1 #ifdef USE_PRAGMA_IDENT_HDR
2 #pragma ident "@(#)blockOffsetTable.hpp 1.57 07/05/05 17:05:43 JVM"
3 #endif
4 /*
5 * Copyright 2000-2006 Sun Microsystems, Inc. All Rights Reserved.
6 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
7 *
8 * This code is free software; you can redistribute it and/or modify it
9 * under the terms of the GNU General Public License version 2 only, as
10 * published by the Free Software Foundation.
11 *
12 * This code is distributed in the hope that it will be useful, but WITHOUT
13 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 * version 2 for more details (a copy is included in the LICENSE file that
16 * accompanied this code).
17 *
18 * You should have received a copy of the GNU General Public License version
19 * 2 along with this work; if not, write to the Free Software Foundation,
20 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
21 *
22 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
23 * CA 95054 USA or visit www.sun.com if you need additional information or
24 * have any questions.
25 *
26 */
27
28 // The CollectedHeap type requires subtypes to implement a method
29 // "block_start". For some subtypes, notably generational
30 // systems using card-table-based write barriers, the efficiency of this
31 // operation may be important. Implementations of the "BlockOffsetArray"
32 // class may be useful in providing such efficient implementations.
33 //
34 // BlockOffsetTable (abstract)
35 // - BlockOffsetArray (abstract)
36 // - BlockOffsetArrayNonContigSpace
37 // - BlockOffsetArrayContigSpace
38 //
39
40 class ContiguousSpace;
41 class SerializeOopClosure;
42
43 //////////////////////////////////////////////////////////////////////////
44 // The BlockOffsetTable "interface"
45 //////////////////////////////////////////////////////////////////////////
46 class BlockOffsetTable VALUE_OBJ_CLASS_SPEC {
47 friend class VMStructs;
48 protected:
49 // These members describe the region covered by the table.
50
51 // The space this table is covering.
52 HeapWord* _bottom; // == reserved.start
53 HeapWord* _end; // End of currently allocated region.
54
55 public:
56 // Initialize the table to cover the given space.
57 // The contents of the initial table are undefined.
58 BlockOffsetTable(HeapWord* bottom, HeapWord* end):
59 _bottom(bottom), _end(end) {
60 assert(_bottom <= _end, "arguments out of order");
61 }
62
63 // Note that the committed size of the covered space may have changed,
64 // so the table size might also wish to change.
65 virtual void resize(size_t new_word_size) = 0;
66
67 virtual void set_bottom(HeapWord* new_bottom) {
68 assert(new_bottom <= _end, "new_bottom > _end");
69 _bottom = new_bottom;
70 resize(pointer_delta(_end, _bottom));
71 }
72
73 // Requires "addr" to be contained by a block, and returns the address of
74 // the start of that block.
75 virtual HeapWord* block_start_unsafe(const void* addr) const = 0;
76
77 // Returns the address of the start of the block containing "addr", or
78 // else "null" if it is covered by no block.
79 HeapWord* block_start(const void* addr) const;
80 };
81
82 //////////////////////////////////////////////////////////////////////////
83 // One implementation of "BlockOffsetTable," the BlockOffsetArray,
84 // divides the covered region into "N"-word subregions (where
85 // "N" = 2^"LogN". An array with an entry for each such subregion
86 // indicates how far back one must go to find the start of the
87 // chunk that includes the first word of the subregion.
88 //
89 // Each BlockOffsetArray is owned by a Space. However, the actual array
90 // may be shared by several BlockOffsetArrays; this is useful
91 // when a single resizable area (such as a generation) is divided up into
92 // several spaces in which contiguous allocation takes place. (Consider,
93 // for example, the garbage-first generation.)
94
95 // Here is the shared array type.
96 //////////////////////////////////////////////////////////////////////////
97 // BlockOffsetSharedArray
98 //////////////////////////////////////////////////////////////////////////
99 class BlockOffsetSharedArray: public CHeapObj {
100 friend class BlockOffsetArray;
101 friend class BlockOffsetArrayNonContigSpace;
102 friend class BlockOffsetArrayContigSpace;
103 friend class VMStructs;
104
105 private:
106 enum SomePrivateConstants {
107 LogN = 9,
108 LogN_words = LogN - LogHeapWordSize,
109 N_bytes = 1 << LogN,
110 N_words = 1 << LogN_words
111 };
112
113 // The reserved region covered by the shared array.
