1 /*
2 * Copyright (c) 2001, 2018, 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.
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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
21 * questions.
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23 */
24
25 #include "precompiled.hpp"
26 #include "gc/shared/cardTableRS.hpp"
27 #include "gc/shared/genCollectedHeap.hpp"
28 #include "gc/shared/genOopClosures.hpp"
29 #include "gc/shared/generation.hpp"
30 #include "gc/shared/space.inline.hpp"
31 #include "memory/allocation.inline.hpp"
32 #include "oops/access.inline.hpp"
33 #include "oops/oop.inline.hpp"
34 #include "runtime/atomic.hpp"
35 #include "runtime/java.hpp"
36 #include "runtime/os.hpp"
37 #include "utilities/macros.hpp"
38
39 class HasAccumulatedModifiedOopsClosure : public CLDClosure {
40 bool _found;
41 public:
42 HasAccumulatedModifiedOopsClosure() : _found(false) {}
43 void do_cld(ClassLoaderData* cld) {
44 if (_found) {
45 return;
46 }
47
48 if (cld->has_accumulated_modified_oops()) {
49 _found = true;
50 }
51 }
52 bool found() {
53 return _found;
54 }
55 };
56
57 bool CLDRemSet::mod_union_is_clear() {
58 HasAccumulatedModifiedOopsClosure closure;
59 ClassLoaderDataGraph::cld_do(&closure);
60
61 return !closure.found();
62 }
63
64
65 class ClearCLDModUnionClosure : public CLDClosure {
66 public:
67 void do_cld(ClassLoaderData* cld) {
68 if (cld->has_accumulated_modified_oops()) {
69 cld->clear_accumulated_modified_oops();
70 }
71 }
72 };
73
74 void CLDRemSet::clear_mod_union() {
75 ClearCLDModUnionClosure closure;
76 ClassLoaderDataGraph::cld_do(&closure);
77 }
78
79
80 jbyte CardTableRS::find_unused_youngergenP_card_value() {
81 for (jbyte v = youngergenP1_card;
82 v < cur_youngergen_and_prev_nonclean_card;
83 v++) {
84 bool seen = false;
85 for (int g = 0; g < _regions_to_iterate; g++) {
86 if (_last_cur_val_in_gen[g] == v) {
87 seen = true;
88 break;
89 }
90 }
91 if (!seen) {
92 return v;
93 }
94 }
95 ShouldNotReachHere();
96 return 0;
97 }
98
99 void CardTableRS::prepare_for_younger_refs_iterate(bool parallel) {
100 // Parallel or sequential, we must always set the prev to equal the
101 // last one written.
102 if (parallel) {
103 // Find a parallel value to be used next.
104 jbyte next_val = find_unused_youngergenP_card_value();
105 set_cur_youngergen_card_val(next_val);
106
107 } else {
108 // In an sequential traversal we will always write youngergen, so that
109 // the inline barrier is correct.
110 set_cur_youngergen_card_val(youngergen_card);
111 }
112 }
113
114 void CardTableRS::younger_refs_iterate(Generation* g,
115 OopsInGenClosure* blk,
116 uint n_threads) {
117 // The indexing in this array is slightly odd. We want to access
118 // the old generation record here, which is at index 2.
119 _last_cur_val_in_gen[2] = cur_youngergen_card_val();
120 g->younger_refs_iterate(blk, n_threads);
121 }
122
123 inline bool ClearNoncleanCardWrapper::clear_card(jbyte* entry) {
124 if (_is_par) {
125 return clear_card_parallel(entry);
126 } else {
127 return clear_card_serial(entry);
128 }
129 }
130
131 inline bool ClearNoncleanCardWrapper::clear_card_parallel(jbyte* entry) {
132 while (true) {
133 // In the parallel case, we may have to do this several times.
134 jbyte entry_val = *entry;
135 assert(entry_val != CardTableRS::clean_card_val(),
136 "We shouldn't be looking at clean cards, and this should "
137 "be the only place they get cleaned.");
138 if (CardTableRS::card_is_dirty_wrt_gen_iter(entry_val)
139 || _ct->is_prev_youngergen_card_val(entry_val)) {
140 jbyte res =
141 Atomic::cmpxchg(CardTableRS::clean_card_val(), entry, entry_val);
142 if (res == entry_val) {
143 break;
144 } else {
145 assert(res == CardTableRS::cur_youngergen_and_prev_nonclean_card,
146 "The CAS above should only fail if another thread did "
147 "a GC write barrier.");
148 }
149 } else if (entry_val ==
150 CardTableRS::cur_youngergen_and_prev_nonclean_card) {
151 // Parallelism shouldn't matter in this case. Only the thread
152 // assigned to scan the card should change this value.
