1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
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24
25 #ifndef SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP
26 #define SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP
27
28 #include "gc/g1/g1RegionToSpaceMapper.hpp"
29 #include "memory/memRegion.hpp"
30 #include "memory/virtualspace.hpp"
31 #include "utilities/globalDefinitions.hpp"
32
33 // Forward declarations
34 class G1BlockOffsetTable;
35 class G1ContiguousSpace;
36
37 // This implementation of "G1BlockOffsetTable" divides the covered region
38 // into "N"-word subregions (where "N" = 2^"LogN". An array with an entry
39 // for each such subregion indicates how far back one must go to find the
40 // start of the chunk that includes the first word of the subregion.
41 //
42 // Each G1BlockOffsetTablePart is owned by a G1ContiguousSpace.
43
44 class G1BlockOffsetTable: public CHeapObj<mtGC> {
45 friend class G1BlockOffsetTablePart;
46 friend class VMStructs;
47
48 private:
49 // The reserved region covered by the table.
50 MemRegion _reserved;
51
52 // Array for keeping offsets for retrieving object start fast given an
53 // address.
54 u_char* _offset_array; // byte array keeping backwards offsets
55
56 void check_offset(size_t offset, const char* msg) const {
57 assert(offset <= N_words,
58 "%s - offset: " SIZE_FORMAT ", N_words: %u",
59 msg, offset, (uint)N_words);
60 }
61
62 // Bounds checking accessors:
63 // For performance these have to devolve to array accesses in product builds.
64 inline u_char offset_array(size_t index) const;
65
66 void set_offset_array_raw(size_t index, u_char offset) {
67 _offset_array[index] = offset;
68 }
69
70 inline void set_offset_array(size_t index, u_char offset);
71
72 inline void set_offset_array(size_t index, HeapWord* high, HeapWord* low);
73
74 inline void set_offset_array(size_t left, size_t right, u_char offset);
75
76 bool is_card_boundary(HeapWord* p) const;
77
78 void check_index(size_t index, const char* msg) const NOT_DEBUG_RETURN;
79
80 public:
81
82 // Return the number of slots needed for an offset array
83 // that covers mem_region_words words.
84 static size_t compute_size(size_t mem_region_words) {
85 size_t number_of_slots = (mem_region_words / N_words);
86 return ReservedSpace::allocation_align_size_up(number_of_slots);
87 }
88
89 // Returns how many bytes of the heap a single byte of the BOT corresponds to.
90 static size_t heap_map_factor() {
91 return N_bytes;
92 }
93
94 enum SomePublicConstants {
95 LogN = 9,
96 LogN_words = LogN - LogHeapWordSize,
97 N_bytes = 1 << LogN,
98 N_words = 1 << LogN_words
99 };
100
101 // Initialize the table to cover from "base" to (at least)
102 // "base + init_word_size". In the future, the table may be expanded
103 // (see "resize" below) up to the size of "_reserved" (which must be at
104 // least "init_word_size".) The contents of the initial table are
105 // undefined; it is the responsibility of the constituent
106 // G1BlockOffsetTable(s) to initialize cards.
107 G1BlockOffsetTable(MemRegion heap, G1RegionToSpaceMapper* storage);
108
109 // Return the appropriate index into "_offset_array" for "p".
110 inline size_t index_for(const void* p) const;
111 inline size_t index_for_raw(const void* p) const;
112
113 // Return the address indicating the start of the region corresponding to
114 // "index" in "_offset_array".
115 inline HeapWord* address_for_index(size_t index) const;
116 // Variant of address_for_index that does not check the index for validity.
117 inline HeapWord* address_for_index_raw(size_t index) const {
118 return _reserved.start() + (index << LogN_words);
119 }
120 };
121
122 class G1BlockOffsetTablePart VALUE_OBJ_CLASS_SPEC {
123 friend class G1BlockOffsetTable;
124 friend class VMStructs;
125 private:
126 enum SomePrivateConstants {
127 N_words = G1BlockOffsetTable::N_words,
128 LogN = G1BlockOffsetTable::LogN
129 };
130
131 // allocation boundary at which offset array must be updated
132 HeapWord* _next_offset_threshold;
133 size_t _next_offset_index; // index corresponding to that boundary
134
135 // This is the global BlockOffsetTable.
136 G1BlockOffsetTable* _bot;
137
138 // The space that owns this subregion.