114 MemRegion _reserved;
115
116 // End of the current committed region.
117 HeapWord* _end;
118
119 // Array for keeping offsets for retrieving object start fast given an
120 // address.
121 VirtualSpace _vs;
122 u_char* _offset_array; // byte array keeping backwards offsets
123
124 protected:
125 // Bounds checking accessors:
126 // For performance these have to devolve to array accesses in product builds.
127 u_char offset_array(size_t index) const {
128 assert(index < _vs.committed_size(), "index out of range");
129 return _offset_array[index];
130 }
131 void set_offset_array(size_t index, u_char offset) {
132 assert(index < _vs.committed_size(), "index out of range");
133 _offset_array[index] = offset;
134 }
135 void set_offset_array(size_t index, HeapWord* high, HeapWord* low) {
136 assert(index < _vs.committed_size(), "index out of range");
137 assert(high >= low, "addresses out of order");
138 assert(pointer_delta(high, low) <= N_words, "offset too large");
139 _offset_array[index] = (u_char)pointer_delta(high, low);
140 }
141 void set_offset_array(HeapWord* left, HeapWord* right, u_char offset) {
142 assert(index_for(right - 1) < _vs.committed_size(),
143 "right address out of range");
144 assert(left < right, "Heap addresses out of order");
145 size_t num_cards = pointer_delta(right, left) >> LogN_words;
146 memset(&_offset_array[index_for(left)], offset, num_cards);
147 }
148
149 void set_offset_array(size_t left, size_t right, u_char offset) {
150 assert(right < _vs.committed_size(), "right address out of range");
151 assert(left <= right, "indexes out of order");
152 size_t num_cards = right - left + 1;
153 memset(&_offset_array[left], offset, num_cards);
154 }
155
156 void check_offset_array(size_t index, HeapWord* high, HeapWord* low) const {
157 assert(index < _vs.committed_size(), "index out of range");
158 assert(high >= low, "addresses out of order");
159 assert(pointer_delta(high, low) <= N_words, "offset too large");
160 assert(_offset_array[index] == pointer_delta(high, low),
161 "Wrong offset");
162 }
163
164 bool is_card_boundary(HeapWord* p) const;
165
166 // Return the number of slots needed for an offset array
167 // that covers mem_region_words words.
168 // We always add an extra slot because if an object
169 // ends on a card boundary we put a 0 in the next
170 // offset array slot, so we want that slot always
171 // to be reserved.
172
173 size_t compute_size(size_t mem_region_words) {
174 size_t number_of_slots = (mem_region_words / N_words) + 1;
175 return ReservedSpace::allocation_align_size_up(number_of_slots);
176 }
177
178 public:
179 // Initialize the table to cover from "base" to (at least)
180 // "base + init_word_size". In the future, the table may be expanded
181 // (see "resize" below) up to the size of "_reserved" (which must be at
182 // least "init_word_size".) The contents of the initial table are
183 // undefined; it is the responsibility of the constituent
184 // BlockOffsetTable(s) to initialize cards.
185 BlockOffsetSharedArray(MemRegion reserved, size_t init_word_size);
186
187 // Notes a change in the committed size of the region covered by the
188 // table. The "new_word_size" may not be larger than the size of the
189 // reserved region this table covers.
190 void resize(size_t new_word_size);
191
192 void set_bottom(HeapWord* new_bottom);
193
194 // Updates all the BlockOffsetArray's sharing this shared array to
195 // reflect the current "top"'s of their spaces.
196 void update_offset_arrays(); // Not yet implemented!
197
198 // Return the appropriate index into "_offset_array" for "p".
199 size_t index_for(const void* p) const;
200
201 // Return the address indicating the start of the region corresponding to
202 // "index" in "_offset_array".
