1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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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 returns "NULL."
126 SparsePRTEntry* entry_for_region_ind(RegionIdx_t region_ind) const;
127
128 // Requires that the caller hold a lock preventing parallel modifying
129 // operations, and that the the table be less than completely full. If
130 // an entry for "region_ind" is already in the table, finds it and
131 // returns its address; otherwise allocates, initializes, inserts and
132 // returns a new entry for "region_ind".
133 SparsePRTEntry* entry_for_region_ind_create(RegionIdx_t region_ind);
134
135 // Returns the index of the next free entry in "_entries".
136 int alloc_entry();
137 // Declares the entry "fi" to be free. (It must have already been
138 // deleted from any bucket lists.
139 void free_entry(int fi);
140
141 public:
142 RSHashTable(size_t capacity);
143 ~RSHashTable();
144
145 // Attempts to ensure that the given card_index in the given region is in
146 // the sparse table. If successful (because the card was already
147 // present, or because it was successfully added) returns "true".
148 // Otherwise, returns "false" to indicate that the addition would
149 // overflow the entry for the region. The caller must transfer these
150 // entries to a larger-capacity representation.
151 bool add_card(RegionIdx_t region_id, CardIdx_t card_index);
152
153 bool get_cards(RegionIdx_t region_id, CardIdx_t* cards);
154
155 bool delete_entry(RegionIdx_t region_id);
156
157 bool contains_card(RegionIdx_t region_id, CardIdx_t card_index) const;
158
159 void add_entry(SparsePRTEntry* e);
160
161 SparsePRTEntry* get_entry(RegionIdx_t region_id);
162
163 void clear();
164
165 size_t capacity() const { return _capacity; }
166 size_t capacity_mask() const { return _capacity_mask; }
167 size_t occupied_entries() const { return _occupied_entries; }
168 size_t occupied_cards() const { return _occupied_cards; }
169 size_t mem_size() const;
170
171 SparsePRTEntry* entry(int i) const { return (SparsePRTEntry*)((char*)_entries + SparsePRTEntry::size() * i); }
172
173 void print();
174 };
175
176 // ValueObj because will be embedded in HRRS iterator.
177 class RSHashTableIter VALUE_OBJ_CLASS_SPEC {
178 int _tbl_ind; // [-1, 0.._rsht->_capacity)
179 int _bl_ind; // [-1, 0.._rsht->_capacity)
180 short _card_ind; // [0..SparsePRTEntry::cards_num())
181 RSHashTable* _rsht;
182
183 // If the bucket list pointed to by _bl_ind contains a card, sets
184 // _bl_ind to the index of that entry, and returns the card.
185 // Otherwise, returns SparseEntry::NullEntry.
186 CardIdx_t find_first_card_in_list();
187
188 // Computes the proper card index for the card whose offset in the
189 // current region (as indicated by _bl_ind) is "ci".
190 // This is subject to errors when there is iteration concurrent with
191 // modification, but these errors should be benign.
192 size_t compute_card_ind(CardIdx_t ci);
193
194 public:
195 RSHashTableIter(RSHashTable* rsht) :
196 _tbl_ind(RSHashTable::NullEntry), // So that first increment gets to 0.
197 _bl_ind(RSHashTable::NullEntry),
198 _card_ind((SparsePRTEntry::cards_num() - 1)),
199 _rsht(rsht) {}
200
201 bool has_next(size_t& card_index);
202 };
203
204 // Concurrent access to a SparsePRT must be serialized by some external mutex.
205
206 class SparsePRTIter;
207 class SparsePRTCleanupTask;
208
209 class SparsePRT VALUE_OBJ_CLASS_SPEC {
210 friend class SparsePRTCleanupTask;
211
212 // Iterations are done on the _cur hash table, since they only need to
213 // see entries visible at the start of a collection pause.
214 // All other operations are done using the _next hash table.
215 RSHashTable* _cur;
216 RSHashTable* _next;
217
218 HeapRegion* _hr;
219
220 enum SomeAdditionalPrivateConstants {
221 InitialCapacity = 16
222 };
223
224 void expand();
225
226 bool _expanded;
227
228 bool expanded() { return _expanded; }
229 void set_expanded(bool b) { _expanded = b; }
230
231 SparsePRT* _next_expanded;
232
233 SparsePRT* next_expanded() { return _next_expanded; }
234 void set_next_expanded(SparsePRT* nxt) { _next_expanded = nxt; }
235
236 bool should_be_on_expanded_list();
237
238 static SparsePRT* _head_expanded_list;
239
240 public:
241 SparsePRT(HeapRegion* hr);
242
243 ~SparsePRT();
244
245 size_t occupied() const { return _next->occupied_cards(); }
246 size_t mem_size() const;
247
248 // Attempts to ensure that the given card_index in the given region is in
249 // the sparse table. If successful (because the card was already
250 // present, or because it was successfully added) returns "true".
251 // Otherwise, returns "false" to indicate that the addition would
252 // overflow the entry for the region. The caller must transfer these
253 // entries to a larger-capacity representation.
254 bool add_card(RegionIdx_t region_id, CardIdx_t card_index);
255
256 // If the table hold an entry for "region_ind", Copies its
257 // cards into "cards", which must be an array of length at least
258 // "SparePRTEntry::cards_num()", and returns "true"; otherwise,
259 // returns "false".
260 bool get_cards(RegionIdx_t region_ind, CardIdx_t* cards);
261
262 // Return the pointer to the entry associated with the given region.
263 SparsePRTEntry* get_entry(RegionIdx_t region_ind);
264
265 // If there is an entry for "region_ind", removes it and return "true";
266 // otherwise returns "false."
267 bool delete_entry(RegionIdx_t region_ind);
268
269 // Clear the table, and reinitialize to initial capacity.
270 void clear();
271
272 // Ensure that "_cur" and "_next" point to the same table.
273 void cleanup();
274
275 // Clean up all tables on the expanded list. Called single threaded.
276 static void cleanup_all();
277 RSHashTable* cur() const { return _cur; }
278
279 static void add_to_expanded_list(SparsePRT* sprt);
280 static SparsePRT* get_from_expanded_list();
281
282 // The purpose of these three methods is to help the GC workers
283 // during the cleanup pause to recreate the expanded list, purging
284 // any tables from it that belong to regions that are freed during
285 // cleanup (if we don't purge those tables, there is a race that
286 // causes various crashes; see CR 7014261).
287 //
288 // We chose to recreate the expanded list, instead of purging
289 // entries from it by iterating over it, to avoid this serial phase
290 // at the end of the cleanup pause.
291 //
292 // The three methods below work as follows:
293 // * reset_for_cleanup_tasks() : Nulls the expanded list head at the
294 // start of the cleanup pause.
295 // * do_cleanup_work() : Called by the cleanup workers for every
296 // region that is not free / is being freed by the cleanup
297 // pause. It creates a list of expanded tables whose head / tail
298 // are on the thread-local SparsePRTCleanupTask object.
299 // * finish_cleanup_task() : Called by the cleanup workers after
300 // they complete their cleanup task. It adds the local list into
301 // the global expanded list. It assumes that the
302 // ParGCRareEvent_lock is being held to ensure MT-safety.
303 static void reset_for_cleanup_tasks();
304 void do_cleanup_work(SparsePRTCleanupTask* sprt_cleanup_task);
305 static void finish_cleanup_task(SparsePRTCleanupTask* sprt_cleanup_task);
306
307 bool contains_card(RegionIdx_t region_id, CardIdx_t card_index) const {
308 return _next->contains_card(region_id, card_index);
309 }
310 };
311
312 class SparsePRTIter: public RSHashTableIter {
313 public:
314 SparsePRTIter(const SparsePRT* sprt) :
315 RSHashTableIter(sprt->cur()) {}
316
317 bool has_next(size_t& card_index) {
318 return RSHashTableIter::has_next(card_index);
319 }
320 };
321
322 // This allows each worker during a cleanup pause to create a
323 // thread-local list of sparse tables that have been expanded and need
324 // to be processed at the beginning of the next GC pause. This lists
325 // are concatenated into the single expanded list at the end of the
326 // cleanup pause.
327 class SparsePRTCleanupTask VALUE_OBJ_CLASS_SPEC {
328 private:
329 SparsePRT* _head;
330 SparsePRT* _tail;
331
332 public:
333 SparsePRTCleanupTask() : _head(NULL), _tail(NULL) { }
334
335 void add(SparsePRT* sprt);
336 SparsePRT* head() { return _head; }
337 SparsePRT* tail() { return _tail; }
338 };
339
340 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_SPARSEPRT_HPP