1 /* 2 * Copyright (c) 2001, 2016, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 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). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #ifndef SHARE_VM_GC_G1_SPARSEPRT_HPP 26 #define SHARE_VM_GC_G1_SPARSEPRT_HPP 27 28 #include "gc/g1/g1CollectedHeap.hpp" 29 #include "gc/g1/heapRegion.hpp" 30 #include "gc/shared/cardTableModRefBS.hpp" 31 #include "memory/allocation.hpp" 32 #include "runtime/mutex.hpp" 33 #include "utilities/align.hpp" 34 #include "utilities/globalDefinitions.hpp" 35 36 // Sparse remembered set for a heap region (the "owning" region). Maps 37 // indices of other regions to short sequences of cards in the other region 38 // that might contain pointers into the owner region. 39 40 // These tables only expand while they are accessed in parallel -- 41 // deletions may be done in single-threaded code. This allows us to allow 42 // unsynchronized reads/iterations, as long as expansions caused by 43 // insertions only enqueue old versions for deletions, but do not delete 44 // old versions synchronously. 45 46 class SparsePRTEntry: public CHeapObj<mtGC> { 47 private: 48 // The type of a card entry. 49 typedef uint16_t card_elem_t; 50 51 // We need to make sizeof(SparsePRTEntry) an even multiple of maximum member size, 52 // in order to force correct alignment that could otherwise cause SIGBUS errors 53 // when reading the member variables. This calculates the minimum number of card 54 // array elements required to get that alignment. 55 static const size_t card_array_alignment = sizeof(int) / sizeof(card_elem_t); 56 57 RegionIdx_t _region_ind; 58 int _next_index; 59 int _next_null; 60 // The actual cards stored in this array. 61 // WARNING: Don't put any data members beyond this line. Card array has, in fact, variable length. 62 // It should always be the last data member. 63 card_elem_t _cards[card_array_alignment]; 64 65 // Copy the current entry's cards into "cards". 66 inline void copy_cards(card_elem_t* cards) const; 67 public: 68 // Returns the size of the entry, used for entry allocation. 69 static size_t size() { return sizeof(SparsePRTEntry) + sizeof(card_elem_t) * (cards_num() - card_array_alignment); } 70 // Returns the size of the card array. 71 static int cards_num() { 72 return align_up((int)G1RSetSparseRegionEntries, (int)card_array_alignment); 73 } 74 75 // Set the region_ind to the given value, and delete all cards. 76 inline void init(RegionIdx_t region_ind); 77 78 RegionIdx_t r_ind() const { return _region_ind; } 79 bool valid_entry() const { return r_ind() >= 0; } 80 void set_r_ind(RegionIdx_t rind) { _region_ind = rind; } 81 82 int next_index() const { return _next_index; } 83 int* next_index_addr() { return &_next_index; } 84 void set_next_index(int ni) { _next_index = ni; } 85 86 // Returns "true" iff the entry contains the given card index. 87 inline bool contains_card(CardIdx_t card_index) const; 88 89 // Returns the number of non-NULL card entries. 90 inline int num_valid_cards() const { return _next_null; } 91 92 // Requires that the entry not contain the given card index. If there is 93 // space available, add the given card index to the entry and return 94 // "true"; otherwise, return "false" to indicate that the entry is full. 95 enum AddCardResult { 96 overflow, 97 found, 98 added 99 }; 100 inline AddCardResult add_card(CardIdx_t card_index); 101 102 // Copy the current entry's cards into the "_card" array of "e." 103 inline void copy_cards(SparsePRTEntry* e) const; 104 105 inline CardIdx_t card(int i) const { 106 assert(i >= 0, "must be nonnegative"); 107 assert(i < cards_num(), "range checking"); 108 return (CardIdx_t)_cards[i]; 109 } 110 }; 111 112 class RSHashTable : public CHeapObj<mtGC> { 113 114 friend class RSHashTableIter; 115 116 117 // Inverse maximum hash table occupancy used. 118 static float TableOccupancyFactor; 119 120 size_t _num_entries; 121 122 size_t _capacity; 123 size_t _capacity_mask; 124 size_t _occupied_entries; 125 size_t _occupied_cards; 126 127 SparsePRTEntry* _entries; 128 int* _buckets; 129 int _free_region; 130 int _free_list; 131 132 // Requires that the caller hold a lock preventing parallel modifying 133 // operations, and that the the table be less than completely full. If 134 // an entry for "region_ind" is already in the table, finds it and 135 // returns its address; otherwise allocates, initializes, inserts and 136 // returns a new entry for "region_ind". 137 SparsePRTEntry* entry_for_region_ind_create(RegionIdx_t region_ind); 138 139 // Returns the index of the next free entry in "_entries". 140 int alloc_entry(); 141 // Declares the entry "fi" to be free. (It must have already been 142 // deleted from any bucket lists. 143 void free_entry(int fi); 144 145 public: 146 RSHashTable(size_t capacity); 147 ~RSHashTable(); 148 149 static const int NullEntry = -1; 150 151 bool should_expand() const { return _occupied_entries == _num_entries; } 152 153 // Attempts to ensure that the given card_index in the given region is in 154 // the sparse table. If successful (because the card was already 155 // present, or because it was successfully added) returns "true". 156 // Otherwise, returns "false" to indicate that the addition would 157 // overflow the entry for the region. The caller must transfer these 158 // entries to a larger-capacity representation. 159 bool add_card(RegionIdx_t region_id, CardIdx_t card_index); 160 161 bool get_cards(RegionIdx_t region_id, CardIdx_t* cards); 162 163 bool delete_entry(RegionIdx_t region_id); 164 165 bool contains_card(RegionIdx_t region_id, CardIdx_t card_index) const; 166 167 void add_entry(SparsePRTEntry* e); 168 169 SparsePRTEntry* get_entry(RegionIdx_t region_id) const; 170 171 void clear(); 172 173 size_t capacity() const { return _capacity; } 174 size_t capacity_mask() const { return _capacity_mask; } 175 size_t occupied_entries() const { return _occupied_entries; } 176 size_t occupied_cards() const { return _occupied_cards; } 177 size_t mem_size() const; 178 // The number of SparsePRTEntry instances available. 179 size_t num_entries() const { return _num_entries; } 180 181 SparsePRTEntry* entry(int i) const { 182 assert(i >= 0 && (size_t)i < _num_entries, "precondition"); 183 return (SparsePRTEntry*)((char*)_entries + SparsePRTEntry::size() * i); 184 } 185 186 void print(); 187 }; 188 189 // ValueObj because will be embedded in HRRS iterator. 190 class RSHashTableIter VALUE_OBJ_CLASS_SPEC { 191 // Return value indicating "invalid/no card". 192 static const int NoCardFound = -1; 193 194 int _tbl_ind; // [-1, 0.._rsht->_capacity) 195 int _bl_ind; // [-1, 0.._rsht->_capacity) 196 short _card_ind; // [0..SparsePRTEntry::cards_num()) 197 RSHashTable* _rsht; 198 199 // If the bucket list pointed to by _bl_ind contains a card, sets 200 // _bl_ind to the index of that entry, 201 // Returns the card found if there is, otherwise returns InvalidCard. 202 CardIdx_t find_first_card_in_list(); 203 204 // Computes the proper card index for the card whose offset in the 205 // current region (as indicated by _bl_ind) is "ci". 206 // This is subject to errors when there is iteration concurrent with 207 // modification, but these errors should be benign. 208 size_t compute_card_ind(CardIdx_t ci); 209 210 public: 211 RSHashTableIter(RSHashTable* rsht) : 212 _tbl_ind(RSHashTable::NullEntry), // So that first increment gets to 0. 213 _bl_ind(RSHashTable::NullEntry), 214 _card_ind((SparsePRTEntry::cards_num() - 1)), 215 _rsht(rsht) {} 216 217 bool has_next(size_t& card_index); 218 }; 219 220 // Concurrent access to a SparsePRT must be serialized by some external mutex. 221 222 class SparsePRTIter; 223 class SparsePRTCleanupTask; 224 225 class SparsePRT VALUE_OBJ_CLASS_SPEC { 226 friend class SparsePRTCleanupTask; 227 228 // Iterations are done on the _cur hash table, since they only need to 229 // see entries visible at the start of a collection pause. 230 // All other operations are done using the _next hash table. 