1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_VM_GC_SHARED_SPACE_INLINE_HPP
26 #define SHARE_VM_GC_SHARED_SPACE_INLINE_HPP
27
28 #include "gc/serial/markSweep.inline.hpp"
29 #include "gc/shared/collectedHeap.hpp"
30 #include "gc/shared/generation.hpp"
31 #include "gc/shared/liveRange.hpp"
32 #include "gc/shared/space.hpp"
33 #include "gc/shared/spaceDecorator.hpp"
34 #include "memory/universe.hpp"
35 #include "runtime/prefetch.inline.hpp"
36 #include "runtime/safepoint.hpp"
37
38 inline HeapWord* Space::block_start(const void* p) {
39 return block_start_const(p);
40 }
41
42 inline HeapWord* OffsetTableContigSpace::allocate(size_t size) {
43 HeapWord* res = ContiguousSpace::allocate(size);
44 if (res != NULL) {
45 _offsets.alloc_block(res, size);
46 }
47 return res;
48 }
49
50 // Because of the requirement of keeping "_offsets" up to date with the
51 // allocations, we sequentialize these with a lock. Therefore, best if
52 // this is used for larger LAB allocations only.
53 inline HeapWord* OffsetTableContigSpace::par_allocate(size_t size) {
54 MutexLocker x(&_par_alloc_lock);
55 // This ought to be just "allocate", because of the lock above, but that
56 // ContiguousSpace::allocate asserts that either the allocating thread
57 // holds the heap lock or it is the VM thread and we're at a safepoint.
58 // The best I (dld) could figure was to put a field in ContiguousSpace
59 // meaning "locking at safepoint taken care of", and set/reset that
60 // here. But this will do for now, especially in light of the comment
61 // above. Perhaps in the future some lock-free manner of keeping the
62 // coordination.
63 HeapWord* res = ContiguousSpace::par_allocate(size);
64 if (res != NULL) {
65 _offsets.alloc_block(res, size);
66 }
67 return res;
68 }
69
70 inline HeapWord*
71 OffsetTableContigSpace::block_start_const(const void* p) const {
72 return _offsets.block_start(p);
73 }
74
75 size_t CompactibleSpace::obj_size(const HeapWord* addr) const {
76 return oop(addr)->size();
77 }
78
79 template <class SpaceType>
80 inline void CompactibleSpace::scan_and_forward(SpaceType* space, CompactPoint* cp) {
81 // Compute the new addresses for the live objects and store it in the mark
82 // Used by universe::mark_sweep_phase2()
83 HeapWord* compact_top; // This is where we are currently compacting to.
84
85 // We're sure to be here before any objects are compacted into this
86 // space, so this is a good time to initialize this:
87 space->set_compaction_top(space->bottom());
88
89 if (cp->space == NULL) {
90 assert(cp->gen != NULL, "need a generation");
91 assert(cp->threshold == NULL, "just checking");
92 assert(cp->gen->first_compaction_space() == space, "just checking");
93 cp->space = cp->gen->first_compaction_space();
94 compact_top = cp->space->bottom();
95 cp->space->set_compaction_top(compact_top);
96 cp->threshold = cp->space->initialize_threshold();
97 } else {
98 compact_top = cp->space->compaction_top();
99 }
100
101 // We allow some amount of garbage towards the bottom of the space, so
102 // we don't start compacting before there is a significant gain to be made.
103 // Occasionally, we want to ensure a full compaction, which is determined
104 // by the MarkSweepAlwaysCompactCount parameter.
105 uint invocations = MarkSweep::total_invocations();
106 bool skip_dead = ((invocations % MarkSweepAlwaysCompactCount) != 0);
107
108 size_t allowed_deadspace = 0;
109 if (skip_dead) {
110 const size_t ratio = space->allowed_dead_ratio();
111 allowed_deadspace = (space->capacity() * ratio / 100) / HeapWordSize;
112 }
113
114 HeapWord* q = space->bottom();
115 HeapWord* t = space->scan_limit();
116
117 HeapWord* end_of_live= q; // One byte beyond the last byte of the last
118 // live object.
119 HeapWord* first_dead = space->end(); // The first dead object.
120 LiveRange* liveRange = NULL; // The current live range, recorded in the
121 // first header of preceding free area.
122 space->_first_dead = first_dead;
123
124 const intx interval = PrefetchScanIntervalInBytes;
125
126 while (q < t) {
127 assert(!space->scanned_block_is_obj(q) ||
128 oop(q)->mark()->is_marked() || oop(q)->mark()->is_unlocked() ||
129 oop(q)->mark()->has_bias_pattern(),
130 "these are the only valid states during a mark sweep");
131 if (space->scanned_block_is_obj(q) && oop(q)->is_gc_marked()) {
132 // prefetch beyond q
133 Prefetch::write(q, interval);
134 size_t size = space->scanned_block_size(q);
135 compact_top = cp->space->forward(oop(q), size, cp, compact_top);
136 q += size;
137 end_of_live = q;
138 } else {
139 // run over all the contiguous dead objects
140 HeapWord* end = q;
141 do {
142 // prefetch beyond end
143 Prefetch::write(end, interval);
144 end += space->scanned_block_size(end);
145 } while (end < t && (!space->scanned_block_is_obj(end) || !oop(end)->is_gc_marked()));
146
147 // see if we might want to pretend this object is alive so that
148 // we don't have to compact quite as often.
149 if (allowed_deadspace > 0 && q == compact_top) {
150 size_t sz = pointer_delta(end, q);
151 if (space->insert_deadspace(allowed_deadspace, q, sz)) {
152 compact_top = cp->space->forward(oop(q), sz, cp, compact_top);
153 q = end;
154 end_of_live = end;
155 continue;
156 }
157 }
158
159 // otherwise, it really is a free region.
160
161 // for the previous LiveRange, record the end of the live objects.
162 if (liveRange) {
163 liveRange->set_end(q);
164 }
165
166 // record the current LiveRange object.
167 // liveRange->start() is overlaid on the mark word.
168 liveRange = (LiveRange*)q;
169 liveRange->set_start(end);
170 liveRange->set_end(end);
171
172 // see if this is the first dead region.
173 if (q < first_dead) {
174 first_dead = q;
175 }
176
177 // move on to the next object
178 q = end;
179 }
180 }
181
182 assert(q == t, "just checking");
183 if (liveRange != NULL) {
184 liveRange->set_end(q);
185 }
186 space->_end_of_live = end_of_live;
187 if (end_of_live < first_dead) {
188 first_dead = end_of_live;
189 }
190 space->_first_dead = first_dead;
191
192 // save the compaction_top of the compaction space.
193 cp->space->set_compaction_top(compact_top);
194 }
195
196 template <class SpaceType>
197 inline void CompactibleSpace::scan_and_adjust_pointers(SpaceType* space) {
198 // adjust all the interior pointers to point at the new locations of objects
199 // Used by MarkSweep::mark_sweep_phase3()
200
201 HeapWord* q = space->bottom();
202 HeapWord* t = space->_end_of_live; // Established by "prepare_for_compaction".
203
204 assert(space->_first_dead <= space->_end_of_live, "Stands to reason, no?");
205
206 if (q < t && space->_first_dead > q && !oop(q)->is_gc_marked()) {
207 // we have a chunk of the space which hasn't moved and we've
208 // reinitialized the mark word during the previous pass, so we can't
209 // use is_gc_marked for the traversal.
210 HeapWord* end = space->_first_dead;
211
212 while (q < end) {
213 // I originally tried to conjoin "block_start(q) == q" to the
214 // assertion below, but that doesn't work, because you can't
215 // accurately traverse previous objects to get to the current one
216 // after their pointers have been
217 // updated, until the actual compaction is done. dld, 4/00
218 assert(space->block_is_obj(q), "should be at block boundaries, and should be looking at objs");
219
220 // point all the oops to the new location
221 size_t size = MarkSweep::adjust_pointers(oop(q));
222 size = space->adjust_obj_size(size);
223
224 q += size;
225 }
226
227 if (space->_first_dead == t) {
228 q = t;
229 } else {
230 // $$$ This is funky. Using this to read the previously written
231 // LiveRange. See also use below.
232 q = (HeapWord*)oop(space->_first_dead)->mark()->decode_pointer();
233 }
234 }
235
236 const intx interval = PrefetchScanIntervalInBytes;
237
238 debug_only(HeapWord* prev_q = NULL);
239 while (q < t) {
240 // prefetch beyond q
241 Prefetch::write(q, interval);
242 if (oop(q)->is_gc_marked()) {
243 // q is alive
244 // point all the oops to the new location
245 size_t size = MarkSweep::adjust_pointers(oop(q));
246 size = space->adjust_obj_size(size);
247 debug_only(prev_q = q);
248 q += size;
249 } else {
250 // q is not a live object, so its mark should point at the next
251 // live object
252 debug_only(prev_q = q);
253 q = (HeapWord*) oop(q)->mark()->decode_pointer();
254 assert(q > prev_q, "we should be moving forward through memory");
255 }
256 }
257
258 assert(q == t, "just checking");
259 }
260
261 template <class SpaceType>
262 inline void CompactibleSpace::scan_and_compact(SpaceType* space) {
263 // Copy all live objects to their new location
264 // Used by MarkSweep::mark_sweep_phase4()
265
266 HeapWord* q = space->bottom();
267 HeapWord* const t = space->_end_of_live;
268 debug_only(HeapWord* prev_q = NULL);
269
270 if (q < t && space->_first_dead > q && !oop(q)->is_gc_marked()) {
271 #ifdef ASSERT // Debug only
272 // we have a chunk of the space which hasn't moved and we've reinitialized
273 // the mark word during the previous pass, so we can't use is_gc_marked for
274 // the traversal.
275 HeapWord* const end = space->_first_dead;
276
277 while (q < end) {
278 size_t size = space->obj_size(q);
279 assert(!oop(q)->is_gc_marked(), "should be unmarked (special dense prefix handling)");
280 prev_q = q;
281 q += size;
282 }
283 #endif
284
285 if (space->_first_dead == t) {
286 q = t;
287 } else {
288 // $$$ Funky
289 q = (HeapWord*) oop(space->_first_dead)->mark()->decode_pointer();
290 }
291 }
292
293 const intx scan_interval = PrefetchScanIntervalInBytes;
294 const intx copy_interval = PrefetchCopyIntervalInBytes;
295 while (q < t) {
296 if (!oop(q)->is_gc_marked()) {
297 // mark is pointer to next marked oop
298 debug_only(prev_q = q);
299 q = (HeapWord*) oop(q)->mark()->decode_pointer();
300 assert(q > prev_q, "we should be moving forward through memory");
301 } else {
302 // prefetch beyond q
303 Prefetch::read(q, scan_interval);
304
305 // size and destination
306 size_t size = space->obj_size(q);
307 HeapWord* compaction_top = (HeapWord*)oop(q)->forwardee();
308
309 // prefetch beyond compaction_top
310 Prefetch::write(compaction_top, copy_interval);
311
312 // copy object and reinit its mark
313 assert(q != compaction_top, "everything in this pass should be moving");
314 Copy::aligned_conjoint_words(q, compaction_top, size);
315 oop(compaction_top)->init_mark();
316 assert(oop(compaction_top)->klass() != NULL, "should have a class");
317
318 debug_only(prev_q = q);
319 q += size;
320 }
321 }
322
323 // Let's remember if we were empty before we did the compaction.
324 bool was_empty = space->used_region().is_empty();
325 // Reset space after compaction is complete
326 space->reset_after_compaction();
327 // We do this clear, below, since it has overloaded meanings for some
328 // space subtypes. For example, OffsetTableContigSpace's that were
329 // compacted into will have had their offset table thresholds updated
330 // continuously, but those that weren't need to have their thresholds
331 // re-initialized. Also mangles unused area for debugging.
332 if (space->used_region().is_empty()) {
333 if (!was_empty) space->clear(SpaceDecorator::Mangle);
334 } else {
335 if (ZapUnusedHeapArea) space->mangle_unused_area();
336 }
337 }
338
339 size_t ContiguousSpace::scanned_block_size(const HeapWord* addr) const {
340 return oop(addr)->size();
341 }
342
343 #endif // SHARE_VM_GC_SHARED_SPACE_INLINE_HPP