1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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24
25 // The CollectedHeap type requires subtypes to implement a method
26 // "block_start". For some subtypes, notably generational
27 // systems using card-table-based write barriers, the efficiency of this
28 // operation may be important. Implementations of the "BlockOffsetArray"
29 // class may be useful in providing such efficient implementations.
30 //
31 // BlockOffsetTable (abstract)
32 // - BlockOffsetArray (abstract)
33 // - BlockOffsetArrayNonContigSpace
34 // - BlockOffsetArrayContigSpace
35 //
36
37 class ContiguousSpace;
38 class SerializeOopClosure;
39
40 //////////////////////////////////////////////////////////////////////////
41 // The BlockOffsetTable "interface"
42 //////////////////////////////////////////////////////////////////////////
43 class BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
44 friend class VMStructs;
45 protected:
46 // These members describe the region covered by the table.
47
48 // The space this table is covering.
49 HeapWord* _bottom; // == reserved.start
50 HeapWord* _end; // End of currently allocated region.
51
52 public:
53 // Initialize the table to cover the given space.
54 // The contents of the initial table are undefined.
55 BlockOffsetTable(HeapWord* bottom, HeapWord* end):
56 _bottom(bottom), _end(end) {
57 assert(_bottom <= _end, "arguments out of order");
58 }
59
60 // Note that the committed size of the covered space may have changed,
61 // so the table size might also wish to change.
62 virtual void resize(size_t new_word_size) = 0;
63
64 virtual void set_bottom(HeapWord* new_bottom) {
65 assert(new_bottom <= _end, "new_bottom > _end");
66 _bottom = new_bottom;
67 resize(pointer_delta(_end, _bottom));
68 }
69
70 // Requires "addr" to be contained by a block, and returns the address of
71 // the start of that block.
72 virtual HeapWord* block_start_unsafe(const void* addr) const = 0;
73
74 // Returns the address of the start of the block containing "addr", or
75 // else "null" if it is covered by no block.
76 HeapWord* block_start(const void* addr) const;
77 };
78
79 //////////////////////////////////////////////////////////////////////////
80 // One implementation of "BlockOffsetTable," the BlockOffsetArray,
81 // divides the covered region into "N"-word subregions (where
82 // "N" = 2^"LogN". An array with an entry for each such subregion
83 // indicates how far back one must go to find the start of the
84 // chunk that includes the first word of the subregion.
85 //
86 // Each BlockOffsetArray is owned by a Space. However, the actual array
87 // may be shared by several BlockOffsetArrays; this is useful
88 // when a single resizable area (such as a generation) is divided up into
89 // several spaces in which contiguous allocation takes place. (Consider,
90 // for example, the garbage-first generation.)
91
92 // Here is the shared array type.
93 //////////////////////////////////////////////////////////////////////////
94 // BlockOffsetSharedArray
95 //////////////////////////////////////////////////////////////////////////
96 class BlockOffsetSharedArray: public CHeapObj {
97 friend class BlockOffsetArray;
98 friend class BlockOffsetArrayNonContigSpace;
99 friend class BlockOffsetArrayContigSpace;
100 friend class VMStructs;
101
102 private:
103 enum SomePrivateConstants {
104 LogN = 9,
105 LogN_words = LogN - LogHeapWordSize,
106 N_bytes = 1 << LogN,
107 N_words = 1 << LogN_words
108 };
109
110 bool _init_to_zero;
111
112 // The reserved region covered by the shared array.
113 MemRegion _reserved;
114
115 // End of the current committed region.
116 HeapWord* _end;
117
118 // Array for keeping offsets for retrieving object start fast given an
119 // address.
120 VirtualSpace _vs;
121 u_char* _offset_array; // byte array keeping backwards offsets
122
123 protected:
124 // Bounds checking accessors:
125 // For performance these have to devolve to array accesses in product builds.
126 u_char offset_array(size_t index) const {
127 assert(index < _vs.committed_size(), "index out of range");
128 return _offset_array[index];
129 }
130 // An assertion-checking helper method for the set_offset_array() methods below.