203 HeapWord* address_for_index(size_t index) const;
204
205 // Shared space support
206 void serialize(SerializeOopClosure* soc, HeapWord* start, HeapWord* end);
207 };
208
209 //////////////////////////////////////////////////////////////////////////
210 // The BlockOffsetArray whose subtypes use the BlockOffsetSharedArray.
211 //////////////////////////////////////////////////////////////////////////
212 class BlockOffsetArray: public BlockOffsetTable {
213 friend class VMStructs;
214 protected:
215 // The following enums are used by do_block_internal() below
216 enum Action {
217 Action_single, // BOT records a single block (see single_block())
218 Action_mark, // BOT marks the start of a block (see mark_block())
219 Action_check // Check that BOT records block correctly
220 // (see verify_single_block()).
221 };
222
223 enum SomePrivateConstants {
224 N_words = BlockOffsetSharedArray::N_words,
225 LogN = BlockOffsetSharedArray::LogN,
226 // entries "e" of at least N_words mean "go back by Base^(e-N_words)."
227 // All entries are less than "N_words + N_powers".
228 LogBase = 4,
229 Base = (1 << LogBase),
230 N_powers = 14
231 };
232
233 static size_t power_to_cards_back(uint i) {
234 return 1 << (LogBase * i);
235 }
236 static size_t power_to_words_back(uint i) {
237 return power_to_cards_back(i) * N_words;
238 }
239 static size_t entry_to_cards_back(u_char entry) {
240 assert(entry >= N_words, "Precondition");
241 return power_to_cards_back(entry - N_words);
242 }
243 static size_t entry_to_words_back(u_char entry) {
244 assert(entry >= N_words, "Precondition");
245 return power_to_words_back(entry - N_words);
246 }
247
248 // The shared array, which is shared with other BlockOffsetArray's
249 // corresponding to different spaces within a generation or span of
250 // memory.
251 BlockOffsetSharedArray* _array;
252
253 // The space that owns this subregion.
254 Space* _sp;
255
256 // If true, array entries are initialized to 0; otherwise, they are
257 // initialized to point backwards to the beginning of the covered region.
258 bool _init_to_zero;
259
260 // Sets the entries
261 // corresponding to the cards starting at "start" and ending at "end"
262 // to point back to the card before "start": the interval [start, end)
263 // is right-open.
264 void set_remainder_to_point_to_start(HeapWord* start, HeapWord* end);
265 // Same as above, except that the args here are a card _index_ interval
266 // that is closed: [start_index, end_index]
267 void set_remainder_to_point_to_start_incl(size_t start, size_t end);
268
269 // A helper function for BOT adjustment/verification work
270 void do_block_internal(HeapWord* blk_start, HeapWord* blk_end, Action action);
271
272 public:
273 // The space may not have its bottom and top set yet, which is why the
274 // region is passed as a parameter. If "init_to_zero" is true, the
275 // elements of the array are initialized to zero. Otherwise, they are
276 // initialized to point backwards to the beginning.
277 BlockOffsetArray(BlockOffsetSharedArray* array, MemRegion mr,
278 bool init_to_zero);
279
280 // Note: this ought to be part of the constructor, but that would require
281 // "this" to be passed as a parameter to a member constructor for
282 // the containing concrete subtype of Space.
283 // This would be legal C++, but MS VC++ doesn't allow it.
284 void set_space(Space* sp) { _sp = sp; }
285
286 // Resets the covered region to the given "mr".
287 void set_region(MemRegion mr) {
288 _bottom = mr.start();
289 _end = mr.end();
290 }
291
292 // Note that the committed size of the covered space may have changed,
293 // so the table size might also wish to change.
294 virtual void resize(size_t new_word_size) {
295 HeapWord* new_end = _bottom + new_word_size;
296 if (_end < new_end && !init_to_zero()) {
297 // verify that the old and new boundaries are also card boundaries
298 assert(_array->is_card_boundary(_end),
299 "_end not a card boundary");
300 assert(_array->is_card_boundary(new_end),
301 "new _end would not be a card boundary");
302 // set all the newly added cards
303 _array->set_offset_array(_end, new_end, N_words);
304 }
305 _end = new_end; // update _end
306 }
307
308 // Adjust the BOT to show that it has a single block in the
309 // range [blk_start, blk_start + size). All necessary BOT
310 // cards are adjusted, but _unallocated_block isn't.
