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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 "gc_implementation/g1/g1RegionToSpaceMapper.hpp"
29 #include "memory/memRegion.hpp"
30 #include "runtime/virtualspace.hpp"
31 #include "utilities/globalDefinitions.hpp"
32
33 // The CollectedHeap type requires subtypes to implement a method
34 // "block_start". For some subtypes, notably generational
35 // systems using card-table-based write barriers, the efficiency of this
36 // operation may be important. Implementations of the "BlockOffsetArray"
37 // class may be useful in providing such efficient implementations.
38 //
39 // While generally mirroring the structure of the BOT for GenCollectedHeap,
40 // the following types are tailored more towards G1's uses; these should,
41 // however, be merged back into a common BOT to avoid code duplication
42 // and reduce maintenance overhead.
43 //
44 // G1BlockOffsetTable (abstract)
45 // -- G1BlockOffsetArray (uses G1BlockOffsetSharedArray)
46 // -- G1BlockOffsetArrayContigSpace
47 //
48 // A main impediment to the consolidation of this code might be the
49 // effect of making some of the block_start*() calls non-const as
50 // below. Whether that might adversely affect performance optimizations
51 // that compilers might normally perform in the case of non-G1
52 // collectors needs to be carefully investigated prior to any such
53 // consolidation.
54
55 // Forward declarations
56 class G1BlockOffsetSharedArray;
57 class G1OffsetTableContigSpace;
58
59 class G1BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
60 friend class VMStructs;
61 protected:
62 // These members describe the region covered by the table.
63
64 // The space this table is covering.
65 HeapWord* _bottom; // == reserved.start
66 HeapWord* _end; // End of currently allocated region.
67
68 public:
69 // Initialize the table to cover the given space.
70 // The contents of the initial table are undefined.
71 G1BlockOffsetTable(HeapWord* bottom, HeapWord* end) :
72 _bottom(bottom), _end(end)
73 {
74 assert(_bottom <= _end, "arguments out of order");
75 }
76
77 // Note that the committed size of the covered space may have changed,
78 // so the table size might also wish to change.
79 virtual void resize(size_t new_word_size) = 0;
80
81 virtual void set_bottom(HeapWord* new_bottom) {
82 assert(new_bottom <= _end,
83 err_msg("new_bottom (" PTR_FORMAT ") > _end (" PTR_FORMAT ")",
84 p2i(new_bottom), p2i(_end)));
85 _bottom = new_bottom;
86 resize(pointer_delta(_end, _bottom));
87 }
88
89 // Requires "addr" to be contained by a block, and returns the address of
90 // the start of that block. (May have side effects, namely updating of
91 // shared array entries that "point" too far backwards. This can occur,
92 // for example, when LAB allocation is used in a space covered by the
93 // table.)
94 virtual HeapWord* block_start_unsafe(const void* addr) = 0;
95 // Same as above, but does not have any of the possible side effects
96 // discussed above.
97 virtual HeapWord* block_start_unsafe_const(const void* addr) const = 0;
98
99 // Returns the address of the start of the block containing "addr", or
100 // else "null" if it is covered by no block. (May have side effects,
101 // namely updating of shared array entries that "point" too far
102 // backwards. This can occur, for example, when lab allocation is used
103 // in a space covered by the table.)
104 inline HeapWord* block_start(const void* addr);
105 // Same as above, but does not have any of the possible side effects
106 // discussed above.
107 inline HeapWord* block_start_const(const void* addr) const;
108 };
109
110 class G1BlockOffsetSharedArrayMappingChangedListener : public G1MappingChangedListener {
111 public:
112 virtual void on_commit(uint start_idx, size_t num_regions);
113 };
114
115 // This implementation of "G1BlockOffsetTable" divides the covered region
116 // into "N"-word subregions (where "N" = 2^"LogN". An array with an entry
117 // for each such subregion indicates how far back one must go to find the
118 // start of the chunk that includes the first word of the subregion.
119 //
120 // Each BlockOffsetArray is owned by a Space. However, the actual array
121 // may be shared by several BlockOffsetArrays; this is useful
122 // when a single resizable area (such as a generation) is divided up into
123 // several spaces in which contiguous allocation takes place,
124 // such as, for example, in G1 or in the train generation.)
125
126 // Here is the shared array type.
127
128 class G1BlockOffsetSharedArray: public CHeapObj<mtGC> {
129 friend class G1BlockOffsetArray;
130 friend class G1BlockOffsetArrayContigSpace;
131 friend class VMStructs;
132
133 private:
134 G1BlockOffsetSharedArrayMappingChangedListener _listener;
135 // The reserved region covered by the shared array.