131 void check_reducing_assertion(bool reducing);
132
133 void set_offset_array(size_t index, u_char offset, bool reducing = false) {
134 check_reducing_assertion(reducing);
135 assert(index < _vs.committed_size(), "index out of range");
136 assert(!reducing || _offset_array[index] >= offset, "Not reducing");
137 _offset_array[index] = offset;
138 }
139
140 void set_offset_array(size_t index, HeapWord* high, HeapWord* low, bool reducing = false) {
141 check_reducing_assertion(reducing);
142 assert(index < _vs.committed_size(), "index out of range");
143 assert(high >= low, "addresses out of order");
144 assert(pointer_delta(high, low) <= N_words, "offset too large");
145 assert(!reducing || _offset_array[index] >= (u_char)pointer_delta(high, low),
146 "Not reducing");
147 _offset_array[index] = (u_char)pointer_delta(high, low);
148 }
149
150 void set_offset_array(HeapWord* left, HeapWord* right, u_char offset, bool reducing = false) {
151 check_reducing_assertion(reducing);
152 assert(index_for(right - 1) < _vs.committed_size(),
153 "right address out of range");
154 assert(left < right, "Heap addresses out of order");
155 size_t num_cards = pointer_delta(right, left) >> LogN_words;
156
157 // Below, we may use an explicit loop instead of memset()
158 // because on certain platforms memset() can give concurrent
159 // readers "out-of-thin-air," phantom zeros; see 6948537.
160 if (UseMemSetInBOT) {
161 memset(&_offset_array[index_for(left)], offset, num_cards);
162 } else {
163 size_t i = index_for(left);
164 const size_t end = i + num_cards;
165 for (; i < end; i++) {
166 // Elided until CR 6977974 is fixed properly.
167 // assert(!reducing || _offset_array[i] >= offset, "Not reducing");
168 _offset_array[i] = offset;
169 }
170 }
171 }
172
173 void set_offset_array(size_t left, size_t right, u_char offset, bool reducing = false) {
174 check_reducing_assertion(reducing);
175 assert(right < _vs.committed_size(), "right address out of range");
176 assert(left <= right, "indexes out of order");
177 size_t num_cards = right - left + 1;
178
179 // Below, we may use an explicit loop instead of memset
180 // because on certain platforms memset() can give concurrent
181 // readers "out-of-thin-air," phantom zeros; see 6948537.
182 if (UseMemSetInBOT) {
183 memset(&_offset_array[left], offset, num_cards);
184 } else {
185 size_t i = left;
186 const size_t end = i + num_cards;
187 for (; i < end; i++) {
188 // Elided until CR 6977974 is fixed properly.
189 // assert(!reducing || _offset_array[i] >= offset, "Not reducing");
190 _offset_array[i] = offset;
191 }
192 }
193 }
194
195 void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
196 assert(index < _vs.committed_size(), "index out of range");
197 assert(high >= low, "addresses out of order");
198 assert(pointer_delta(high, low) <= N_words, "offset too large");
199 assert(_offset_array[index] == pointer_delta(high, low),
200 "Wrong offset");
201 }
202
203 bool is_card_boundary(HeapWord* p) const;
204
205 // Return the number of slots needed for an offset array
206 // that covers mem_region_words words.
207 // We always add an extra slot because if an object
208 // ends on a card boundary we put a 0 in the next
209 // offset array slot, so we want that slot always
210 // to be reserved.
211
212 size_t compute_size(size_t mem_region_words) {
213 size_t number_of_slots = (mem_region_words / N_words) + 1;
214 return ReservedSpace::allocation_align_size_up(number_of_slots);
215 }
216
217 public:
218 // Initialize the table to cover from "base" to (at least)
219 // "base + init_word_size". In the future, the table may be expanded
220 // (see "resize" below) up to the size of "_reserved" (which must be at
221 // least "init_word_size".) The contents of the initial table are
222 // undefined; it is the responsibility of the constituent
223 // BlockOffsetTable(s) to initialize cards.
224 BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
225
226 // Notes a change in the committed size of the region covered by the
227 // table. The "new_word_size" may not be larger than the size of the
228 // reserved region this table covers.
229 void resize(size_t new_word_size);
230
231 void set_bottom(HeapWord* new_bottom);
232
233 // Whether entries should be initialized to zero. Used currently only for
234 // error checking.
235 void set_init_to_zero(bool val) { _init_to_zero = val; }
236 bool init_to_zero() { return _init_to_zero; }
237
238 // Updates all the BlockOffsetArray's sharing this shared array to
239 // reflect the current "top"'s of their spaces.
240 void update_offset_arrays(); // Not yet implemented!
241
242 // Return the appropriate index into "_offset_array" for "p".
