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24
25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_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 // While generally mirroring the structure of the BOT for GenCollectedHeap,
39 // the following types are tailored more towards G1's uses; these should,
40 // however, be merged back into a common BOT to avoid code duplication
41 // and reduce maintenance overhead.
42 //
43 // G1BlockOffsetTable (abstract)
44 // -- G1BlockOffsetArray (uses G1BlockOffsetSharedArray)
45 // -- G1BlockOffsetArrayContigSpace
46 //
47 // A main impediment to the consolidation of this code might be the
48 // effect of making some of the block_start*() calls non-const as
49 // below. Whether that might adversely affect performance optimizations
50 // that compilers might normally perform in the case of non-G1
51 // collectors needs to be carefully investigated prior to any such
52 // consolidation.
53
54 // Forward declarations
55 class ContiguousSpace;
56 class G1BlockOffsetSharedArray;
57
58 class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
59 friend class VMStructs;
60 protected:
61 // These members describe the region covered by the table.
62
63 // The space this table is covering.
64 HeapWord* _bottom; // == reserved.start
65 HeapWord* _end; // End of currently allocated region.
66
67 public:
68 // Initialize the table to cover the given space.
69 // The contents of the initial table are undefined.
70 G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) :
71 _bottom(bottom), _end(end)
72 {
73 assert(_bottom <= _end, "arguments out of order");
74 }
75
76 // Note that the committed size of the covered space may have changed,
77 // so the table size might also wish to change.
78 virtual void resize(size_t new_word_size) = 0;
79
80 virtual void set_bottom(HeapWord* new_bottom) {
81 assert(new_bottom <= _end, "new_bottom > _end");
82 _bottom = new_bottom;
83 resize(pointer_delta(_end, _bottom));
84 }
85
86 // Requires "addr" to be contained by a block, and returns the address of
87 // the start of that block. (May have side effects, namely updating of
88 // shared array entries that "point" too far backwards. This can occur,
89 // for example, when LAB allocation is used in a space covered by the
90 // table.)
91 virtual HeapWord* block_start_unsafe(const void* addr) = 0;
92 // Same as above, but does not have any of the possible side effects
93 // discussed above.
94 virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0;
95
96 // Returns the address of the start of the block containing "addr", or
97 // else "null" if it is covered by no block. (May have side effects,
98 // namely updating of shared array entries that "point" too far
99 // backwards. This can occur, for example, when lab allocation is used
100 // in a space covered by the table.)
101 inline HeapWord* block_start(const void* addr);
102 // Same as above, but does not have any of the possible side effects
103 // discussed above.
104 inline HeapWord* block_start_const(const void* addr) const;
105 };
106
107 // This implementation of "G1BlockOffsetTable" divides the covered region
108 // into "N"-word subregions (where "N" = 2^"LogN". An array with an entry
109 // for each such subregion indicates how far back one must go to find the
110 // start of the chunk that includes the first word of the subregion.
111 //
112 // Each BlockOffsetArray is owned by a Space. However, the actual array
113 // may be shared by several BlockOffsetArrays; this is useful
114 // when a single resizable area (such as a generation) is divided up into
115 // several spaces in which contiguous allocation takes place,
116 // such as, for example, in G1 or in the train generation.)
117
118 // Here is the shared array type.
119
120 class G1BlockOffsetSharedArray: public CHeapObj {
121 friend class G1BlockOffsetArray;
122 friend class G1BlockOffsetArrayContigSpace;
123 friend class VMStructs;
124
125 private:
126 // The reserved region covered by the shared array.
127 MemRegion _reserved;
128
129 // End of the current committed region.
130 HeapWord* _end;
131
132 // Array for keeping offsets for retrieving object start fast given an
133 // address.
134 VirtualSpace _vs;
135 u_char* _offset_array; // byte array keeping backwards offsets
136
137 // Bounds checking accessors:
138 // For performance these have to devolve to array accesses in product builds.
