1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_VM_GC_SHARED_BLOCKOFFSETTABLE_HPP
26 #define SHARE_VM_GC_SHARED_BLOCKOFFSETTABLE_HPP
27
28 #include "gc/shared/memset_with_concurrent_readers.hpp"
29 #include "memory/allocation.hpp"
30 #include "memory/memRegion.hpp"
31 #include "memory/virtualspace.hpp"
32 #include "runtime/globals.hpp"
33 #include "utilities/globalDefinitions.hpp"
34 #include "utilities/macros.hpp"
35
36 // The CollectedHeap type requires subtypes to implement a method
37 // "block_start". For some subtypes, notably generational
38 // systems using card-table-based write barriers, the efficiency of this
39 // operation may be important. Implementations of the "BlockOffsetArray"
40 // class may be useful in providing such efficient implementations.
41 //
42 // BlockOffsetTable (abstract)
43 // - BlockOffsetArray (abstract)
44 // - BlockOffsetArrayNonContigSpace
45 // - BlockOffsetArrayContigSpace
46 //
47
48 class ContiguousSpace;
49
50 class BOTConstants : public AllStatic {
51 public:
52 static const uint LogN = 9;
53 static const uint LogN_words = LogN - LogHeapWordSize;
54 static const uint N_bytes = 1 << LogN;
55 static const uint N_words = 1 << LogN_words;
56 // entries "e" of at least N_words mean "go back by Base^(e-N_words)."
57 // All entries are less than "N_words + N_powers".
58 static const uint LogBase = 4;
59 static const uint Base = (1 << LogBase);
60 static const uint N_powers = 14;
61
62 static size_t power_to_cards_back(uint i) {
63 return (size_t)1 << (LogBase * i);
64 }
65 static size_t power_to_words_back(uint i) {
66 return power_to_cards_back(i) * N_words;
67 }
68 static size_t entry_to_cards_back(u_char entry) {
69 assert(entry >= N_words, "Precondition");
70 return power_to_cards_back(entry - N_words);
71 }
72 static size_t entry_to_words_back(u_char entry) {
73 assert(entry >= N_words, "Precondition");
74 return power_to_words_back(entry - N_words);
75 }
76 };
77
78 //////////////////////////////////////////////////////////////////////////
79 // The BlockOffsetTable "interface"
80 //////////////////////////////////////////////////////////////////////////
81 class BlockOffsetTable {
82 friend class VMStructs;
83 protected:
84 // These members describe the region covered by the table.
85
86 // The space this table is covering.
87 HeapWord* _bottom; // == reserved.start
88 HeapWord* _end; // End of currently allocated region.
89
90 public:
91 // Initialize the table to cover the given space.
92 // The contents of the initial table are undefined.
93 BlockOffsetTable(HeapWord* bottom, HeapWord* end):
94 _bottom(bottom), _end(end) {
95 assert(_bottom <= _end, "arguments out of order");
96 }
97
98 // Note that the committed size of the covered space may have changed,
99 // so the table size might also wish to change.
100 virtual void resize(size_t new_word_size) = 0;
101
102 virtual void set_bottom(HeapWord* new_bottom) {
103 assert(new_bottom <= _end, "new_bottom > _end");
104 _bottom = new_bottom;
105 resize(pointer_delta(_end, _bottom));
106 }
107
108 // Requires "addr" to be contained by a block, and returns the address of
109 // the start of that block.
110 virtual HeapWord* block_start_unsafe(const void* addr) const = 0;
111
112 // Returns the address of the start of the block containing "addr", or
113 // else "null" if it is covered by no block.
114 HeapWord* block_start(const void* addr) const;
115 };
116
117 //////////////////////////////////////////////////////////////////////////
118 // One implementation of "BlockOffsetTable," the BlockOffsetArray,
119 // divides the covered region into "N"-word subregions (where
120 // "N" = 2^"LogN". An array with an entry for each such subregion
121 // indicates how far back one must go to find the start of the
122 // chunk that includes the first word of the subregion.
123 //
124 // Each BlockOffsetArray is owned by a Space. However, the actual array
125 // may be shared by several BlockOffsetArrays; this is useful
126 // when a single resizable area (such as a generation) is divided up into
127 // several spaces in which contiguous allocation takes place. (Consider,
128 // for example, the garbage-first generation.)
