Sat, 23 Nov 2013 12:25:13 +0100
8028128: Add a type safe alternative for working with counter based data
Reviewed-by: dholmes, egahlin
1 /*
2 * Copyright (c) 2001, 2012, 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
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
25 #include "precompiled.hpp"
26 #include "classfile/systemDictionary.hpp"
27 #include "gc_implementation/parallelScavenge/objectStartArray.hpp"
28 #include "gc_implementation/parallelScavenge/parallelScavengeHeap.hpp"
29 #include "gc_implementation/parallelScavenge/psMarkSweep.hpp"
30 #include "gc_implementation/parallelScavenge/psMarkSweepDecorator.hpp"
31 #include "gc_implementation/shared/liveRange.hpp"
32 #include "gc_implementation/shared/markSweep.inline.hpp"
33 #include "gc_implementation/shared/spaceDecorator.hpp"
34 #include "oops/oop.inline.hpp"
36 PSMarkSweepDecorator* PSMarkSweepDecorator::_destination_decorator = NULL;
39 void PSMarkSweepDecorator::set_destination_decorator_tenured() {
40 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
41 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
43 _destination_decorator = heap->old_gen()->object_mark_sweep();
44 }
46 void PSMarkSweepDecorator::advance_destination_decorator() {
47 ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
48 assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");
50 assert(_destination_decorator != NULL, "Sanity");
52 PSMarkSweepDecorator* first = heap->old_gen()->object_mark_sweep();
53 PSMarkSweepDecorator* second = heap->young_gen()->eden_mark_sweep();
54 PSMarkSweepDecorator* third = heap->young_gen()->from_mark_sweep();
55 PSMarkSweepDecorator* fourth = heap->young_gen()->to_mark_sweep();
57 if ( _destination_decorator == first ) {
58 _destination_decorator = second;
59 } else if ( _destination_decorator == second ) {
60 _destination_decorator = third;
61 } else if ( _destination_decorator == third ) {
62 _destination_decorator = fourth;
63 } else {
64 fatal("PSMarkSweep attempting to advance past last compaction area");
65 }
66 }
68 PSMarkSweepDecorator* PSMarkSweepDecorator::destination_decorator() {
69 assert(_destination_decorator != NULL, "Sanity");
71 return _destination_decorator;
72 }
74 // FIX ME FIX ME FIX ME FIX ME!!!!!!!!!
75 // The object forwarding code is duplicated. Factor this out!!!!!
76 //
77 // This method "precompacts" objects inside its space to dest. It places forwarding
78 // pointers into markOops for use by adjust_pointers. If "dest" should overflow, we
79 // finish by compacting into our own space.
81 void PSMarkSweepDecorator::precompact() {
82 // Reset our own compact top.
83 set_compaction_top(space()->bottom());
85 /* We allow some amount of garbage towards the bottom of the space, so
86 * we don't start compacting before there is a significant gain to be made.
87 * Occasionally, we want to ensure a full compaction, which is determined
88 * by the MarkSweepAlwaysCompactCount parameter. This is a significant
89 * performance improvement!
90 */
91 bool skip_dead = ((PSMarkSweep::total_invocations() % MarkSweepAlwaysCompactCount) != 0);
93 size_t allowed_deadspace = 0;
94 if (skip_dead) {
95 const size_t ratio = allowed_dead_ratio();
96 allowed_deadspace = space()->capacity_in_words() * ratio / 100;
97 }
99 // Fetch the current destination decorator
100 PSMarkSweepDecorator* dest = destination_decorator();
101 ObjectStartArray* start_array = dest->start_array();
103 HeapWord* compact_top = dest->compaction_top();
104 HeapWord* compact_end = dest->space()->end();
106 HeapWord* q = space()->bottom();
107 HeapWord* t = space()->top();
109 HeapWord* end_of_live= q; /* One byte beyond the last byte of the last
110 live object. */
111 HeapWord* first_dead = space()->end(); /* The first dead object. */
112 LiveRange* liveRange = NULL; /* The current live range, recorded in the
113 first header of preceding free area. */
114 _first_dead = first_dead;
116 const intx interval = PrefetchScanIntervalInBytes;
118 while (q < t) {
119 assert(oop(q)->mark()->is_marked() || oop(q)->mark()->is_unlocked() ||
120 oop(q)->mark()->has_bias_pattern(),
121 "these are the only valid states during a mark sweep");
122 if (oop(q)->is_gc_marked()) {
123 /* prefetch beyond q */
124 Prefetch::write(q, interval);
125 size_t size = oop(q)->size();
127 size_t compaction_max_size = pointer_delta(compact_end, compact_top);
129 // This should only happen if a space in the young gen overflows the
130 // old gen. If that should happen, we null out the start_array, because
131 // the young spaces are not covered by one.
