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 //////////////////////////////////////////////////////////////////////////
50 // The BlockOffsetTable "interface"
51 //////////////////////////////////////////////////////////////////////////
52 class BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
53 friend class VMStructs;
54 protected:
55 // These members describe the region covered by the table.
56
57 // The space this table is covering.
58 HeapWord* _bottom; // == reserved.start
59 HeapWord* _end; // End of currently allocated region.
60
61 public:
62 // Initialize the table to cover the given space.
63 // The contents of the initial table are undefined.
64 BlockOffsetTable(HeapWord* bottom, HeapWord* end):
65 _bottom(bottom), _end(end) {
66 assert(_bottom <= _end, "arguments out of order");
67 }
68
69 // Note that the committed size of the covered space may have changed,
70 // so the table size might also wish to change.
71 virtual void resize(size_t new_word_size) = 0;
72
73 virtual void set_bottom(HeapWord* new_bottom) {
74 assert(new_bottom <= _end, "new_bottom > _end");
75 _bottom = new_bottom;
76 resize(pointer_delta(_end, _bottom));
77 }
78
79 // Requires "addr" to be contained by a block, and returns the address of
80 // the start of that block.
81 virtual HeapWord* block_start_unsafe(const void* addr) const = 0;
82
83 // Returns the address of the start of the block containing "addr", or
84 // else "null" if it is covered by no block.
85 HeapWord* block_start(const void* addr) const;
86 };
87
88 //////////////////////////////////////////////////////////////////////////
89 // One implementation of "BlockOffsetTable," the BlockOffsetArray,
90 // divides the covered region into "N"-word subregions (where
91 // "N" = 2^"LogN". An array with an entry for each such subregion
92 // indicates how far back one must go to find the start of the
93 // chunk that includes the first word of the subregion.
94 //
95 // Each BlockOffsetArray is owned by a Space. However, the actual array
96 // may be shared by several BlockOffsetArrays; this is useful
97 // when a single resizable area (such as a generation) is divided up into
98 // several spaces in which contiguous allocation takes place. (Consider,
99 // for example, the garbage-first generation.)
100
101 // Here is the shared array type.
102 //////////////////////////////////////////////////////////////////////////
103 // BlockOffsetSharedArray
104 //////////////////////////////////////////////////////////////////////////
105 class BlockOffsetSharedArray: public CHeapObj<mtGC> {
106 friend class BlockOffsetArray;
107 friend class BlockOffsetArrayNonContigSpace;
108 friend class BlockOffsetArrayContigSpace;
109 friend class VMStructs;
110
111 private:
112 enum SomePrivateConstants {
113 LogN = 9,
114 LogN_words = LogN - LogHeapWordSize,
115 N_bytes = 1 << LogN,
116 N_words = 1 << LogN_words
117 };
118
119 bool _init_to_zero;
120
121 // The reserved region covered by the shared array.
122 MemRegion _reserved;
123
124 // End of the current committed region.
125 HeapWord* _end;
126
127 // Array for keeping offsets for retrieving object start fast given an
128 // address.
129 VirtualSpace _vs;
130 u_char* _offset_array; // byte array keeping backwards offsets
131
132 void fill_range(size_t start, size_t num_cards, u_char offset) {
133 void* start_ptr = &_offset_array[start];
134 #if INCLUDE_ALL_GCS
135 // If collector is concurrent, special handling may be needed.
136 assert(!UseG1GC, "Shouldn't be here when using G1");
137 if (UseConcMarkSweepGC) {
138 memset_with_concurrent_readers(start_ptr, offset, num_cards);
139 return;
140 }
141 #endif // INCLUDE_ALL_GCS
142 memset(start_ptr, offset, num_cards);
143 }
144
145 protected:
146 // Bounds checking accessors:
147 // For performance these have to devolve to array accesses in product builds.
148 u_char offset_array(size_t index) const {
149 assert(index < _vs.committed_size(), "index out of range");
150 return _offset_array[index];
151 }
152 // An assertion-checking helper method for the set_offset_array() methods below.
153 void check_reducing_assertion(bool reducing);
154
155 void set_offset_array(size_t index, u_char offset, bool reducing = false) {
156 check_reducing_assertion(reducing);
157 assert(index < _vs.committed_size(), "index out of range");
158 assert(!reducing || _offset_array[index] >= offset, "Not reducing");
159 _offset_array[index] = offset;
160 }
161
162 void set_offset_array(size_t index, HeapWord* high, HeapWord* low, bool reducing = false) {
163 check_reducing_assertion(reducing);
164 assert(index < _vs.committed_size(), "index out of range");
165 assert(high >= low, "addresses out of order");
166 assert(pointer_delta(high, low) <= N_words, "offset too large");
167 assert(!reducing || _offset_array[index] >= (u_char)pointer_delta(high, low),
168 "Not reducing");
169 _offset_array[index] = (u_char)pointer_delta(high, low);
170 }
171
172 void set_offset_array(HeapWord* left, HeapWord* right, u_char offset, bool reducing = false) {
173 check_reducing_assertion(reducing);
174 assert(index_for(right - 1) < _vs.committed_size(),
175 "right address out of range");
176 assert(left < right, "Heap addresses out of order");
177 size_t num_cards = pointer_delta(right, left) >> LogN_words;
178
179 fill_range(index_for(left), num_cards, offset);
180 }
181
182 void set_offset_array(size_t left, size_t right, u_char offset, bool reducing = false) {
183 check_reducing_assertion(reducing);
184 assert(right < _vs.committed_size(), "right address out of range");
185 assert(left <= right, "indexes out of order");
186 size_t num_cards = right - left + 1;
187
188 fill_range(left, num_cards, offset);
189 }
190
191 void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
192 assert(index < _vs.committed_size(), "index out of range");
193 assert(high >= low, "addresses out of order");
194 assert(pointer_delta(high, low) <= N_words, "offset too large");
195 assert(_offset_array[index] == pointer_delta(high, low),
196 "Wrong offset");
197 }
198
199 bool is_card_boundary(HeapWord* p) const;
200
201 // Return the number of slots needed for an offset array
202 // that covers mem_region_words words.
203 // We always add an extra slot because if an object
204 // ends on a card boundary we put a 0 in the next
205 // offset array slot, so we want that slot always
206 // to be reserved.
207
208 size_t compute_size(size_t mem_region_words) {
209 size_t number_of_slots = (mem_region_words / N_words) + 1;
210 return ReservedSpace::allocation_align_size_up(number_of_slots);
211 }
212
213 public:
214 // Initialize the table to cover from "base" to (at least)
215 // "base + init_word_size". In the future, the table may be expanded
216 // (see "resize" below) up to the size of "_reserved" (which must be at
217 // least "init_word_size".) The contents of the initial table are
218 // undefined; it is the responsibility of the constituent
219 // BlockOffsetTable(s) to initialize cards.
220 BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
221
222 // Notes a change in the committed size of the region covered by the
223 // table. The "new_word_size" may not be larger than the size of the
224 // reserved region this table covers.
225 void resize(size_t new_word_size);
226
227 void set_bottom(HeapWord* new_bottom);
228
229 // Whether entries should be initialized to zero. Used currently only for
230 // error checking.
231 void set_init_to_zero(bool val) { _init_to_zero = val; }
232 bool init_to_zero() { return _init_to_zero; }
233
234 // Updates all the BlockOffsetArray's sharing this shared array to
235 // reflect the current "top"'s of their spaces.
236 void update_offset_arrays(); // Not yet implemented!
237
238 // Return the appropriate index into "_offset_array" for "p".
239 size_t index_for(const void* p) const;
240
241 // Return the address indicating the start of the region corresponding to
242 // "index" in "_offset_array".
243 HeapWord* address_for_index(size_t index) const;
244 };
245
246 //////////////////////////////////////////////////////////////////////////
247 // The BlockOffsetArray whose subtypes use the BlockOffsetSharedArray.
