1 /*
2 * Copyright (c) 2000, 2015, 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/blockOffsetTable.inline.hpp"
27 #include "gc/shared/collectedHeap.inline.hpp"
28 #include "gc/shared/space.inline.hpp"
29 #include "memory/iterator.hpp"
30 #include "memory/universe.hpp"
31 #include "oops/oop.inline.hpp"
32 #include "runtime/java.hpp"
33 #include "services/memTracker.hpp"
34
35 //////////////////////////////////////////////////////////////////////
36 // BlockOffsetSharedArray
37 //////////////////////////////////////////////////////////////////////
38
39 BlockOffsetSharedArray::BlockOffsetSharedArray(MemRegion reserved,
40 size_t init_word_size):
41 _reserved(reserved), _end(NULL)
42 {
43 size_t size = compute_size(reserved.word_size());
44 ReservedSpace rs(size);
45 if (!rs.is_reserved()) {
46 vm_exit_during_initialization("Could not reserve enough space for heap offset array");
47 }
48
49 MemTracker::record_virtual_memory_type((address)rs.base(), mtGC);
50
51 if (!_vs.initialize(rs, 0)) {
52 vm_exit_during_initialization("Could not reserve enough space for heap offset array");
53 }
54 _offset_array = (u_char*)_vs.low_boundary();
55 resize(init_word_size);
56 if (TraceBlockOffsetTable) {
57 gclog_or_tty->print_cr("BlockOffsetSharedArray::BlockOffsetSharedArray: ");
58 gclog_or_tty->print_cr(" "
59 " rs.base(): " INTPTR_FORMAT
60 " rs.size(): " INTPTR_FORMAT
61 " rs end(): " INTPTR_FORMAT,
62 p2i(rs.base()), rs.size(), p2i(rs.base() + rs.size()));
63 gclog_or_tty->print_cr(" "
64 " _vs.low_boundary(): " INTPTR_FORMAT
65 " _vs.high_boundary(): " INTPTR_FORMAT,
66 p2i(_vs.low_boundary()),
67 p2i(_vs.high_boundary()));
68 }
69 }
70
71 void BlockOffsetSharedArray::resize(size_t new_word_size) {
72 assert(new_word_size <= _reserved.word_size(), "Resize larger than reserved");
73 size_t new_size = compute_size(new_word_size);
74 size_t old_size = _vs.committed_size();
75 size_t delta;
76 char* high = _vs.high();
77 _end = _reserved.start() + new_word_size;
78 if (new_size > old_size) {
79 delta = ReservedSpace::page_align_size_up(new_size - old_size);
80 assert(delta > 0, "just checking");
81 if (!_vs.expand_by(delta)) {
82 // Do better than this for Merlin
83 vm_exit_out_of_memory(delta, OOM_MMAP_ERROR, "offset table expansion");
84 }
85 assert(_vs.high() == high + delta, "invalid expansion");
86 } else {
87 delta = ReservedSpace::page_align_size_down(old_size - new_size);
88 if (delta == 0) return;
89 _vs.shrink_by(delta);
90 assert(_vs.high() == high - delta, "invalid expansion");
91 }
92 }
93
94 bool BlockOffsetSharedArray::is_card_boundary(HeapWord* p) const {
95 assert(p >= _reserved.start(), "just checking");
96 size_t delta = pointer_delta(p, _reserved.start());
97 return (delta & right_n_bits(LogN_words)) == (size_t)NoBits;
98 }
99
100
101 //////////////////////////////////////////////////////////////////////
102 // BlockOffsetArray
103 //////////////////////////////////////////////////////////////////////
104
105 BlockOffsetArray::BlockOffsetArray(BlockOffsetSharedArray* array,
106 MemRegion mr, bool init_to_zero_) :
107 BlockOffsetTable(mr.start(), mr.end()),
108 _array(array)
109 {
110 assert(_bottom <= _end, "arguments out of order");
111 set_init_to_zero(init_to_zero_);
112 if (!init_to_zero_) {
113 // initialize cards to point back to mr.start()
114 set_remainder_to_point_to_start(mr.start() + N_words, mr.end());
115 _array->set_offset_array(0, 0); // set first card to 0
116 }
117 }
118
119
120 // The arguments follow the normal convention of denoting
121 // a right-open interval: [start, end)
122 void
123 BlockOffsetArray::
124 set_remainder_to_point_to_start(HeapWord* start, HeapWord* end, bool reducing) {
125
126 check_reducing_assertion(reducing);
127 if (start >= end) {
128 // The start address is equal to the end address (or to
129 // the right of the end address) so there are not cards
130 // that need to be updated..
