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