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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 // Nothing to do. The BOT is hard-wired to be part of the HeapRegion, and we cannot
114 // retrieve it here since this would cause firing of several asserts. The code
115 // executed after commit of a region already needs to do some re-initialization of
116 // the HeapRegion, so we combine that.
117 }
118 };
119
120 // This implementation of "G1BlockOffsetTable" divides the covered region
121 // into "N"-word subregions (where "N" = 2^"LogN". An array with an entry
122 // for each such subregion indicates how far back one must go to find the
123 // start of the chunk that includes the first word of the subregion.
124 //
125 // Each BlockOffsetArray is owned by a Space. However, the actual array
126 // may be shared by several BlockOffsetArrays; this is useful
127 // when a single resizable area (such as a generation) is divided up into
128 // several spaces in which contiguous allocation takes place,
129 // such as, for example, in G1 or in the train generation.)
130
131 // Here is the shared array type.
132
133 class G1BlockOffsetSharedArray: public CHeapObj<mtGC> {
134 friend class G1BlockOffsetArray;
135 friend class G1BlockOffsetArrayContigSpace;
136 friend class VMStructs;
137
138 private:
139 G1BlockOffsetSharedArrayMappingChangedListener _listener;
140 // The reserved region covered by the shared array.
141 MemRegion _reserved;
142
143 // End of the current committed region.
144 HeapWord* _end;
145
146 // Array for keeping offsets for retrieving object start fast given an
147 // address.
148 u_char* _offset_array; // byte array keeping backwards offsets
149
150 void check_offset(size_t offset, const char* msg) const {
151 assert(offset <= N_words,
152 err_msg("%s - "
153 "offset: " SIZE_FORMAT", N_words: %u",
154 msg, offset, (uint)N_words));
155 }
156
157 // Bounds checking accessors:
158 // For performance these have to devolve to array accesses in product builds.
159 inline u_char offset_array(size_t index) const;
160
161 void set_offset_array_raw(size_t index, u_char offset) {
162 _offset_array[index] = offset;
163 }
164
165 inline void set_offset_array(size_t index, u_char offset);
166
167 inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);
168
169 inline void set_offset_array(size_t left, size_t right, u_char offset);
170
171 bool is_card_boundary(HeapWord* p) const;
172
173 public:
174
175 // Return the number of slots needed for an offset array
176 // that covers mem_region_words words.
177 static size_t compute_size(size_t mem_region_words) {
178 size_t number_of_slots = (mem_region_words / N_words);
179 return ReservedSpace::allocation_align_size_up(number_of_slots);
180 }
181
182 enum SomePublicConstants {
183 LogN = 9,
184 LogN_words = LogN - LogHeapWordSize,
185 N_bytes = 1 << LogN,
186 N_words = 1 << LogN_words
187 };
188
189 // Initialize the table to cover from "base" to (at least)
190 // "base + init_word_size". In the future, the table may be expanded
191 // (see "resize" below) up to the size of "_reserved" (which must be at
192 // least "init_word_size".) The contents of the initial table are
193 // undefined; it is the responsibility of the constituent
194 // G1BlockOffsetTable(s) to initialize cards.
195 G1BlockOffsetSharedArray(MemRegion heap, G1RegionToSpaceMapper* storage);
196
197 // Return the appropriate index into "_offset_array" for "p".
198 inline size_t index_for(const void* p) const;
199 inline size_t index_for_raw(const void* p) const;
200
201 // Return the address indicating the start of the region corresponding to
202 // "index" in "_offset_array".
203 inline HeapWord* address_for_index(size_t index) const;
204 // Variant of address_for_index that does not check the index for validity.
205 inline HeapWord* address_for_index_raw(size_t index) const {
206 return _reserved.start() + (index << LogN_words);
207 }
208 };
209
210 // And here is the G1BlockOffsetTable subtype that uses the array.
211
212 class G1BlockOffsetArray: public G1BlockOffsetTable {
213 friend class G1BlockOffsetSharedArray;
214 friend class G1BlockOffsetArrayContigSpace;
215 friend class VMStructs;
216 private:
217 enum SomePrivateConstants {
218 N_words = G1BlockOffsetSharedArray::N_words,
219 LogN = G1BlockOffsetSharedArray::LogN
220 };
221
222 // This is the array, which can be shared by several BlockOffsetArray's
223 // servicing different
224 G1BlockOffsetSharedArray* _array;
225
226 // The space that owns this subregion.
227 G1OffsetTableContigSpace* _gsp;
228
229 // The portion [_unallocated_block, _sp.end()) of the space that
230 // is a single block known not to contain any objects.
231 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
232 HeapWord* _unallocated_block;
233
234 // Sets the entries
235 // corresponding to the cards starting at "start" and ending at "end"
236 // to point back to the card before "start": the interval [start, end)
237 // is right-open.
238 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
239 // Same as above, except that the args here are a card _index_ interval
240 // that is closed: [start_index, end_index]
241 void set_remainder_to_point_to_start_incl(size_t start, size_t end);
242
243 protected:
244
245 G1OffsetTableContigSpace* gsp() const { return _gsp; }
246
247 inline size_t block_size(const HeapWord* p) const;
248
249 // Returns the address of a block whose start is at most "addr".
