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.
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
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "gc/shared/cardTableRS.hpp"
27 #include "gc/shared/genCollectedHeap.hpp"
28 #include "gc/shared/generation.hpp"
29 #include "gc/shared/space.inline.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "oops/access.inline.hpp"
32 #include "oops/oop.inline.hpp"
33 #include "runtime/atomic.hpp"
34 #include "runtime/java.hpp"
35 #include "runtime/os.hpp"
36 #include "utilities/macros.hpp"
37
38 class HasAccumulatedModifiedOopsClosure : public CLDClosure {
39 bool _found;
40 public:
41 HasAccumulatedModifiedOopsClosure() : _found(false) {}
42 void do_cld(ClassLoaderData* cld) {
43 if (_found) {
44 return;
45 }
46
47 if (cld->has_accumulated_modified_oops()) {
48 _found = true;
49 }
50 }
51 bool found() {
52 return _found;
53 }
54 };
55
56 bool CLDRemSet::mod_union_is_clear() {
57 HasAccumulatedModifiedOopsClosure closure;
58 ClassLoaderDataGraph::cld_do(&closure);
59
60 return !closure.found();
61 }
62
63
64 class ClearCLDModUnionClosure : public CLDClosure {
65 public:
66 void do_cld(ClassLoaderData* cld) {
67 if (cld->has_accumulated_modified_oops()) {
68 cld->clear_accumulated_modified_oops();
69 }
70 }
71 };
72
73 void CLDRemSet::clear_mod_union() {
74 ClearCLDModUnionClosure closure;
75 ClassLoaderDataGraph::cld_do(&closure);
76 }
77
78
79 jbyte CardTableRS::find_unused_youngergenP_card_value() {
80 for (jbyte v = youngergenP1_card;
81 v < cur_youngergen_and_prev_nonclean_card;
82 v++) {
83 bool seen = false;
84 for (int g = 0; g < _regions_to_iterate; g++) {
85 if (_last_cur_val_in_gen[g] == v) {
86 seen = true;
87 break;
88 }
89 }
90 if (!seen) {
91 return v;
92 }
93 }
94 ShouldNotReachHere();
95 return 0;
96 }
97
98 void CardTableRS::prepare_for_younger_refs_iterate(bool parallel) {
99 // Parallel or sequential, we must always set the prev to equal the
100 // last one written.
101 if (parallel) {
102 // Find a parallel value to be used next.
103 jbyte next_val = find_unused_youngergenP_card_value();
104 set_cur_youngergen_card_val(next_val);
105
106 } else {
107 // In an sequential traversal we will always write youngergen, so that
108 // the inline barrier is correct.
109 set_cur_youngergen_card_val(youngergen_card);
110 }
111 }
112
113 void CardTableRS::younger_refs_iterate(Generation* g,
114 OopsInGenClosure* blk,
115 uint n_threads) {
116 // The indexing in this array is slightly odd. We want to access
117 // the old generation record here, which is at index 2.
118 _last_cur_val_in_gen[2] = cur_youngergen_card_val();
119 g->younger_refs_iterate(blk, n_threads);
120 }
121
122 inline bool ClearNoncleanCardWrapper::clear_card(jbyte* entry) {
123 if (_is_par) {
124 return clear_card_parallel(entry);
125 } else {
126 return clear_card_serial(entry);
127 }
128 }
129
130 inline bool ClearNoncleanCardWrapper::clear_card_parallel(jbyte* entry) {
131 while (true) {
132 // In the parallel case, we may have to do this several times.
133 jbyte entry_val = *entry;
134 assert(entry_val != CardTableRS::clean_card_val(),
135 "We shouldn't be looking at clean cards, and this should "
136 "be the only place they get cleaned.");
137 if (CardTableRS::card_is_dirty_wrt_gen_iter(entry_val)
138 || _ct->is_prev_youngergen_card_val(entry_val)) {
139 jbyte res =
140 Atomic::cmpxchg(CardTableRS::clean_card_val(), entry, entry_val);
141 if (res == entry_val) {
142 break;
143 } else {
144 assert(res == CardTableRS::cur_youngergen_and_prev_nonclean_card,
145 "The CAS above should only fail if another thread did "
146 "a GC write barrier.");
147 }
148 } else if (entry_val ==
149 CardTableRS::cur_youngergen_and_prev_nonclean_card) {
150 // Parallelism shouldn't matter in this case. Only the thread
151 // assigned to scan the card should change this value.
