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

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 * 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_G1_SPARSEPRT_HPP

#define SHARE_VM_GC_G1_SPARSEPRT_HPP

#include "gc/g1/g1CollectedHeap.hpp"

#include "gc/g1/heapRegion.hpp"

#include "gc/shared/cardTableModRefBS.hpp"

#include "memory/allocation.hpp"

#include "runtime/mutex.hpp"

#include "utilities/globalDefinitions.hpp"

// Sparse remembered set for a heap region (the "owning" region).  Maps

// indices of other regions to short sequences of cards in the other region

// that might contain pointers into the owner region.

// These tables only expand while they are accessed in parallel --

// deletions may be done in single-threaded code.  This allows us to allow

// unsynchronized reads/iterations, as long as expansions caused by

// insertions only enqueue old versions for deletions, but do not delete

// old versions synchronously.

class SparsePRTEntry: public CHeapObj<mtGC> {

private:

  // The type of a card entry.

  typedef uint16_t card_elem_t;

  // We need to make sizeof(SparsePRTEntry) an even multiple of maximum member size,

  // in order to force correct alignment that could otherwise cause SIGBUS errors

  // when reading the member variables. This calculates the minimum number of card

  // array elements required to get that alignment.

  static const size_t card_array_alignment = sizeof(int) / sizeof(card_elem_t);

  RegionIdx_t _region_ind;

  int         _next_index;

  int         _next_null;

  // The actual cards stored in this array.

  // WARNING: Don't put any data members beyond this line. Card array has, in fact, variable length.

  // It should always be the last data member.

  card_elem_t _cards[card_array_alignment];

  // Copy the current entry's cards into "cards".

  inline void copy_cards(card_elem_t* cards) const;

public:

  // Returns the size of the entry, used for entry allocation.

  static size_t size() { return sizeof(SparsePRTEntry) + sizeof(card_elem_t) * (cards_num() - card_array_alignment); }

  // Returns the size of the card array.

  static int cards_num() {

    return align_up((int)G1RSetSparseRegionEntries, (int)card_array_alignment);

  }

  // Set the region_ind to the given value, and delete all cards.

  inline void init(RegionIdx_t region_ind);

  RegionIdx_t r_ind() const { return _region_ind; }

  bool valid_entry() const { return r_ind() >= 0; }

  void set_r_ind(RegionIdx_t rind) { _region_ind = rind; }

  int next_index() const { return _next_index; }

  int* next_index_addr() { return &_next_index; }

  void set_next_index(int ni) { _next_index = ni; }

  // Returns "true" iff the entry contains the given card index.

  inline bool contains_card(CardIdx_t card_index) const;

  // Returns the number of non-NULL card entries.

  inline int num_valid_cards() const { return _next_null; }

  // Requires that the entry not contain the given card index.  If there is

  // space available, add the given card index to the entry and return

  // "true"; otherwise, return "false" to indicate that the entry is full.

  enum AddCardResult {

    overflow,

    found,

    added

  };

  inline AddCardResult add_card(CardIdx_t card_index);

  // Copy the current entry's cards into the "_card" array of "e."

  inline void copy_cards(SparsePRTEntry* e) const;

  inline CardIdx_t card(int i) const {

    assert(i >= 0, "must be nonnegative");

    assert(i < cards_num(), "range checking");

    return (CardIdx_t)_cards[i];

  }

};

class RSHashTable : public CHeapObj<mtGC> {

  friend class RSHashTableIter;

  // Inverse maximum hash table occupancy used.

  static float TableOccupancyFactor;

  size_t _num_entries;

  size_t _capacity;

  size_t _capacity_mask;

  size_t _occupied_entries;

  size_t _occupied_cards;

  SparsePRTEntry* _entries;

  int* _buckets;

  int  _free_region;

  int  _free_list;

  // Requires that the caller hold a lock preventing parallel modifying

  // operations, and that the the table be less than completely full.  If

  // an entry for "region_ind" is already in the table, finds it and

  // returns its address; otherwise allocates, initializes, inserts and

  // returns a new entry for "region_ind".

