1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
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  24 
  25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_SPARSEPRT_HPP
  26 #define SHARE_VM_GC_IMPLEMENTATION_G1_SPARSEPRT_HPP
  27 
  28 #include "gc_implementation/g1/g1CollectedHeap.hpp"
  29 #include "gc_implementation/g1/heapRegion.hpp"
  30 #include "memory/allocation.hpp"
  31 #include "memory/cardTableModRefBS.hpp"
  32 #include "runtime/mutex.hpp"
  33 #include "utilities/globalDefinitions.hpp"
  34 
  35 // Sparse remembered set for a heap region (the "owning" region).  Maps
  36 // indices of other regions to short sequences of cards in the other region
  37 // that might contain pointers into the owner region.
  38 
  39 // These tables only expand while they are accessed in parallel --
  40 // deletions may be done in single-threaded code.  This allows us to allow
  41 // unsynchronized reads/iterations, as long as expansions caused by
  42 // insertions only enqueue old versions for deletions, but do not delete
  43 // old versions synchronously.
  44 
  45 class SparsePRTEntry: public CHeapObj<mtGC> {
  46 public:
  47   enum SomePublicConstants {
  48     NullEntry     = -1,
  49     UnrollFactor  =  4
  50   };
  51 private:
  52   RegionIdx_t _region_ind;
  53   int         _next_index;
  54   CardIdx_t   _cards[1];
  55   // WARNING: Don't put any data members beyond this line. Card array has, in fact, variable length.
  56   // It should always be the last data member.
  57 public:
  58   // Returns the size of the entry, used for entry allocation.
  59   static size_t size() { return sizeof(SparsePRTEntry) + sizeof(CardIdx_t) * (cards_num() - 1); }
  60   // Returns the size of the card array.
  61   static int cards_num() {
  62     // The number of cards should be a multiple of 4, because that's our current
  63     // unrolling factor.
  64     static const int s = MAX2<int>(G1RSetSparseRegionEntries & ~(UnrollFactor - 1), UnrollFactor);
  65     return s;
  66   }
  67 
  68   // Set the region_ind to the given value, and delete all cards.
  69   inline void init(RegionIdx_t region_ind);
  70 
  71   RegionIdx_t r_ind() const { return _region_ind; }
  72   bool valid_entry() const { return r_ind() >= 0; }
  73   void set_r_ind(RegionIdx_t rind) { _region_ind = rind; }
  74 
  75   int next_index() const { return _next_index; }
  76   int* next_index_addr() { return &_next_index; }
  77   void set_next_index(int ni) { _next_index = ni; }
  78 
  79   // Returns "true" iff the entry contains the given card index.
  80   inline bool contains_card(CardIdx_t card_index) const;
  81 
  82   // Returns the number of non-NULL card entries.
  83   inline int num_valid_cards() const;
  84 
  85   // Requires that the entry not contain the given card index.  If there is
  86   // space available, add the given card index to the entry and return
  87   // "true"; otherwise, return "false" to indicate that the entry is full.
  88   enum AddCardResult {
  89     overflow,
  90     found,
  91     added
  92   };
  93   inline AddCardResult add_card(CardIdx_t card_index);
  94 
  95   // Copy the current entry's cards into "cards".
  96   inline void copy_cards(CardIdx_t* cards) const;
  97   // Copy the current entry's cards into the "_card" array of "e."
  98   inline void copy_cards(SparsePRTEntry* e) const;
  99 
 100   inline CardIdx_t card(int i) const { return _cards[i]; }
 101 };
 102 
 103 
 104 class RSHashTable : public CHeapObj<mtGC> {
 105 
 106   friend class RSHashTableIter;
 107 
 108   enum SomePrivateConstants {
 109     NullEntry = -1
 110   };
 111 
 112   size_t _capacity;
 113   size_t _capacity_mask;
 114   size_t _occupied_entries;
 115   size_t _occupied_cards;
 116 
 117   SparsePRTEntry* _entries;
 118   int* _buckets;
 119   int  _free_region;
 120   int  _free_list;
 121 
 122   // Requires that the caller hold a lock preventing parallel modifying
 123   // operations, and that the the table be less than completely full.  If
 124   // an entry for "region_ind" is already in the table, finds it and
 125   // returns its address; otherwise allocates, initializes, inserts and
 126   // returns a new entry for "region_ind".
 127   SparsePRTEntry* entry_for_region_ind_create(RegionIdx_t region_ind);
 128 
 129   // Returns the index of the next free entry in "_entries".