152 *entry = _ct->cur_youngergen_card_val();
153 break;
154 } else {
155 assert(entry_val == _ct->cur_youngergen_card_val(),
156 "Should be the only possibility.");
157 // In this case, the card was clean before, and become
158 // cur_youngergen only because of processing of a promoted object.
159 // We don't have to look at the card.
160 return false;
161 }
162 }
163 return true;
164 }
165
166
167 inline bool ClearNoncleanCardWrapper::clear_card_serial(jbyte* entry) {
168 jbyte entry_val = *entry;
169 assert(entry_val != CardTableRS::clean_card_val(),
170 "We shouldn't be looking at clean cards, and this should "
171 "be the only place they get cleaned.");
172 assert(entry_val != CardTableRS::cur_youngergen_and_prev_nonclean_card,
173 "This should be possible in the sequential case.");
174 *entry = CardTableRS::clean_card_val();
175 return true;
176 }
177
178 ClearNoncleanCardWrapper::ClearNoncleanCardWrapper(
179 DirtyCardToOopClosure* dirty_card_closure, CardTableRS* ct, bool is_par) :
180 _dirty_card_closure(dirty_card_closure), _ct(ct), _is_par(is_par) {
181 }
182
183 bool ClearNoncleanCardWrapper::is_word_aligned(jbyte* entry) {
184 return (((intptr_t)entry) & (BytesPerWord-1)) == 0;
185 }
186
187 // The regions are visited in *decreasing* address order.
188 // This order aids with imprecise card marking, where a dirty
189 // card may cause scanning, and summarization marking, of objects
190 // that extend onto subsequent cards.
191 void ClearNoncleanCardWrapper::do_MemRegion(MemRegion mr) {
192 assert(mr.word_size() > 0, "Error");
193 assert(_ct->is_aligned(mr.start()), "mr.start() should be card aligned");
194 // mr.end() may not necessarily be card aligned.
195 jbyte* cur_entry = _ct->byte_for(mr.last());
196 const jbyte* limit = _ct->byte_for(mr.start());
197 HeapWord* end_of_non_clean = mr.end();
198 HeapWord* start_of_non_clean = end_of_non_clean;
199 while (cur_entry >= limit) {
200 HeapWord* cur_hw = _ct->addr_for(cur_entry);
201 if ((*cur_entry != CardTableRS::clean_card_val()) && clear_card(cur_entry)) {
202 // Continue the dirty range by opening the
203 // dirty window one card to the left.
204 start_of_non_clean = cur_hw;
205 } else {
206 // We hit a "clean" card; process any non-empty
207 // "dirty" range accumulated so far.
208 if (start_of_non_clean < end_of_non_clean) {
209 const MemRegion mrd(start_of_non_clean, end_of_non_clean);
210 _dirty_card_closure->do_MemRegion(mrd);
211 }
212
213 // fast forward through potential continuous whole-word range of clean cards beginning at a word-boundary
214 if (is_word_aligned(cur_entry)) {
215 jbyte* cur_row = cur_entry - BytesPerWord;
216 while (cur_row >= limit && *((intptr_t*)cur_row) == CardTableRS::clean_card_row_val()) {
217 cur_row -= BytesPerWord;
218 }
219 cur_entry = cur_row + BytesPerWord;
220 cur_hw = _ct->addr_for(cur_entry);
221 }
222
223 // Reset the dirty window, while continuing to look
224 // for the next dirty card that will start a
225 // new dirty window.
226 end_of_non_clean = cur_hw;
227 start_of_non_clean = cur_hw;
228 }
229 // Note that "cur_entry" leads "start_of_non_clean" in
230 // its leftward excursion after this point
231 // in the loop and, when we hit the left end of "mr",
232 // will point off of the left end of the card-table
233 // for "mr".
234 cur_entry--;
235 }
236 // If the first card of "mr" was dirty, we will have
237 // been left with a dirty window, co-initial with "mr",
238 // which we now process.
239 if (start_of_non_clean < end_of_non_clean) {
240 const MemRegion mrd(start_of_non_clean, end_of_non_clean);
241 _dirty_card_closure->do_MemRegion(mrd);
242 }
243 }
244
245 // clean (by dirty->clean before) ==> cur_younger_gen
246 // dirty ==> cur_youngergen_and_prev_nonclean_card
247 // precleaned ==> cur_youngergen_and_prev_nonclean_card
248 // prev-younger-gen ==> cur_youngergen_and_prev_nonclean_card
249 // cur-younger-gen ==> cur_younger_gen
250 // cur_youngergen_and_prev_nonclean_card ==> no change.