131 return;
132 }
133
134 // Write the backskip value for each region.
135 //
136 // offset
137 // card 2nd 3rd
138 // | +- 1st | |
139 // v v v v
140 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-
141 // |x|0|0|0|0|0|0|0|1|1|1|1|1|1| ... |1|1|1|1|2|2|2|2|2|2| ...
142 // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-
143 // 11 19 75
144 // 12
145 //
146 // offset card is the card that points to the start of an object
147 // x - offset value of offset card
148 // 1st - start of first logarithmic region
149 // 0 corresponds to logarithmic value N_words + 0 and 2**(3 * 0) = 1
150 // 2nd - start of second logarithmic region
151 // 1 corresponds to logarithmic value N_words + 1 and 2**(3 * 1) = 8
152 // 3rd - start of third logarithmic region
153 // 2 corresponds to logarithmic value N_words + 2 and 2**(3 * 2) = 64
154 //
155 // integer below the block offset entry is an example of
156 // the index of the entry
157 //
158 // Given an address,
159 // Find the index for the address
160 // Find the block offset table entry
161 // Convert the entry to a back slide
162 // (e.g., with today's, offset = 0x81 =>
163 // back slip = 2**(3*(0x81 - N_words)) = 2**3) = 8
164 // Move back N (e.g., 8) entries and repeat with the
165 // value of the new entry
166 //
167 size_t start_card = _array->index_for(start);
168 size_t end_card = _array->index_for(end-1);
169 assert(start ==_array->address_for_index(start_card), "Precondition");
170 assert(end ==_array->address_for_index(end_card)+N_words, "Precondition");
171 set_remainder_to_point_to_start_incl(start_card, end_card, reducing); // closed interval
172 }
173
174
175 // Unlike the normal convention in this code, the argument here denotes
176 // a closed, inclusive interval: [start_card, end_card], cf set_remainder_to_point_to_start()
177 // above.
178 void
179 BlockOffsetArray::set_remainder_to_point_to_start_incl(size_t start_card, size_t end_card, bool reducing) {
180
181 check_reducing_assertion(reducing);
182 if (start_card > end_card) {
183 return;
184 }
185 assert(start_card > _array->index_for(_bottom), "Cannot be first card");
186 assert(_array->offset_array(start_card-1) <= N_words,
187 "Offset card has an unexpected value");
188 size_t start_card_for_region = start_card;
189 u_char offset = max_jubyte;
190 for (int i = 0; i < N_powers; i++) {
191 // -1 so that the the card with the actual offset is counted. Another -1
192 // so that the reach ends in this region and not at the start
193 // of the next.
194 size_t reach = start_card - 1 + (power_to_cards_back(i+1) - 1);
195 offset = N_words + i;
196 if (reach >= end_card) {
197 _array->set_offset_array(start_card_for_region, end_card, offset, reducing);
198 start_card_for_region = reach + 1;
199 break;
200 }
201 _array->set_offset_array(start_card_for_region, reach, offset, reducing);
202 start_card_for_region = reach + 1;
203 }
204 assert(start_card_for_region > end_card, "Sanity check");
205 DEBUG_ONLY(check_all_cards(start_card, end_card);)
206 }
207
208 // The card-interval [start_card, end_card] is a closed interval; this
209 // is an expensive check -- use with care and only under protection of
210 // suitable flag.