153 *entry = _ct->cur_youngergen_card_val();
154 break;
155 } else {
156 assert(entry_val == _ct->cur_youngergen_card_val(),
157 "Should be the only possibility.");
158 // In this case, the card was clean before, and become
159 // cur_youngergen only because of processing of a promoted object.
160 // We don't have to look at the card.
161 return false;
162 }
163 }
164 return true;
165 }
166
167
168 inline bool ClearNoncleanCardWrapper::clear_card_serial(jbyte* entry) {
169 jbyte entry_val = *entry;
170 assert(entry_val != CardTableRS::clean_card_val(),
171 "We shouldn't be looking at clean cards, and this should "
172 "be the only place they get cleaned.");
173 assert(entry_val != CardTableRS::cur_youngergen_and_prev_nonclean_card,
174 "This should be possible in the sequential case.");
175 *entry = CardTableRS::clean_card_val();
176 return true;
177 }
178
179 ClearNoncleanCardWrapper::ClearNoncleanCardWrapper(
180 DirtyCardToOopClosure* dirty_card_closure, CardTableRS* ct, bool is_par) :
181 _dirty_card_closure(dirty_card_closure), _ct(ct), _is_par(is_par) {
182 }
183
184 bool ClearNoncleanCardWrapper::is_word_aligned(jbyte* entry) {
185 return (((intptr_t)entry) & (BytesPerWord-1)) == 0;
186 }
187
188 // The regions are visited in *decreasing* address order.
189 // This order aids with imprecise card marking, where a dirty
190 // card may cause scanning, and summarization marking, of objects
191 // that extend onto subsequent cards.
192 void ClearNoncleanCardWrapper::do_MemRegion(MemRegion mr) {
193 assert(mr.word_size() > 0, "Error");
194 assert(_ct->is_aligned(mr.start()), "mr.start() should be card aligned");
195 // mr.end() may not necessarily be card aligned.
196 jbyte* cur_entry = _ct->byte_for(mr.last());
197 const jbyte* limit = _ct->byte_for(mr.start());
198 HeapWord* end_of_non_clean = mr.end();
199 HeapWord* start_of_non_clean = end_of_non_clean;
200 while (cur_entry >= limit) {
201 HeapWord* cur_hw = _ct->addr_for(cur_entry);
202 if ((*cur_entry != CardTableRS::clean_card_val()) && clear_card(cur_entry)) {
203 // Continue the dirty range by opening the
204 // dirty window one card to the left.
205 start_of_non_clean = cur_hw;
206 } else {
207 // We hit a "clean" card; process any non-empty
208 // "dirty" range accumulated so far.
209 if (start_of_non_clean < end_of_non_clean) {
210 const MemRegion mrd(start_of_non_clean, end_of_non_clean);
211 _dirty_card_closure->do_MemRegion(mrd);
212 }
213
214 // fast forward through potential continuous whole-word range of clean cards beginning at a word-boundary
215 if (is_word_aligned(cur_entry)) {
216 jbyte* cur_row = cur_entry - BytesPerWord;
217 while (cur_row >= limit && *((intptr_t*)cur_row) == CardTableRS::clean_card_row_val()) {
218 cur_row -= BytesPerWord;
219 }
220 cur_entry = cur_row + BytesPerWord;
221 cur_hw = _ct->addr_for(cur_entry);
222 }
223
224 // Reset the dirty window, while continuing to look
225 // for the next dirty card that will start a
226 // new dirty window.
227 end_of_non_clean = cur_hw;
228 start_of_non_clean = cur_hw;
229 }
230 // Note that "cur_entry" leads "start_of_non_clean" in
231 // its leftward excursion after this point
232 // in the loop and, when we hit the left end of "mr",
233 // will point off of the left end of the card-table
234 // for "mr".
235 cur_entry--;
236 }
237 // If the first card of "mr" was dirty, we will have
238 // been left with a dirty window, co-initial with "mr",
239 // which we now process.
