src/hotspot/share/gc/serial/defNewGeneration.hpp

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#ifndef SHARE_GC_SERIAL_DEFNEWGENERATION_HPP
#define SHARE_GC_SERIAL_DEFNEWGENERATION_HPP

#include "gc/serial/cSpaceCounters.hpp"
#include "gc/serial/generation.hpp"
#include "gc/serial/tenuredGeneration.hpp"
#include "gc/shared/ageTable.hpp"
#include "gc/shared/copyFailedInfo.hpp"
#include "gc/shared/gc_globals.hpp"
#include "gc/shared/generationCounters.hpp"
#include "gc/shared/stringdedup/stringDedup.hpp"
#include "gc/shared/tlab_globals.hpp"
#include "utilities/align.hpp"
#include "utilities/stack.hpp"

class ContiguousSpace;
class CSpaceCounters;
class OldGenScanClosure;
class YoungGenScanClosure;
class DefNewTracer;
class SerialHeap;
class STWGCTimer;

// DefNewGeneration is a young generation containing eden, from- and
// to-space.

class DefNewGeneration: public Generation {
  friend class VMStructs;

  TenuredGeneration* _old_gen;

  uint        _tenuring_threshold;   // Tenuring threshold for next collection.
  AgeTable    _age_table;
  // Size of object to pretenure in words; command line provides bytes
  size_t      _pretenure_size_threshold_words;

  // ("Weak") Reference processing support
  SpanSubjectToDiscoveryClosure _span_based_discoverer;
  ReferenceProcessor* _ref_processor;

  AgeTable*   age_table() { return &_age_table; }

  // Initialize state to optimistically assume no promotion failure will
  // happen.
  void   init_assuming_no_promotion_failure();
  // True iff a promotion has failed in the current collection.
  bool   _promotion_failed;
  bool   promotion_failed() { return _promotion_failed; }
  PromotionFailedInfo _promotion_failed_info;

  // Handling promotion failure.  A young generation collection
  // can fail if a live object cannot be copied out of its
  // location in eden or from-space during the collection.  If
  // a collection fails, the young generation is left in a
  // consistent state such that it can be collected by a
  // full collection.
  //   Before the collection
  //     Objects are in eden or from-space
  //     All roots into the young generation point into eden or from-space.
  //
  //   After a failed collection
  //     Objects may be in eden, from-space, or to-space
  //     An object A in eden or from-space may have a copy B
  //       in to-space.  If B exists, all roots that once pointed
  //       to A must now point to B.
  //     All objects in the young generation are unmarked.
  //     Eden, from-space, and to-space will all be collected by
  //       the full collection.
  void handle_promotion_failure(oop);

  // In the absence of promotion failure, we wouldn't look at "from-space"
  // objects after a young-gen collection.  When promotion fails, however,
  // the subsequent full collection will look at from-space objects:
  // therefore we must remove their forwarding pointers.
  void remove_forwarding_pointers();

  Stack<oop, mtGC> _promo_failure_scan_stack;
  void drain_promo_failure_scan_stack(void);
  bool _promo_failure_drain_in_progress;

  // Performance Counters
  GenerationCounters*  _gen_counters;
  CSpaceCounters*      _eden_counters;
  CSpaceCounters*      _from_counters;
  CSpaceCounters*      _to_counters;

  // sizing information
  size_t               _max_eden_size;
  size_t               _max_survivor_size;

  // Tenuring
  void adjust_desired_tenuring_threshold();

  // Spaces
  ContiguousSpace* _eden_space;
  ContiguousSpace* _from_space;
  ContiguousSpace* _to_space;

  STWGCTimer* _gc_timer;

  DefNewTracer* _gc_tracer;

  StringDedup::Requests _string_dedup_requests;

  // Return the size of a survivor space if this generation were of size
  // gen_size.
  size_t compute_survivor_size(size_t gen_size, size_t alignment) const {
    size_t n = gen_size / (SurvivorRatio + 2);
    return n > alignment ? align_down(n, alignment) : alignment;
  }

 public:
  DefNewGeneration(ReservedSpace rs,
                   size_t initial_byte_size,
                   size_t min_byte_size,
                   size_t max_byte_size,
                   const char* policy="Serial young collection pauses");