211 void BlockOffsetArray::check_all_cards(size_t start_card, size_t end_card) const {
212
213 if (end_card < start_card) {
214 return;
215 }
216 guarantee(_array->offset_array(start_card) == N_words, "Wrong value in second card");
217 u_char last_entry = N_words;
218 for (size_t c = start_card + 1; c <= end_card; c++ /* yeah! */) {
219 u_char entry = _array->offset_array(c);
220 guarantee(entry >= last_entry, "Monotonicity");
221 if (c - start_card > power_to_cards_back(1)) {
222 guarantee(entry > N_words, "Should be in logarithmic region");
223 }
224 size_t backskip = entry_to_cards_back(entry);
225 size_t landing_card = c - backskip;
226 guarantee(landing_card >= (start_card - 1), "Inv");
227 if (landing_card >= start_card) {
228 guarantee(_array->offset_array(landing_card) <= entry, "Monotonicity");
229 } else {
230 guarantee(landing_card == (start_card - 1), "Tautology");
231 // Note that N_words is the maximum offset value
232 guarantee(_array->offset_array(landing_card) <= N_words, "Offset value");
233 }
234 last_entry = entry; // remember for monotonicity test
235 }
236 }
237
238
239 void
240 BlockOffsetArray::alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
241 assert(blk_start != NULL && blk_end > blk_start,
242 "phantom block");
243 single_block(blk_start, blk_end);
244 }
245
246 // Action_mark - update the BOT for the block [blk_start, blk_end).
247 // Current typical use is for splitting a block.
248 // Action_single - udpate the BOT for an allocation.
249 // Action_verify - BOT verification.
250 void
251 BlockOffsetArray::do_block_internal(HeapWord* blk_start,
252 HeapWord* blk_end,
253 Action action, bool reducing) {
254 assert(Universe::heap()->is_in_reserved(blk_start),
255 "reference must be into the heap");
256 assert(Universe::heap()->is_in_reserved(blk_end-1),
257 "limit must be within the heap");
258 // This is optimized to make the test fast, assuming we only rarely
259 // cross boundaries.
260 uintptr_t end_ui = (uintptr_t)(blk_end - 1);
261 uintptr_t start_ui = (uintptr_t)blk_start;
262 // Calculate the last card boundary preceding end of blk
263 intptr_t boundary_before_end = (intptr_t)end_ui;
264 clear_bits(boundary_before_end, right_n_bits(LogN));
265 if (start_ui <= (uintptr_t)boundary_before_end) {
266 // blk starts at or crosses a boundary
267 // Calculate index of card on which blk begins
268 size_t start_index = _array->index_for(blk_start);
269 // Index of card on which blk ends
270 size_t end_index = _array->index_for(blk_end - 1);
271 // Start address of card on which blk begins
272 HeapWord* boundary = _array->address_for_index(start_index);
273 assert(boundary <= blk_start, "blk should start at or after boundary");
274 if (blk_start != boundary) {
275 // blk starts strictly after boundary
276 // adjust card boundary and start_index forward to next card
277 boundary += N_words;
278 start_index++;
279 }
280 assert(start_index <= end_index, "monotonicity of index_for()");
281 assert(boundary <= (HeapWord*)boundary_before_end, "tautology");
282 switch (action) {
283 case Action_mark: {
284 if (init_to_zero()) {
285 _array->set_offset_array(start_index, boundary, blk_start, reducing);
286 break;
287 } // Else fall through to the next case
288 }
289 case Action_single: {
290 _array->set_offset_array(start_index, boundary, blk_start, reducing);
291 // We have finished marking the "offset card". We need to now
292 // mark the subsequent cards that this blk spans.
293 if (start_index < end_index) {
294 HeapWord* rem_st = _array->address_for_index(start_index) + N_words;
295 HeapWord* rem_end = _array->address_for_index(end_index) + N_words;
296 set_remainder_to_point_to_start(rem_st, rem_end, reducing);
297 }
298 break;
299 }
300 case Action_check: {
301 _array->check_offset_array(start_index, boundary, blk_start);
302 // We have finished checking the "offset card". We need to now
303 // check the subsequent cards that this blk spans.
304 check_all_cards(start_index + 1, end_index);
305 break;
306 }
307 default:
308 ShouldNotReachHere();
309 }
310 }
311 }
312
313 // The range [blk_start, blk_end) represents a single contiguous block
314 // of storage; modify the block offset table to represent this
315 // information; Right-open interval: [blk_start, blk_end)
316 // NOTE: this method does _not_ adjust _unallocated_block.