240 if (start_of_non_clean < end_of_non_clean) {
241 const MemRegion mrd(start_of_non_clean, end_of_non_clean);
242 _dirty_card_closure->do_MemRegion(mrd);
243 }
244 }
245
246 // clean (by dirty->clean before) ==> cur_younger_gen
247 // dirty ==> cur_youngergen_and_prev_nonclean_card
248 // precleaned ==> cur_youngergen_and_prev_nonclean_card
249 // prev-younger-gen ==> cur_youngergen_and_prev_nonclean_card
250 // cur-younger-gen ==> cur_younger_gen
251 // cur_youngergen_and_prev_nonclean_card ==> no change.
252 void CardTableRS::write_ref_field_gc_par(void* field, oop new_val) {
253 volatile jbyte* entry = byte_for(field);
254 do {
255 jbyte entry_val = *entry;
256 // We put this first because it's probably the most common case.
257 if (entry_val == clean_card_val()) {
258 // No threat of contention with cleaning threads.
259 *entry = cur_youngergen_card_val();
260 return;
261 } else if (card_is_dirty_wrt_gen_iter(entry_val)
262 || is_prev_youngergen_card_val(entry_val)) {
263 // Mark it as both cur and prev youngergen; card cleaning thread will
264 // eventually remove the previous stuff.
265 jbyte new_val = cur_youngergen_and_prev_nonclean_card;
266 jbyte res = Atomic::cmpxchg(new_val, entry, entry_val);
267 // Did the CAS succeed?
268 if (res == entry_val) return;
269 // Otherwise, retry, to see the new value.
270 continue;
271 } else {
272 assert(entry_val == cur_youngergen_and_prev_nonclean_card
273 || entry_val == cur_youngergen_card_val(),
274 "should be only possibilities.");
275 return;
276 }
277 } while (true);
278 }
279
280 void CardTableRS::younger_refs_in_space_iterate(Space* sp,
281 OopsInGenClosure* cl,
282 uint n_threads) {
283 verify_used_region_at_save_marks(sp);
284
285 const MemRegion urasm = sp->used_region_at_save_marks();
286 non_clean_card_iterate_possibly_parallel(sp, urasm, cl, this, n_threads);
287 }
288
289 #ifdef ASSERT
290 void CardTableRS::verify_used_region_at_save_marks(Space* sp) const {
291 MemRegion ur = sp->used_region();
292 MemRegion urasm = sp->used_region_at_save_marks();
293
294 assert(ur.contains(urasm),
295 "Did you forget to call save_marks()? "
296 "[" PTR_FORMAT ", " PTR_FORMAT ") is not contained in "
297 "[" PTR_FORMAT ", " PTR_FORMAT ")",
298 p2i(urasm.start()), p2i(urasm.end()), p2i(ur.start()), p2i(ur.end()));
299 }
300 #endif
301
302 void CardTableRS::clear_into_younger(Generation* old_gen) {
303 assert(GenCollectedHeap::heap()->is_old_gen(old_gen),
304 "Should only be called for the old generation");
305 // The card tables for the youngest gen need never be cleared.
306 // There's a bit of subtlety in the clear() and invalidate()
307 // methods that we exploit here and in invalidate_or_clear()
308 // below to avoid missing cards at the fringes. If clear() or
309 // invalidate() are changed in the future, this code should
310 // be revisited. 20040107.ysr
311 clear(old_gen->prev_used_region());
312 }
313
314 void CardTableRS::invalidate_or_clear(Generation* old_gen) {
315 assert(GenCollectedHeap::heap()->is_old_gen(old_gen),
316 "Should only be called for the old generation");
317 // Invalidate the cards for the currently occupied part of
318 // the old generation and clear the cards for the
319 // unoccupied part of the generation (if any, making use
320 // of that generation's prev_used_region to determine that
321 // region). No need to do anything for the youngest
322 // generation. Also see note#20040107.ysr above.