136 MemRegion _reserved;
137
138 // End of the current committed region.
139 HeapWord* _end;
140
141 // Array for keeping offsets for retrieving object start fast given an
142 // address.
143 u_char* _offset_array; // byte array keeping backwards offsets
144
145 void check_offset(size_t offset, const char* msg) const {
146 assert(offset <= N_words,
147 err_msg("%s - "
148 "offset: " SIZE_FORMAT", N_words: %u",
149 msg, offset, (uint)N_words));
150 }
151
152 // Bounds checking accessors:
153 // For performance these have to devolve to array accesses in product builds.
154 inline u_char offset_array(size_t index) const;
155
156 void set_offset_array(HeapWord* left, HeapWord* right, u_char offset);
157
158 void set_offset_array_raw(size_t index, u_char offset) {
159 _offset_array[index] = offset;
160 }
161
162 inline void set_offset_array(size_t index, u_char offset);
163
164 inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);
165
166 inline void set_offset_array(size_t left, size_t right, u_char offset);
167
168 inline void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const;
169
170 bool is_card_boundary(HeapWord* p) const;
171
172 public:
173
174 // Return the number of slots needed for an offset array
175 // that covers mem_region_words words.
176 static size_t compute_size(size_t mem_region_words) {
177 size_t number_of_slots = (mem_region_words / N_words);
178 return ReservedSpace::allocation_align_size_up(number_of_slots);
179 }
180
181 enum SomePublicConstants {
182 LogN = 9,
183 LogN_words = LogN - LogHeapWordSize,
184 N_bytes = 1 << LogN,
185 N_words = 1 << LogN_words
186 };
187
188 // Initialize the table to cover from "base" to (at least)
189 // "base + init_word_size". In the future, the table may be expanded
190 // (see "resize" below) up to the size of "_reserved" (which must be at
191 // least "init_word_size".) The contents of the initial table are
192 // undefined; it is the responsibility of the constituent
193 // G1BlockOffsetTable(s) to initialize cards.
194 G1BlockOffsetSharedArray(MemRegion heap, G1RegionToSpaceMapper* storage);
195
196 void set_bottom(HeapWord* new_bottom);
197
198 // Return the appropriate index into "_offset_array" for "p".
199 inline size_t index_for(const void* p) const;
200 inline size_t index_for_raw(const void* p) const;
201
202 // Return the address indicating the start of the region corresponding to
203 // "index" in "_offset_array".
204 inline HeapWord* address_for_index(size_t index) const;
205 // Variant of address_for_index that does not check the index for validity.
206 inline HeapWord* address_for_index_raw(size_t index) const {
207 return _reserved.start() + (index << LogN_words);
208 }
209 };
210
211 // And here is the G1BlockOffsetTable subtype that uses the array.
212
213 class G1BlockOffsetArray: public G1BlockOffsetTable {
214 friend class G1BlockOffsetSharedArray;
215 friend class G1BlockOffsetArrayContigSpace;
216 friend class VMStructs;
217 private:
218 enum SomePrivateConstants {
219 N_words = G1BlockOffsetSharedArray::N_words,
220 LogN = G1BlockOffsetSharedArray::LogN
221 };
222
223 // The following enums are used by do_block_helper
224 enum Action {
225 Action_single, // BOT records a single block (see single_block())
226 Action_mark, // BOT marks the start of a block (see mark_block())
227 Action_check // Check that BOT records block correctly
228 // (see verify_single_block()).
229 };
230
231 // This is the array, which can be shared by several BlockOffsetArray's
232 // servicing different
233 G1BlockOffsetSharedArray* _array;
234
235 // The space that owns this subregion.
236 G1OffsetTableContigSpace* _gsp;
237
238 // If true, array entries are initialized to 0; otherwise, they are
239 // initialized to point backwards to the beginning of the covered region.
240 bool _init_to_zero;
241
242 // The portion [_unallocated_block, _sp.end()) of the space that
243 // is a single block known not to contain any objects.
244 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
245 HeapWord* _unallocated_block;
246
247 // Sets the entries
248 // corresponding to the cards starting at "start" and ending at "end"
249 // to point back to the card before "start": the interval [start, end)
250 // is right-open.
251 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
252 // Same as above, except that the args here are a card _index_ interval
253 // that is closed: [start_index, end_index]
254 void set_remainder_to_point_to_start_incl(size_t start, size_t end);
255
256 // A helper function for BOT adjustment/verification work
257 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);
258
259 protected:
260
261 G1OffsetTableContigSpace* gsp() const { return _gsp; }
262
263 inline size_t block_size(const HeapWord* p) const;
264
265 // Returns the address of a block whose start is at most "addr".