317 void
318 BlockOffsetArray::single_block(HeapWord* blk_start,
319 HeapWord* blk_end) {
320 do_block_internal(blk_start, blk_end, Action_single);
321 }
322
323 void BlockOffsetArray::verify() const {
324 // For each entry in the block offset table, verify that
325 // the entry correctly finds the start of an object at the
326 // first address covered by the block or to the left of that
327 // first address.
328
329 size_t next_index = 1;
330 size_t last_index = last_active_index();
331
332 // Use for debugging. Initialize to NULL to distinguish the
333 // first iteration through the while loop.
334 HeapWord* last_p = NULL;
335 HeapWord* last_start = NULL;
336 oop last_o = NULL;
337
338 while (next_index <= last_index) {
339 // Use an address past the start of the address for
340 // the entry.
341 HeapWord* p = _array->address_for_index(next_index) + 1;
342 if (p >= _end) {
343 // That's all of the allocated block table.
344 return;
345 }
346 // block_start() asserts that start <= p.
347 HeapWord* start = block_start(p);
348 // First check if the start is an allocated block and only
349 // then if it is a valid object.
350 oop o = oop(start);
351 assert(!Universe::is_fully_initialized() ||
352 _sp->is_free_block(start) ||
353 o->is_oop_or_null(), "Bad object was found");
354 next_index++;
355 last_p = p;
356 last_start = start;
357 last_o = o;
358 }
359 }
360
361 //////////////////////////////////////////////////////////////////////
362 // BlockOffsetArrayNonContigSpace
363 //////////////////////////////////////////////////////////////////////
364
365 // The block [blk_start, blk_end) has been allocated;
366 // adjust the block offset table to represent this information;
367 // NOTE: Clients of BlockOffsetArrayNonContigSpace: consider using
368 // the somewhat more lightweight split_block() or
369 // (when init_to_zero()) mark_block() wherever possible.
370 // right-open interval: [blk_start, blk_end)
371 void
372 BlockOffsetArrayNonContigSpace::alloc_block(HeapWord* blk_start,
373 HeapWord* blk_end) {
374 assert(blk_start != NULL && blk_end > blk_start,
375 "phantom block");
376 single_block(blk_start, blk_end);
377 allocated(blk_start, blk_end);
378 }
379
380 // Adjust BOT to show that a previously whole block has been split
381 // into two. We verify the BOT for the first part (prefix) and
382 // update the BOT for the second part (suffix).
383 // blk is the start of the block
384 // blk_size is the size of the original block
385 // left_blk_size is the size of the first part of the split
386 void BlockOffsetArrayNonContigSpace::split_block(HeapWord* blk,
387 size_t blk_size,
388 size_t left_blk_size) {
389 // Verify that the BOT shows [blk, blk + blk_size) to be one block.
390 verify_single_block(blk, blk_size);
391 // Update the BOT to indicate that [blk + left_blk_size, blk + blk_size)
392 // is one single block.
393 assert(blk_size > 0, "Should be positive");
394 assert(left_blk_size > 0, "Should be positive");
395 assert(left_blk_size < blk_size, "Not a split");
396
397 // Start addresses of prefix block and suffix block.
398 HeapWord* pref_addr = blk;
399 HeapWord* suff_addr = blk + left_blk_size;
400 HeapWord* end_addr = blk + blk_size;
401
402 // Indices for starts of prefix block and suffix block.
403 size_t pref_index = _array->index_for(pref_addr);
404 if (_array->address_for_index(pref_index) != pref_addr) {
405 // pref_addr does not begin pref_index
406 pref_index++;
407 }
408
409 size_t suff_index = _array->index_for(suff_addr);
410 if (_array->address_for_index(suff_index) != suff_addr) {
411 // suff_addr does not begin suff_index
412 suff_index++;
413 }
414
415 // Definition: A block B, denoted [B_start, B_end) __starts__
416 // a card C, denoted [C_start, C_end), where C_start and C_end
417 // are the heap addresses that card C covers, iff
418 // B_start <= C_start < B_end.