139 G1ContiguousSpace* _space;
140
141 // Sets the entries
142 // corresponding to the cards starting at "start" and ending at "end"
143 // to point back to the card before "start": the interval [start, end)
144 // is right-open.
145 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
146 // Same as above, except that the args here are a card _index_ interval
147 // that is closed: [start_index, end_index]
148 void set_remainder_to_point_to_start_incl(size_t start, size_t end);
149
150 // Zero out the entry for _bottom (offset will be zero). Does not check for availability of the
151 // memory first.
152 void zero_bottom_entry_raw();
153 // Variant of initialize_threshold that does not check for availability of the
154 // memory first.
155 HeapWord* initialize_threshold_raw();
156
157 inline size_t block_size(const HeapWord* p) const;
158
159 // Returns the address of a block whose start is at most "addr".
160 // If "has_max_index" is true, "assumes "max_index" is the last valid one
161 // in the array.
162 inline HeapWord* block_at_or_preceding(const void* addr,
163 bool has_max_index,
164 size_t max_index) const;
165
166 // "q" is a block boundary that is <= "addr"; "n" is the address of the
167 // next block (or the end of the space.) Return the address of the
168 // beginning of the block that contains "addr". Does so without side
169 // effects (see, e.g., spec of block_start.)
170 inline HeapWord* forward_to_block_containing_addr_const(HeapWord* q, HeapWord* n,
171 const void* addr) const;
172
173 // "q" is a block boundary that is <= "addr"; return the address of the
174 // beginning of the block that contains "addr". May have side effects
175 // on "this", by updating imprecise entries.
176 inline HeapWord* forward_to_block_containing_addr(HeapWord* q,
177 const void* addr);
178
179 // "q" is a block boundary that is <= "addr"; "n" is the address of the
180 // next block (or the end of the space.) Return the address of the
181 // beginning of the block that contains "addr". May have side effects
182 // on "this", by updating imprecise entries.
183 HeapWord* forward_to_block_containing_addr_slow(HeapWord* q,
184 HeapWord* n,
185 const void* addr);
186
187 // Requires that "*threshold_" be the first array entry boundary at or
188 // above "blk_start", and that "*index_" be the corresponding array
189 // index. If the block starts at or crosses "*threshold_", records
190 // "blk_start" as the appropriate block start for the array index
191 // starting at "*threshold_", and for any other indices crossed by the
192 // block. Updates "*threshold_" and "*index_" to correspond to the first
193 // index after the block end.
194 void alloc_block_work(HeapWord** threshold_, size_t* index_,
195 HeapWord* blk_start, HeapWord* blk_end);
196
197 void check_all_cards(size_t left_card, size_t right_card) const;
198
199 public:
200 // The elements of the array are initialized to zero.
201 G1BlockOffsetTablePart(G1BlockOffsetTable* array, G1ContiguousSpace* gsp);
202
203 void verify() const;
204
205 // Returns the address of the start of the block containing "addr", or
206 // else "null" if it is covered by no block. (May have side effects,
207 // namely updating of shared array entries that "point" too far
208 // backwards. This can occur, for example, when lab allocation is used
209 // in a space covered by the table.)
210 inline HeapWord* block_start(const void* addr);
211 // Same as above, but does not have any of the possible side effects
212 // discussed above.
213 inline HeapWord* block_start_const(const void* addr) const;
214
215 // Initialize the threshold to reflect the first boundary after the
216 // bottom of the covered region.
217 HeapWord* initialize_threshold();
218
219 void reset_bot() {
220 zero_bottom_entry_raw();
221 initialize_threshold_raw();
222 }
223
224 // Return the next threshold, the point at which the table should be
225 // updated.
226 HeapWord* threshold() const { return _next_offset_threshold; }
227
228 // These must be guaranteed to work properly (i.e., do nothing)
229 // when "blk_start" ("blk" for second version) is "NULL". In this
230 // implementation, that's true because NULL is represented as 0, and thus
231 // never exceeds the "_next_offset_threshold".
232 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
233 if (blk_end > _next_offset_threshold) {
234 alloc_block_work(&_next_offset_threshold, &_next_offset_index, blk_start, blk_end);
235 }
236 }
237 void alloc_block(HeapWord* blk, size_t size) {
238 alloc_block(blk, blk+size);
239 }
240
241 void set_for_starts_humongous(HeapWord* obj_top, size_t fill_size);
242
243 void print_on(outputStream* out) PRODUCT_RETURN;
244 };
245
246 #endif // SHARE_VM_GC_G1_G1BLOCKOFFSETTABLE_HPP