323 MemRegion used_mr = old_gen->used_region();
324 MemRegion to_be_cleared_mr = old_gen->prev_used_region().minus(used_mr);
325 if (!to_be_cleared_mr.is_empty()) {
326 clear(to_be_cleared_mr);
327 }
328 invalidate(used_mr);
329 }
330
331
332 class VerifyCleanCardClosure: public OopClosure {
333 private:
334 HeapWord* _boundary;
335 HeapWord* _begin;
336 HeapWord* _end;
337 protected:
338 template <class T> void do_oop_work(T* p) {
339 HeapWord* jp = (HeapWord*)p;
340 assert(jp >= _begin && jp < _end,
341 "Error: jp " PTR_FORMAT " should be within "
342 "[_begin, _end) = [" PTR_FORMAT "," PTR_FORMAT ")",
343 p2i(jp), p2i(_begin), p2i(_end));
344 oop obj = RawAccess<>::oop_load(p);
345 guarantee(obj == NULL || (HeapWord*)obj >= _boundary,
346 "pointer " PTR_FORMAT " at " PTR_FORMAT " on "
347 "clean card crosses boundary" PTR_FORMAT,
348 p2i(obj), p2i(jp), p2i(_boundary));
349 }
350
351 public:
352 VerifyCleanCardClosure(HeapWord* b, HeapWord* begin, HeapWord* end) :
353 _boundary(b), _begin(begin), _end(end) {
354 assert(b <= begin,
355 "Error: boundary " PTR_FORMAT " should be at or below begin " PTR_FORMAT,
356 p2i(b), p2i(begin));
357 assert(begin <= end,
358 "Error: begin " PTR_FORMAT " should be strictly below end " PTR_FORMAT,
359 p2i(begin), p2i(end));
360 }
361
362 virtual void do_oop(oop* p) { VerifyCleanCardClosure::do_oop_work(p); }
363 virtual void do_oop(narrowOop* p) { VerifyCleanCardClosure::do_oop_work(p); }
364 };
365
366 class VerifyCTSpaceClosure: public SpaceClosure {
367 private:
368 CardTableRS* _ct;
369 HeapWord* _boundary;
370 public:
371 VerifyCTSpaceClosure(CardTableRS* ct, HeapWord* boundary) :
372 _ct(ct), _boundary(boundary) {}
373 virtual void do_space(Space* s) { _ct->verify_space(s, _boundary); }
374 };
375
376 class VerifyCTGenClosure: public GenCollectedHeap::GenClosure {
377 CardTableRS* _ct;
378 public:
379 VerifyCTGenClosure(CardTableRS* ct) : _ct(ct) {}
380 void do_generation(Generation* gen) {
381 // Skip the youngest generation.
382 if (GenCollectedHeap::heap()->is_young_gen(gen)) {
383 return;
384 }
385 // Normally, we're interested in pointers to younger generations.
386 VerifyCTSpaceClosure blk(_ct, gen->reserved().start());
387 gen->space_iterate(&blk, true);
388 }
389 };
390
391 void CardTableRS::verify_space(Space* s, HeapWord* gen_boundary) {
392 // We don't need to do young-gen spaces.
393 if (s->end() <= gen_boundary) return;
394 MemRegion used = s->used_region();
395
396 jbyte* cur_entry = byte_for(used.start());
397 jbyte* limit = byte_after(used.last());
398 while (cur_entry < limit) {
399 if (*cur_entry == clean_card_val()) {
400 jbyte* first_dirty = cur_entry+1;
401 while (first_dirty < limit &&
402 *first_dirty == clean_card_val()) {
403 first_dirty++;
404 }
405 // If the first object is a regular object, and it has a
406 // young-to-old field, that would mark the previous card.
407 HeapWord* boundary = addr_for(cur_entry);
408 HeapWord* end = (first_dirty >= limit) ? used.end() : addr_for(first_dirty);
409 HeapWord* boundary_block = s->block_start(boundary);
410 HeapWord* begin = boundary; // Until proven otherwise.
411 HeapWord* start_block = boundary_block; // Until proven otherwise.
412 if (boundary_block < boundary) {
413 if (s->block_is_obj(boundary_block) && s->obj_is_alive(boundary_block)) {
414 oop boundary_obj = oop(boundary_block);
415 if (!boundary_obj->is_objArray() &&
416 !boundary_obj->is_typeArray()) {
417 guarantee(cur_entry > byte_for(used.start()),
418 "else boundary would be boundary_block");
419 if (*byte_for(boundary_block) != clean_card_val()) {
420 begin = boundary_block + s->block_size(boundary_block);
421 start_block = begin;
422 }
423 }
424 }
425 }
426 // Now traverse objects until end.