243 size_t index_for(const void* p) const;
244
245 // Return the address indicating the start of the region corresponding to
246 // "index" in "_offset_array".
247 HeapWord* address_for_index(size_t index) const;
248
249 // Return the address "p" incremented by the size of
250 // a region. This method does not align the address
251 // returned to the start of a region. It is a simple
252 // primitive.
253 HeapWord* inc_by_region_size(HeapWord* p) const { return p + N_words; }
254
255 // Shared space support
256 void serialize(SerializeOopClosure* soc, HeapWord* start, HeapWord* end);
257 };
258
259 //////////////////////////////////////////////////////////////////////////
260 // The BlockOffsetArray whose subtypes use the BlockOffsetSharedArray.
261 //////////////////////////////////////////////////////////////////////////
262 class BlockOffsetArray: public BlockOffsetTable {
263 friend class VMStructs;
264 friend class G1BlockOffsetArray; // temp. until we restructure and cleanup
265 protected:
266 // The following enums are used by do_block_internal() below
267 enum Action {
268 Action_single, // BOT records a single block (see single_block())
269 Action_mark, // BOT marks the start of a block (see mark_block())
270 Action_check // Check that BOT records block correctly
271 // (see verify_single_block()).
272 };
273
274 enum SomePrivateConstants {
275 N_words = BlockOffsetSharedArray::N_words,
276 LogN = BlockOffsetSharedArray::LogN,
277 // entries "e" of at least N_words mean "go back by Base^(e-N_words)."
278 // All entries are less than "N_words + N_powers".
279 LogBase = 4,
280 Base = (1 << LogBase),
281 N_powers = 14
282 };
283
284 static size_t power_to_cards_back(uint i) {
285 return (size_t)(1 << (LogBase * i));
286 }
287 static size_t power_to_words_back(uint i) {
288 return power_to_cards_back(i) * N_words;
289 }
290 static size_t entry_to_cards_back(u_char entry) {
291 assert(entry >= N_words, "Precondition");
292 return power_to_cards_back(entry - N_words);
293 }
294 static size_t entry_to_words_back(u_char entry) {
295 assert(entry >= N_words, "Precondition");
296 return power_to_words_back(entry - N_words);
297 }
298
299 // The shared array, which is shared with other BlockOffsetArray's
300 // corresponding to different spaces within a generation or span of
301 // memory.
302 BlockOffsetSharedArray* _array;
303
304 // The space that owns this subregion.
305 Space* _sp;
306
307 // If true, array entries are initialized to 0; otherwise, they are
308 // initialized to point backwards to the beginning of the covered region.
309 bool _init_to_zero;
310
311 // An assertion-checking helper method for the set_remainder*() methods below.
312 void check_reducing_assertion(bool reducing) { _array->check_reducing_assertion(reducing); }
313
314 // Sets the entries
315 // corresponding to the cards starting at "start" and ending at "end"
316 // to point back to the card before "start": the interval [start, end)
317 // is right-open. The last parameter, reducing, indicates whether the
318 // updates to individual entries always reduce the entry from a higher
319 // to a lower value. (For example this would hold true during a temporal
320 // regime during which only block splits were updating the BOT.
321 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end, bool reducing = false);
322 // Same as above, except that the args here are a card _index_ interval
323 // that is closed: [start_index, end_index]
324 void set_remainder_to_point_to_start_incl(size_t start, size_t end, bool reducing = false);
325
326 // A helper function for BOT adjustment/verification work
327 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action, bool reducing = false);
328
329 public:
330 // The space may not have its bottom and top set yet, which is why the
331 // region is passed as a parameter. If "init_to_zero" is true, the
332 // elements of the array are initialized to zero. Otherwise, they are
333 // initialized to point backwards to the beginning.
334 BlockOffsetArray(BlockOffsetSharedArray* array, MemRegion mr,
335 bool init_to_zero_);
336
337 // Note: this ought to be part of the constructor, but that would require
338 // "this" to be passed as a parameter to a member constructor for
339 // the containing concrete subtype of Space.
340 // This would be legal C++, but MS VC++ doesn't allow it.
341 void set_space(Space* sp) { _sp = sp; }
342
343 // Resets the covered region to the given "mr".
344 void set_region(MemRegion mr) {
345 _bottom = mr.start();
346 _end = mr.end();
347 }
348
349 // Note that the committed size of the covered space may have changed,
350 // so the table size might also wish to change.