266 // If "has_max_index" is true, "assumes "max_index" is the last valid one
267 // in the array.
268 inline HeapWord* block_at_or_preceding(const void* addr,
269 bool has_max_index,
270 size_t max_index) const;
271
272 // "q" is a block boundary that is <= "addr"; "n" is the address of the
273 // next block (or the end of the space.) Return the address of the
274 // beginning of the block that contains "addr". Does so without side
275 // effects (see, e.g., spec of block_start.)
276 inline HeapWord*
277 forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
278 const void* addr) const;
279
280 // "q" is a block boundary that is <= "addr"; return the address of the
281 // beginning of the block that contains "addr". May have side effects
282 // on "this", by updating imprecise entries.
283 inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
284 const void* addr);
285
286 // "q" is a block boundary that is <= "addr"; "n" is the address of the
287 // next block (or the end of the space.) Return the address of the
288 // beginning of the block that contains "addr". May have side effects
289 // on "this", by updating imprecise entries.
290 HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
291 HeapWord* n,
292 const void* addr);
293
294 // Requires that "*threshold_" be the first array entry boundary at or
295 // above "blk_start", and that "*index_" be the corresponding array
296 // index. If the block starts at or crosses "*threshold_", records
297 // "blk_start" as the appropriate block start for the array index
298 // starting at "*threshold_", and for any other indices crossed by the
299 // block. Updates "*threshold_" and "*index_" to correspond to the first
300 // index after the block end.
301 void alloc_block_work2(HeapWord** threshold_, size_t* index_,
302 HeapWord* blk_start, HeapWord* blk_end);
303
304 public:
305 // The space may not have it's bottom and top set yet, which is why the
306 // region is passed as a parameter. If "init_to_zero" is true, the
307 // elements of the array are initialized to zero. Otherwise, they are
308 // initialized to point backwards to the beginning.
309 G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr,
310 bool init_to_zero);
311
312 // Note: this ought to be part of the constructor, but that would require
313 // "this" to be passed as a parameter to a member constructor for
314 // the containing concrete subtype of Space.
315 // This would be legal C++, but MS VC++ doesn't allow it.
316 void set_space(G1OffsetTableContigSpace* sp);
317
318 // Resets the covered region to the given "mr".
319 void set_region(MemRegion mr);
320
321 // Resets the covered region to one with the same _bottom as before but
322 // the "new_word_size".
323 void resize(size_t new_word_size);
324
325 // These must be guaranteed to work properly (i.e., do nothing)
326 // when "blk_start" ("blk" for second version) is "NULL".
327 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
328 virtual void alloc_block(HeapWord* blk, size_t size) {
329 alloc_block(blk, blk + size);
330 }
331
332 // The following methods are useful and optimized for a
333 // general, non-contiguous space.
334
335 // Given a block [blk_start, blk_start + full_blk_size), and
336 // a left_blk_size < full_blk_size, adjust the BOT to show two
337 // blocks [blk_start, blk_start + left_blk_size) and
338 // [blk_start + left_blk_size, blk_start + full_blk_size).
339 // It is assumed (and verified in the non-product VM) that the
340 // BOT was correct for the original block.
341 void split_block(HeapWord* blk_start, size_t full_blk_size,
342 size_t left_blk_size);
343
344 // Adjust the BOT to show that it has a single block in the
345 // range [blk_start, blk_start + size). All necessary BOT
346 // cards are adjusted, but _unallocated_block isn't.
347 void single_block(HeapWord* blk_start, HeapWord* blk_end);
348 void single_block(HeapWord* blk, size_t size) {
349 single_block(blk, blk + size);
350 }
351
352 // Adjust BOT to show that it has a block in the range
353 // [blk_start, blk_start + size). Only the first card
354 // of BOT is touched. It is assumed (and verified in the
355 // non-product VM) that the remaining cards of the block
356 // are correct.
357 void mark_block(HeapWord* blk_start, HeapWord* blk_end);
358 void mark_block(HeapWord* blk, size_t size) {
359 mark_block(blk, blk + size);
360 }
361
362 // Adjust _unallocated_block to indicate that a particular
363 // block has been newly allocated or freed. It is assumed (and
364 // verified in the non-product VM) that the BOT is correct for
365 // the given block.
366 inline void allocated(HeapWord* blk_start, HeapWord* blk_end) {
367 // Verify that the BOT shows [blk, blk + blk_size) to be one block.