129
130 // Here is the shared array type.
131 //////////////////////////////////////////////////////////////////////////
132 // BlockOffsetSharedArray
133 //////////////////////////////////////////////////////////////////////////
134 class BlockOffsetSharedArray: public CHeapObj<mtGC> {
135 friend class BlockOffsetArray;
136 friend class BlockOffsetArrayNonContigSpace;
137 friend class BlockOffsetArrayContigSpace;
138 friend class VMStructs;
139
140 private:
141 bool _init_to_zero;
142
143 // The reserved region covered by the shared array.
144 MemRegion _reserved;
145
146 // End of the current committed region.
147 HeapWord* _end;
148
149 // Array for keeping offsets for retrieving object start fast given an
150 // address.
151 VirtualSpace _vs;
152 u_char* _offset_array; // byte array keeping backwards offsets
153
154 void fill_range(size_t start, size_t num_cards, u_char offset) {
155 void* start_ptr = &_offset_array[start];
156 // If collector is concurrent, special handling may be needed.
157 G1GC_ONLY(assert(!UseG1GC, "Shouldn't be here when using G1");)
158 #if INCLUDE_CMSGC
159 if (UseConcMarkSweepGC) {
160 memset_with_concurrent_readers(start_ptr, offset, num_cards);
161 return;
162 }
163 #endif // INCLUDE_CMSGC
164 memset(start_ptr, offset, num_cards);
165 }
166
167 protected:
168 // Bounds checking accessors:
169 // For performance these have to devolve to array accesses in product builds.
170 u_char offset_array(size_t index) const {
171 assert(index < _vs.committed_size(), "index out of range");
172 return _offset_array[index];
173 }
174 // An assertion-checking helper method for the set_offset_array() methods below.
175 void check_reducing_assertion(bool reducing);
176
177 void set_offset_array(size_t index, u_char offset, bool reducing = false) {
178 check_reducing_assertion(reducing);
179 assert(index < _vs.committed_size(), "index out of range");
180 assert(!reducing || _offset_array[index] >= offset, "Not reducing");
181 _offset_array[index] = offset;
182 }
183
184 void set_offset_array(size_t index, HeapWord* high, HeapWord* low, bool reducing = false) {
185 check_reducing_assertion(reducing);
186 assert(index < _vs.committed_size(), "index out of range");
187 assert(high >= low, "addresses out of order");
188 assert(pointer_delta(high, low) <= BOTConstants::N_words, "offset too large");
189 assert(!reducing || _offset_array[index] >= (u_char)pointer_delta(high, low),
190 "Not reducing");
191 _offset_array[index] = (u_char)pointer_delta(high, low);
192 }
193
194 void set_offset_array(HeapWord* left, HeapWord* right, u_char offset, bool reducing = false) {
195 check_reducing_assertion(reducing);
196 assert(index_for(right - 1) < _vs.committed_size(),
197 "right address out of range");
198 assert(left < right, "Heap addresses out of order");
199 size_t num_cards = pointer_delta(right, left) >> BOTConstants::LogN_words;
200
201 fill_range(index_for(left), num_cards, offset);
202 }
203
204 void set_offset_array(size_t left, size_t right, u_char offset, bool reducing = false) {
205 check_reducing_assertion(reducing);
206 assert(right < _vs.committed_size(), "right address out of range");
207 assert(left <= right, "indexes out of order");
208 size_t num_cards = right - left + 1;
209
210 fill_range(left, num_cards, offset);
211 }
212
213 void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
214 assert(index < _vs.committed_size(), "index out of range");
215 assert(high >= low, "addresses out of order");
216 assert(pointer_delta(high, low) <= BOTConstants::N_words, "offset too large");
217 assert(_offset_array[index] == pointer_delta(high, low),
218 "Wrong offset");
219 }
220
221 bool is_card_boundary(HeapWord* p) const;
222
223 // Return the number of slots needed for an offset array
224 // that covers mem_region_words words.
225 // We always add an extra slot because if an object
226 // ends on a card boundary we put a 0 in the next
227 // offset array slot, so we want that slot always
228 // to be reserved.
