1 /*
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24
25 #ifndef SHARE_VM_MEMORY_CARDTABLEMODREFBS_HPP
26 #define SHARE_VM_MEMORY_CARDTABLEMODREFBS_HPP
27
28 #include "memory/modRefBarrierSet.hpp"
29 #include "oops/oop.hpp"
30 #include "oops/oop.inline2.hpp"
31
32 // This kind of "BarrierSet" allows a "CollectedHeap" to detect and
33 // enumerate ref fields that have been modified (since the last
34 // enumeration.)
35
36 // As it currently stands, this barrier is *imprecise*: when a ref field in
37 // an object "o" is modified, the card table entry for the card containing
38 // the head of "o" is dirtied, not necessarily the card containing the
39 // modified field itself. For object arrays, however, the barrier *is*
40 // precise; only the card containing the modified element is dirtied.
41 // Any MemRegionClosures used to scan dirty cards should take these
42 // considerations into account.
43
44 class Generation;
45 class OopsInGenClosure;
46 class DirtyCardToOopClosure;
47 class ClearNoncleanCardWrapper;
48
49 class CardTableModRefBS: public ModRefBarrierSet {
50 // Some classes get to look at some private stuff.
51 friend class BytecodeInterpreter;
52 friend class VMStructs;
53 friend class CardTableRS;
54 friend class CheckForUnmarkedOops; // Needs access to raw card bytes.
55 friend class SharkBuilder;
56 #ifndef PRODUCT
57 // For debugging.
58 friend class GuaranteeNotModClosure;
59 #endif
60 protected:
61
62 enum CardValues {
63 clean_card = -1,
64 // The mask contains zeros in places for all other values.
65 clean_card_mask = clean_card - 31,
66
67 dirty_card = 0,
68 precleaned_card = 1,
69 claimed_card = 2,
70 deferred_card = 4,
71 last_card = 8,
72 CT_MR_BS_last_reserved = 16
73 };
74
75 // a word's worth (row) of clean card values
76 static const intptr_t clean_card_row = (intptr_t)(-1);
77
78 // dirty and precleaned are equivalent wrt younger_refs_iter.
79 static bool card_is_dirty_wrt_gen_iter(jbyte cv) {
80 return cv == dirty_card || cv == precleaned_card;
81 }
82
83 // Returns "true" iff the value "cv" will cause the card containing it
84 // to be scanned in the current traversal. May be overridden by
85 // subtypes.
86 virtual bool card_will_be_scanned(jbyte cv) {
87 return CardTableModRefBS::card_is_dirty_wrt_gen_iter(cv);
88 }
89
90 // Returns "true" iff the value "cv" may have represented a dirty card at
91 // some point.
92 virtual bool card_may_have_been_dirty(jbyte cv) {
93 return card_is_dirty_wrt_gen_iter(cv);
94 }
95
96 // The declaration order of these const fields is important; see the
97 // constructor before changing.
98 const MemRegion _whole_heap; // the region covered by the card table
99 size_t _guard_index; // index of very last element in the card
100 // table; it is set to a guard value
101 // (last_card) and should never be modified
102 size_t _last_valid_index; // index of the last valid element
103 const size_t _page_size; // page size used when mapping _byte_map
104 size_t _byte_map_size; // in bytes
105 jbyte* _byte_map; // the card marking array
106
107 int _cur_covered_regions;
108 // The covered regions should be in address order.
109 MemRegion* _covered;
110 // The committed regions correspond one-to-one to the covered regions.
111 // They represent the card-table memory that has been committed to service
112 // the corresponding covered region. It may be that committed region for
113 // one covered region corresponds to a larger region because of page-size
114 // roundings. Thus, a committed region for one covered region may
115 // actually extend onto the card-table space for the next covered region.
116 MemRegion* _committed;
117
118 // The last card is a guard card, and we commit the page for it so
119 // we can use the card for verification purposes. We make sure we never
120 // uncommit the MemRegion for that page.
121 MemRegion _guard_region;
122
123 protected:
124 // Initialization utilities; covered_words is the size of the covered region
125 // in, um, words.
126 inline size_t cards_required(size_t covered_words) {
127 // Add one for a guard card, used to detect errors.
128 const size_t words = align_size_up(covered_words, card_size_in_words);
129 return words / card_size_in_words + 1;
130 }
131
132 inline size_t compute_byte_map_size();
133
134 // Finds and return the index of the region, if any, to which the given
135 // region would be contiguous. If none exists, assign a new region and
136 // returns its index. Requires that no more than the maximum number of
137 // covered regions defined in the constructor are ever in use.
138 int find_covering_region_by_base(HeapWord* base);
139
140 // Same as above, but finds the region containing the given address
141 // instead of starting at a given base address.