 130   int alloc_entry();
 131   // Declares the entry "fi" to be free.  (It must have already been
 132   // deleted from any bucket lists.
 133   void free_entry(int fi);
 134 
 135 public:
 136   RSHashTable(size_t capacity);
 137   ~RSHashTable();
 138 
 139   // Attempts to ensure that the given card_index in the given region is in
 140   // the sparse table.  If successful (because the card was already
 141   // present, or because it was successfully added) returns "true".
 142   // Otherwise, returns "false" to indicate that the addition would
 143   // overflow the entry for the region.  The caller must transfer these
 144   // entries to a larger-capacity representation.
 145   bool add_card(RegionIdx_t region_id, CardIdx_t card_index);
 146 
 147   bool get_cards(RegionIdx_t region_id, CardIdx_t* cards);
 148 
 149   bool delete_entry(RegionIdx_t region_id);
 150 
 151   bool contains_card(RegionIdx_t region_id, CardIdx_t card_index) const;
 152 
 153   void add_entry(SparsePRTEntry* e);
 154 
 155   SparsePRTEntry* get_entry(RegionIdx_t region_id) const;
 156 
 157   void clear();
 158 
 159   size_t capacity() const      { return _capacity;       }
 160   size_t capacity_mask() const { return _capacity_mask;  }
 161   size_t occupied_entries() const { return _occupied_entries; }
 162   size_t occupied_cards() const   { return _occupied_cards;   }
 163   size_t mem_size() const;
 164 
 165   SparsePRTEntry* entry(int i) const { return (SparsePRTEntry*)((char*)_entries + SparsePRTEntry::size() * i); }
 166 
 167   void print();
 168 };
 169 
 170 // ValueObj because will be embedded in HRRS iterator.
 171 class RSHashTableIter VALUE_OBJ_CLASS_SPEC {
 172   int _tbl_ind;         // [-1, 0.._rsht->_capacity)
 173   int _bl_ind;          // [-1, 0.._rsht->_capacity)
 174   short _card_ind;      // [0..SparsePRTEntry::cards_num())
 175   RSHashTable* _rsht;
 176 
 177   // If the bucket list pointed to by _bl_ind contains a card, sets
 178   // _bl_ind to the index of that entry, and returns the card.
 179   // Otherwise, returns SparseEntry::NullEntry.
 180   CardIdx_t find_first_card_in_list();
 181 
 182   // Computes the proper card index for the card whose offset in the
 183   // current region (as indicated by _bl_ind) is "ci".
 184   // This is subject to errors when there is iteration concurrent with
 185   // modification, but these errors should be benign.
 186   size_t compute_card_ind(CardIdx_t ci);
 187 
 188 public:
 189   RSHashTableIter(RSHashTable* rsht) :
 190     _tbl_ind(RSHashTable::NullEntry), // So that first increment gets to 0.
 191     _bl_ind(RSHashTable::NullEntry),
 192     _card_ind((SparsePRTEntry::cards_num() - 1)),
 193     _rsht(rsht) {}
 194 
 195   bool has_next(size_t& card_index);
 196 };
 197 
 198 // Concurrent access to a SparsePRT must be serialized by some external mutex.
 199 
 200 class SparsePRTIter;
 201 class SparsePRTCleanupTask;
 202 
 203 class SparsePRT VALUE_OBJ_CLASS_SPEC {
 204   friend class SparsePRTCleanupTask;
 205 
 206   //  Iterations are done on the _cur hash table, since they only need to
 207   //  see entries visible at the start of a collection pause.
 208   //  All other operations are done using the _next hash table.
 209   RSHashTable* _cur;
 210   RSHashTable* _next;
 211 
 212   HeapRegion* _hr;
 213 
 214   enum SomeAdditionalPrivateConstants {
 215     InitialCapacity = 16
 216   };
 217 
 218   void expand();
 219 
 220   bool _expanded;
 221 
 222   bool expanded() { return _expanded; }
 223   void set_expanded(bool b) { _expanded = b; }
 224 
 225   SparsePRT* _next_expanded;
 226 
 227   SparsePRT* next_expanded() { return _next_expanded; }
 228   void set_next_expanded(SparsePRT* nxt) { _next_expanded = nxt; }
 229 
 230   bool should_be_on_expanded_list();
 231 
 232   static SparsePRT* _head_expanded_list;
 233 
 234 public:
 235   SparsePRT(HeapRegion* hr);
 236 
 237   ~SparsePRT();
 238 
 239   size_t occupied() const { return _next->occupied_cards(); }
 240   size_t mem_size() const;
 241 
 242   // Attempts to ensure that the given card_index in the given region is in
 243   // the sparse table.  If successful (because the card was already
 244   // present, or because it was successfully added) returns "true".