311 void single_block(HeapWord* blk_start, HeapWord* blk_end);
312 void single_block(HeapWord* blk, size_t size) {
313 single_block(blk, blk + size);
314 }
315
316 // When the alloc_block() call returns, the block offset table should
317 // have enough information such that any subsequent block_start() call
318 // with an argument equal to an address that is within the range
319 // [blk_start, blk_end) would return the value blk_start, provided
320 // there have been no calls in between that reset this information
321 // (e.g. see BlockOffsetArrayNonContigSpace::single_block() call
322 // for an appropriate range covering the said interval).
323 // These methods expect to be called with [blk_start, blk_end)
324 // representing a block of memory in the heap.
325 virtual void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
326 void alloc_block(HeapWord* blk, size_t size) {
327 alloc_block(blk, blk + size);
328 }
329
330 // If true, initialize array slots with no allocated blocks to zero.
331 // Otherwise, make them point back to the front.
332 bool init_to_zero() { return _init_to_zero; }
333
334 // Debugging
335 // Return the index of the last entry in the "active" region.
336 virtual size_t last_active_index() const = 0;
337 // Verify the block offset table
338 void verify() const;
339 void check_all_cards(size_t left_card, size_t right_card) const;
340 };
341
342 ////////////////////////////////////////////////////////////////////////////
343 // A subtype of BlockOffsetArray that takes advantage of the fact
344 // that its underlying space is a NonContiguousSpace, so that some
345 // specialized interfaces can be made available for spaces that
346 // manipulate the table.
347 ////////////////////////////////////////////////////////////////////////////
348 class BlockOffsetArrayNonContigSpace: public BlockOffsetArray {
349 friend class VMStructs;
350 private:
351 // The portion [_unallocated_block, _sp.end()) of the space that
352 // is a single block known not to contain any objects.
353 // NOTE: See BlockOffsetArrayUseUnallocatedBlock flag.
354 HeapWord* _unallocated_block;
355
356 public:
357 BlockOffsetArrayNonContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
358 BlockOffsetArray(array, mr, false),
359 _unallocated_block(_bottom) { }
360
361 // accessor
362 HeapWord* unallocated_block() const {
363 assert(BlockOffsetArrayUseUnallocatedBlock,
364 "_unallocated_block is not being maintained");
365 return _unallocated_block;
366 }
367
368 void set_unallocated_block(HeapWord* block) {
369 assert(BlockOffsetArrayUseUnallocatedBlock,
370 "_unallocated_block is not being maintained");
371 assert(block >= _bottom && block <= _end, "out of range");
372 _unallocated_block = block;
373 }
374
375 // These methods expect to be called with [blk_start, blk_end)
376 // representing a block of memory in the heap.
377 void alloc_block(HeapWord* blk_start, HeapWord* blk_end);
378 void alloc_block(HeapWord* blk, size_t size) {
379 alloc_block(blk, blk + size);
380 }
381
382 // The following methods are useful and optimized for a
383 // non-contiguous space.
384
385 // Given a block [blk_start, blk_start + full_blk_size), and
386 // a left_blk_size < full_blk_size, adjust the BOT to show two
387 // blocks [blk_start, blk_start + left_blk_size) and
388 // [blk_start + left_blk_size, blk_start + full_blk_size).
389 // It is assumed (and verified in the non-product VM) that the
390 // BOT was correct for the original block.
391 void split_block(HeapWord* blk_start, size_t full_blk_size,
392 size_t left_blk_size);
393
394 // Adjust BOT to show that it has a block in the range
395 // [blk_start, blk_start + size). Only the first card
396 // of BOT is touched. It is assumed (and verified in the
397 // non-product VM) that the remaining cards of the block
398 // are correct.
399 void mark_block(HeapWord* blk_start, HeapWord* blk_end);
400 void mark_block(HeapWord* blk, size_t size) {
401 mark_block(blk, blk + size);
402 }
403
404 // Adjust _unallocated_block to indicate that a particular
405 // block has been newly allocated or freed. It is assumed (and
406 // verified in the non-product VM) that the BOT is correct for
407 // the given block.