142 int find_covering_region_containing(HeapWord* addr);
143
144 // Resize one of the regions covered by the remembered set.
145 virtual void resize_covered_region(MemRegion new_region);
146
147 // Returns the leftmost end of a committed region corresponding to a
148 // covered region before covered region "ind", or else "NULL" if "ind" is
149 // the first covered region.
150 HeapWord* largest_prev_committed_end(int ind) const;
151
152 // Returns the part of the region mr that doesn't intersect with
153 // any committed region other than self. Used to prevent uncommitting
154 // regions that are also committed by other regions. Also protects
155 // against uncommitting the guard region.
156 MemRegion committed_unique_to_self(int self, MemRegion mr) const;
157
158 // Mapping from address to card marking array entry
159 jbyte* byte_for(const void* p) const {
160 assert(_whole_heap.contains(p),
161 err_msg("Attempt to access p = "PTR_FORMAT" out of bounds of "
162 " card marking array's _whole_heap = ["PTR_FORMAT","PTR_FORMAT")",
163 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end())));
164 jbyte* result = &byte_map_base[uintptr_t(p) >> card_shift];
165 assert(result >= _byte_map && result < _byte_map + _byte_map_size,
166 "out of bounds accessor for card marking array");
167 return result;
168 }
169
170 // The card table byte one after the card marking array
171 // entry for argument address. Typically used for higher bounds
172 // for loops iterating through the card table.
173 jbyte* byte_after(const void* p) const {
174 return byte_for(p) + 1;
175 }
176
177 // Iterate over the portion of the card-table which covers the given
178 // region mr in the given space and apply cl to any dirty sub-regions
179 // of mr. Dirty cards are _not_ cleared by the iterator method itself,
180 // but closures may arrange to do so on their own should they so wish.
181 void non_clean_card_iterate_serial(MemRegion mr, MemRegionClosure* cl);
182
183 // A variant of the above that will operate in a parallel mode if
184 // worker threads are available, and clear the dirty cards as it
185 // processes them.
186 // XXX ??? MemRegionClosure above vs OopsInGenClosure below XXX
187 // XXX some new_dcto_cl's take OopClosure's, plus as above there are
188 // some MemRegionClosures. Clean this up everywhere. XXX
189 void non_clean_card_iterate_possibly_parallel(Space* sp, MemRegion mr,
190 OopsInGenClosure* cl, CardTableRS* ct);
191
192 private:
193 // Work method used to implement non_clean_card_iterate_possibly_parallel()
194 // above in the parallel case.
195 void non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,
196 OopsInGenClosure* cl, CardTableRS* ct,
197 int n_threads);
198
199 protected:
200 // Dirty the bytes corresponding to "mr" (not all of which must be
201 // covered.)
202 void dirty_MemRegion(MemRegion mr);
203
204 // Clear (to clean_card) the bytes entirely contained within "mr" (not
205 // all of which must be covered.)
206 void clear_MemRegion(MemRegion mr);
207
208 // *** Support for parallel card scanning.
209
210 // This is an array, one element per covered region of the card table.
211 // Each entry is itself an array, with one element per chunk in the
212 // covered region. Each entry of these arrays is the lowest non-clean
213 // card of the corresponding chunk containing part of an object from the
214 // previous chunk, or else NULL.
215 typedef jbyte* CardPtr;
216 typedef CardPtr* CardArr;
217 CardArr* _lowest_non_clean;
218 size_t* _lowest_non_clean_chunk_size;
219 uintptr_t* _lowest_non_clean_base_chunk_index;
220 int* _last_LNC_resizing_collection;
221
222 // Initializes "lowest_non_clean" to point to the array for the region
223 // covering "sp", and "lowest_non_clean_base_chunk_index" to the chunk
224 // index of the corresponding to the first element of that array.
225 // Ensures that these arrays are of sufficient size, allocating if necessary.
226 // May be called by several threads concurrently.
227 void get_LNC_array_for_space(Space* sp,
228 jbyte**& lowest_non_clean,
229 uintptr_t& lowest_non_clean_base_chunk_index,
230 size_t& lowest_non_clean_chunk_size);
231
232 // Returns the number of chunks necessary to cover "mr".
233 size_t chunks_to_cover(MemRegion mr) {
234 return (size_t)(addr_to_chunk_index(mr.last()) -
235 addr_to_chunk_index(mr.start()) + 1);
236 }
237
238 // Returns the index of the chunk in a stride which
239 // covers the given address.
240 uintptr_t addr_to_chunk_index(const void* addr) {
241 uintptr_t card = (uintptr_t) byte_for(addr);
242 return card / ParGCCardsPerStrideChunk;
243 }
244
245 // Apply cl, which must either itself apply dcto_cl or be dcto_cl,
246 // to the cards in the stride (of n_strides) within the given space.