231 RSHashTable* _cur; 232 RSHashTable* _next; 233 234 HeapRegion* _hr; 235 236 enum SomeAdditionalPrivateConstants { 237 InitialCapacity = 16 238 }; 239 240 void expand(); 241 242 bool _expanded; 243 244 bool expanded() { return _expanded; } 245 void set_expanded(bool b) { _expanded = b; } 246 247 SparsePRT* _next_expanded; 248 249 SparsePRT* next_expanded() { return _next_expanded; } 250 void set_next_expanded(SparsePRT* nxt) { _next_expanded = nxt; } 251 252 bool should_be_on_expanded_list(); 253 254 static SparsePRT* volatile _head_expanded_list; 255 256 public: 257 SparsePRT(HeapRegion* hr); 258 259 ~SparsePRT(); 260 261 size_t occupied() const { return _next->occupied_cards(); } 262 size_t mem_size() const; 263 264 // Attempts to ensure that the given card_index in the given region is in 265 // the sparse table. If successful (because the card was already 266 // present, or because it was successfully added) returns "true". 267 // Otherwise, returns "false" to indicate that the addition would 268 // overflow the entry for the region. The caller must transfer these 269 // entries to a larger-capacity representation. 270 bool add_card(RegionIdx_t region_id, CardIdx_t card_index); 271 272 // Return the pointer to the entry associated with the given region. 273 SparsePRTEntry* get_entry(RegionIdx_t region_ind); 274 275 // If there is an entry for "region_ind", removes it and return "true"; 276 // otherwise returns "false." 277 bool delete_entry(RegionIdx_t region_ind); 278 279 // Clear the table, and reinitialize to initial capacity. 280 void clear(); 281 282 // Ensure that "_cur" and "_next" point to the same table. 283 void cleanup(); 284 285 // Clean up all tables on the expanded list. Called single threaded. 286 static void cleanup_all(); 287 RSHashTable* cur() const { return _cur; } 288 289 static void add_to_expanded_list(SparsePRT* sprt); 290 static SparsePRT* get_from_expanded_list(); 291 292 // The purpose of these three methods is to help the GC workers 293 // during the cleanup pause to recreate the expanded list, purging 294 // any tables from it that belong to regions that are freed during 295 // cleanup (if we don't purge those tables, there is a race that 296 // causes various crashes; see CR 7014261). 297 // 298 // We chose to recreate the expanded list, instead of purging 299 // entries from it by iterating over it, to avoid this serial phase 300 // at the end of the cleanup pause. 301 // 302 // The three methods below work as follows: 303 // * reset_for_cleanup_tasks() : Nulls the expanded list head at the 304 // start of the cleanup pause. 305 // * do_cleanup_work() : Called by the cleanup workers for every 306 // region that is not free / is being freed by the cleanup 307 // pause. It creates a list of expanded tables whose head / tail 308 // are on the thread-local SparsePRTCleanupTask object. 309 // * finish_cleanup_task() : Called by the cleanup workers after 310 // they complete their cleanup task. It adds the local list into 311 // the global expanded list. It assumes that the 312 // ParGCRareEvent_lock is being held to ensure MT-safety. 313 static void reset_for_cleanup_tasks(); 314 void do_cleanup_work(SparsePRTCleanupTask* sprt_cleanup_task); 315 static void finish_cleanup_task(SparsePRTCleanupTask* sprt_cleanup_task); 316 317 bool contains_card(RegionIdx_t region_id, CardIdx_t card_index) const { 318 return _next->contains_card(region_id, card_index); 319 } 320 }; 321 322 class SparsePRTIter: public RSHashTableIter { 323 public: 324 SparsePRTIter(const SparsePRT* sprt) : 325 RSHashTableIter(sprt->cur()) {} 326 327 bool has_next(size_t& card_index) { 328 return RSHashTableIter::has_next(card_index); 329 } 330 }; 331 332 // This allows each worker during a cleanup pause to create a 333 // thread-local list of sparse tables that have been expanded and need 334 // to be processed at the beginning of the next GC pause. This lists 335 // are concatenated into the single expanded list at the end of the 336 // cleanup pause. 337 class SparsePRTCleanupTask VALUE_OBJ_CLASS_SPEC { 338 private: 339 SparsePRT* _head; 340 SparsePRT* _tail; 341 342 public: 343 SparsePRTCleanupTask() : _head(NULL), _tail(NULL) { } 344 345 void add(SparsePRT* sprt); 346 SparsePRT* head() { return _head; } 347 SparsePRT* tail() { return _tail; } 348 }; 349 350 #endif // SHARE_VM_GC_G1_SPARSEPRT_HPP