251 void CardTableRS::write_ref_field_gc_par(void* field, oop new_val) {
252 volatile jbyte* entry = byte_for(field);
253 do {
254 jbyte entry_val = *entry;
255 // We put this first because it's probably the most common case.
256 if (entry_val == clean_card_val()) {
257 // No threat of contention with cleaning threads.
258 *entry = cur_youngergen_card_val();
259 return;
260 } else if (card_is_dirty_wrt_gen_iter(entry_val)
261 || is_prev_youngergen_card_val(entry_val)) {
262 // Mark it as both cur and prev youngergen; card cleaning thread will
263 // eventually remove the previous stuff.
264 jbyte new_val = cur_youngergen_and_prev_nonclean_card;
265 jbyte res = Atomic::cmpxchg(new_val, entry, entry_val);
266 // Did the CAS succeed?
267 if (res == entry_val) return;
268 // Otherwise, retry, to see the new value.
269 continue;
270 } else {
271 assert(entry_val == cur_youngergen_and_prev_nonclean_card
272 || entry_val == cur_youngergen_card_val(),
273 "should be only possibilities.");
274 return;
275 }
276 } while (true);
277 }
278
279 void CardTableRS::younger_refs_in_space_iterate(Space* sp,
280 OopsInGenClosure* cl,
281 uint n_threads) {
282 verify_used_region_at_save_marks(sp);
283
284 const MemRegion urasm = sp->used_region_at_save_marks();
285 non_clean_card_iterate_possibly_parallel(sp, urasm, cl, this, n_threads);
286 }
287
288 #ifdef ASSERT
289 void CardTableRS::verify_used_region_at_save_marks(Space* sp) const {
290 MemRegion ur = sp->used_region();
291 MemRegion urasm = sp->used_region_at_save_marks();
292
293 assert(ur.contains(urasm),
294 "Did you forget to call save_marks()? "
295 "[" PTR_FORMAT ", " PTR_FORMAT ") is not contained in "
296 "[" PTR_FORMAT ", " PTR_FORMAT ")",
297 p2i(urasm.start()), p2i(urasm.end()), p2i(ur.start()), p2i(ur.end()));
298 }
299 #endif
300
301 void CardTableRS::clear_into_younger(Generation* old_gen) {
302 assert(GenCollectedHeap::heap()->is_old_gen(old_gen),
303 "Should only be called for the old generation");
304 // The card tables for the youngest gen need never be cleared.
305 // There's a bit of subtlety in the clear() and invalidate()
306 // methods that we exploit here and in invalidate_or_clear()
307 // below to avoid missing cards at the fringes. If clear() or
308 // invalidate() are changed in the future, this code should
309 // be revisited. 20040107.ysr
310 clear(old_gen->prev_used_region());
311 }
312
313 void CardTableRS::invalidate_or_clear(Generation* old_gen) {
314 assert(GenCollectedHeap::heap()->is_old_gen(old_gen),
315 "Should only be called for the old generation");
316 // Invalidate the cards for the currently occupied part of
317 // the old generation and clear the cards for the
318 // unoccupied part of the generation (if any, making use
319 // of that generation's prev_used_region to determine that
320 // region). No need to do anything for the youngest
321 // generation. Also see note#20040107.ysr above.
322 MemRegion used_mr = old_gen->used_region();
323 MemRegion to_be_cleared_mr = old_gen->prev_used_region().minus(used_mr);
324 if (!to_be_cleared_mr.is_empty()) {
325 clear(to_be_cleared_mr);
326 }
327 invalidate(used_mr);
328 }
329
330
331 class VerifyCleanCardClosure: public OopClosure {
332 private:
333 HeapWord* _boundary;
334 HeapWord* _begin;
335 HeapWord* _end;
336 protected:
337 template <class T> void do_oop_work(T* p) {
338 HeapWord* jp = (HeapWord*)p;
339 assert(jp >= _begin && jp < _end,
340 "Error: jp " PTR_FORMAT " should be within "
341 "[_begin, _end) = [" PTR_FORMAT "," PTR_FORMAT ")",
342 p2i(jp), p2i(_begin), p2i(_end));
343 oop obj = RawAccess<>::oop_load(p);
344 guarantee(obj == NULL || (HeapWord*)obj >= _boundary,
345 "pointer " PTR_FORMAT " at " PTR_FORMAT " on "
346 "clean card crosses boundary" PTR_FORMAT,
347 p2i(obj), p2i(jp), p2i(_boundary));
348 }
349
350 public:
351 VerifyCleanCardClosure(HeapWord* b, HeapWord* begin, HeapWord* end) :
352 _boundary(b), _begin(begin), _end(end) {
353 assert(b <= begin,
354 "Error: boundary " PTR_FORMAT " should be at or below begin " PTR_FORMAT,
355 p2i(b), p2i(begin));
356 assert(begin <= end,
357 "Error: begin " PTR_FORMAT " should be strictly below end " PTR_FORMAT,
358 p2i(begin), p2i(end));
359 }
360
361 virtual void do_oop(oop* p) { VerifyCleanCardClosure::do_oop_work(p); }
362 virtual void do_oop(narrowOop* p) { VerifyCleanCardClosure::do_oop_work(p); }
363 };
364
365 class VerifyCTSpaceClosure: public SpaceClosure {
366 private:
367 CardTableRS* _ct;
368 HeapWord* _boundary;
369 public:
370 VerifyCTSpaceClosure(CardTableRS* ct, HeapWord* boundary) :
371 _ct(ct), _boundary(boundary) {}
372 virtual void do_space(Space* s) { _ct->verify_space(s, _boundary); }
373 };
374
375 class VerifyCTGenClosure: public GenCollectedHeap::GenClosure {
376 CardTableRS* _ct;
377 public:
378 VerifyCTGenClosure(CardTableRS* ct) : _ct(ct) {}
379 void do_generation(Generation* gen) {
380 // Skip the youngest generation.
381 if (GenCollectedHeap::heap()->is_young_gen(gen)) {
382 return;
383 }
384 // Normally, we're interested in pointers to younger generations.
385 VerifyCTSpaceClosure blk(_ct, gen->reserved().start());
386 gen->space_iterate(&blk, true);
387 }
388 };
389
390 void CardTableRS::verify_space(Space* s, HeapWord* gen_boundary) {
391 // We don't need to do young-gen spaces.
392 if (s->end() <= gen_boundary) return;
393 MemRegion used = s->used_region();
394
395 jbyte* cur_entry = byte_for(used.start());
396 jbyte* limit = byte_after(used.last());
397 while (cur_entry < limit) {
398 if (*cur_entry == clean_card_val()) {
399 jbyte* first_dirty = cur_entry+1;
400 while (first_dirty < limit &&
401 *first_dirty == clean_card_val()) {
402 first_dirty++;
403 }
404 // If the first object is a regular object, and it has a
405 // young-to-old field, that would mark the previous card.
406 HeapWord* boundary = addr_for(cur_entry);
407 HeapWord* end = (first_dirty >= limit) ? used.end() : addr_for(first_dirty);
408 HeapWord* boundary_block = s->block_start(boundary);
409 HeapWord* begin = boundary; // Until proven otherwise.
410 HeapWord* start_block = boundary_block; // Until proven otherwise.
411 if (boundary_block < boundary) {
412 if (s->block_is_obj(boundary_block) && s->obj_is_alive(boundary_block)) {
413 oop boundary_obj = oop(boundary_block);
414 if (!boundary_obj->is_objArray() &&
415 !boundary_obj->is_typeArray()) {
416 guarantee(cur_entry > byte_for(used.start()),
417 "else boundary would be boundary_block");
418 if (*byte_for(boundary_block) != clean_card_val()) {
419 begin = boundary_block + s->block_size(boundary_block);
420 start_block = begin;
421 }
422 }
423 }
424 }
425 // Now traverse objects until end.
426 if (begin < end) {
427 MemRegion mr(begin, end);
428 VerifyCleanCardClosure verify_blk(gen_boundary, begin, end);
429 for (HeapWord* cur = start_block; cur < end; cur += s->block_size(cur)) {
430 if (s->block_is_obj(cur) && s->obj_is_alive(cur)) {
431 oop(cur)->oop_iterate_no_header(&verify_blk, mr);
432 }
433 }
434 }
435 cur_entry = first_dirty;
436 } else {
437 // We'd normally expect that cur_youngergen_and_prev_nonclean_card
438 // is a transient value, that cannot be in the card table
439 // except during GC, and thus assert that:
440 // guarantee(*cur_entry != cur_youngergen_and_prev_nonclean_card,
441 // "Illegal CT value");
442 // That however, need not hold, as will become clear in the
443 // following...
444
445 // We'd normally expect that if we are in the parallel case,
446 // we can't have left a prev value (which would be different
447 // from the current value) in the card table, and so we'd like to
448 // assert that:
449 // guarantee(cur_youngergen_card_val() == youngergen_card
450 // || !is_prev_youngergen_card_val(*cur_entry),
451 // "Illegal CT value");
452 // That, however, may not hold occasionally, because of
453 // CMS or MSC in the old gen. To wit, consider the
454 // following two simple illustrative scenarios:
455 // (a) CMS: Consider the case where a large object L
456 // spanning several cards is allocated in the old
457 // gen, and has a young gen reference stored in it, dirtying
458 // some interior cards. A young collection scans the card,
459 // finds a young ref and installs a youngergenP_n value.
460 // L then goes dead. Now a CMS collection starts,
461 // finds L dead and sweeps it up. Assume that L is
462 // abutting _unallocated_blk, so _unallocated_blk is
463 // adjusted down to (below) L. Assume further that
464 // no young collection intervenes during this CMS cycle.
465 // The next young gen cycle will not get to look at this
466 // youngergenP_n card since it lies in the unoccupied
467 // part of the space.
468 // Some young collections later the blocks on this
469 // card can be re-allocated either due to direct allocation
470 // or due to absorbing promotions. At this time, the
471 // before-gc verification will fail the above assert.
472 // (b) MSC: In this case, an object L with a young reference
473 // is on a card that (therefore) holds a youngergen_n value.
474 // Suppose also that L lies towards the end of the used
475 // the used space before GC. An MSC collection
476 // occurs that compacts to such an extent that this
477 // card is no longer in the occupied part of the space.
478 // Since current code in MSC does not always clear cards
479 // in the unused part of old gen, this stale youngergen_n
480 // value is left behind and can later be covered by
481 // an object when promotion or direct allocation
482 // re-allocates that part of the heap.
483 //
484 // Fortunately, the presence of such stale card values is
485 // "only" a minor annoyance in that subsequent young collections
486 // might needlessly scan such cards, but would still never corrupt
487 // the heap as a result. However, it's likely not to be a significant
488 // performance inhibitor in practice. For instance,
489 // some recent measurements with unoccupied cards eagerly cleared
490 // out to maintain this invariant, showed next to no
491 // change in young collection times; of course one can construct
492 // degenerate examples where the cost can be significant.)
493 // Note, in particular, that if the "stale" card is modified
494 // after re-allocation, it would be dirty, not "stale". Thus,
495 // we can never have a younger ref in such a card and it is
496 // safe not to scan that card in any collection. [As we see
497 // below, we do some unnecessary scanning
498 // in some cases in the current parallel scanning algorithm.]
499 //
500 // The main point below is that the parallel card scanning code
501 // deals correctly with these stale card values. There are two main
502 // cases to consider where we have a stale "young gen" value and a
503 // "derivative" case to consider, where we have a stale
504 // "cur_younger_gen_and_prev_non_clean" value, as will become
505 // apparent in the case analysis below.
506 // o Case 1. If the stale value corresponds to a younger_gen_n
507 // value other than the cur_younger_gen value then the code
508 // treats this as being tantamount to a prev_younger_gen
509 // card. This means that the card may be unnecessarily scanned.
510 // There are two sub-cases to consider:
511 // o Case 1a. Let us say that the card is in the occupied part
512 // of the generation at the time the collection begins. In
513 // that case the card will be either cleared when it is scanned
514 // for young pointers, or will be set to cur_younger_gen as a
515 // result of promotion. (We have elided the normal case where
516 // the scanning thread and the promoting thread interleave
517 // possibly resulting in a transient
518 // cur_younger_gen_and_prev_non_clean value before settling
519 // to cur_younger_gen. [End Case 1a.]