 245   // Otherwise, returns "false" to indicate that the addition would
 246   // overflow the entry for the region.  The caller must transfer these
 247   // entries to a larger-capacity representation.
 248   bool add_card(RegionIdx_t region_id, CardIdx_t card_index);
 249 
 250   // If the table hold an entry for "region_ind",  Copies its
 251   // cards into "cards", which must be an array of length at least
 252   // "SparePRTEntry::cards_num()", and returns "true"; otherwise,
 253   // returns "false".
 254   bool get_cards(RegionIdx_t region_ind, CardIdx_t* cards);
 255 
 256   // Return the pointer to the entry associated with the given region.
 257   SparsePRTEntry* get_entry(RegionIdx_t region_ind);
 258 
 259   // If there is an entry for "region_ind", removes it and return "true";
 260   // otherwise returns "false."
 261   bool delete_entry(RegionIdx_t region_ind);
 262 
 263   // Clear the table, and reinitialize to initial capacity.
 264   void clear();
 265 
 266   // Ensure that "_cur" and "_next" point to the same table.
 267   void cleanup();
 268 
 269   // Clean up all tables on the expanded list.  Called single threaded.
 270   static void cleanup_all();
 271   RSHashTable* cur() const { return _cur; }
 272 
 273   static void add_to_expanded_list(SparsePRT* sprt);
 274   static SparsePRT* get_from_expanded_list();
 275 
 276   // The purpose of these three methods is to help the GC workers
 277   // during the cleanup pause to recreate the expanded list, purging
 278   // any tables from it that belong to regions that are freed during
 279   // cleanup (if we don't purge those tables, there is a race that
 280   // causes various crashes; see CR 7014261).
 281   //
 282   // We chose to recreate the expanded list, instead of purging
 283   // entries from it by iterating over it, to avoid this serial phase
 284   // at the end of the cleanup pause.
 285   //
 286   // The three methods below work as follows:
 287   // * reset_for_cleanup_tasks() : Nulls the expanded list head at the
 288   //   start of the cleanup pause.
 289   // * do_cleanup_work() : Called by the cleanup workers for every
 290   //   region that is not free / is being freed by the cleanup
 291   //   pause. It creates a list of expanded tables whose head / tail
 292   //   are on the thread-local SparsePRTCleanupTask object.
 293   // * finish_cleanup_task() : Called by the cleanup workers after
 294   //   they complete their cleanup task. It adds the local list into
 295   //   the global expanded list. It assumes that the
 296   //   ParGCRareEvent_lock is being held to ensure MT-safety.
 297   static void reset_for_cleanup_tasks();
 298   void do_cleanup_work(SparsePRTCleanupTask* sprt_cleanup_task);
 299   static void finish_cleanup_task(SparsePRTCleanupTask* sprt_cleanup_task);
 300 
 301   bool contains_card(RegionIdx_t region_id, CardIdx_t card_index) const {
 302     return _next->contains_card(region_id, card_index);
 303   }
 304 };
 305 
 306 class SparsePRTIter: public RSHashTableIter {
 307 public:
 308   SparsePRTIter(const SparsePRT* sprt) :
 309     RSHashTableIter(sprt->cur()) {}
 310 
 311   bool has_next(size_t& card_index) {
 312     return RSHashTableIter::has_next(card_index);
 313   }
 314 };
 315 
 316 // This allows each worker during a cleanup pause to create a
 317 // thread-local list of sparse tables that have been expanded and need
 318 // to be processed at the beginning of the next GC pause. This lists
 319 // are concatenated into the single expanded list at the end of the
 320 // cleanup pause.
 321 class SparsePRTCleanupTask VALUE_OBJ_CLASS_SPEC {
 322 private:
 323   SparsePRT* _head;
 324   SparsePRT* _tail;
 325 
 326 public:
 327   SparsePRTCleanupTask() : _head(NULL), _tail(NULL) { }
 328 
 329   void add(SparsePRT* sprt);
 330   SparsePRT* head() { return _head; }
 331   SparsePRT* tail() { return _tail; }
 332 };
 333 
 334 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_SPARSEPRT_HPP