351 virtual void resize(size_t new_word_size) {
352 HeapWord* new_end = _bottom + new_word_size;
353 if (_end < new_end && !init_to_zero()) {
354 // verify that the old and new boundaries are also card boundaries
355 assert(_array->is_card_boundary(_end),
356 "_end not a card boundary");
357 assert(_array->is_card_boundary(new_end),
358 "new _end would not be a card boundary");
359 // set all the newly added cards
360 _array->set_offset_array(_end, new_end, N_words);
361 }
362 _end = new_end; // update _end
363 }
364
365 // Adjust the BOT to show that it has a single block in the
366 // range [blk_start, blk_start + size). All necessary BOT
367 // cards are adjusted, but _unallocated_block isn't.
368 void single_block(HeapWord* blk_start, HeapWord* blk_end);
369 void single_block(HeapWord* blk, size_t size) {
370 single_block(blk, blk + size);
371 }
372
373 // When the alloc_block() call returns, the block offset table should
374 // have enough information such that any subsequent block_start() call
375 // with an argument equal to an address that is within the range
376 // [blk_start, blk_end) would return the value blk_start, provided
377 // there have been no calls in between that reset this information
378 // (e.g. see BlockOffsetArrayNonContigSpace::single_block() call
379 // for an appropriate range covering the said interval).
380 // These methods expect to be called with [blk_start, blk_end)
381 // representing a block of memory in the heap.
382 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
383 void alloc_block(HeapWord* blk, size_t size) {
384 alloc_block(blk, blk + size);
385 }
386
387 // If true, initialize array slots with no allocated blocks to zero.
388 // Otherwise, make them point back to the front.
389 bool init_to_zero() { return _init_to_zero; }
390 // Corresponding setter
391 void set_init_to_zero(bool val) {
392 _init_to_zero = val;
393 assert(_array != NULL, "_array should be non-NULL");
394 _array->set_init_to_zero(val);
395 }
396
397 // Debugging
398 // Return the index of the last entry in the "active" region.
399 virtual size_t last_active_index() const = 0;
400 // Verify the block offset table
401 void verify() const;
402 void check_all_cards(size_t left_card, size_t right_card) const;
403 };
404
405 ////////////////////////////////////////////////////////////////////////////
406 // A subtype of BlockOffsetArray that takes advantage of the fact
407 // that its underlying space is a NonContiguousSpace, so that some
408 // specialized interfaces can be made available for spaces that
409 // manipulate the table.
410 ////////////////////////////////////////////////////////////////////////////
411 class BlockOffsetArrayNonContigSpace: public BlockOffsetArray {
412 friend class VMStructs;
413 private:
414 // The portion [_unallocated_block, _sp.end()) of the space that
415 // is a single block known not to contain any objects.
416 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
417 HeapWord* _unallocated_block;
418
419 public:
420 BlockOffsetArrayNonContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
421 BlockOffsetArray(array, mr, false),
422 _unallocated_block(_bottom) { }
423
424 // accessor
425 HeapWord* unallocated_block() const {
426 assert(BlockOffsetArrayUseUnallocatedBlock,
427 "_unallocated_block is not being maintained");
428 return _unallocated_block;
429 }
430
431 void set_unallocated_block(HeapWord* block) {
432 assert(BlockOffsetArrayUseUnallocatedBlock,
433 "_unallocated_block is not being maintained");
434 assert(block >= _bottom && block <= _end, "out of range");
435 _unallocated_block = block;
436 }
437
438 // These methods expect to be called with [blk_start, blk_end)
439 // representing a block of memory in the heap.
440 void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
441 void alloc_block(HeapWord* blk, size_t size) {
442 alloc_block(blk, blk + size);
443 }
444
445 // The following methods are useful and optimized for a
446 // non-contiguous space.
447
448 // Given a block [blk_start, blk_start + full_blk_size), and
449 // a left_blk_size < full_blk_size, adjust the BOT to show two
450 // blocks [blk_start, blk_start + left_blk_size) and
451 // [blk_start + left_blk_size, blk_start + full_blk_size).
452 // It is assumed (and verified in the non-product VM) that the
453 // BOT was correct for the original block.
454 void split_block(HeapWord* blk_start, size_t full_blk_size,
455 size_t left_blk_size);
456
457 // Adjust BOT to show that it has a block in the range
458 // [blk_start, blk_start + size). Only the first card
459 // of BOT is touched. It is assumed (and verified in the
460 // non-product VM) that the remaining cards of the block
461 // are correct.
462 void mark_block(HeapWord* blk_start, HeapWord* blk_end, bool reducing = false);
463 void mark_block(HeapWord* blk, size_t size, bool reducing = false) {
464 mark_block(blk, blk + size, reducing);
465 }
466
467 // Adjust _unallocated_block to indicate that a particular
468 // block has been newly allocated or freed. It is assumed (and
469 // verified in the non-product VM) that the BOT is correct for
470 // the given block.
471 void allocated(HeapWord* blk_start, HeapWord* blk_end, bool reducing = false) {
472 // Verify that the BOT shows [blk, blk + blk_size) to be one block.
473 verify_single_block(blk_start, blk_end);
474 if (BlockOffsetArrayUseUnallocatedBlock) {
475 _unallocated_block = MAX2(_unallocated_block, blk_end);
476 }
477 }
478
479 void allocated(HeapWord* blk, size_t size, bool reducing = false) {
480 allocated(blk, blk + size, reducing);
481 }
482
483 void freed(HeapWord* blk_start, HeapWord* blk_end);
484 void freed(HeapWord* blk, size_t size);
485
486 HeapWord* block_start_unsafe(const void* addr) const;
487
488 // Requires "addr" to be the start of a card and returns the
489 // start of the block that contains the given address.
490 HeapWord* block_start_careful(const void* addr) const;
491
492 // Verification & debugging: ensure that the offset table reflects
493 // the fact that the block [blk_start, blk_end) or [blk, blk + size)
494 // is a single block of storage. NOTE: can't const this because of
495 // call to non-const do_block_internal() below.
496 void verify_single_block(HeapWord* blk_start, HeapWord* blk_end)
497 PRODUCT_RETURN;
498 void verify_single_block(HeapWord* blk, size_t size) PRODUCT_RETURN;
499
500 // Verify that the given block is before _unallocated_block
501 void verify_not_unallocated(HeapWord* blk_start, HeapWord* blk_end)
502 const PRODUCT_RETURN;
503 void verify_not_unallocated(HeapWord* blk, size_t size)
504 const PRODUCT_RETURN;
505
506 // Debugging support
507 virtual size_t last_active_index() const;
508 };
509
510 ////////////////////////////////////////////////////////////////////////////
511 // A subtype of BlockOffsetArray that takes advantage of the fact
512 // that its underlying space is a ContiguousSpace, so that its "active"
513 // region can be more efficiently tracked (than for a non-contiguous space).
514 ////////////////////////////////////////////////////////////////////////////
515 class BlockOffsetArrayContigSpace: public BlockOffsetArray {
516 friend class VMStructs;
517 private:
518 // allocation boundary at which offset array must be updated
519 HeapWord* _next_offset_threshold;
520 size_t _next_offset_index; // index corresponding to that boundary
521
522 // Work function when allocation start crosses threshold.
523 void alloc_block_work(HeapWord* blk_start, HeapWord* blk_end);
524
525 public:
526 BlockOffsetArrayContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
527 BlockOffsetArray(array, mr, true) {
528 _next_offset_threshold = NULL;
529 _next_offset_index = 0;
530 }
531
532 void set_contig_space(ContiguousSpace* sp) { set_space((Space*)sp); }
533
534 // Initialize the threshold for an empty heap.
535 HeapWord* initialize_threshold();
536 // Zero out the entry for _bottom (offset will be zero)
537 void zero_bottom_entry();
538
539 // Return the next threshold, the point at which the table should be
540 // updated.
541 HeapWord* threshold() const { return _next_offset_threshold; }
542
543 // In general, these methods expect to be called with
544 // [blk_start, blk_end) representing a block of memory in the heap.
545 // In this implementation, however, we are OK even if blk_start and/or
546 // blk_end are NULL because NULL is represented as 0, and thus
547 // never exceeds the "_next_offset_threshold".
548 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
549 if (blk_end > _next_offset_threshold) {
550 alloc_block_work(blk_start, blk_end);
551 }
552 }
553 void alloc_block(HeapWord* blk, size_t size) {
554 alloc_block(blk, blk + size);
555 }
556
557 HeapWord* block_start_unsafe(const void* addr) const;
558
559 void serialize(SerializeOopClosure* soc);
560
561 // Debugging support
562 virtual size_t last_active_index() const;
563 };