419 //
420 // We say that a card C "is started by" a block B, iff
421 // B "starts" C.
422 //
423 // Note that the cardinality of the set of cards {C}
424 // started by a block B can be 0, 1, or more.
425 //
426 // Below, pref_index and suff_index are, respectively, the
427 // first (least) card indices that the prefix and suffix of
428 // the split start; end_index is one more than the index of
429 // the last (greatest) card that blk starts.
430 size_t end_index = _array->index_for(end_addr - 1) + 1;
431
432 // Calculate the # cards that the prefix and suffix affect.
433 size_t num_pref_cards = suff_index - pref_index;
434
435 size_t num_suff_cards = end_index - suff_index;
436 // Change the cards that need changing
437 if (num_suff_cards > 0) {
438 HeapWord* boundary = _array->address_for_index(suff_index);
439 // Set the offset card for suffix block
440 _array->set_offset_array(suff_index, boundary, suff_addr, true /* reducing */);
441 // Change any further cards that need changing in the suffix
442 if (num_pref_cards > 0) {
443 if (num_pref_cards >= num_suff_cards) {
444 // Unilaterally fix all of the suffix cards: closed card
445 // index interval in args below.
446 set_remainder_to_point_to_start_incl(suff_index + 1, end_index - 1, true /* reducing */);
447 } else {
448 // Unilaterally fix the first (num_pref_cards - 1) following
449 // the "offset card" in the suffix block.
450 size_t right_most_fixed_index = suff_index + num_pref_cards - 1;
451 set_remainder_to_point_to_start_incl(suff_index + 1,
452 right_most_fixed_index, true /* reducing */);
453 // Fix the appropriate cards in the remainder of the
454 // suffix block -- these are the first num_pref_cards
455 // cards in each power block of the "old" ranges plumbed
456 // from pref_addr.
457 uint i = 1;
458 size_t back_by = power_to_cards_back(i);
459
460 while (i < N_powers) {
461 back_by = power_to_cards_back(i);
462 if (back_by > num_pref_cards) {
463 break;
464 }
465 i++;
466 }
467
468 // Fix the first power block with back_by > num_pref_cards.
469 size_t left_index = right_most_fixed_index + 1;
470 size_t right_index = pref_index + back_by + num_pref_cards;
471 if (right_index >= end_index - 1) { // last iteration
472 right_index = end_index - 1;
473 }
474
475 // Fill in the remainder of this "power block", if it
476 // is non-null.
477 if (left_index <= right_index) {
478 _array->set_offset_array(left_index, right_index,
479 N_words + i - 1, true /* reducing */);
480 debug_only(right_most_fixed_index = right_index;)
481 }
482 // Nothing may actually have been fixed if the region fixed by
483 // the call to set_remainder_to_point_to_start_incl() aligns
484 // evenly with the power block boundaries but still increment
485 // to the next power block. Otherwise, this same power block will
486 // be tried again but there is no safety check against the
487 // right_most_fixed_index.
488 i++;
489 // Fix the rest of the power blocks.
490 while (i < N_powers) {
491 size_t back_by = power_to_cards_back(i);
492 size_t left_index = pref_index + back_by;
493 size_t right_index = left_index + num_pref_cards;
494 if (right_index >= end_index - 1) { // last iteration
495 right_index = end_index - 1;
496 if (left_index > right_index) {
497 break;
498 }
499 }
500 assert(left_index <= right_index, "Error");
501 assert(left_index > right_most_fixed_index, "Overwriting already fixed area");
502 _array->set_offset_array(left_index, right_index, N_words + i - 1, true /* reducing */);
503 debug_only(right_most_fixed_index = right_index;)
504 i++;
505 }
506 }
507 } // else no more cards to fix in suffix
508 } // else nothing needs to be done
509 // Verify that we did the right thing
510 verify_single_block(pref_addr, left_blk_size);
511 verify_single_block(suff_addr, blk_size - left_blk_size);
512 }
513
514
515 // Mark the BOT such that if [blk_start, blk_end) straddles a card
516 // boundary, the card following the first such boundary is marked
517 // with the appropriate offset.