408 void allocated(HeapWord* blk_start, HeapWord* blk_end) {
409 // Verify that the BOT shows [blk, blk + blk_size) to be one block.
410 verify_single_block(blk_start, blk_end);
411 if (BlockOffsetArrayUseUnallocatedBlock) {
412 _unallocated_block = MAX2(_unallocated_block, blk_end);
413 }
414 }
415
416 void allocated(HeapWord* blk, size_t size) {
417 allocated(blk, blk + size);
418 }
419
420 void freed(HeapWord* blk_start, HeapWord* blk_end);
421 void freed(HeapWord* blk, size_t size) {
422 freed(blk, blk + size);
423 }
424
425 HeapWord* block_start_unsafe(const void* addr) const;
426
427 // Requires "addr" to be the start of a card and returns the
428 // start of the block that contains the given address.
429 HeapWord* block_start_careful(const void* addr) const;
430
431
432 // Verification & debugging: ensure that the offset table reflects
433 // the fact that the block [blk_start, blk_end) or [blk, blk + size)
434 // is a single block of storage. NOTE: can't const this because of
435 // call to non-const do_block_internal() below.
436 void verify_single_block(HeapWord* blk_start, HeapWord* blk_end)
437 PRODUCT_RETURN;
438 void verify_single_block(HeapWord* blk, size_t size) PRODUCT_RETURN;
439
440 // Verify that the given block is before _unallocated_block
441 void verify_not_unallocated(HeapWord* blk_start, HeapWord* blk_end)
442 const PRODUCT_RETURN;
443 void verify_not_unallocated(HeapWord* blk, size_t size)
444 const PRODUCT_RETURN;
445
446 // Debugging support
447 virtual size_t last_active_index() const;
448 };
449
450 ////////////////////////////////////////////////////////////////////////////
451 // A subtype of BlockOffsetArray that takes advantage of the fact
452 // that its underlying space is a ContiguousSpace, so that its "active"
453 // region can be more efficiently tracked (than for a non-contiguous space).
454 ////////////////////////////////////////////////////////////////////////////
455 class BlockOffsetArrayContigSpace: public BlockOffsetArray {
456 friend class VMStructs;
457 private:
458 // allocation boundary at which offset array must be updated
459 HeapWord* _next_offset_threshold;
460 size_t _next_offset_index; // index corresponding to that boundary
461
462 // Work function when allocation start crosses threshold.
463 void alloc_block_work(HeapWord* blk_start, HeapWord* blk_end);
464
465 public:
466 BlockOffsetArrayContigSpace(BlockOffsetSharedArray* array, MemRegion mr):
467 BlockOffsetArray(array, mr, true) {
468 _next_offset_threshold = NULL;
469 _next_offset_index = 0;
470 }
471
472 void set_contig_space(ContiguousSpace* sp) { set_space((Space*)sp); }
473
474 // Initialize the threshold for an empty heap.
475 HeapWord* initialize_threshold();
476 // Zero out the entry for _bottom (offset will be zero)
477 void zero_bottom_entry();
478
479 // Return the next threshold, the point at which the table should be
480 // updated.
481 HeapWord* threshold() const { return _next_offset_threshold; }
482
483 // In general, these methods expect to be called with
484 // [blk_start, blk_end) representing a block of memory in the heap.
485 // In this implementation, however, we are OK even if blk_start and/or
486 // blk_end are NULL because NULL is represented as 0, and thus
487 // never exceeds the "_next_offset_threshold".
488 void alloc_block(HeapWord* blk_start, HeapWord* blk_end) {
489 if (blk_end > _next_offset_threshold) {
490 alloc_block_work(blk_start, blk_end);
491 }
492 }
493 void alloc_block(HeapWord* blk, size_t size) {
494 alloc_block(blk, blk + size);
495 }
496
497 HeapWord* block_start_unsafe(const void* addr) const;
498
499 void serialize(SerializeOopClosure* soc);
500
501 // Debugging support
502 virtual size_t last_active_index() const;
503 };