  // allocate and initialize ("weak") refs processing support
  void ref_processor_init();
  ReferenceProcessor* ref_processor() { return _ref_processor; }

  // Accessing spaces
  ContiguousSpace* eden() const           { return _eden_space; }
  ContiguousSpace* from() const           { return _from_space; }
  ContiguousSpace* to()   const           { return _to_space;   }

  // Space enquiries
  size_t capacity() const;
  size_t used() const;
  size_t free() const;
  size_t max_capacity() const;
  size_t capacity_before_gc() const;

  // Returns "TRUE" iff "p" points into the used areas in each space of young-gen.
  bool is_in(const void* p) const;

  // Return an estimate of the maximum allocation that could be performed
  // in the generation without triggering any collection or expansion
  // activity.  It is "unsafe" because no locks are taken; the result
  // should be treated as an approximation, not a guarantee, for use in
  // heuristic resizing decisions.
  size_t unsafe_max_alloc_nogc() const;

  size_t max_eden_size() const              { return _max_eden_size; }
  size_t max_survivor_size() const          { return _max_survivor_size; }

  // Thread-local allocation buffers
  size_t tlab_capacity() const;
  size_t tlab_used() const;
  size_t unsafe_max_tlab_alloc() const;

  // Grow the generation by the specified number of bytes.
  // The size of bytes is assumed to be properly aligned.
  // Return true if the expansion was successful.
  bool expand(size_t bytes);


  // Iteration
  void object_iterate(ObjectClosure* blk);

  HeapWord* block_start(const void* p) const;

  // Allocation support
  bool should_allocate(size_t word_size, bool is_tlab) {
    assert(UseTLAB || !is_tlab, "Should not allocate tlab");
    assert(word_size != 0, "precondition");

    size_t overflow_limit    = (size_t)1 << (BitsPerSize_t - LogHeapWordSize);

    const bool overflows     = word_size >= overflow_limit;
    const bool check_too_big = _pretenure_size_threshold_words > 0;
    const bool not_too_big   = word_size < _pretenure_size_threshold_words;
    const bool size_ok       = is_tlab || !check_too_big || not_too_big;

    bool result = !overflows &&
                  size_ok;

    return result;
  }

  // Allocate requested size or return null; single-threaded and lock-free versions.
  HeapWord* allocate(size_t word_size);
  HeapWord* par_allocate(size_t word_size);

  void gc_epilogue(bool full);

  // For Old collection (part of running Full GC), the DefNewGeneration can
  // contribute the free part of "to-space" as the scratch space.
  void contribute_scratch(void*& scratch, size_t& num_words);

  // Reset for contribution of "to-space".
  void reset_scratch();

  // GC support
  void compute_new_size();

  bool collect(bool clear_all_soft_refs);

  oop copy_to_survivor_space(oop old);
  uint tenuring_threshold() { return _tenuring_threshold; }

  // Performance Counter support
  void update_counters();

  // Printing
  const char* name() const { return "DefNew"; }

  void print_on(outputStream* st) const;

  void verify();

  bool promo_failure_scan_is_complete() const {
    return _promo_failure_scan_stack.is_empty();
  }

  DefNewTracer* gc_tracer() const { return _gc_tracer; }

 protected:
  // If clear_space is true, clear the survivor spaces.  Eden is
  // cleared if the minimum size of eden is 0.  If mangle_space
  // is true, also mangle the space in debug mode.
  void compute_space_boundaries(uintx minimum_eden_size,
                                bool clear_space,
                                bool mangle_space);

  // Return adjusted new size for NewSizeThreadIncrease.
  // If any overflow happens, revert to previous new size.
  size_t adjust_for_thread_increase(size_t new_size_candidate,
                                    size_t new_size_before,
                                    size_t alignment,
                                    size_t thread_increase_size) const;

  size_t calculate_thread_increase_size(int threads_count) const;


  // Scavenge support
  void swap_spaces();
};

#endif // SHARE_GC_SERIAL_DEFNEWGENERATION_HPP