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