t decrement_affiliated_region_count_without_lock();

  // Return the updated value of affiliated_region_count
  size_t increase_affiliated_region_count(size_t delta);

  // Return the updated value of affiliated_region_count
  size_t decrease_affiliated_region_count(size_t delta);

  void establish_usage(size_t num_regions, size_t num_bytes, size_t humongous_waste);

  void increase_used(size_t bytes);
  void decrease_used(size_t bytes);

  void increase_humongous_waste(size_t bytes);
  void decrease_humongous_waste(size_t bytes);
  size_t get_humongous_waste() const { return _humongous_waste; }

  virtual bool is_concurrent_mark_in_progress() = 0;
  void confirm_heuristics_mode();

  virtual void record_success_concurrent(bool abbreviated);
};

#endif // SHARE_VM_GC_SHENANDOAH_SHENANDOAHGENERATION_HPP