248 //////////////////////////////////////////////////////////////////////////
249 class BlockOffsetArray: public BlockOffsetTable {
250 friend class VMStructs;
251 friend class G1BlockOffsetArray; // temp. until we restructure and cleanup
252 protected:
253 // The following enums are used by do_block_internal() below
254 enum Action {
255 Action_single, // BOT records a single block (see single_block())
256 Action_mark, // BOT marks the start of a block (see mark_block())
257 Action_check // Check that BOT records block correctly
258 // (see verify_single_block()).
259 };
260
261 enum SomePrivateConstants {
262 N_words = BlockOffsetSharedArray::N_words,
263 LogN = BlockOffsetSharedArray::LogN,
264 // entries "e" of at least N_words mean "go back by Base^(e-N_words)."
265 // All entries are less than "N_words + N_powers".
266 LogBase = 4,
267 Base = (1 << LogBase),
268 N_powers = 14
269 };
270
271 static size_t power_to_cards_back(uint i) {
272 return (size_t)1 << (LogBase * i);
273 }
274 static size_t power_to_words_back(uint i) {
275 return power_to_cards_back(i) * N_words;
276 }
277 static size_t entry_to_cards_back(u_char entry) {
278 assert(entry >= N_words, "Precondition");
279 return power_to_cards_back(entry - N_words);
280 }
281 static size_t entry_to_words_back(u_char entry) {
282 assert(entry >= N_words, "Precondition");
283 return power_to_words_back(entry - N_words);
284 }
285
286 // The shared array, which is shared with other BlockOffsetArray's
287 // corresponding to different spaces within a generation or span of
288 // memory.
289 BlockOffsetSharedArray* _array;
290
291 // The space that owns this subregion.
292 Space* _sp;
293
294 // If true, array entries are initialized to 0; otherwise, they are
295 // initialized to point backwards to the beginning of the covered region.
296 bool _init_to_zero;
297
298 // An assertion-checking helper method for the set_remainder*() methods below.
299 void check_reducing_assertion(bool reducing) { _array->check_reducing_assertion(reducing); }
300
301 // Sets the entries
302 // corresponding to the cards starting at "start" and ending at "end"
303 // to point back to the card before "start": the interval [start, end)
304 // is right-open. The last parameter, reducing, indicates whether the
305 // updates to individual entries always reduce the entry from a higher
306 // to a lower value. (For example this would hold true during a temporal
307 // regime during which only block splits were updating the BOT.
308 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end, bool reducing = false);
309 // Same as above, except that the args here are a card _index_ interval
310 // that is closed: [start_index, end_index]
311 void set_remainder_to_point_to_start_incl(size_t start, size_t end, bool reducing = false);
312
313 // A helper function for BOT adjustment/verification work
314 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action, bool reducing = false);
315
316 public:
317 // The space may not have its bottom and top set yet, which is why the
318 // region is passed as a parameter. If "init_to_zero" is true, the
319 // elements of the array are initialized to zero. Otherwise, they are
320 // initialized to point backwards to the beginning.
321 BlockOffsetArray(BlockOffsetSharedArray* array, MemRegion mr,
322 bool init_to_zero_);
323
324 // Note: this ought to be part of the constructor, but that would require
325 // "this" to be passed as a parameter to a member constructor for
326 // the containing concrete subtype of Space.
327 // This would be legal C++, but MS VC++ doesn't allow it.
328 void set_space(Space* sp) { _sp = sp; }
329
330 // Resets the covered region to the given "mr".
331 void set_region(MemRegion mr) {
332 _bottom = mr.start();
333 _end = mr.end();
334 }
335
336 // Note that the committed size of the covered space may have changed,
337 // so the table size might also wish to change.
338 virtual void resize(size_t new_word_size) {
339 HeapWord* new_end = _bottom + new_word_size;
340 if (_end < new_end && !init_to_zero()) {
341 // verify that the old and new boundaries are also card boundaries
342 assert(_array->is_card_boundary(_end),
343 "_end not a card boundary");
344 assert(_array->is_card_boundary(new_end),
345 "new _end would not be a card boundary");
346 // set all the newly added cards
347 _array->set_offset_array(_end, new_end, N_words);
348 }
349 _end = new_end; // update _end
350 }
351
352 // Adjust the BOT to show that it has a single block in the
353 // range [blk_start, blk_start + size). All necessary BOT
354 // cards are adjusted, but _unallocated_block isn't.
