jdk/src/hotspot/share/gc/shared/cardTableModRefBS.hpp

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#ifndef SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP
#define SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP

#include "gc/shared/modRefBarrierSet.hpp"
#include "utilities/align.hpp"

// This kind of "BarrierSet" allows a "CollectedHeap" to detect and
// enumerate ref fields that have been modified (since the last
// enumeration.)

// As it currently stands, this barrier is *imprecise*: when a ref field in
// an object "o" is modified, the card table entry for the card containing
// the head of "o" is dirtied, not necessarily the card containing the
// modified field itself.  For object arrays, however, the barrier *is*
// precise; only the card containing the modified element is dirtied.
// Closures used to scan dirty cards should take these
// considerations into account.

class CardTableModRefBS: public ModRefBarrierSet {
  // Some classes get to look at some private stuff.
  friend class VMStructs;
 protected:

  enum CardValues {
    clean_card                  = -1,
    // The mask contains zeros in places for all other values.
    clean_card_mask             = clean_card - 31,

    dirty_card                  =  0,
    precleaned_card             =  1,
    claimed_card                =  2,
    deferred_card               =  4,
    last_card                   =  8,
    CT_MR_BS_last_reserved      = 16
  };

  // Used in support of ReduceInitialCardMarks; only consulted if COMPILER2
  // or INCLUDE_JVMCI is being used
  bool _defer_initial_card_mark;

  // a word's worth (row) of clean card values
  static const intptr_t clean_card_row = (intptr_t)(-1);

  // The declaration order of these const fields is important; see the
  // constructor before changing.
  const MemRegion _whole_heap;       // the region covered by the card table
  size_t          _guard_index;      // index of very last element in the card
                                     // table; it is set to a guard value
                                     // (last_card) and should never be modified
  size_t          _last_valid_index; // index of the last valid element
  const size_t    _page_size;        // page size used when mapping _byte_map
  size_t          _byte_map_size;    // in bytes
  jbyte*          _byte_map;         // the card marking array

  // Some barrier sets create tables whose elements correspond to parts of
  // the heap; the CardTableModRefBS is an example.  Such barrier sets will
  // normally reserve space for such tables, and commit parts of the table
  // "covering" parts of the heap that are committed. At most one covered
  // region per generation is needed.
  static const int _max_covered_regions = 2;

  int _cur_covered_regions;

  // The covered regions should be in address order.
  MemRegion* _covered;
  // The committed regions correspond one-to-one to the covered regions.
  // They represent the card-table memory that has been committed to service
  // the corresponding covered region.  It may be that committed region for
  // one covered region corresponds to a larger region because of page-size
  // roundings.  Thus, a committed region for one covered region may
  // actually extend onto the card-table space for the next covered region.
  MemRegion* _committed;

  // The last card is a guard card, and we commit the page for it so
  // we can use the card for verification purposes. We make sure we never
  // uncommit the MemRegion for that page.
  MemRegion _guard_region;

  inline size_t compute_byte_map_size();

  // Finds and return the index of the region, if any, to which the given
  // region would be contiguous.  If none exists, assign a new region and
  // returns its index.  Requires that no more than the maximum number of
  // covered regions defined in the constructor are ever in use.
  int find_covering_region_by_base(HeapWord* base);

  // Same as above, but finds the region containing the given address
  // instead of starting at a given base address.
  int find_covering_region_containing(HeapWord* addr);

  // Resize one of the regions covered by the remembered set.
  virtual void resize_covered_region(MemRegion new_region);

  // Returns the leftmost end of a committed region corresponding to a
  // covered region before covered region "ind", or else "NULL" if "ind" is
  // the first covered region.
  HeapWord* largest_prev_committed_end(int ind) const;

  // Returns the part of the region mr that doesn't intersect with
  // any committed region other than self.  Used to prevent uncommitting
  // regions that are also committed by other regions.  Also protects
  // against uncommitting the guard region.
  MemRegion committed_unique_to_self(int self, MemRegion mr) const;

  // Mapping from address to card marking array entry
  jbyte* byte_for(const void* p) const {
    assert(_whole_heap.contains(p),
           "Attempt to access p = " PTR_FORMAT " out of bounds of "
           " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
           p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
    jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
    assert(result >= _byte_map && result < _byte_map + _byte_map_size,
           "out of bounds accessor for card marking array");
    return result;
  }

  // The card table byte one after the card marking array
  // entry for argument address. Typically used for higher bounds
  // for loops iterating through the card table.
  jbyte* byte_after(const void* p) const {
    return byte_for(p) + 1;
  }

  // Dirty the bytes corresponding to "mr" (not all of which must be
  // covered.)
  void dirty_MemRegion(MemRegion mr);

  // Clear (to clean_card) the bytes entirely contained within "mr" (not
  // all of which must be covered.)
  void clear_MemRegion(MemRegion mr);

 public:
  // Constants
  enum SomePublicConstants {
    card_shift                  = 9,
    card_size                   = 1 << card_shift,
    card_size_in_words          = card_size / sizeof(HeapWord)
  };

  static int clean_card_val()      { return clean_card; }
  static int clean_card_mask_val() { return clean_card_mask; }
  static int dirty_card_val()      { return dirty_card; }
  static int claimed_card_val()    { return claimed_card; }
  static int precleaned_card_val() { return precleaned_card; }
  static int deferred_card_val()   { return deferred_card; }

  virtual void initialize();

  // *** Barrier set functions.

  // Initialization utilities; covered_words is the size of the covered region
  // in, um, words.
  inline size_t cards_required(size_t covered_words) {
    // Add one for a guard card, used to detect errors.
    const size_t words = align_up(covered_words, card_size_in_words);
    return words / card_size_in_words + 1;
  }

 protected:
  CardTableModRefBS(MemRegion whole_heap, const BarrierSet::FakeRtti& fake_rtti);
  ~CardTableModRefBS();

 public:
  void write_region(MemRegion mr) {
    dirty_MemRegion(mr);
  }

 protected:
  void write_ref_array_work(MemRegion mr) {
    dirty_MemRegion(mr);
  }

 public:
  bool is_aligned(HeapWord* addr) {
    return is_card_aligned(addr);
  }

  // *** Card-table-barrier-specific things.

  // Record a reference update. Note that these versions are precise!
  // The scanning code has to handle the fact that the write barrier may be
  // either precise or imprecise. We make non-virtual inline variants of
  // these functions here for performance.
  template <DecoratorSet decorators, typename T>
  void write_ref_field_post(T* field, oop newVal);

  // These are used by G1, when it uses the card table as a temporary data
  // structure for card claiming.
  bool is_card_dirty(size_t card_index) {
    return _byte_map[card_index] == dirty_card_val();
  }

  void mark_card_dirty(size_t card_index) {
    _byte_map[card_index] = dirty_card_val();
  }

  bool is_card_clean(size_t card_index) {
    return _byte_map[card_index] == clean_card_val();
  }

  // Card marking array base (adjusted for heap low boundary)
  // This would be the 0th element of _byte_map, if the heap started at 0x0.
  // But since the heap starts at some higher address, this points to somewhere
  // before the beginning of the actual _byte_map.
  jbyte* byte_map_base;

  // Return true if "p" is at the start of a card.
  bool is_card_aligned(HeapWord* p) {
    jbyte* pcard = byte_for(p);
    return (addr_for(pcard) == p);
  }

  HeapWord* align_to_card_boundary(HeapWord* p) {
    jbyte* pcard = byte_for(p + card_size_in_words - 1);
    return addr_for(pcard);
  }

  // The kinds of precision a CardTableModRefBS may offer.
  enum PrecisionStyle {
    Precise,
    ObjHeadPreciseArray
  };

  // Tells what style of precision this card table offers.
  PrecisionStyle precision() {
    return ObjHeadPreciseArray; // Only one supported for now.
  }

  // ModRefBS functions.
  virtual void invalidate(MemRegion mr);
  void clear(MemRegion mr);
  void dirty(MemRegion mr);

  // *** Card-table-RemSet-specific things.

  static uintx ct_max_alignment_constraint();

  // Apply closure "cl" to the dirty cards containing some part of
  // MemRegion "mr".
  void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);

  // Return the MemRegion corresponding to the first maximal run
  // of dirty cards lying completely within MemRegion mr.
  // If reset is "true", then sets those card table entries to the given
  // value.
  MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
                                         int reset_val);