427 if (begin < end) {
428 MemRegion mr(begin, end);
429 VerifyCleanCardClosure verify_blk(gen_boundary, begin, end);
430 for (HeapWord* cur = start_block; cur < end; cur += s->block_size(cur)) {
431 if (s->block_is_obj(cur) && s->obj_is_alive(cur)) {
432 oop(cur)->oop_iterate_no_header(&verify_blk, mr);
433 }
434 }
435 }
436 cur_entry = first_dirty;
437 } else {
438 // We'd normally expect that cur_youngergen_and_prev_nonclean_card
439 // is a transient value, that cannot be in the card table
440 // except during GC, and thus assert that:
441 // guarantee(*cur_entry != cur_youngergen_and_prev_nonclean_card,
442 // "Illegal CT value");
443 // That however, need not hold, as will become clear in the
444 // following...
445
446 // We'd normally expect that if we are in the parallel case,
447 // we can't have left a prev value (which would be different
448 // from the current value) in the card table, and so we'd like to
449 // assert that:
450 // guarantee(cur_youngergen_card_val() == youngergen_card
451 // || !is_prev_youngergen_card_val(*cur_entry),
452 // "Illegal CT value");
453 // That, however, may not hold occasionally, because of
454 // CMS or MSC in the old gen. To wit, consider the
455 // following two simple illustrative scenarios:
456 // (a) CMS: Consider the case where a large object L
457 // spanning several cards is allocated in the old
458 // gen, and has a young gen reference stored in it, dirtying
459 // some interior cards. A young collection scans the card,
460 // finds a young ref and installs a youngergenP_n value.
461 // L then goes dead. Now a CMS collection starts,
462 // finds L dead and sweeps it up. Assume that L is
463 // abutting _unallocated_blk, so _unallocated_blk is
464 // adjusted down to (below) L. Assume further that
465 // no young collection intervenes during this CMS cycle.
466 // The next young gen cycle will not get to look at this
467 // youngergenP_n card since it lies in the unoccupied
468 // part of the space.
469 // Some young collections later the blocks on this
470 // card can be re-allocated either due to direct allocation
471 // or due to absorbing promotions. At this time, the
472 // before-gc verification will fail the above assert.
473 // (b) MSC: In this case, an object L with a young reference
474 // is on a card that (therefore) holds a youngergen_n value.
475 // Suppose also that L lies towards the end of the used
476 // the used space before GC. An MSC collection
477 // occurs that compacts to such an extent that this
478 // card is no longer in the occupied part of the space.
479 // Since current code in MSC does not always clear cards
480 // in the unused part of old gen, this stale youngergen_n
481 // value is left behind and can later be covered by
482 // an object when promotion or direct allocation
483 // re-allocates that part of the heap.
484 //
485 // Fortunately, the presence of such stale card values is
486 // "only" a minor annoyance in that subsequent young collections
487 // might needlessly scan such cards, but would still never corrupt
488 // the heap as a result. However, it's likely not to be a significant
489 // performance inhibitor in practice. For instance,
490 // some recent measurements with unoccupied cards eagerly cleared
491 // out to maintain this invariant, showed next to no
492 // change in young collection times; of course one can construct
493 // degenerate examples where the cost can be significant.)
494 // Note, in particular, that if the "stale" card is modified
495 // after re-allocation, it would be dirty, not "stale". Thus,
496 // we can never have a younger ref in such a card and it is
497 // safe not to scan that card in any collection. [As we see
498 // below, we do some unnecessary scanning
499 // in some cases in the current parallel scanning algorithm.]
500 //
501 // The main point below is that the parallel card scanning code
502 // deals correctly with these stale card values. There are two main
503 // cases to consider where we have a stale "young gen" value and a
504 // "derivative" case to consider, where we have a stale
505 // "cur_younger_gen_and_prev_non_clean" value, as will become
506 // apparent in the case analysis below.
507 // o Case 1. If the stale value corresponds to a younger_gen_n
508 // value other than the cur_younger_gen value then the code
509 // treats this as being tantamount to a prev_younger_gen
510 // card. This means that the card may be unnecessarily scanned.
511 // There are two sub-cases to consider:
512 // o Case 1a. Let us say that the card is in the occupied part
513 // of the generation at the time the collection begins. In
514 // that case the card will be either cleared when it is scanned
515 // for young pointers, or will be set to cur_younger_gen as a
516 // result of promotion. (We have elided the normal case where
517 // the scanning thread and the promoting thread interleave
518 // possibly resulting in a transient
519 // cur_younger_gen_and_prev_non_clean value before settling
520 // to cur_younger_gen. [End Case 1a.]