518 // NOTE: this method does _not_ adjust _unallocated_block or
519 // any cards subsequent to the first one.
520 void
521 BlockOffsetArrayNonContigSpace::mark_block(HeapWord* blk_start,
522 HeapWord* blk_end, bool reducing) {
523 do_block_internal(blk_start, blk_end, Action_mark, reducing);
524 }
525
526 HeapWord* BlockOffsetArrayNonContigSpace::block_start_unsafe(
527 const void* addr) const {
528 assert(_array->offset_array(0) == 0, "objects can't cross covered areas");
529 assert(_bottom <= addr && addr < _end,
530 "addr must be covered by this Array");
531 // Must read this exactly once because it can be modified by parallel
532 // allocation.
533 HeapWord* ub = _unallocated_block;
534 if (BlockOffsetArrayUseUnallocatedBlock && addr >= ub) {
535 assert(ub < _end, "tautology (see above)");
536 return ub;
537 }
538
539 // Otherwise, find the block start using the table.
540 size_t index = _array->index_for(addr);
541 HeapWord* q = _array->address_for_index(index);
542
543 uint offset = _array->offset_array(index); // Extend u_char to uint.
544 while (offset >= N_words) {
545 // The excess of the offset from N_words indicates a power of Base
546 // to go back by.
547 size_t n_cards_back = entry_to_cards_back(offset);
548 q -= (N_words * n_cards_back);
549 assert(q >= _sp->bottom(),
550 err_msg("q = " PTR_FORMAT " crossed below bottom = " PTR_FORMAT,
551 p2i(q), p2i(_sp->bottom())));
552 assert(q < _sp->end(),
553 err_msg("q = " PTR_FORMAT " crossed above end = " PTR_FORMAT,
554 p2i(q), p2i(_sp->end())));
555 index -= n_cards_back;
556 offset = _array->offset_array(index);
557 }
558 assert(offset < N_words, "offset too large");
559 index--;
560 q -= offset;
561 assert(q >= _sp->bottom(),
562 err_msg("q = " PTR_FORMAT " crossed below bottom = " PTR_FORMAT,
563 p2i(q), p2i(_sp->bottom())));
564 assert(q < _sp->end(),
565 err_msg("q = " PTR_FORMAT " crossed above end = " PTR_FORMAT,
566 p2i(q), p2i(_sp->end())));
567 HeapWord* n = q;
568
569 while (n <= addr) {
570 debug_only(HeapWord* last = q); // for debugging
571 q = n;
572 n += _sp->block_size(n);
573 assert(n > q,
574 err_msg("Looping at n = " PTR_FORMAT " with last = " PTR_FORMAT","
575 " while querying blk_start(" PTR_FORMAT ")"
576 " on _sp = [" PTR_FORMAT "," PTR_FORMAT ")",
577 p2i(n), p2i(last), p2i(addr), p2i(_sp->bottom()), p2i(_sp->end())));
578 }
579 assert(q <= addr,
580 err_msg("wrong order for current (" INTPTR_FORMAT ")" " <= arg (" INTPTR_FORMAT ")",
581 p2i(q), p2i(addr)));
582 assert(addr <= n,
583 err_msg("wrong order for arg (" INTPTR_FORMAT ") <= next (" INTPTR_FORMAT ")",
584 p2i(addr), p2i(n)));
585 return q;
586 }
587
588 HeapWord* BlockOffsetArrayNonContigSpace::block_start_careful(
589 const void* addr) const {
590 assert(_array->offset_array(0) == 0, "objects can't cross covered areas");
591
592 assert(_bottom <= addr && addr < _end,
593 "addr must be covered by this Array");
594 // Must read this exactly once because it can be modified by parallel
595 // allocation.
596 HeapWord* ub = _unallocated_block;
597 if (BlockOffsetArrayUseUnallocatedBlock && addr >= ub) {
598 assert(ub < _end, "tautology (see above)");
599 return ub;
600 }
601
602 // Otherwise, find the block start using the table, but taking
603 // care (cf block_start_unsafe() above) not to parse any objects/blocks
604 // on the cards themselves.