520 // o Case 1b. Consider now the case when the card is in the unoccupied
521 // part of the space which becomes occupied because of promotions
522 // into it during the current young GC. In this case the card
523 // will never be scanned for young references. The current
524 // code will set the card value to either
525 // cur_younger_gen_and_prev_non_clean or leave
526 // it with its stale value -- because the promotions didn't
527 // result in any younger refs on that card. Of these two
528 // cases, the latter will be covered in Case 1a during
529 // a subsequent scan. To deal with the former case, we need
530 // to further consider how we deal with a stale value of
531 // cur_younger_gen_and_prev_non_clean in our case analysis
532 // below. This we do in Case 3 below. [End Case 1b]
533 // [End Case 1]
534 // o Case 2. If the stale value corresponds to cur_younger_gen being
535 // a value not necessarily written by a current promotion, the
536 // card will not be scanned by the younger refs scanning code.
537 // (This is OK since as we argued above such cards cannot contain
538 // any younger refs.) The result is that this value will be
539 // treated as a prev_younger_gen value in a subsequent collection,
540 // which is addressed in Case 1 above. [End Case 2]
541 // o Case 3. We here consider the "derivative" case from Case 1b. above
542 // because of which we may find a stale
543 // cur_younger_gen_and_prev_non_clean card value in the table.
544 // Once again, as in Case 1, we consider two subcases, depending
545 // on whether the card lies in the occupied or unoccupied part
546 // of the space at the start of the young collection.
547 // o Case 3a. Let us say the card is in the occupied part of
548 // the old gen at the start of the young collection. In that
549 // case, the card will be scanned by the younger refs scanning
550 // code which will set it to cur_younger_gen. In a subsequent
551 // scan, the card will be considered again and get its final
552 // correct value. [End Case 3a]
553 // o Case 3b. Now consider the case where the card is in the
554 // unoccupied part of the old gen, and is occupied as a result
555 // of promotions during thus young gc. In that case,
556 // the card will not be scanned for younger refs. The presence
557 // of newly promoted objects on the card will then result in
558 // its keeping the value cur_younger_gen_and_prev_non_clean
559 // value, which we have dealt with in Case 3 here. [End Case 3b]
560 // [End Case 3]
561 //
562 // (Please refer to the code in the helper class
563 // ClearNonCleanCardWrapper and in CardTable for details.)
564 //
565 // The informal arguments above can be tightened into a formal
566 // correctness proof and it behooves us to write up such a proof,
567 // or to use model checking to prove that there are no lingering
568 // concerns.
569 //
570 // Clearly because of Case 3b one cannot bound the time for
571 // which a card will retain what we have called a "stale" value.
572 // However, one can obtain a Loose upper bound on the redundant
573 // work as a result of such stale values. Note first that any
574 // time a stale card lies in the occupied part of the space at
575 // the start of the collection, it is scanned by younger refs
576 // code and we can define a rank function on card values that
577 // declines when this is so. Note also that when a card does not
578 // lie in the occupied part of the space at the beginning of a
579 // young collection, its rank can either decline or stay unchanged.
580 // In this case, no extra work is done in terms of redundant
581 // younger refs scanning of that card.
582 // Then, the case analysis above reveals that, in the worst case,
583 // any such stale card will be scanned unnecessarily at most twice.
584 //
585 // It is nonetheless advisable to try and get rid of some of this
586 // redundant work in a subsequent (low priority) re-design of
587 // the card-scanning code, if only to simplify the underlying
588 // state machine analysis/proof. ysr 1/28/2002. XXX
589 cur_entry++;
590 }
591 }
592 }
593
594 void CardTableRS::verify() {
595 // At present, we only know how to verify the card table RS for
596 // generational heaps.
597 VerifyCTGenClosure blk(this);
598 GenCollectedHeap::heap()->generation_iterate(&blk, false);
599 CardTable::verify();
600 }
601
602 CardTableRS::CardTableRS(MemRegion whole_heap, bool scanned_concurrently) :
603 CardTable(whole_heap, scanned_concurrently),
604 _cur_youngergen_card_val(youngergenP1_card),
605 // LNC functionality
606 _lowest_non_clean(NULL),
607 _lowest_non_clean_chunk_size(NULL),
608 _lowest_non_clean_base_chunk_index(NULL),
609 _last_LNC_resizing_collection(NULL)
610 {
611 // max_gens is really GenCollectedHeap::heap()->gen_policy()->number_of_generations()
612 // (which is always 2, young & old), but GenCollectedHeap has not been initialized yet.