521 // o Case 1b. Consider now the case when the card is in the unoccupied
522 // part of the space which becomes occupied because of promotions
523 // into it during the current young GC. In this case the card
524 // will never be scanned for young references. The current
525 // code will set the card value to either
526 // cur_younger_gen_and_prev_non_clean or leave
527 // it with its stale value -- because the promotions didn't
528 // result in any younger refs on that card. Of these two
529 // cases, the latter will be covered in Case 1a during
530 // a subsequent scan. To deal with the former case, we need
531 // to further consider how we deal with a stale value of
532 // cur_younger_gen_and_prev_non_clean in our case analysis
533 // below. This we do in Case 3 below. [End Case 1b]
534 // [End Case 1]
535 // o Case 2. If the stale value corresponds to cur_younger_gen being
536 // a value not necessarily written by a current promotion, the
537 // card will not be scanned by the younger refs scanning code.
538 // (This is OK since as we argued above such cards cannot contain
539 // any younger refs.) The result is that this value will be
540 // treated as a prev_younger_gen value in a subsequent collection,
541 // which is addressed in Case 1 above. [End Case 2]
542 // o Case 3. We here consider the "derivative" case from Case 1b. above
543 // because of which we may find a stale
544 // cur_younger_gen_and_prev_non_clean card value in the table.
545 // Once again, as in Case 1, we consider two subcases, depending
546 // on whether the card lies in the occupied or unoccupied part
547 // of the space at the start of the young collection.
548 // o Case 3a. Let us say the card is in the occupied part of
549 // the old gen at the start of the young collection. In that
550 // case, the card will be scanned by the younger refs scanning
551 // code which will set it to cur_younger_gen. In a subsequent
552 // scan, the card will be considered again and get its final
553 // correct value. [End Case 3a]
554 // o Case 3b. Now consider the case where the card is in the
555 // unoccupied part of the old gen, and is occupied as a result
556 // of promotions during thus young gc. In that case,
557 // the card will not be scanned for younger refs. The presence
558 // of newly promoted objects on the card will then result in
559 // its keeping the value cur_younger_gen_and_prev_non_clean
560 // value, which we have dealt with in Case 3 here. [End Case 3b]
561 // [End Case 3]
562 //
563 // (Please refer to the code in the helper class
564 // ClearNonCleanCardWrapper and in CardTable for details.)
565 //
566 // The informal arguments above can be tightened into a formal
567 // correctness proof and it behooves us to write up such a proof,
568 // or to use model checking to prove that there are no lingering
569 // concerns.
570 //
571 // Clearly because of Case 3b one cannot bound the time for
572 // which a card will retain what we have called a "stale" value.
573 // However, one can obtain a Loose upper bound on the redundant
574 // work as a result of such stale values. Note first that any
575 // time a stale card lies in the occupied part of the space at
576 // the start of the collection, it is scanned by younger refs
577 // code and we can define a rank function on card values that
578 // declines when this is so. Note also that when a card does not
579 // lie in the occupied part of the space at the beginning of a
580 // young collection, its rank can either decline or stay unchanged.
581 // In this case, no extra work is done in terms of redundant
582 // younger refs scanning of that card.
583 // Then, the case analysis above reveals that, in the worst case,
584 // any such stale card will be scanned unnecessarily at most twice.
585 //
586 // It is nonetheless advisable to try and get rid of some of this
587 // redundant work in a subsequent (low priority) re-design of
588 // the card-scanning code, if only to simplify the underlying
589 // state machine analysis/proof. ysr 1/28/2002. XXX
590 cur_entry++;
591 }
592 }
593 }
594
595 void CardTableRS::verify() {
596 // At present, we only know how to verify the card table RS for
597 // generational heaps.
598 VerifyCTGenClosure blk(this);
599 GenCollectedHeap::heap()->generation_iterate(&blk, false);
600 CardTable::verify();
601 }
602
603 CardTableRS::CardTableRS(MemRegion whole_heap, bool scanned_concurrently) :
604 CardTable(whole_heap, scanned_concurrently),
605 _cur_youngergen_card_val(youngergenP1_card),
606 // LNC functionality
607 _lowest_non_clean(NULL),
608 _lowest_non_clean_chunk_size(NULL),
609 _lowest_non_clean_base_chunk_index(NULL),
610 _last_LNC_resizing_collection(NULL)
611 {
612 // max_gens is really GenCollectedHeap::heap()->gen_policy()->number_of_generations()
613 // (which is always 2, young & old), but GenCollectedHeap has not been initialized yet.