229
230 size_t compute_size(size_t mem_region_words) {
231 size_t number_of_slots = (mem_region_words / BOTConstants::N_words) + 1;
232 return ReservedSpace::allocation_align_size_up(number_of_slots);
233 }
234
235 public:
236 // Initialize the table to cover from "base" to (at least)
237 // "base + init_word_size". In the future, the table may be expanded
238 // (see "resize" below) up to the size of "_reserved" (which must be at
239 // least "init_word_size".) The contents of the initial table are
240 // undefined; it is the responsibility of the constituent
241 // BlockOffsetTable(s) to initialize cards.
242 BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
243
244 // Notes a change in the committed size of the region covered by the
245 // table. The "new_word_size" may not be larger than the size of the
246 // reserved region this table covers.
247 void resize(size_t new_word_size);
248
249 void set_bottom(HeapWord* new_bottom);
250
251 // Whether entries should be initialized to zero. Used currently only for
252 // error checking.
253 void set_init_to_zero(bool val) { _init_to_zero = val; }
254 bool init_to_zero() { return _init_to_zero; }
255
256 // Updates all the BlockOffsetArray's sharing this shared array to
257 // reflect the current "top"'s of their spaces.
258 void update_offset_arrays(); // Not yet implemented!
259
260 // Return the appropriate index into "_offset_array" for "p".
261 size_t index_for(const void* p) const;
262
263 // Return the address indicating the start of the region corresponding to
264 // "index" in "_offset_array".
265 HeapWord* address_for_index(size_t index) const;
266 };
267
268 //////////////////////////////////////////////////////////////////////////
269 // The BlockOffsetArray whose subtypes use the BlockOffsetSharedArray.
270 //////////////////////////////////////////////////////////////////////////
271 class BlockOffsetArray: public BlockOffsetTable {
272 friend class VMStructs;
273 protected:
274 // The following enums are used by do_block_internal() below
275 enum Action {
276 Action_single, // BOT records a single block (see single_block())
277 Action_mark, // BOT marks the start of a block (see mark_block())
278 Action_check // Check that BOT records block correctly
279 // (see verify_single_block()).
280 };
281
282 // The shared array, which is shared with other BlockOffsetArray's
283 // corresponding to different spaces within a generation or span of
284 // memory.
285 BlockOffsetSharedArray* _array;
286
287 // The space that owns this subregion.
288 Space* _sp;
289
290 // If true, array entries are initialized to 0; otherwise, they are
291 // initialized to point backwards to the beginning of the covered region.
292 bool _init_to_zero;
293
294 // An assertion-checking helper method for the set_remainder*() methods below.
295 void check_reducing_assertion(bool reducing) { _array->check_reducing_assertion(reducing); }
296
297 // Sets the entries
298 // corresponding to the cards starting at "start" and ending at "end"
299 // to point back to the card before "start": the interval [start, end)
300 // is right-open. The last parameter, reducing, indicates whether the
301 // updates to individual entries always reduce the entry from a higher
302 // to a lower value. (For example this would hold true during a temporal
303 // regime during which only block splits were updating the BOT.
304 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end, bool reducing = false);
305 // Same as above, except that the args here are a card _index_ interval
306 // that is closed: [start_index, end_index]
307 void set_remainder_to_point_to_start_incl(size_t start, size_t end, bool reducing = false);
308
309 // A helper function for BOT adjustment/verification work
310 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action, bool reducing = false);
311
312 public:
313 // The space may not have its bottom and top set yet, which is why the
314 // region is passed as a parameter. If "init_to_zero" is true, the
315 // elements of the array are initialized to zero. Otherwise, they are
316 // initialized to point backwards to the beginning.
317 BlockOffsetArray(BlockOffsetSharedArray* array, MemRegion mr,
318 bool init_to_zero_);
319
320 // Note: this ought to be part of the constructor, but that would require
321 // "this" to be passed as a parameter to a member constructor for
322 // the containing concrete subtype of Space.
323 // This would be legal C++, but MS VC++ doesn't allow it.
324 void set_space(Space* sp) { _sp = sp; }
325
326 // Resets the covered region to the given "mr".
327 void set_region(MemRegion mr) {
328 _bottom = mr.start();
329 _end = mr.end();
330 }
331
332 // Note that the committed size of the covered space may have changed,
333 // so the table size might also wish to change.