  SparsePRTEntry* entry_for_region_ind_create(RegionIdx_t region_ind);

  // Returns the index of the next free entry in "_entries".

  int alloc_entry();

  // Declares the entry "fi" to be free.  (It must have already been

  // deleted from any bucket lists.

  void free_entry(int fi);

public:

  RSHashTable(size_t capacity);

  ~RSHashTable();

  static const int NullEntry = -1;

  bool should_expand() const { return _occupied_entries == _num_entries; }

  // Attempts to ensure that the given card_index in the given region is in

  // the sparse table.  If successful (because the card was already

  // present, or because it was successfully added) returns "true".

  // Otherwise, returns "false" to indicate that the addition would

  // overflow the entry for the region.  The caller must transfer these

  // entries to a larger-capacity representation.

  bool add_card(RegionIdx_t region_id, CardIdx_t card_index);

  bool get_cards(RegionIdx_t region_id, CardIdx_t* cards);

  bool delete_entry(RegionIdx_t region_id);

  bool contains_card(RegionIdx_t region_id, CardIdx_t card_index) const;

  void add_entry(SparsePRTEntry* e);

  SparsePRTEntry* get_entry(RegionIdx_t region_id) const;

  void clear();

  size_t capacity() const      { return _capacity; }

  size_t capacity_mask() const { return _capacity_mask;  }

  size_t occupied_entries() const { return _occupied_entries; }

  size_t occupied_cards() const   { return _occupied_cards; }

  size_t mem_size() const;

  // The number of SparsePRTEntry instances available.

  size_t num_entries() const { return _num_entries; }

  SparsePRTEntry* entry(int i) const {

    assert(i >= 0 && (size_t)i < _num_entries, "precondition");

    return (SparsePRTEntry*)((char*)_entries + SparsePRTEntry::size() * i);

  }

  void print();

};

// ValueObj because will be embedded in HRRS iterator.

class RSHashTableIter VALUE_OBJ_CLASS_SPEC {

  // Return value indicating "invalid/no card".

  static const int NoCardFound = -1;

  int _tbl_ind;         // [-1, 0.._rsht->_capacity)

  int _bl_ind;          // [-1, 0.._rsht->_capacity)

  short _card_ind;      // [0..SparsePRTEntry::cards_num())

  RSHashTable* _rsht;

  // If the bucket list pointed to by _bl_ind contains a card, sets

  // _bl_ind to the index of that entry,

  // Returns the card found if there is, otherwise returns InvalidCard.

  CardIdx_t find_first_card_in_list();

  // Computes the proper card index for the card whose offset in the

  // current region (as indicated by _bl_ind) is "ci".

  // This is subject to errors when there is iteration concurrent with

  // modification, but these errors should be benign.

  size_t compute_card_ind(CardIdx_t ci);

public:

  RSHashTableIter(RSHashTable* rsht) :

    _tbl_ind(RSHashTable::NullEntry), // So that first increment gets to 0.

    _bl_ind(RSHashTable::NullEntry),

    _card_ind((SparsePRTEntry::cards_num() - 1)),

    _rsht(rsht) {}

  bool has_next(size_t& card_index);

};

// Concurrent access to a SparsePRT must be serialized by some external mutex.

class SparsePRTIter;

class SparsePRTCleanupTask;

class SparsePRT VALUE_OBJ_CLASS_SPEC {

  friend class SparsePRTCleanupTask;

  //  Iterations are done on the _cur hash table, since they only need to

  //  see entries visible at the start of a collection pause.

  //  All other operations are done using the _next hash table.

  RSHashTable* _cur;

  RSHashTable* _next;

  HeapRegion* _hr;

  enum SomeAdditionalPrivateConstants {

    InitialCapacity = 16

  };

  void expand();

  bool _expanded;

  bool expanded() { return _expanded; }

  void set_expanded(bool b) { _expanded = b; }

  SparsePRT* _next_expanded;

  SparsePRT* next_expanded() { return _next_expanded; }

  void set_next_expanded(SparsePRT* nxt) { _next_expanded = nxt; }

  bool should_be_on_expanded_list();

  static SparsePRT* volatile _head_expanded_list;

public:

  SparsePRT(HeapRegion* hr);

  ~SparsePRT();

  size_t occupied() const { return _next->occupied_cards(); }

  size_t mem_size() const;

  // Attempts to ensure that the given card_index in the given region is in

  // the sparse table.  If successful (because the card was already

  // present, or because it was successfully added) returns "true".

  // Otherwise, returns "false" to indicate that the addition would

  // overflow the entry for the region.  The caller must transfer these

  // entries to a larger-capacity representation.

  bool add_card(RegionIdx_t region_id, CardIdx_t card_index);

  // Return the pointer to the entry associated with the given region.

  SparsePRTEntry* get_entry(RegionIdx_t region_ind);

  // If there is an entry for "region_ind", removes it and return "true";

  // otherwise returns "false."

  bool delete_entry(RegionIdx_t region_ind);

  // Clear the table, and reinitialize to initial capacity.

  void clear();

  // Ensure that "_cur" and "_next" point to the same table.

  void cleanup();

  // Clean up all tables on the expanded list.  Called single threaded.

  static void cleanup_all();

  RSHashTable* cur() const { return _cur; }

  static void add_to_expanded_list(SparsePRT* sprt);

  static SparsePRT* get_from_expanded_list();

  // The purpose of these three methods is to help the GC workers

  // during the cleanup pause to recreate the expanded list, purging

  // any tables from it that belong to regions that are freed during

  // cleanup (if we don't purge those tables, there is a race that

  // causes various crashes; see CR 7014261).

  //

  // We chose to recreate the expanded list, instead of purging

  // entries from it by iterating over it, to avoid this serial phase

  // at the end of the cleanup pause.

  //

  // The three methods below work as follows:

  // * reset_for_cleanup_tasks() : Nulls the expanded list head at the

  //   start of the cleanup pause.

  // * do_cleanup_work() : Called by the cleanup workers for every

  //   region that is not free / is being freed by the cleanup

  //   pause. It creates a list of expanded tables whose head / tail

  //   are on the thread-local SparsePRTCleanupTask object.

  // * finish_cleanup_task() : Called by the cleanup workers after

  //   they complete their cleanup task. It adds the local list into

  //   the global expanded list. It assumes that the

  //   ParGCRareEvent_lock is being held to ensure MT-safety.

  static void reset_for_cleanup_tasks();

  void do_cleanup_work(SparsePRTCleanupTask* sprt_cleanup_task);

  static void finish_cleanup_task(SparsePRTCleanupTask* sprt_cleanup_task);

  bool contains_card(RegionIdx_t region_id, CardIdx_t card_index) const {

    return _next->contains_card(region_id, card_index);

  }

};

class SparsePRTIter: public RSHashTableIter {

public:

  SparsePRTIter(const SparsePRT* sprt) :

    RSHashTableIter(sprt->cur()) {}

  bool has_next(size_t& card_index) {

    return RSHashTableIter::has_next(card_index);

  }

};

// This allows each worker during a cleanup pause to create a

// thread-local list of sparse tables that have been expanded and need

// to be processed at the beginning of the next GC pause. This lists

// are concatenated into the single expanded list at the end of the

// cleanup pause.

class SparsePRTCleanupTask VALUE_OBJ_CLASS_SPEC {

private:

  SparsePRT* _head;

  SparsePRT* _tail;

public:

  SparsePRTCleanupTask() : _head(NULL), _tail(NULL) { }

  void add(SparsePRT* sprt);

  SparsePRT* head() { return _head; }

  SparsePRT* tail() { return _tail; }

};

#endif // SHARE_VM_GC_G1_SPARSEPRT_HPP