355 void single_block(HeapWord* blk_start, HeapWord* blk_end);
356 void single_block(HeapWord* blk, size_t size) {
357 single_block(blk, blk + size);
358 }
359
360 // When the alloc_block() call returns, the block offset table should
361 // have enough information such that any subsequent block_start() call
362 // with an argument equal to an address that is within the range
363 // [blk_start, blk_end) would return the value blk_start, provided
364 // there have been no calls in between that reset this information
365 // (e.g. see BlockOffsetArrayNonContigSpace::single_block() call
366 // for an appropriate range covering the said interval).
367 // These methods expect to be called with [blk_start, blk_end)
368 // representing a block of memory in the heap.
369 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
370 void alloc_block(HeapWord* blk, size_t size) {
371 alloc_block(blk, blk + size);
372 }
373
374 // If true, initialize array slots with no allocated blocks to zero.
375 // Otherwise, make them point back to the front.
376 bool init_to_zero() { return _init_to_zero; }
377 // Corresponding setter
378 void set_init_to_zero(bool val) {
379 _init_to_zero = val;
380 assert(_array != NULL, "_array should be non-NULL");
381 _array->set_init_to_zero(val);
382 }
383
384 // Debugging
385 // Return the index of the last entry in the "active" region.
386 virtual size_t last_active_index() const = 0;
387 // Verify the block offset table
388 void verify() const;
389 void check_all_cards(size_t left_card, size_t right_card) const;
390 };
391
392 ////////////////////////////////////////////////////////////////////////////
393 // A subtype of BlockOffsetArray that takes advantage of the fact
394 // that its underlying space is a NonContiguousSpace, so that some
395 // specialized interfaces can be made available for spaces that
396 // manipulate the table.
397 ////////////////////////////////////////////////////////////////////////////
398 class BlockOffsetArrayNonContigSpace: public BlockOffsetArray {
399 friend class VMStructs;
400 private:
401 // The portion [_unallocated_block, _sp.end()) of the space that
402 // is a single block known not to contain any objects.
403 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
404 HeapWord* _unallocated_block;
405
406 public:
407 BlockOffsetArrayNonContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
408 BlockOffsetArray(array, mr, false),
409 _unallocated_block(_bottom) { }
410
411 // Accessor
412 HeapWord* unallocated_block() const {
413 assert(BlockOffsetArrayUseUnallocatedBlock,
414 "_unallocated_block is not being maintained");
415 return _unallocated_block;
416 }
417
418 void set_unallocated_block(HeapWord* block) {
419 assert(BlockOffsetArrayUseUnallocatedBlock,
420 "_unallocated_block is not being maintained");
421 assert(block >= _bottom && block <= _end, "out of range");
422 _unallocated_block = block;
423 }
424
425 // These methods expect to be called with [blk_start, blk_end)
426 // representing a block of memory in the heap.
427 void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
428 void alloc_block(HeapWord* blk, size_t size) {
429 alloc_block(blk, blk + size);
430 }
431
432 // The following methods are useful and optimized for a
433 // non-contiguous space.
434
435 // Given a block [blk_start, blk_start + full_blk_size), and
436 // a left_blk_size < full_blk_size, adjust the BOT to show two
437 // blocks [blk_start, blk_start + left_blk_size) and
438 // [blk_start + left_blk_size, blk_start + full_blk_size).
439 // It is assumed (and verified in the non-product VM) that the
440 // BOT was correct for the original block.
441 void split_block(HeapWord* blk_start, size_t full_blk_size,
442 size_t left_blk_size);
443
444 // Adjust BOT to show that it has a block in the range
445 // [blk_start, blk_start + size). Only the first card
446 // of BOT is touched. It is assumed (and verified in the
447 // non-product VM) that the remaining cards of the block
448 // are correct.
449 void mark_block(HeapWord* blk_start, HeapWord* blk_end, bool reducing = false);
450 void mark_block(HeapWord* blk, size_t size, bool reducing = false) {
451 mark_block(blk, blk + size, reducing);
452 }
453
454 // Adjust _unallocated_block to indicate that a particular
455 // block has been newly allocated or freed. It is assumed (and
456 // verified in the non-product VM) that the BOT is correct for
457 // the given block.
458 void allocated(HeapWord* blk_start, HeapWord* blk_end, bool reducing = false) {
459 // Verify that the BOT shows [blk, blk + blk_size) to be one block.
460 verify_single_block(blk_start, blk_end);
461 if (BlockOffsetArrayUseUnallocatedBlock) {
462 _unallocated_block = MAX2(_unallocated_block, blk_end);
463 }
464 }
465
466 void allocated(HeapWord* blk, size_t size, bool reducing = false) {
467 allocated(blk, blk + size, reducing);
468 }
469
470 void freed(HeapWord* blk_start, HeapWord* blk_end);
471 void freed(HeapWord* blk, size_t size);
472
473 HeapWord* block_start_unsafe(const void* addr) const;
474
475 // Requires "addr" to be the start of a card and returns the
476 // start of the block that contains the given address.
477 HeapWord* block_start_careful(const void* addr) const;
478
479 // Verification & debugging: ensure that the offset table reflects
480 // the fact that the block [blk_start, blk_end) or [blk, blk + size)
481 // is a single block of storage. NOTE: can't const this because of
482 // call to non-const do_block_internal() below.
483 void verify_single_block(HeapWord* blk_start, HeapWord* blk_end)
484 PRODUCT_RETURN;
485 void verify_single_block(HeapWord* blk, size_t size) PRODUCT_RETURN;
486
487 // Verify that the given block is before _unallocated_block
488 void verify_not_unallocated(HeapWord* blk_start, HeapWord* blk_end)
489 const PRODUCT_RETURN;
490 void verify_not_unallocated(HeapWord* blk, size_t size)
491 const PRODUCT_RETURN;
492
493 // Debugging support
494 virtual size_t last_active_index() const;
495 };
496
497 ////////////////////////////////////////////////////////////////////////////
498 // A subtype of BlockOffsetArray that takes advantage of the fact
499 // that its underlying space is a ContiguousSpace, so that its "active"
500 // region can be more efficiently tracked (than for a non-contiguous space).
501 ////////////////////////////////////////////////////////////////////////////
502 class BlockOffsetArrayContigSpace: public BlockOffsetArray {
503 friend class VMStructs;
504 private:
505 // allocation boundary at which offset array must be updated
506 HeapWord* _next_offset_threshold;
507 size_t _next_offset_index; // index corresponding to that boundary
508
509 // Work function when allocation start crosses threshold.
510 void alloc_block_work(HeapWord* blk_start, HeapWord* blk_end);
511
512 public:
513 BlockOffsetArrayContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
514 BlockOffsetArray(array, mr, true) {
515 _next_offset_threshold = NULL;
516 _next_offset_index = 0;
517 }
518
519 void set_contig_space(ContiguousSpace* sp) { set_space((Space*)sp); }
520
521 // Initialize the threshold for an empty heap.
522 HeapWord* initialize_threshold();
523 // Zero out the entry for _bottom (offset will be zero)
524 void zero_bottom_entry();
525
526 // Return the next threshold, the point at which the table should be
527 // updated.
528 HeapWord* threshold() const { return _next_offset_threshold; }
529
530 // In general, these methods expect to be called with
531 // [blk_start, blk_end) representing a block of memory in the heap.
532 // In this implementation, however, we are OK even if blk_start and/or
533 // blk_end are NULL because NULL is represented as 0, and thus
534 // never exceeds the "_next_offset_threshold".
535 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
536 if (blk_end > _next_offset_threshold) {
537 alloc_block_work(blk_start, blk_end);
538 }
539 }
540 void alloc_block(HeapWord* blk, size_t size) {
541 alloc_block(blk, blk + size);
542 }
543
544 HeapWord* block_start_unsafe(const void* addr) const;
545
546 // Debugging support
547 virtual size_t last_active_index() const;
548 };
549
550 #endif // SHARE_VM_GC_SHARED_BLOCKOFFSETTABLE_HPP