132 while(size > compaction_max_size) {
133 // First record the last compact_top
134 dest->set_compaction_top(compact_top);
136 // Advance to the next compaction decorator
137 advance_destination_decorator();
138 dest = destination_decorator();
140 // Update compaction info
141 start_array = dest->start_array();
142 compact_top = dest->compaction_top();
143 compact_end = dest->space()->end();
144 assert(compact_top == dest->space()->bottom(), "Advanced to space already in use");
145 assert(compact_end > compact_top, "Must always be space remaining");
146 compaction_max_size =
147 pointer_delta(compact_end, compact_top);
148 }
150 // store the forwarding pointer into the mark word
151 if (q != compact_top) {
152 oop(q)->forward_to(oop(compact_top));
153 assert(oop(q)->is_gc_marked(), "encoding the pointer should preserve the mark");
154 } else {
155 // if the object isn't moving we can just set the mark to the default
156 // mark and handle it specially later on.
157 oop(q)->init_mark();
158 assert(oop(q)->forwardee() == NULL, "should be forwarded to NULL");
159 }
161 // Update object start array
162 if (start_array) {
163 start_array->allocate_block(compact_top);
164 }
166 compact_top += size;
167 assert(compact_top <= dest->space()->end(),
168 "Exceeding space in destination");
170 q += size;
171 end_of_live = q;
172 } else {
173 /* run over all the contiguous dead objects */
174 HeapWord* end = q;
175 do {
176 /* prefetch beyond end */
177 Prefetch::write(end, interval);
178 end += oop(end)->size();
179 } while (end < t && (!oop(end)->is_gc_marked()));
181 /* see if we might want to pretend this object is alive so that
182 * we don't have to compact quite as often.
183 */
184 if (allowed_deadspace > 0 && q == compact_top) {
185 size_t sz = pointer_delta(end, q);
186 if (insert_deadspace(allowed_deadspace, q, sz)) {
187 size_t compaction_max_size = pointer_delta(compact_end, compact_top);
189 // This should only happen if a space in the young gen overflows the
190 // old gen. If that should happen, we null out the start_array, because
191 // the young spaces are not covered by one.
192 while (sz > compaction_max_size) {
193 // First record the last compact_top
194 dest->set_compaction_top(compact_top);
196 // Advance to the next compaction decorator
197 advance_destination_decorator();
198 dest = destination_decorator();
200 // Update compaction info
201 start_array = dest->start_array();
202 compact_top = dest->compaction_top();
203 compact_end = dest->space()->end();
204 assert(compact_top == dest->space()->bottom(), "Advanced to space already in use");
205 assert(compact_end > compact_top, "Must always be space remaining");
206 compaction_max_size =
207 pointer_delta(compact_end, compact_top);
208 }
210 // store the forwarding pointer into the mark word
211 if (q != compact_top) {
212 oop(q)->forward_to(oop(compact_top));
213 assert(oop(q)->is_gc_marked(), "encoding the pointer should preserve the mark");
214 } else {
215 // if the object isn't moving we can just set the mark to the default
216 // mark and handle it specially later on.
217 oop(q)->init_mark();
218 assert(oop(q)->forwardee() == NULL, "should be forwarded to NULL");
219 }
221 // Update object start array
222 if (start_array) {
223 start_array->allocate_block(compact_top);
224 }
226 compact_top += sz;
227 assert(compact_top <= dest->space()->end(),
228 "Exceeding space in destination");
230 q = end;
231 end_of_live = end;
232 continue;
233 }
234 }
236 /* for the previous LiveRange, record the end of the live objects. */
237 if (liveRange) {
238 liveRange->set_end(q);
239 }
241 /* record the current LiveRange object.
242 * liveRange->start() is overlaid on the mark word.
243 */
244 liveRange = (LiveRange*)q;
245 liveRange->set_start(end);
246 liveRange->set_end(end);
248 /* see if this is the first dead region. */
249 if (q < first_dead) {
250 first_dead = q;
251 }
253 /* move on to the next object */
254 q = end;
255 }
256 }
258 assert(q == t, "just checking");
259 if (liveRange != NULL) {
260 liveRange->set_end(q);
261 }
262 _end_of_live = end_of_live;
263 if (end_of_live < first_dead) {
264 first_dead = end_of_live;
265 }
266 _first_dead = first_dead;
268 // Update compaction top
269 dest->set_compaction_top(compact_top);
270 }
272 bool PSMarkSweepDecorator::insert_deadspace(size_t& allowed_deadspace_words,
273 HeapWord* q, size_t deadlength) {
274 if (allowed_deadspace_words >= deadlength) {
275 allowed_deadspace_words -= deadlength;
276 CollectedHeap::fill_with_object(q, deadlength);
277 oop(q)->set_mark(oop(q)->mark()->set_marked());
278 assert((int) deadlength == oop(q)->size(), "bad filler object size");
279 // Recall that we required "q == compaction_top".
280 return true;
281 } else {
282 allowed_deadspace_words = 0;
283 return false;
284 }
285 }
287 void PSMarkSweepDecorator::adjust_pointers() {
288 // adjust all the interior pointers to point at the new locations of objects
289 // Used by MarkSweep::mark_sweep_phase3()
291 HeapWord* q = space()->bottom();
292 HeapWord* t = _end_of_live; // Established by "prepare_for_compaction".
294 assert(_first_dead <= _end_of_live, "Stands to reason, no?");
296 if (q < t && _first_dead > q &&
297 !oop(q)->is_gc_marked()) {
298 // we have a chunk of the space which hasn't moved and we've
299 // reinitialized the mark word during the previous pass, so we can't
300 // use is_gc_marked for the traversal.
301 HeapWord* end = _first_dead;
303 while (q < end) {
304 // point all the oops to the new location
305 size_t size = oop(q)->adjust_pointers();
306 q += size;
307 }
309 if (_first_dead == t) {
310 q = t;
311 } else {
312 // $$$ This is funky. Using this to read the previously written
313 // LiveRange. See also use below.
314 q = (HeapWord*)oop(_first_dead)->mark()->decode_pointer();
315 }
316 }
317 const intx interval = PrefetchScanIntervalInBytes;
319 debug_only(HeapWord* prev_q = NULL);
320 while (q < t) {
321 // prefetch beyond q
322 Prefetch::write(q, interval);
323 if (oop(q)->is_gc_marked()) {
324 // q is alive
325 // point all the oops to the new location
326 size_t size = oop(q)->adjust_pointers();
327 debug_only(prev_q = q);
328 q += size;
329 } else {
330 // q is not a live object, so its mark should point at the next
331 // live object
332 debug_only(prev_q = q);
333 q = (HeapWord*) oop(q)->mark()->decode_pointer();
334 assert(q > prev_q, "we should be moving forward through memory");
335 }
336 }
338 assert(q == t, "just checking");
339 }
341 void PSMarkSweepDecorator::compact(bool mangle_free_space ) {
342 // Copy all live objects to their new location
343 // Used by MarkSweep::mark_sweep_phase4()
345 HeapWord* q = space()->bottom();
346 HeapWord* const t = _end_of_live;
347 debug_only(HeapWord* prev_q = NULL);
349 if (q < t && _first_dead > q &&
350 !oop(q)->is_gc_marked()) {
351 #ifdef ASSERT
352 // we have a chunk of the space which hasn't moved and we've reinitialized the
353 // mark word during the previous pass, so we can't use is_gc_marked for the
354 // traversal.
355 HeapWord* const end = _first_dead;
357 while (q < end) {
358 size_t size = oop(q)->size();
359 assert(!oop(q)->is_gc_marked(), "should be unmarked (special dense prefix handling)");
360 debug_only(prev_q = q);
361 q += size;
362 }
363 #endif
365 if (_first_dead == t) {
366 q = t;
367 } else {
368 // $$$ Funky
369 q = (HeapWord*) oop(_first_dead)->mark()->decode_pointer();
370 }
371 }
373 const intx scan_interval = PrefetchScanIntervalInBytes;
374 const intx copy_interval = PrefetchCopyIntervalInBytes;
376 while (q < t) {
377 if (!oop(q)->is_gc_marked()) {
378 // mark is pointer to next marked oop
379 debug_only(prev_q = q);
380 q = (HeapWord*) oop(q)->mark()->decode_pointer();
381 assert(q > prev_q, "we should be moving forward through memory");
382 } else {
383 // prefetch beyond q
384 Prefetch::read(q, scan_interval);
386 // size and destination
387 size_t size = oop(q)->size();
388 HeapWord* compaction_top = (HeapWord*)oop(q)->forwardee();
390 // prefetch beyond compaction_top
391 Prefetch::write(compaction_top, copy_interval);
393 // copy object and reinit its mark
394 assert(q != compaction_top, "everything in this pass should be moving");
395 Copy::aligned_conjoint_words(q, compaction_top, size);
396 oop(compaction_top)->init_mark();
397 assert(oop(compaction_top)->klass() != NULL, "should have a class");
399 debug_only(prev_q = q);
400 q += size;
401 }
402 }
404 assert(compaction_top() >= space()->bottom() && compaction_top() <= space()->end(),
405 "should point inside space");
406 space()->set_top(compaction_top());
408 if (mangle_free_space) {
409 space()->mangle_unused_area();
410 }
411 }