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
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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/cardTableBarrierSet.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