  // Provide read-only access to the card table array.
  const jbyte* byte_for_const(const void* p) const {
    return byte_for(p);
  }
  const jbyte* byte_after_const(const void* p) const {
    return byte_after(p);
  }

  // Mapping from card marking array entry to address of first word
  HeapWord* addr_for(const jbyte* p) const {
    assert(p >= _byte_map && p < _byte_map + _byte_map_size,
           "out of bounds access to card marking array. p: " PTR_FORMAT
           " _byte_map: " PTR_FORMAT " _byte_map + _byte_map_size: " PTR_FORMAT,
           p2i(p), p2i(_byte_map), p2i(_byte_map + _byte_map_size));
    size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
    HeapWord* result = (HeapWord*) (delta << card_shift);
    assert(_whole_heap.contains(result),
           "Returning result = " PTR_FORMAT " out of bounds of "
           " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
           p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
    return result;
  }

  // Mapping from address to card marking array index.
  size_t index_for(void* p) {
    assert(_whole_heap.contains(p),
           "Attempt to access p = " PTR_FORMAT " out of bounds of "
           " card marking array's _whole_heap = [" PTR_FORMAT "," PTR_FORMAT ")",
           p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end()));
    return byte_for(p) - _byte_map;
  }

  const jbyte* byte_for_index(const size_t card_index) const {
    return _byte_map + card_index;
  }

  // Print a description of the memory for the barrier set
  virtual void print_on(outputStream* st) const;

  void verify();
  void verify_guard();

  // val_equals -> it will check that all cards covered by mr equal val
  // !val_equals -> it will check that all cards covered by mr do not equal val
  void verify_region(MemRegion mr, jbyte val, bool val_equals) PRODUCT_RETURN;
  void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;
  void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;

  // ReduceInitialCardMarks
  void initialize_deferred_card_mark_barriers();

  // If the CollectedHeap was asked to defer a store barrier above,
  // this informs it to flush such a deferred store barrier to the
  // remembered set.
  void flush_deferred_card_mark_barrier(JavaThread* thread);

  // Can a compiler initialize a new object without store barriers?
  // This permission only extends from the creation of a new object
  // via a TLAB up to the first subsequent safepoint. If such permission
  // is granted for this heap type, the compiler promises to call
  // defer_store_barrier() below on any slow path allocation of
  // a new object for which such initializing store barriers will
  // have been elided. G1, like CMS, allows this, but should be
  // ready to provide a compensating write barrier as necessary
  // if that storage came out of a non-young region. The efficiency
  // of this implementation depends crucially on being able to
  // answer very efficiently in constant time whether a piece of
  // storage in the heap comes from a young region or not.
  // See ReduceInitialCardMarks.
  virtual bool can_elide_tlab_store_barriers() const {
    return true;
  }

  // If a compiler is eliding store barriers for TLAB-allocated objects,
  // we will be informed of a slow-path allocation by a call
  // to on_slowpath_allocation_exit() below. Such a call precedes the
  // initialization of the object itself, and no post-store-barriers will
  // be issued. Some heap types require that the barrier strictly follows
  // the initializing stores. (This is currently implemented by deferring the
  // barrier until the next slow-path allocation or gc-related safepoint.)
  // This interface answers whether a particular barrier type needs the card
  // mark to be thus strictly sequenced after the stores.
  virtual bool card_mark_must_follow_store() const = 0;

  virtual bool is_in_young(oop obj) const = 0;

  virtual void on_slowpath_allocation_exit(JavaThread* thread, oop new_obj);
  virtual void flush_deferred_barriers(JavaThread* thread);

  virtual void make_parsable(JavaThread* thread) { flush_deferred_card_mark_barrier(thread); }

  template <DecoratorSet decorators, typename BarrierSetT = CardTableModRefBS>
  class AccessBarrier: public ModRefBarrierSet::AccessBarrier<decorators, BarrierSetT> {};
};

template<>
struct BarrierSet::GetName<CardTableModRefBS> {
  static const BarrierSet::Name value = BarrierSet::CardTableModRef;
};

template<>
struct BarrierSet::GetType<BarrierSet::CardTableModRef> {
  typedef CardTableModRefBS type;
};

#endif // SHARE_VM_GC_SHARED_CARDTABLEMODREFBS_HPP