139 u_char offset_array(size_t index) const {
140 assert(index < _vs.committed_size(), "index out of range");
141 return _offset_array[index];
142 }
143
144 void set_offset_array(size_t index, u_char offset) {
145 assert(index < _vs.committed_size(), "index out of range");
146 assert(offset <= N_words, "offset too large");
147 _offset_array[index] = offset;
148 }
149
150 void set_offset_array(size_t index, HeapWord* high, HeapWord* low) {
151 assert(index < _vs.committed_size(), "index out of range");
152 assert(high >= low, "addresses out of order");
153 assert(pointer_delta(high, low) <= N_words, "offset too large");
154 _offset_array[index] = (u_char) pointer_delta(high, low);
155 }
156
157 void set_offset_array(HeapWord* left, HeapWord* right, u_char offset) {
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 memset(&_offset_array[index_for(left)], offset, num_cards);
163 }
164
165 void set_offset_array(size_t left, size_t right, u_char offset) {
166 assert(right < _vs.committed_size(), "right address out of range");
167 assert(left <= right, "indexes out of order");
168 size_t num_cards = right - left + 1;
169 memset(&_offset_array[left], offset, num_cards);
170 }
171
172 void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
173 assert(index < _vs.committed_size(), "index out of range");
174 assert(high >= low, "addresses out of order");
175 assert(pointer_delta(high, low) <= N_words, "offset too large");
176 assert(_offset_array[index] == pointer_delta(high, low),
177 "Wrong offset");
178 }
179
180 bool is_card_boundary(HeapWord* p) const;
181
182 // Return the number of slots needed for an offset array
183 // that covers mem_region_words words.
184 // We always add an extra slot because if an object
185 // ends on a card boundary we put a 0 in the next
186 // offset array slot, so we want that slot always
187 // to be reserved.
188
189 size_t compute_size(size_t mem_region_words) {
190 size_t number_of_slots = (mem_region_words / N_words) + 1;
191 return ReservedSpace::page_align_size_up(number_of_slots);
192 }
193
194 public:
195 enum SomePublicConstants {
196 LogN = 9,
197 LogN_words = LogN - LogHeapWordSize,
198 N_bytes = 1 << LogN,
199 N_words = 1 << LogN_words
200 };
201
202 // Initialize the table to cover from "base" to (at least)
203 // "base + init_word_size". In the future, the table may be expanded
204 // (see "resize" below) up to the size of "_reserved" (which must be at
205 // least "init_word_size".) The contents of the initial table are
206 // undefined; it is the responsibility of the constituent
207 // G1BlockOffsetTable(s) to initialize cards.
208 G1BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
209
210 // Notes a change in the committed size of the region covered by the
211 // table. The "new_word_size" may not be larger than the size of the
212 // reserved region this table covers.
213 void resize(size_t new_word_size);
214
215 void set_bottom(HeapWord* new_bottom);
216
217 // Updates all the BlockOffsetArray's sharing this shared array to
218 // reflect the current "top"'s of their spaces.
219 void update_offset_arrays();
220
221 // Return the appropriate index into "_offset_array" for "p".
222 inline size_t index_for(const void* p) const;
223
224 // Return the address indicating the start of the region corresponding to
225 // "index" in "_offset_array".
226 inline HeapWord* address_for_index(size_t index) const;
227 };
228
229 // And here is the G1BlockOffsetTable subtype that uses the array.
230
231 class G1BlockOffsetArray: public G1BlockOffsetTable {
232 friend class G1BlockOffsetSharedArray;
233 friend class G1BlockOffsetArrayContigSpace;
234 friend class VMStructs;
235 private:
236 enum SomePrivateConstants {
237 N_words = G1BlockOffsetSharedArray::N_words,
238 LogN = G1BlockOffsetSharedArray::LogN
239 };
240
241 // The following enums are used by do_block_helper
242 enum Action {
243 Action_single, // BOT records a single block (see single_block())
244 Action_mark, // BOT marks the start of a block (see mark_block())
245 Action_check // Check that BOT records block correctly
246 // (see verify_single_block()).
247 };
248
249 // This is the array, which can be shared by several BlockOffsetArray's
250 // servicing different
251 G1BlockOffsetSharedArray* _array;
252
253 // The space that owns this subregion.
254 Space* _sp;
255
256 // If "_sp" is a contiguous space, the field below is the view of "_sp"
257 // as a contiguous space, else NULL.
258 ContiguousSpace* _csp;
259
260 // If true, array entries are initialized to 0; otherwise, they are
261 // initialized to point backwards to the beginning of the covered region.
262 bool _init_to_zero;
263
264 // The portion [_unallocated_block, _sp.end()) of the space that
265 // is a single block known not to contain any objects.
266 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
267 HeapWord* _unallocated_block;
268
269 // Sets the entries
270 // corresponding to the cards starting at "start" and ending at "end"
271 // to point back to the card before "start": the interval [start, end)
272 // is right-open.
273 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
274 // Same as above, except that the args here are a card _index_ interval
275 // that is closed: [start_index, end_index]
276 void set_remainder_to_point_to_start_incl(size_t start, size_t end);
277
278 // A helper function for BOT adjustment/verification work
279 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);
280
281 protected:
282
283 ContiguousSpace* csp() const { return _csp; }
284
285 // Returns the address of a block whose start is at most "addr".
286 // If "has_max_index" is true, "assumes "max_index" is the last valid one
287 // in the array.
288 inline HeapWord* block_at_or_preceding(const void* addr,
289 bool has_max_index,
290 size_t max_index) const;
291
292 // "q" is a block boundary that is <= "addr"; "n" is the address of the
293 // next block (or the end of the space.) Return the address of the
294 // beginning of the block that contains "addr". Does so without side
295 // effects (see, e.g., spec of block_start.)
296 inline HeapWord*
297 forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
298 const void* addr) const;
299
300 // "q" is a block boundary that is <= "addr"; return the address of the
301 // beginning of the block that contains "addr". May have side effects
302 // on "this", by updating imprecise entries.
303 inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
304 const void* addr);
305
306 // "q" is a block boundary that is <= "addr"; "n" is the address of the
307 // next block (or the end of the space.) Return the address of the
308 // beginning of the block that contains "addr". May have side effects
309 // on "this", by updating imprecise entries.
310 HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
311 HeapWord* n,
312 const void* addr);
313
314 // Requires that "*threshold_" be the first array entry boundary at or
315 // above "blk_start", and that "*index_" be the corresponding array
316 // index. If the block starts at or crosses "*threshold_", records
317 // "blk_start" as the appropriate block start for the array index
318 // starting at "*threshold_", and for any other indices crossed by the
319 // block. Updates "*threshold_" and "*index_" to correspond to the first
320 // index after the block end.
321 void alloc_block_work2(HeapWord** threshold_, size_t* index_,
322 HeapWord* blk_start, HeapWord* blk_end);
323
324 public:
325 // The space may not have it's bottom and top set yet, which is why the
326 // region is passed as a parameter. If "init_to_zero" is true, the
327 // elements of the array are initialized to zero. Otherwise, they are
328 // initialized to point backwards to the beginning.
329 G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr,
330 bool init_to_zero);
331
332 // Note: this ought to be part of the constructor, but that would require
333 // "this" to be passed as a parameter to a member constructor for
334 // the containing concrete subtype of Space.
335 // This would be legal C++, but MS VC++ doesn't allow it.
336 void set_space(Space* sp);
337
338 // Resets the covered region to the given "mr".
339 void set_region(MemRegion mr);
340
341 // Resets the covered region to one with the same _bottom as before but
342 // the "new_word_size".
343 void resize(size_t new_word_size);
344
345 // These must be guaranteed to work properly (i.e., do nothing)
346 // when "blk_start" ("blk" for second version) is "NULL".
347 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
348 virtual void alloc_block(HeapWord* blk, size_t size) {
349 alloc_block(blk, blk + size);
350 }
351
352 // The following methods are useful and optimized for a
353 // general, non-contiguous space.
354
355 // The given arguments are required to be the starts of adjacent ("blk1"
356 // before "blk2") well-formed blocks covered by "this". After this call,
357 // they should be considered to form one block.
358 virtual void join_blocks(HeapWord* blk1, HeapWord* blk2);
359
360 // Given a block [blk_start, blk_start + full_blk_size), and
361 // a left_blk_size < full_blk_size, adjust the BOT to show two
362 // blocks [blk_start, blk_start + left_blk_size) and
363 // [blk_start + left_blk_size, blk_start + full_blk_size).
364 // It is assumed (and verified in the non-product VM) that the
365 // BOT was correct for the original block.
366 void split_block(HeapWord* blk_start, size_t full_blk_size,
367 size_t left_blk_size);
368
369 // Adjust the BOT to show that it has a single block in the
370 // range [blk_start, blk_start + size). All necessary BOT
371 // cards are adjusted, but _unallocated_block isn't.
372 void single_block(HeapWord* blk_start, HeapWord* blk_end);
373 void single_block(HeapWord* blk, size_t size) {
374 single_block(blk, blk + size);
375 }
376
377 // Adjust BOT to show that it has a block in the range
378 // [blk_start, blk_start + size). Only the first card
379 // of BOT is touched. It is assumed (and verified in the
380 // non-product VM) that the remaining cards of the block
381 // are correct.
382 void mark_block(HeapWord* blk_start, HeapWord* blk_end);
383 void mark_block(HeapWord* blk, size_t size) {
384 mark_block(blk, blk + size);
385 }
386
387 // Adjust _unallocated_block to indicate that a particular
388 // block has been newly allocated or freed. It is assumed (and
389 // verified in the non-product VM) that the BOT is correct for
390 // the given block.
391 inline void allocated(HeapWord* blk_start, HeapWord* blk_end) {
392 // Verify that the BOT shows [blk, blk + blk_size) to be one block.
393 verify_single_block(blk_start, blk_end);
394 if (BlockOffsetArrayUseUnallocatedBlock) {
395 _unallocated_block = MAX2(_unallocated_block, blk_end);
396 }
397 }
398
399 inline void allocated(HeapWord* blk, size_t size) {
400 allocated(blk, blk + size);
401 }
402
403 inline void freed(HeapWord* blk_start, HeapWord* blk_end);
404
405 inline void freed(HeapWord* blk, size_t size);
406
407 virtual HeapWord* block_start_unsafe(const void* addr);
408 virtual HeapWord* block_start_unsafe_const(const void* addr) const;
409
410 // Requires "addr" to be the start of a card and returns the
411 // start of the block that contains the given address.
412 HeapWord* block_start_careful(const void* addr) const;
413
414 // If true, initialize array slots with no allocated blocks to zero.
415 // Otherwise, make them point back to the front.
416 bool init_to_zero() { return _init_to_zero; }
417
418 // Verification & debugging - ensure that the offset table reflects the fact
419 // that the block [blk_start, blk_end) or [blk, blk + size) is a
420 // single block of storage. NOTE: can;t const this because of
421 // call to non-const do_block_internal() below.
422 inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) {
423 if (VerifyBlockOffsetArray) {
424 do_block_internal(blk_start, blk_end, Action_check);
425 }
426 }
427
428 inline void verify_single_block(HeapWord* blk, size_t size) {
429 verify_single_block(blk, blk + size);
430 }
431
432 // Verify that the given block is before _unallocated_block
433 inline void verify_not_unallocated(HeapWord* blk_start,
434 HeapWord* blk_end) const {
435 if (BlockOffsetArrayUseUnallocatedBlock) {
436 assert(blk_start < blk_end, "Block inconsistency?");
437 assert(blk_end <= _unallocated_block, "_unallocated_block problem");
438 }
439 }
440
441 inline void verify_not_unallocated(HeapWord* blk, size_t size) const {
442 verify_not_unallocated(blk, blk + size);
443 }
444
445 void check_all_cards(size_t left_card, size_t right_card) const;
446 };
447
448 // A subtype of BlockOffsetArray that takes advantage of the fact
449 // that its underlying space is a ContiguousSpace, so that its "active"
450 // region can be more efficiently tracked (than for a non-contiguous space).
451 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
452 friend class VMStructs;
453
454 // allocation boundary at which offset array must be updated
455 HeapWord* _next_offset_threshold;
456 size_t _next_offset_index; // index corresponding to that boundary
457
458 // Work function to be called when allocation start crosses the next
459 // threshold in the contig space.
460 void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
461 alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
462 blk_start, blk_end);
463 }
464
465
466 public:
467 G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
468
469 // Initialize the threshold to reflect the first boundary after the
470 // bottom of the covered region.
471 HeapWord* initialize_threshold();
472
473 // Zero out the entry for _bottom (offset will be zero).
474 void zero_bottom_entry();
475
476 // Return the next threshold, the point at which the table should be
477 // updated.
478 HeapWord* threshold() const { return _next_offset_threshold; }
479
480 // These must be guaranteed to work properly (i.e., do nothing)
481 // when "blk_start" ("blk" for second version) is "NULL". In this
482 // implementation, that's true because NULL is represented as 0, and thus
483 // never exceeds the "_next_offset_threshold".
484 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
485 if (blk_end > _next_offset_threshold)
486 alloc_block_work1(blk_start, blk_end);
487 }
488 void alloc_block(HeapWord* blk, size_t size) {
489 alloc_block(blk, blk+size);
490 }
491
492 HeapWord* block_start_unsafe(const void* addr);
493 HeapWord* block_start_unsafe_const(const void* addr) const;
494 };
495
496 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP