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