605 size_t index = _array->index_for(addr);
606 assert(_array->address_for_index(index) == addr,
607 "arg should be start of card");
608
609 HeapWord* q = (HeapWord*)addr;
610 uint offset;
611 do {
612 offset = _array->offset_array(index);
613 if (offset < N_words) {
614 q -= offset;
615 } else {
616 size_t n_cards_back = entry_to_cards_back(offset);
617 q -= (n_cards_back * N_words);
618 index -= n_cards_back;
619 }
620 } while (offset >= N_words);
621 assert(q <= addr, "block start should be to left of arg");
622 return q;
623 }
624
625 #ifndef PRODUCT
626 // Verification & debugging - ensure that the offset table reflects the fact
627 // that the block [blk_start, blk_end) or [blk, blk + size) is a
628 // single block of storage. NOTE: can't const this because of
629 // call to non-const do_block_internal() below.
630 void BlockOffsetArrayNonContigSpace::verify_single_block(
631 HeapWord* blk_start, HeapWord* blk_end) {
632 if (VerifyBlockOffsetArray) {
633 do_block_internal(blk_start, blk_end, Action_check);
634 }
635 }
636
637 void BlockOffsetArrayNonContigSpace::verify_single_block(
638 HeapWord* blk, size_t size) {
639 verify_single_block(blk, blk + size);
640 }
641
642 // Verify that the given block is before _unallocated_block
643 void BlockOffsetArrayNonContigSpace::verify_not_unallocated(
644 HeapWord* blk_start, HeapWord* blk_end) const {
645 if (BlockOffsetArrayUseUnallocatedBlock) {
646 assert(blk_start < blk_end, "Block inconsistency?");
647 assert(blk_end <= _unallocated_block, "_unallocated_block problem");
648 }
649 }
650
651 void BlockOffsetArrayNonContigSpace::verify_not_unallocated(
652 HeapWord* blk, size_t size) const {
653 verify_not_unallocated(blk, blk + size);
654 }
655 #endif // PRODUCT
656
657 size_t BlockOffsetArrayNonContigSpace::last_active_index() const {
658 if (_unallocated_block == _bottom) {
659 return 0;
660 } else {
661 return _array->index_for(_unallocated_block - 1);
662 }
663 }
664
665 //////////////////////////////////////////////////////////////////////
666 // BlockOffsetArrayContigSpace
667 //////////////////////////////////////////////////////////////////////
668
669 HeapWord* BlockOffsetArrayContigSpace::block_start_unsafe(const void* addr) const {
670 assert(_array->offset_array(0) == 0, "objects can't cross covered areas");
671
672 // Otherwise, find the block start using the table.
673 assert(_bottom <= addr && addr < _end,
674 "addr must be covered by this Array");
675 size_t index = _array->index_for(addr);
676 // We must make sure that the offset table entry we use is valid. If
677 // "addr" is past the end, start at the last known one and go forward.
678 index = MIN2(index, _next_offset_index-1);
679 HeapWord* q = _array->address_for_index(index);
680
681 uint offset = _array->offset_array(index); // Extend u_char to uint.
682 while (offset > N_words) {
683 // The excess of the offset from N_words indicates a power of Base
684 // to go back by.
