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