247 void process_stride(Space* sp,
248 MemRegion used,
249 jint stride, int n_strides,
250 OopsInGenClosure* cl,
251 CardTableRS* ct,
252 jbyte** lowest_non_clean,
253 uintptr_t lowest_non_clean_base_chunk_index,
254 size_t lowest_non_clean_chunk_size);
255
256 // Makes sure that chunk boundaries are handled appropriately, by
257 // adjusting the min_done of dcto_cl, and by using a special card-table
258 // value to indicate how min_done should be set.
259 void process_chunk_boundaries(Space* sp,
260 DirtyCardToOopClosure* dcto_cl,
261 MemRegion chunk_mr,
262 MemRegion used,
263 jbyte** lowest_non_clean,
264 uintptr_t lowest_non_clean_base_chunk_index,
265 size_t lowest_non_clean_chunk_size);
266
267 public:
268 // Constants
269 enum SomePublicConstants {
270 card_shift = 9,
271 card_size = 1 << card_shift,
272 card_size_in_words = card_size / sizeof(HeapWord)
273 };
274
275 static int clean_card_val() { return clean_card; }
276 static int clean_card_mask_val() { return clean_card_mask; }
277 static int dirty_card_val() { return dirty_card; }
278 static int claimed_card_val() { return claimed_card; }
279 static int precleaned_card_val() { return precleaned_card; }
280 static int deferred_card_val() { return deferred_card; }
281
282 // For RTTI simulation.
283 bool is_a(BarrierSet::Name bsn) {
284 return bsn == BarrierSet::CardTableModRef || ModRefBarrierSet::is_a(bsn);
285 }
286
287 CardTableModRefBS(MemRegion whole_heap);
288 ~CardTableModRefBS();
289
290 virtual void initialize();
291
292 // *** Barrier set functions.
293
294 bool has_write_ref_pre_barrier() { return false; }
295
296 // Record a reference update. Note that these versions are precise!
297 // The scanning code has to handle the fact that the write barrier may be
298 // either precise or imprecise. We make non-virtual inline variants of
299 // these functions here for performance.
300 protected:
301 void write_ref_field_work(oop obj, size_t offset, oop newVal);
302 virtual void write_ref_field_work(void* field, oop newVal, bool release = false);
303 public:
304
305 bool has_write_ref_array_opt() { return true; }
306 bool has_write_region_opt() { return true; }
307
308 inline void inline_write_region(MemRegion mr) {
309 dirty_MemRegion(mr);
310 }
311 protected:
312 void write_region_work(MemRegion mr) {
313 inline_write_region(mr);
314 }
315 public:
316
317 inline void inline_write_ref_array(MemRegion mr) {
318 dirty_MemRegion(mr);
319 }
320 protected:
321 void write_ref_array_work(MemRegion mr) {
322 inline_write_ref_array(mr);
323 }
324 public:
325
326 bool is_aligned(HeapWord* addr) {
327 return is_card_aligned(addr);
328 }
329
330 // *** Card-table-barrier-specific things.
331
332 template <class T> inline void inline_write_ref_field_pre(T* field, oop newVal) {}
333
334 template <class T> inline void inline_write_ref_field(T* field, oop newVal, bool release) {
335 jbyte* byte = byte_for((void*)field);
336 if (release) {
337 // Perform a releasing store if requested.
338 OrderAccess::release_store((volatile jbyte*) byte, dirty_card);
339 } else {
340 *byte = dirty_card;
341 }
342 }
343
344 // These are used by G1, when it uses the card table as a temporary data
345 // structure for card claiming.
346 bool is_card_dirty(size_t card_index) {
347 return _byte_map[card_index] == dirty_card_val();
348 }
349
350 void mark_card_dirty(size_t card_index) {
351 _byte_map[card_index] = dirty_card_val();
352 }
353
354 bool is_card_clean(size_t card_index) {
355 return _byte_map[card_index] == clean_card_val();
356 }
357
358 // Card marking array base (adjusted for heap low boundary)
359 // This would be the 0th element of _byte_map, if the heap started at 0x0.
360 // But since the heap starts at some higher address, this points to somewhere
361 // before the beginning of the actual _byte_map.
362 jbyte* byte_map_base;
363
364 // Return true if "p" is at the start of a card.
365 bool is_card_aligned(HeapWord* p) {
366 jbyte* pcard = byte_for(p);
367 return (addr_for(pcard) == p);
368 }
369
370 HeapWord* align_to_card_boundary(HeapWord* p) {
371 jbyte* pcard = byte_for(p + card_size_in_words - 1);
372 return addr_for(pcard);
373 }
374
375 // The kinds of precision a CardTableModRefBS may offer.
376 enum PrecisionStyle {
377 Precise,
378 ObjHeadPreciseArray
379 };
380
381 // Tells what style of precision this card table offers.
382 PrecisionStyle precision() {
383 return ObjHeadPreciseArray; // Only one supported for now.
384 }
385
386 // ModRefBS functions.
387 virtual void invalidate(MemRegion mr, bool whole_heap = false);
388 void clear(MemRegion mr);
389 void dirty(MemRegion mr);
390
391 // *** Card-table-RemSet-specific things.
392
393 // Invoke "cl.do_MemRegion" on a set of MemRegions that collectively
394 // includes all the modified cards (expressing each card as a
395 // MemRegion). Thus, several modified cards may be lumped into one
396 // region. The regions are non-overlapping, and are visited in
397 // *decreasing* address order. (This order aids with imprecise card
398 // marking, where a dirty card may cause scanning, and summarization
399 // marking, of objects that extend onto subsequent cards.)
400 void mod_card_iterate(MemRegionClosure* cl) {
401 non_clean_card_iterate_serial(_whole_heap, cl);
402 }
403
404 // Like the "mod_cards_iterate" above, except only invokes the closure
405 // for cards within the MemRegion "mr" (which is required to be
406 // card-aligned and sized.)
407 void mod_card_iterate(MemRegion mr, MemRegionClosure* cl) {
408 non_clean_card_iterate_serial(mr, cl);
409 }
410
411 static uintx ct_max_alignment_constraint();
412
413 // Apply closure "cl" to the dirty cards containing some part of
414 // MemRegion "mr".
415 void dirty_card_iterate(MemRegion mr, MemRegionClosure* cl);
416
417 // Return the MemRegion corresponding to the first maximal run
418 // of dirty cards lying completely within MemRegion mr.
419 // If reset is "true", then sets those card table entries to the given
420 // value.
421 MemRegion dirty_card_range_after_reset(MemRegion mr, bool reset,
422 int reset_val);
423
424 // Provide read-only access to the card table array.
425 const jbyte* byte_for_const(const void* p) const {
426 return byte_for(p);
427 }
428 const jbyte* byte_after_const(const void* p) const {
429 return byte_after(p);
430 }
431
432 // Mapping from card marking array entry to address of first word
433 HeapWord* addr_for(const jbyte* p) const {
434 assert(p >= _byte_map && p < _byte_map + _byte_map_size,
435 "out of bounds access to card marking array");
436 size_t delta = pointer_delta(p, byte_map_base, sizeof(jbyte));
437 HeapWord* result = (HeapWord*) (delta << card_shift);
438 assert(_whole_heap.contains(result),
439 err_msg("Returning result = "PTR_FORMAT" out of bounds of "
440 " card marking array's _whole_heap = ["PTR_FORMAT","PTR_FORMAT")",
441 p2i(result), p2i(_whole_heap.start()), p2i(_whole_heap.end())));
442 return result;
443 }
444
445 // Mapping from address to card marking array index.
446 size_t index_for(void* p) {
447 assert(_whole_heap.contains(p),
448 err_msg("Attempt to access p = "PTR_FORMAT" out of bounds of "
449 " card marking array's _whole_heap = ["PTR_FORMAT","PTR_FORMAT")",
450 p2i(p), p2i(_whole_heap.start()), p2i(_whole_heap.end())));
451 return byte_for(p) - _byte_map;
452 }
453
454 const jbyte* byte_for_index(const size_t card_index) const {
455 return _byte_map + card_index;
456 }
457
458 // Print a description of the memory for the barrier set
459 virtual void print_on(outputStream* st) const;
460
461 void verify();
462 void verify_guard();
463
464 // val_equals -> it will check that all cards covered by mr equal val
465 // !val_equals -> it will check that all cards covered by mr do not equal val
466 void verify_region(MemRegion mr, jbyte val, bool val_equals) PRODUCT_RETURN;
467 void verify_not_dirty_region(MemRegion mr) PRODUCT_RETURN;
468 void verify_dirty_region(MemRegion mr) PRODUCT_RETURN;
469 };
470
471 class CardTableRS;
472
473 // A specialization for the CardTableRS gen rem set.
474 class CardTableModRefBSForCTRS: public CardTableModRefBS {
475 CardTableRS* _rs;
476 protected:
477 bool card_will_be_scanned(jbyte cv);
478 bool card_may_have_been_dirty(jbyte cv);
479 public:
480 CardTableModRefBSForCTRS(MemRegion whole_heap) :
481 CardTableModRefBS(whole_heap) {}
482
483 void set_CTRS(CardTableRS* rs) { _rs = rs; }
484 };
485
486
487 #endif // SHARE_VM_MEMORY_CARDTABLEMODREFBS_HPP