614 uint max_gens = 2;
615 _last_cur_val_in_gen = NEW_C_HEAP_ARRAY3(jbyte, max_gens + 1,
616 mtGC, CURRENT_PC, AllocFailStrategy::RETURN_NULL);
617 if (_last_cur_val_in_gen == NULL) {
618 vm_exit_during_initialization("Could not create last_cur_val_in_gen array.");
619 }
620 for (uint i = 0; i < max_gens + 1; i++) {
621 _last_cur_val_in_gen[i] = clean_card_val();
622 }
623 }
624
625 CardTableRS::~CardTableRS() {
626 if (_last_cur_val_in_gen) {
627 FREE_C_HEAP_ARRAY(jbyte, _last_cur_val_in_gen);
628 _last_cur_val_in_gen = NULL;
629 }
630 if (_lowest_non_clean) {
631 FREE_C_HEAP_ARRAY(CardArr, _lowest_non_clean);
632 _lowest_non_clean = NULL;
633 }
634 if (_lowest_non_clean_chunk_size) {
635 FREE_C_HEAP_ARRAY(size_t, _lowest_non_clean_chunk_size);
636 _lowest_non_clean_chunk_size = NULL;
637 }
638 if (_lowest_non_clean_base_chunk_index) {
639 FREE_C_HEAP_ARRAY(uintptr_t, _lowest_non_clean_base_chunk_index);
640 _lowest_non_clean_base_chunk_index = NULL;
641 }
642 if (_last_LNC_resizing_collection) {
643 FREE_C_HEAP_ARRAY(int, _last_LNC_resizing_collection);
644 _last_LNC_resizing_collection = NULL;
645 }
646 }
647
648 void CardTableRS::initialize() {
649 CardTable::initialize();
650 _lowest_non_clean =
651 NEW_C_HEAP_ARRAY(CardArr, _max_covered_regions, mtGC);
652 _lowest_non_clean_chunk_size =
653 NEW_C_HEAP_ARRAY(size_t, _max_covered_regions, mtGC);
654 _lowest_non_clean_base_chunk_index =
655 NEW_C_HEAP_ARRAY(uintptr_t, _max_covered_regions, mtGC);
656 _last_LNC_resizing_collection =
657 NEW_C_HEAP_ARRAY(int, _max_covered_regions, mtGC);
658 if (_lowest_non_clean == NULL
659 || _lowest_non_clean_chunk_size == NULL
660 || _lowest_non_clean_base_chunk_index == NULL
661 || _last_LNC_resizing_collection == NULL)
662 vm_exit_during_initialization("couldn't allocate an LNC array.");
663 for (int i = 0; i < _max_covered_regions; i++) {
664 _lowest_non_clean[i] = NULL;
665 _lowest_non_clean_chunk_size[i] = 0;
666 _last_LNC_resizing_collection[i] = -1;
667 }
668 }
669
670 bool CardTableRS::card_will_be_scanned(jbyte cv) {
671 return card_is_dirty_wrt_gen_iter(cv) || is_prev_nonclean_card_val(cv);
672 }
673
674 bool CardTableRS::card_may_have_been_dirty(jbyte cv) {
675 return
676 cv != clean_card &&
677 (card_is_dirty_wrt_gen_iter(cv) ||
678 CardTableRS::youngergen_may_have_been_dirty(cv));
679 }
680
681 void CardTableRS::non_clean_card_iterate_possibly_parallel(
682 Space* sp,
683 MemRegion mr,
684 OopsInGenClosure* cl,
685 CardTableRS* ct,
686 uint n_threads)
687 {
688 if (!mr.is_empty()) {
689 if (n_threads > 0) {
690 non_clean_card_iterate_parallel_work(sp, mr, cl, ct, n_threads);
691 } else {
692 // clear_cl finds contiguous dirty ranges of cards to process and clear.
693
694 // This is the single-threaded version used by DefNew.
695 const bool parallel = false;
696
697 DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(), cl->gen_boundary(), parallel);
698 ClearNoncleanCardWrapper clear_cl(dcto_cl, ct, parallel);
699
700 clear_cl.do_MemRegion(mr);
701 }
702 }
703 }
704
705 void CardTableRS::non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,
706 OopsInGenClosure* cl, CardTableRS* ct,
707 uint n_threads) {
708 fatal("Parallel gc not supported here.");
709 }
710
711 bool CardTableRS::is_in_young(oop obj) const {
712 return GenCollectedHeap::heap()->is_in_young(obj);
713 }