613 uint max_gens = 2;
614 _last_cur_val_in_gen = NEW_C_HEAP_ARRAY3(jbyte, max_gens + 1,
615 mtGC, CURRENT_PC, AllocFailStrategy::RETURN_NULL);
616 if (_last_cur_val_in_gen == NULL) {
617 vm_exit_during_initialization("Could not create last_cur_val_in_gen array.");
618 }
619 for (uint i = 0; i < max_gens + 1; i++) {
620 _last_cur_val_in_gen[i] = clean_card_val();
621 }
622 }
623
624 CardTableRS::~CardTableRS() {
625 if (_last_cur_val_in_gen) {
626 FREE_C_HEAP_ARRAY(jbyte, _last_cur_val_in_gen);
627 _last_cur_val_in_gen = NULL;
628 }
629 if (_lowest_non_clean) {
630 FREE_C_HEAP_ARRAY(CardArr, _lowest_non_clean);
631 _lowest_non_clean = NULL;
632 }
633 if (_lowest_non_clean_chunk_size) {
634 FREE_C_HEAP_ARRAY(size_t, _lowest_non_clean_chunk_size);
635 _lowest_non_clean_chunk_size = NULL;
636 }
637 if (_lowest_non_clean_base_chunk_index) {
638 FREE_C_HEAP_ARRAY(uintptr_t, _lowest_non_clean_base_chunk_index);
639 _lowest_non_clean_base_chunk_index = NULL;
640 }
641 if (_last_LNC_resizing_collection) {
642 FREE_C_HEAP_ARRAY(int, _last_LNC_resizing_collection);
643 _last_LNC_resizing_collection = NULL;
644 }
645 }
646
647 void CardTableRS::initialize() {
648 CardTable::initialize();
649 _lowest_non_clean =
650 NEW_C_HEAP_ARRAY(CardArr, _max_covered_regions, mtGC);
651 _lowest_non_clean_chunk_size =
652 NEW_C_HEAP_ARRAY(size_t, _max_covered_regions, mtGC);
653 _lowest_non_clean_base_chunk_index =
654 NEW_C_HEAP_ARRAY(uintptr_t, _max_covered_regions, mtGC);
655 _last_LNC_resizing_collection =
656 NEW_C_HEAP_ARRAY(int, _max_covered_regions, mtGC);
657 if (_lowest_non_clean == NULL
658 || _lowest_non_clean_chunk_size == NULL
659 || _lowest_non_clean_base_chunk_index == NULL
660 || _last_LNC_resizing_collection == NULL)
661 vm_exit_during_initialization("couldn't allocate an LNC array.");
662 for (int i = 0; i < _max_covered_regions; i++) {
663 _lowest_non_clean[i] = NULL;
664 _lowest_non_clean_chunk_size[i] = 0;
665 _last_LNC_resizing_collection[i] = -1;
666 }
667 }
668
669 bool CardTableRS::card_will_be_scanned(jbyte cv) {
670 return card_is_dirty_wrt_gen_iter(cv) || is_prev_nonclean_card_val(cv);
671 }
672
673 bool CardTableRS::card_may_have_been_dirty(jbyte cv) {
674 return
675 cv != clean_card &&
676 (card_is_dirty_wrt_gen_iter(cv) ||
677 CardTableRS::youngergen_may_have_been_dirty(cv));
678 }
679
680 void CardTableRS::non_clean_card_iterate_possibly_parallel(
681 Space* sp,
682 MemRegion mr,
683 OopsInGenClosure* cl,
684 CardTableRS* ct,
685 uint n_threads)
686 {
687 if (!mr.is_empty()) {
688 if (n_threads > 0) {
689 non_clean_card_iterate_parallel_work(sp, mr, cl, ct, n_threads);
690 } else {
691 // clear_cl finds contiguous dirty ranges of cards to process and clear.
692
693 // This is the single-threaded version used by DefNew.
694 const bool parallel = false;
695
696 DirtyCardToOopClosure* dcto_cl = sp->new_dcto_cl(cl, precision(), cl->gen_boundary(), parallel);
697 ClearNoncleanCardWrapper clear_cl(dcto_cl, ct, parallel);
698
699 clear_cl.do_MemRegion(mr);
700 }
701 }
702 }
703
704 void CardTableRS::non_clean_card_iterate_parallel_work(Space* sp, MemRegion mr,
705 OopsInGenClosure* cl, CardTableRS* ct,
706 uint n_threads) {
707 fatal("Parallel gc not supported here.");
708 }
709
710 bool CardTableRS::is_in_young(oop obj) const {
711 return GenCollectedHeap::heap()->is_in_young(obj);
712 }