Fri, 15 Oct 2010 17:26:56 -0400
6992189: G1: inconsistent base used in sparse rem set iterator
Summary: The remembered set iterator for sparse tables incorrectly assumes that index 0 corresponds to the bottom of the heap, not address 0 as it is the case.
Reviewed-by: ysr, jmasa
1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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25 // Sparse remembered set for a heap region (the "owning" region). Maps
26 // indices of other regions to short sequences of cards in the other region
27 // that might contain pointers into the owner region.
29 // These tables only expand while they are accessed in parallel --
30 // deletions may be done in single-threaded code. This allows us to allow
31 // unsynchronized reads/iterations, as long as expansions caused by
32 // insertions only enqueue old versions for deletions, but do not delete
33 // old versions synchronously.
35 class SparsePRTEntry: public CHeapObj {
36 public:
37 enum SomePublicConstants {
38 NullEntry = -1,
39 UnrollFactor = 4
40 };
41 private:
42 RegionIdx_t _region_ind;
43 int _next_index;
44 CardIdx_t _cards[1];
45 // WARNING: Don't put any data members beyond this line. Card array has, in fact, variable length.
46 // It should always be the last data member.
47 public:
48 // Returns the size of the entry, used for entry allocation.
49 static size_t size() { return sizeof(SparsePRTEntry) + sizeof(CardIdx_t) * (cards_num() - 1); }
50 // Returns the size of the card array.
51 static int cards_num() {
52 // The number of cards should be a multiple of 4, because that's our current
53 // unrolling factor.
54 static const int s = MAX2<int>(G1RSetSparseRegionEntries & ~(UnrollFactor - 1), UnrollFactor);
55 return s;
56 }
58 // Set the region_ind to the given value, and delete all cards.
59 inline void init(RegionIdx_t region_ind);
61 RegionIdx_t r_ind() const { return _region_ind; }
62 bool valid_entry() const { return r_ind() >= 0; }
63 void set_r_ind(RegionIdx_t rind) { _region_ind = rind; }
65 int next_index() const { return _next_index; }
66 int* next_index_addr() { return &_next_index; }
67 void set_next_index(int ni) { _next_index = ni; }
69 // Returns "true" iff the entry contains the given card index.
70 inline bool contains_card(CardIdx_t card_index) const;
72 // Returns the number of non-NULL card entries.
73 inline int num_valid_cards() const;
75 // Requires that the entry not contain the given card index. If there is
76 // space available, add the given card index to the entry and return
77 // "true"; otherwise, return "false" to indicate that the entry is full.
78 enum AddCardResult {
79 overflow,
80 found,
81 added
82 };
83 inline AddCardResult add_card(CardIdx_t card_index);
85 // Copy the current entry's cards into "cards".
86 inline void copy_cards(CardIdx_t* cards) const;
87 // Copy the current entry's cards into the "_card" array of "e."
88 inline void copy_cards(SparsePRTEntry* e) const;
90 inline CardIdx_t card(int i) const { return _cards[i]; }
91 };
94 class RSHashTable : public CHeapObj {
96 friend class RSHashTableIter;
98 enum SomePrivateConstants {
99 NullEntry = -1
100 };
102 size_t _capacity;
103 size_t _capacity_mask;
104 size_t _occupied_entries;
105 size_t _occupied_cards;
107 SparsePRTEntry* _entries;
108 int* _buckets;
109 int _free_region;
110 int _free_list;
112 // Requires that the caller hold a lock preventing parallel modifying
113 // operations, and that the the table be less than completely full. If
114 // an entry for "region_ind" is already in the table, finds it and
115 // returns its address; otherwise returns "NULL."
116 SparsePRTEntry* entry_for_region_ind(RegionIdx_t region_ind) const;
118 // Requires that the caller hold a lock preventing parallel modifying
119 // operations, and that the the table be less than completely full. If
120 // an entry for "region_ind" is already in the table, finds it and
121 // returns its address; otherwise allocates, initializes, inserts and
122 // returns a new entry for "region_ind".
123 SparsePRTEntry* entry_for_region_ind_create(RegionIdx_t region_ind);
125 // Returns the index of the next free entry in "_entries".
126 int alloc_entry();
127 // Declares the entry "fi" to be free. (It must have already been
128 // deleted from any bucket lists.
129 void free_entry(int fi);
131 public:
132 RSHashTable(size_t capacity);
133 ~RSHashTable();
135 // Attempts to ensure that the given card_index in the given region is in
136 // the sparse table. If successful (because the card was already
137 // present, or because it was successfullly added) returns "true".
138 // Otherwise, returns "false" to indicate that the addition would
139 // overflow the entry for the region. The caller must transfer these
140 // entries to a larger-capacity representation.
141 bool add_card(RegionIdx_t region_id, CardIdx_t card_index);
143 bool get_cards(RegionIdx_t region_id, CardIdx_t* cards);
145 bool delete_entry(RegionIdx_t region_id);
147 bool contains_card(RegionIdx_t region_id, CardIdx_t card_index) const;
149 void add_entry(SparsePRTEntry* e);
151 SparsePRTEntry* get_entry(RegionIdx_t region_id);
153 void clear();
155 size_t capacity() const { return _capacity; }
156 size_t capacity_mask() const { return _capacity_mask; }
157 size_t occupied_entries() const { return _occupied_entries; }
158 size_t occupied_cards() const { return _occupied_cards; }
159 size_t mem_size() const;
161 SparsePRTEntry* entry(int i) const { return (SparsePRTEntry*)((char*)_entries + SparsePRTEntry::size() * i); }
163 void print();
164 };
166 // ValueObj because will be embedded in HRRS iterator.
167 class RSHashTableIter VALUE_OBJ_CLASS_SPEC {
168 int _tbl_ind; // [-1, 0.._rsht->_capacity)
169 int _bl_ind; // [-1, 0.._rsht->_capacity)
170 short _card_ind; // [0..SparsePRTEntry::cards_num())
171 RSHashTable* _rsht;
173 // If the bucket list pointed to by _bl_ind contains a card, sets
174 // _bl_ind to the index of that entry, and returns the card.
175 // Otherwise, returns SparseEntry::NullEntry.
176 CardIdx_t find_first_card_in_list();
178 // Computes the proper card index for the card whose offset in the
179 // current region (as indicated by _bl_ind) is "ci".
180 // This is subject to errors when there is iteration concurrent with
181 // modification, but these errors should be benign.
182 size_t compute_card_ind(CardIdx_t ci);
184 public:
185 RSHashTableIter() :
186 _tbl_ind(RSHashTable::NullEntry),
187 _bl_ind(RSHashTable::NullEntry),
188 _card_ind((SparsePRTEntry::cards_num() - 1)),
189 _rsht(NULL) {}
191 void init(RSHashTable* rsht) {
192 _rsht = rsht;
193 _tbl_ind = -1; // So that first increment gets to 0.
194 _bl_ind = RSHashTable::NullEntry;
195 _card_ind = (SparsePRTEntry::cards_num() - 1);
196 }
198 bool has_next(size_t& card_index);
199 };
201 // Concurrent accesss to a SparsePRT must be serialized by some external
202 // mutex.
204 class SparsePRTIter;
206 class SparsePRT VALUE_OBJ_CLASS_SPEC {
207 // Iterations are done on the _cur hash table, since they only need to
208 // see entries visible at the start of a collection pause.
209 // All other operations are done using the _next hash table.
210 RSHashTable* _cur;
211 RSHashTable* _next;
213 HeapRegion* _hr;
215 enum SomeAdditionalPrivateConstants {
216 InitialCapacity = 16
217 };
219 void expand();
221 bool _expanded;
223 bool expanded() { return _expanded; }
224 void set_expanded(bool b) { _expanded = b; }
226 SparsePRT* _next_expanded;
228 SparsePRT* next_expanded() { return _next_expanded; }
229 void set_next_expanded(SparsePRT* nxt) { _next_expanded = nxt; }
231 static SparsePRT* _head_expanded_list;
233 public:
234 SparsePRT(HeapRegion* hr);
236 ~SparsePRT();
238 size_t occupied() const { return _next->occupied_cards(); }
239 size_t mem_size() const;
241 // Attempts to ensure that the given card_index in the given region is in
242 // the sparse table. If successful (because the card was already
243 // present, or because it was successfullly added) returns "true".
244 // Otherwise, returns "false" to indicate that the addition would
245 // overflow the entry for the region. The caller must transfer these
246 // entries to a larger-capacity representation.
247 bool add_card(RegionIdx_t region_id, CardIdx_t card_index);
249 // If the table hold an entry for "region_ind", Copies its
250 // cards into "cards", which must be an array of length at least
251 // "SparePRTEntry::cards_num()", and returns "true"; otherwise,
252 // returns "false".
253 bool get_cards(RegionIdx_t region_ind, CardIdx_t* cards);
255 // Return the pointer to the entry associated with the given region.
256 SparsePRTEntry* get_entry(RegionIdx_t region_ind);
258 // If there is an entry for "region_ind", removes it and return "true";
259 // otherwise returns "false."
260 bool delete_entry(RegionIdx_t region_ind);
262 // Clear the table, and reinitialize to initial capacity.
263 void clear();
265 // Ensure that "_cur" and "_next" point to the same table.
266 void cleanup();
268 // Clean up all tables on the expanded list. Called single threaded.
269 static void cleanup_all();
270 RSHashTable* cur() const { return _cur; }
272 void init_iterator(SparsePRTIter* sprt_iter);
274 static void add_to_expanded_list(SparsePRT* sprt);
275 static SparsePRT* get_from_expanded_list();
277 bool contains_card(RegionIdx_t region_id, CardIdx_t card_index) const {
278 return _next->contains_card(region_id, card_index);
279 }
280 };
283 class SparsePRTIter: public RSHashTableIter {
284 public:
285 SparsePRTIter() : RSHashTableIter() { }
287 void init(const SparsePRT* sprt) {
288 RSHashTableIter::init(sprt->cur());
289 }
290 bool has_next(size_t& card_index) {
291 return RSHashTableIter::has_next(card_index);
292 }
293 };