334 virtual void resize(size_t new_word_size) {
335 HeapWord* new_end = _bottom + new_word_size;
336 if (_end < new_end && !init_to_zero()) {
337 // verify that the old and new boundaries are also card boundaries
338 assert(_array->is_card_boundary(_end),
339 "_end not a card boundary");
340 assert(_array->is_card_boundary(new_end),
341 "new _end would not be a card boundary");
342 // set all the newly added cards
343 _array->set_offset_array(_end, new_end, BOTConstants::N_words);
344 }
345 _end = new_end; // update _end
346 }
347
348 // Adjust the BOT to show that it has a single block in the
349 // range [blk_start, blk_start + size). All necessary BOT
350 // cards are adjusted, but _unallocated_block isn't.
351 void single_block(HeapWord* blk_start, HeapWord* blk_end);
352 void single_block(HeapWord* blk, size_t size) {
353 single_block(blk, blk + size);
354 }
355
356 // When the alloc_block() call returns, the block offset table should
357 // have enough information such that any subsequent block_start() call
358 // with an argument equal to an address that is within the range
359 // [blk_start, blk_end) would return the value blk_start, provided
360 // there have been no calls in between that reset this information
361 // (e.g. see BlockOffsetArrayNonContigSpace::single_block() call
362 // for an appropriate range covering the said interval).
363 // These methods expect to be called with [blk_start, blk_end)
364 // representing a block of memory in the heap.
365 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
366 void alloc_block(HeapWord* blk, size_t size) {
367 alloc_block(blk, blk + size);
368 }
369
370 // If true, initialize array slots with no allocated blocks to zero.
371 // Otherwise, make them point back to the front.
372 bool init_to_zero() { return _init_to_zero; }
373 // Corresponding setter
374 void set_init_to_zero(bool val) {
375 _init_to_zero = val;
376 assert(_array != NULL, "_array should be non-NULL");
377 _array->set_init_to_zero(val);
378 }
379
380 // Debugging
381 // Return the index of the last entry in the "active" region.
382 virtual size_t last_active_index() const = 0;
383 // Verify the block offset table
384 void verify() const;
385 void check_all_cards(size_t left_card, size_t right_card) const;
386 };
387
388 ////////////////////////////////////////////////////////////////////////////
389 // A subtype of BlockOffsetArray that takes advantage of the fact
390 // that its underlying space is a NonContiguousSpace, so that some
391 // specialized interfaces can be made available for spaces that
392 // manipulate the table.
393 ////////////////////////////////////////////////////////////////////////////
394 class BlockOffsetArrayNonContigSpace: public BlockOffsetArray {
395 friend class VMStructs;
396 private:
397 // The portion [_unallocated_block, _sp.end()) of the space that
398 // is a single block known not to contain any objects.
399 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
400 HeapWord* _unallocated_block;
401
402 public:
403 BlockOffsetArrayNonContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
404 BlockOffsetArray(array, mr, false),
405 _unallocated_block(_bottom) { }
406
407 // Accessor
408 HeapWord* unallocated_block() const {
409 assert(BlockOffsetArrayUseUnallocatedBlock,
410 "_unallocated_block is not being maintained");
411 return _unallocated_block;
412 }
413
414 void set_unallocated_block(HeapWord* block) {
415 assert(BlockOffsetArrayUseUnallocatedBlock,
416 "_unallocated_block is not being maintained");
417 assert(block >= _bottom && block <= _end, "out of range");
418 _unallocated_block = block;
419 }
420
421 // These methods expect to be called with [blk_start, blk_end)
422 // representing a block of memory in the heap.
423 void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
424 void alloc_block(HeapWord* blk, size_t size) {
425 alloc_block(blk, blk + size);
426 }
427
428 // The following methods are useful and optimized for a
429 // non-contiguous space.
430
431 // Given a block [blk_start, blk_start + full_blk_size), and
432 // a left_blk_size < full_blk_size, adjust the BOT to show two
433 // blocks [blk_start, blk_start + left_blk_size) and
434 // [blk_start + left_blk_size, blk_start + full_blk_size).
435 // It is assumed (and verified in the non-product VM) that the
436 // BOT was correct for the original block.
437 void split_block(HeapWord* blk_start, size_t full_blk_size,
438 size_t left_blk_size);
439
440 // Adjust BOT to show that it has a block in the range
441 // [blk_start, blk_start + size). Only the first card
442 // of BOT is touched. It is assumed (and verified in the
443 // non-product VM) that the remaining cards of the block
444 // are correct.