685 size_t n_cards_back = entry_to_cards_back(offset);
686 q -= (N_words * n_cards_back);
687 assert(q >= _sp->bottom(), "Went below bottom!");
688 index -= n_cards_back;
689 offset = _array->offset_array(index);
690 }
691 while (offset == N_words) {
692 assert(q >= _sp->bottom(), "Went below bottom!");
693 q -= N_words;
694 index--;
695 offset = _array->offset_array(index);
696 }
697 assert(offset < N_words, "offset too large");
698 q -= offset;
699 HeapWord* n = q;
700
701 while (n <= addr) {
702 debug_only(HeapWord* last = q); // for debugging
703 q = n;
704 n += _sp->block_size(n);
705 }
706 assert(q <= addr, "wrong order for current and arg");
707 assert(addr <= n, "wrong order for arg and next");
708 return q;
709 }
710
711 //
712 // _next_offset_threshold
713 // | _next_offset_index
714 // v v
715 // +-------+-------+-------+-------+-------+
716 // | i-1 | i | i+1 | i+2 | i+3 |
717 // +-------+-------+-------+-------+-------+
718 // ( ^ ]
719 // block-start
720 //
721
722 void BlockOffsetArrayContigSpace::alloc_block_work(HeapWord* blk_start,
723 HeapWord* blk_end) {
724 assert(blk_start != NULL && blk_end > blk_start,
725 "phantom block");
726 assert(blk_end > _next_offset_threshold,
727 "should be past threshold");
728 assert(blk_start <= _next_offset_threshold,
729 "blk_start should be at or before threshold");
730 assert(pointer_delta(_next_offset_threshold, blk_start) <= N_words,
731 "offset should be <= BlockOffsetSharedArray::N");
732 assert(Universe::heap()->is_in_reserved(blk_start),
733 "reference must be into the heap");
734 assert(Universe::heap()->is_in_reserved(blk_end-1),
735 "limit must be within the heap");
736 assert(_next_offset_threshold ==
737 _array->_reserved.start() + _next_offset_index*N_words,
738 "index must agree with threshold");
739
740 debug_only(size_t orig_next_offset_index = _next_offset_index;)
741
742 // Mark the card that holds the offset into the block. Note
743 // that _next_offset_index and _next_offset_threshold are not
744 // updated until the end of this method.
745 _array->set_offset_array(_next_offset_index,
746 _next_offset_threshold,
747 blk_start);
748
749 // We need to now mark the subsequent cards that this blk spans.
750
751 // Index of card on which blk ends.
752 size_t end_index = _array->index_for(blk_end - 1);
753
754 // Are there more cards left to be updated?
755 if (_next_offset_index + 1 <= end_index) {
756 HeapWord* rem_st = _array->address_for_index(_next_offset_index + 1);
757 // Calculate rem_end this way because end_index
758 // may be the last valid index in the covered region.
759 HeapWord* rem_end = _array->address_for_index(end_index) + N_words;
760 set_remainder_to_point_to_start(rem_st, rem_end);
761 }
762
763 // _next_offset_index and _next_offset_threshold updated here.
764 _next_offset_index = end_index + 1;
765 // Calculate _next_offset_threshold this way because end_index
766 // may be the last valid index in the covered region.
767 _next_offset_threshold = _array->address_for_index(end_index) + N_words;
768 assert(_next_offset_threshold >= blk_end, "Incorrect offset threshold");
769
770 #ifdef ASSERT
771 // The offset can be 0 if the block starts on a boundary. That
772 // is checked by an assertion above.
773 size_t start_index = _array->index_for(blk_start);
774 HeapWord* boundary = _array->address_for_index(start_index);
775 assert((_array->offset_array(orig_next_offset_index) == 0 &&
776 blk_start == boundary) ||
777 (_array->offset_array(orig_next_offset_index) > 0 &&
778 _array->offset_array(orig_next_offset_index) <= N_words),
779 "offset array should have been set");
780 for (size_t j = orig_next_offset_index + 1; j <= end_index; j++) {
781 assert(_array->offset_array(j) > 0 &&
782 _array->offset_array(j) <= (u_char) (N_words+N_powers-1),
783 "offset array should have been set");
784 }
785 #endif
786 }
787
788 HeapWord* BlockOffsetArrayContigSpace::initialize_threshold() {
789 assert(!Universe::heap()->is_in_reserved(_array->_offset_array),
790 "just checking");
791 _next_offset_index = _array->index_for(_bottom);
792 _next_offset_index++;
793 _next_offset_threshold =
794 _array->address_for_index(_next_offset_index);
795 return _next_offset_threshold;
796 }
797
798 void BlockOffsetArrayContigSpace::zero_bottom_entry() {
799 assert(!Universe::heap()->is_in_reserved(_array->_offset_array),
800 "just checking");
801 size_t bottom_index = _array->index_for(_bottom);
802 _array->set_offset_array(bottom_index, 0);
803 }
804
805 size_t BlockOffsetArrayContigSpace::last_active_index() const {
806 return _next_offset_index == 0 ? 0 : _next_offset_index - 1;
807 }