250 // If "has_max_index" is true, "assumes "max_index" is the last valid one
251 // in the array.
252 inline HeapWord* block_at_or_preceding(const void* addr,
253 bool has_max_index,
254 size_t max_index) const;
255
256 // "q" is a block boundary that is <= "addr"; "n" is the address of the
257 // next block (or the end of the space.) Return the address of the
258 // beginning of the block that contains "addr". Does so without side
259 // effects (see, e.g., spec of block_start.)
260 inline HeapWord*
261 forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
262 const void* addr) const;
263
264 // "q" is a block boundary that is <= "addr"; return the address of the
265 // beginning of the block that contains "addr". May have side effects
266 // on "this", by updating imprecise entries.
267 inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
268 const void* addr);
269
270 // "q" is a block boundary that is <= "addr"; "n" is the address of the
271 // next block (or the end of the space.) Return the address of the
272 // beginning of the block that contains "addr". May have side effects
273 // on "this", by updating imprecise entries.
274 HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
275 HeapWord* n,
276 const void* addr);
277
278 // Requires that "*threshold_" be the first array entry boundary at or
279 // above "blk_start", and that "*index_" be the corresponding array
280 // index. If the block starts at or crosses "*threshold_", records
281 // "blk_start" as the appropriate block start for the array index
282 // starting at "*threshold_", and for any other indices crossed by the
283 // block. Updates "*threshold_" and "*index_" to correspond to the first
284 // index after the block end.
285 void alloc_block_work2(HeapWord** threshold_, size_t* index_,
286 HeapWord* blk_start, HeapWord* blk_end);
287
288 public:
289 // The space may not have it's bottom and top set yet, which is why the
290 // region is passed as a parameter. The elements of the array are
291 // initialized to zero.
292 G1BlockOffsetArray(G1BlockOffsetSharedArray* array, MemRegion mr);
293
294 // Note: this ought to be part of the constructor, but that would require
295 // "this" to be passed as a parameter to a member constructor for
296 // the containing concrete subtype of Space.
297 // This would be legal C++, but MS VC++ doesn't allow it.
298 void set_space(G1OffsetTableContigSpace* sp);
299
300 // Resets the covered region to one with the same _bottom as before but
301 // the "new_word_size".
302 void resize(size_t new_word_size);
303
304 virtual HeapWord* block_start_unsafe(const void* addr);
305 virtual HeapWord* block_start_unsafe_const(const void* addr) const;
306
307 // Used by region verification. Checks that the contents of the
308 // BOT reflect that there's a single object that spans the address
309 // range [obj_start, obj_start + word_size); returns true if this is
310 // the case, returns false if it's not.
311 bool verify_for_object(HeapWord* obj_start, size_t word_size) const;
312
313 void check_all_cards(size_t left_card, size_t right_card) const;
314
315 virtual void print_on(outputStream* out) PRODUCT_RETURN;
316 };
317
318 // A subtype of BlockOffsetArray that takes advantage of the fact
319 // that its underlying space is a ContiguousSpace, so that its "active"
320 // region can be more efficiently tracked (than for a non-contiguous space).
321 class G1BlockOffsetArrayContigSpace: public G1BlockOffsetArray {
322 friend class VMStructs;
323
324 // allocation boundary at which offset array must be updated
325 HeapWord* _next_offset_threshold;
326 size_t _next_offset_index; // index corresponding to that boundary
327
328 // Work function to be called when allocation start crosses the next
329 // threshold in the contig space.
330 void alloc_block_work1(HeapWord* blk_start, HeapWord* blk_end) {
331 alloc_block_work2(&_next_offset_threshold, &_next_offset_index,
332 blk_start, blk_end);
333 }
334
335 // Variant of zero_bottom_entry that does not check for availability of the
336 // memory first.
337 void zero_bottom_entry_raw();
338 // Variant of initialize_threshold that does not check for availability of the
339 // memory first.
340 HeapWord* initialize_threshold_raw();
341 public:
342 G1BlockOffsetArrayContigSpace(G1BlockOffsetSharedArray* array, MemRegion mr);
343
344 // Initialize the threshold to reflect the first boundary after the
345 // bottom of the covered region.
346 HeapWord* initialize_threshold();
347
348 void reset_bot() {
349 zero_bottom_entry_raw();
350 initialize_threshold_raw();
351 }
352
353 // Return the next threshold, the point at which the table should be
354 // updated.
355 HeapWord* threshold() const { return _next_offset_threshold; }
356
357 // These must be guaranteed to work properly (i.e., do nothing)
358 // when "blk_start" ("blk" for second version) is "NULL". In this
359 // implementation, that's true because NULL is represented as 0, and thus
360 // never exceeds the "_next_offset_threshold".
361 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
362 if (blk_end > _next_offset_threshold)
363 alloc_block_work1(blk_start, blk_end);
364 }
365 void alloc_block(HeapWord* blk, size_t size) {
366 alloc_block(blk, blk+size);
367 }
368
369 HeapWord* block_start_unsafe(const void* addr);
370 HeapWord* block_start_unsafe_const(const void* addr) const;
371
372 void set_for_starts_humongous(HeapWord* new_top);
373
374 virtual void print_on(outputStream* out) PRODUCT_RETURN;
375 };
376
377 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_G1BLOCKOFFSETTABLE_HPP