445 void mark_block(HeapWord* blk_start, HeapWord* blk_end, bool reducing = false);
446 void mark_block(HeapWord* blk, size_t size, bool reducing = false) {
447 mark_block(blk, blk + size, reducing);
448 }
449
450 // Adjust _unallocated_block to indicate that a particular
451 // block has been newly allocated or freed. It is assumed (and
452 // verified in the non-product VM) that the BOT is correct for
453 // the given block.
454 void allocated(HeapWord* blk_start, HeapWord* blk_end, bool reducing = false) {
455 // Verify that the BOT shows [blk, blk + blk_size) to be one block.
456 verify_single_block(blk_start, blk_end);
457 if (BlockOffsetArrayUseUnallocatedBlock) {
458 _unallocated_block = MAX2(_unallocated_block, blk_end);
459 }
460 }
461
462 void allocated(HeapWord* blk, size_t size, bool reducing = false) {
463 allocated(blk, blk + size, reducing);
464 }
465
466 void freed(HeapWord* blk_start, HeapWord* blk_end);
467 void freed(HeapWord* blk, size_t size);
468
469 HeapWord* block_start_unsafe(const void* addr) const;
470
471 // Requires "addr" to be the start of a card and returns the
472 // start of the block that contains the given address.
473 HeapWord* block_start_careful(const void* addr) const;
474
475 // Verification & debugging: ensure that the offset table reflects
476 // the fact that the block [blk_start, blk_end) or [blk, blk + size)
477 // is a single block of storage. NOTE: can't const this because of
478 // call to non-const do_block_internal() below.
479 void verify_single_block(HeapWord* blk_start, HeapWord* blk_end)
480 PRODUCT_RETURN;
481 void verify_single_block(HeapWord* blk, size_t size) PRODUCT_RETURN;
482
483 // Verify that the given block is before _unallocated_block
484 void verify_not_unallocated(HeapWord* blk_start, HeapWord* blk_end)
485 const PRODUCT_RETURN;
486 void verify_not_unallocated(HeapWord* blk, size_t size)
487 const PRODUCT_RETURN;
488
489 // Debugging support
490 virtual size_t last_active_index() const;
491 };
492
493 ////////////////////////////////////////////////////////////////////////////
494 // A subtype of BlockOffsetArray that takes advantage of the fact
495 // that its underlying space is a ContiguousSpace, so that its "active"
496 // region can be more efficiently tracked (than for a non-contiguous space).
497 ////////////////////////////////////////////////////////////////////////////
498 class BlockOffsetArrayContigSpace: public BlockOffsetArray {
499 friend class VMStructs;
500 private:
501 // allocation boundary at which offset array must be updated
502 HeapWord* _next_offset_threshold;
503 size_t _next_offset_index; // index corresponding to that boundary
504
505 // Work function when allocation start crosses threshold.
506 void alloc_block_work(HeapWord* blk_start, HeapWord* blk_end);
507
508 public:
509 BlockOffsetArrayContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
510 BlockOffsetArray(array, mr, true) {
511 _next_offset_threshold = NULL;
512 _next_offset_index = 0;
513 }
514
515 void set_contig_space(ContiguousSpace* sp) { set_space((Space*)sp); }
516
517 // Initialize the threshold for an empty heap.
518 HeapWord* initialize_threshold();
519 // Zero out the entry for _bottom (offset will be zero)
520 void zero_bottom_entry();
521
522 // Return the next threshold, the point at which the table should be
523 // updated.
524 HeapWord* threshold() const { return _next_offset_threshold; }
525
526 // In general, these methods expect to be called with
527 // [blk_start, blk_end) representing a block of memory in the heap.
528 // In this implementation, however, we are OK even if blk_start and/or
529 // blk_end are NULL because NULL is represented as 0, and thus
530 // never exceeds the "_next_offset_threshold".
531 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
532 if (blk_end > _next_offset_threshold) {
533 alloc_block_work(blk_start, blk_end);
534 }
535 }
536 void alloc_block(HeapWord* blk, size_t size) {
537 alloc_block(blk, blk + size);
538 }
539
540 HeapWord* block_start_unsafe(const void* addr) const;
541
542 // Debugging support
543 virtual size_t last_active_index() const;
544 };
545
546 #endif // SHARE_VM_GC_SHARED_BLOCKOFFSETTABLE_HPP