368 verify_single_block(blk_start, blk_end);
369 if (BlockOffsetArrayUseUnallocatedBlock) {
370 _unallocated_block = MAX2(_unallocated_block, blk_end);
371 }
372 }
373
374 inline void allocated(HeapWord* blk, size_t size) {
375 allocated(blk, blk + size);
376 }
377
378 inline void freed(HeapWord* blk_start, HeapWord* blk_end);
379
380 inline void freed(HeapWord* blk, size_t size);
381
382 virtual HeapWord* block_start_unsafe(const void* addr);
383 virtual HeapWord* block_start_unsafe_const(const void* addr) const;
384
385 // Requires "addr" to be the start of a card and returns the
386 // start of the block that contains the given address.
387 HeapWord* block_start_careful(const void* addr) const;
388
389 // If true, initialize array slots with no allocated blocks to zero.
390 // Otherwise, make them point back to the front.
391 bool init_to_zero() { return _init_to_zero; }
392
393 // Verification & debugging - ensure that the offset table reflects the fact
394 // that the block [blk_start, blk_end) or [blk, blk + size) is a
395 // single block of storage. NOTE: can;t const this because of
396 // call to non-const do_block_internal() below.
397 inline void verify_single_block(HeapWord* blk_start, HeapWord* blk_end) {
398 if (VerifyBlockOffsetArray) {
399 do_block_internal(blk_start, blk_end, Action_check);
400 }
401 }
402
403 inline void verify_single_block(HeapWord* blk, size_t size) {
404 verify_single_block(blk, blk + size);
405 }
406
407 // Used by region verification. Checks that the contents of the
408 // BOT reflect that there's a single object that spans the address
409 // range [obj_start, obj_start + word_size); returns true if this is
410 // the case, returns false if it's not.
411 bool verify_for_object(HeapWord* obj_start, size_t word_size) const;
412
413 // Verify that the given block is before _unallocated_block
414 inline void verify_not_unallocated(HeapWord* blk_start,
415 HeapWord* blk_end) const {
416 if (BlockOffsetArrayUseUnallocatedBlock) {
417 assert(blk_start < blk_end, "Block inconsistency?");
418 assert(blk_end <= _unallocated_block, "_unallocated_block problem");
419 }
420 }
421
422 inline void verify_not_unallocated(HeapWord* blk, size_t size) const {
423 verify_not_unallocated(blk, blk + size);
424 }
425
426 void check_all_cards(size_t left_card, size_t right_card) const;
427
428 virtual void print_on(outputStream* out) PRODUCT_RETURN;
429 };
430
431 // A subtype of BlockOffsetArray that takes advantage of the fact
432 // that its underlying space is a ContiguousSpace, so that its "active"
433 // region can be more efficiently tracked (than for a non-contiguous space).
434 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
435 friend class VMStructs;
436
437 // allocation boundary at which offset array must be updated
438 HeapWord* _next_offset_threshold;
439 size_t _next_offset_index; // index corresponding to that boundary
440
441 // Work function to be called when allocation start crosses the next
442 // threshold in the contig space.
443 void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
444 alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
445 blk_start, blk_end);
446 }
447
448 // Variant of zero_bottom_entry that does not check for availability of the
449 // memory first.
450 void zero_bottom_entry_raw();
451 // Variant of initialize_threshold that does not check for availability of the
452 // memory first.
453 HeapWord* initialize_threshold_raw();
454 // Zero out the entry for _bottom (offset will be zero).
455 void zero_bottom_entry();
456 public:
457 G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
458
459 // Initialize the threshold to reflect the first boundary after the
460 // bottom of the covered region.
461 HeapWord* initialize_threshold();
462
463 void reset_bot() {
464 zero_bottom_entry_raw();
465 initialize_threshold_raw();
466 }
467
468 // Return the next threshold, the point at which the table should be
469 // updated.
470 HeapWord* threshold() const { return _next_offset_threshold; }
471
472 // These must be guaranteed to work properly (i.e., do nothing)
473 // when "blk_start" ("blk" for second version) is "NULL". In this
474 // implementation, that's true because NULL is represented as 0, and thus
475 // never exceeds the "_next_offset_threshold".
476 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
477 if (blk_end > _next_offset_threshold)
478 alloc_block_work1(blk_start, blk_end);
479 }
480 void alloc_block(HeapWord* blk, size_t size) {
481 alloc_block(blk, blk+size);
482 }
483
484 HeapWord* block_start_unsafe(const void* addr);
485 HeapWord* block_start_unsafe_const(const void* addr) const;
486
487 void set_for_starts_humongous(HeapWord* new_top);
488
489 virtual void print_on(outputStream* out) PRODUCT_RETURN;
490 };
491
492 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP