1 /*
2 * Copyright (c) 2001, 2010, 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 */
24
25 #include "incls/_precompiled.incl"
26 #include "incls/_g1MarkSweep.cpp.incl"
27
28 class HeapRegion;
29
30 void G1MarkSweep::invoke_at_safepoint(ReferenceProcessor* rp,
31 bool clear_all_softrefs) {
32 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
33
34 SharedHeap* sh = SharedHeap::heap();
35 #ifdef ASSERT
36 if (sh->collector_policy()->should_clear_all_soft_refs()) {
37 assert(clear_all_softrefs, "Policy should have been checked earler");
38 }
39 #endif
40 // hook up weak ref data so it can be used during Mark-Sweep
41 assert(GenMarkSweep::ref_processor() == NULL, "no stomping");
42 assert(rp != NULL, "should be non-NULL");
43 GenMarkSweep::_ref_processor = rp;
44 rp->setup_policy(clear_all_softrefs);
45
46 // When collecting the permanent generation methodOops may be moving,
47 // so we either have to flush all bcp data or convert it into bci.
48 CodeCache::gc_prologue();
49 Threads::gc_prologue();
50
51 // Increment the invocation count for the permanent generation, since it is
52 // implicitly collected whenever we do a full mark sweep collection.
53 sh->perm_gen()->stat_record()->invocations++;
54
55 bool marked_for_unloading = false;
56
57 allocate_stacks();
58
59 // We should save the marks of the currently locked biased monitors.
60 // The marking doesn't preserve the marks of biased objects.
61 BiasedLocking::preserve_marks();
62
63 mark_sweep_phase1(marked_for_unloading, clear_all_softrefs);
64
65 if (VerifyDuringGC) {
66 G1CollectedHeap* g1h = G1CollectedHeap::heap();
67 g1h->checkConcurrentMark();
68 }
69
70 mark_sweep_phase2();
71
72 // Don't add any more derived pointers during phase3
73 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
74
75 mark_sweep_phase3();
76
77 mark_sweep_phase4();
78
79 GenMarkSweep::restore_marks();
80 BiasedLocking::restore_marks();
81 GenMarkSweep::deallocate_stacks();
82
83 // We must invalidate the perm-gen rs, so that it gets rebuilt.
84 GenRemSet* rs = sh->rem_set();
85 rs->invalidate(sh->perm_gen()->used_region(), true /*whole_heap*/);
86
87 // "free at last gc" is calculated from these.
88 // CHF: cheating for now!!!
89 // Universe::set_heap_capacity_at_last_gc(Universe::heap()->capacity());
90 // Universe::set_heap_used_at_last_gc(Universe::heap()->used());
91
92 Threads::gc_epilogue();
93 CodeCache::gc_epilogue();
94
95 // refs processing: clean slate
96 GenMarkSweep::_ref_processor = NULL;
97 }
98
99
100 void G1MarkSweep::allocate_stacks() {
101 GenMarkSweep::_preserved_count_max = 0;
102 GenMarkSweep::_preserved_marks = NULL;
103 GenMarkSweep::_preserved_count = 0;
104 }
105
106 void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
107 bool clear_all_softrefs) {
108 // Recursively traverse all live objects and mark them
109 EventMark m("1 mark object");
110 TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
111 GenMarkSweep::trace(" 1");
112
113 SharedHeap* sh = SharedHeap::heap();
114
115 sh->process_strong_roots(true, // activeate StrongRootsScope
116 true, // Collecting permanent generation.
117 SharedHeap::SO_SystemClasses,
118 &GenMarkSweep::follow_root_closure,
119 &GenMarkSweep::follow_code_root_closure,
120 &GenMarkSweep::follow_root_closure);
121
122 // Process reference objects found during marking
123 ReferenceProcessor* rp = GenMarkSweep::ref_processor();
124 rp->setup_policy(clear_all_softrefs);
125 rp->process_discovered_references(&GenMarkSweep::is_alive,
126 &GenMarkSweep::keep_alive,
127 &GenMarkSweep::follow_stack_closure,
128 NULL);
129
130 // Follow system dictionary roots and unload classes
131 bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
132 assert(GenMarkSweep::_marking_stack.is_empty(),
133 "stack should be empty by now");
134
135 // Follow code cache roots (has to be done after system dictionary,
136 // assumes all live klasses are marked)
137 CodeCache::do_unloading(&GenMarkSweep::is_alive,
138 &GenMarkSweep::keep_alive,
139 purged_class);
140 GenMarkSweep::follow_stack();
141
142 // Update subklass/sibling/implementor links of live klasses
143 GenMarkSweep::follow_weak_klass_links();
144 assert(GenMarkSweep::_marking_stack.is_empty(),
145 "stack should be empty by now");
146
147 // Visit memoized MDO's and clear any unmarked weak refs
148 GenMarkSweep::follow_mdo_weak_refs();
149 assert(GenMarkSweep::_marking_stack.is_empty(), "just drained");
150
151
152 // Visit symbol and interned string tables and delete unmarked oops
153 SymbolTable::unlink(&GenMarkSweep::is_alive);
154 StringTable::unlink(&GenMarkSweep::is_alive);
155
156 assert(GenMarkSweep::_marking_stack.is_empty(),
157 "stack should be empty by now");
158 }
159
160 class G1PrepareCompactClosure: public HeapRegionClosure {
161 ModRefBarrierSet* _mrbs;
162 CompactPoint _cp;
163
164 void free_humongous_region(HeapRegion* hr) {
165 HeapWord* bot = hr->bottom();
166 HeapWord* end = hr->end();
167 assert(hr->startsHumongous(),
168 "Only the start of a humongous region should be freed.");
169 G1CollectedHeap::heap()->free_region(hr);
170 hr->prepare_for_compaction(&_cp);
171 // Also clear the part of the card table that will be unused after
172 // compaction.
173 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
174 }
175
176 public:
177 G1PrepareCompactClosure(CompactibleSpace* cs) :
178 _cp(NULL, cs, cs->initialize_threshold()),
179 _mrbs(G1CollectedHeap::heap()->mr_bs())
180 {}
181 bool doHeapRegion(HeapRegion* hr) {
182 if (hr->isHumongous()) {
183 if (hr->startsHumongous()) {
184 oop obj = oop(hr->bottom());
185 if (obj->is_gc_marked()) {
186 obj->forward_to(obj);
187 } else {
188 free_humongous_region(hr);
189 }
190 } else {
191 assert(hr->continuesHumongous(), "Invalid humongous.");
192 }
193 } else {
194 hr->prepare_for_compaction(&_cp);
195 // Also clear the part of the card table that will be unused after
196 // compaction.
197 _mrbs->clear(MemRegion(hr->compaction_top(), hr->end()));
198 }
199 return false;
200 }
201 };
202
203 // Finds the first HeapRegion.
204 class FindFirstRegionClosure: public HeapRegionClosure {
205 HeapRegion* _a_region;
206 public:
207 FindFirstRegionClosure() : _a_region(NULL) {}
208 bool doHeapRegion(HeapRegion* r) {
209 _a_region = r;
210 return true;
211 }
212 HeapRegion* result() { return _a_region; }
213 };
214
215 void G1MarkSweep::mark_sweep_phase2() {
216 // Now all live objects are marked, compute the new object addresses.
217
218 // It is imperative that we traverse perm_gen LAST. If dead space is
219 // allowed a range of dead object may get overwritten by a dead int
220 // array. If perm_gen is not traversed last a klassOop may get
221 // overwritten. This is fine since it is dead, but if the class has dead
222 // instances we have to skip them, and in order to find their size we
223 // need the klassOop!
224 //
225 // It is not required that we traverse spaces in the same order in
226 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
227 // tracking expects us to do so. See comment under phase4.
228
229 G1CollectedHeap* g1h = G1CollectedHeap::heap();
230 Generation* pg = g1h->perm_gen();
231
232 EventMark m("2 compute new addresses");
233 TraceTime tm("phase 2", PrintGC && Verbose, true, gclog_or_tty);
234 GenMarkSweep::trace("2");
235
236 FindFirstRegionClosure cl;
237 g1h->heap_region_iterate(&cl);
238 HeapRegion *r = cl.result();
239 CompactibleSpace* sp = r;
240 if (r->isHumongous() && oop(r->bottom())->is_gc_marked()) {
241 sp = r->next_compaction_space();
242 }
243
244 G1PrepareCompactClosure blk(sp);
245 g1h->heap_region_iterate(&blk);
246
247 CompactPoint perm_cp(pg, NULL, NULL);
248 pg->prepare_for_compaction(&perm_cp);
249 }
250
251 class G1AdjustPointersClosure: public HeapRegionClosure {
252 public:
253 bool doHeapRegion(HeapRegion* r) {
254 if (r->isHumongous()) {
255 if (r->startsHumongous()) {
256 // We must adjust the pointers on the single H object.
257 oop obj = oop(r->bottom());
258 debug_only(GenMarkSweep::track_interior_pointers(obj));
259 // point all the oops to the new location
260 obj->adjust_pointers();
261 debug_only(GenMarkSweep::check_interior_pointers());
262 }
263 } else {
264 // This really ought to be "as_CompactibleSpace"...
265 r->adjust_pointers();
266 }
267 return false;
268 }
269 };
270
271 void G1MarkSweep::mark_sweep_phase3() {
272 G1CollectedHeap* g1h = G1CollectedHeap::heap();
273 Generation* pg = g1h->perm_gen();
274
275 // Adjust the pointers to reflect the new locations
276 EventMark m("3 adjust pointers");
277 TraceTime tm("phase 3", PrintGC && Verbose, true, gclog_or_tty);
278 GenMarkSweep::trace("3");
279
280 SharedHeap* sh = SharedHeap::heap();
281
282 sh->process_strong_roots(true, // activate StrongRootsScope
283 true, // Collecting permanent generation.
284 SharedHeap::SO_AllClasses,
285 &GenMarkSweep::adjust_root_pointer_closure,
286 NULL, // do not touch code cache here
287 &GenMarkSweep::adjust_pointer_closure);
288
289 g1h->ref_processor()->weak_oops_do(&GenMarkSweep::adjust_root_pointer_closure);
290
291 // Now adjust pointers in remaining weak roots. (All of which should
292 // have been cleared if they pointed to non-surviving objects.)
293 g1h->g1_process_weak_roots(&GenMarkSweep::adjust_root_pointer_closure,
294 &GenMarkSweep::adjust_pointer_closure);
295
296 GenMarkSweep::adjust_marks();
297
298 G1AdjustPointersClosure blk;
299 g1h->heap_region_iterate(&blk);
300 pg->adjust_pointers();
301 }
302
303 class G1SpaceCompactClosure: public HeapRegionClosure {
304 public:
305 G1SpaceCompactClosure() {}
306
307 bool doHeapRegion(HeapRegion* hr) {
308 if (hr->isHumongous()) {
309 if (hr->startsHumongous()) {
310 oop obj = oop(hr->bottom());
311 if (obj->is_gc_marked()) {
312 obj->init_mark();
313 } else {
314 assert(hr->is_empty(), "Should have been cleared in phase 2.");
315 }
316 hr->reset_during_compaction();
317 }
318 } else {
319 hr->compact();
320 }
321 return false;
322 }
323 };
324
325 void G1MarkSweep::mark_sweep_phase4() {
326 // All pointers are now adjusted, move objects accordingly
327
328 // It is imperative that we traverse perm_gen first in phase4. All
329 // classes must be allocated earlier than their instances, and traversing
330 // perm_gen first makes sure that all klassOops have moved to their new
331 // location before any instance does a dispatch through it's klass!
332
333 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
334 // in the same order in phase2, phase3 and phase4. We don't quite do that
335 // here (perm_gen first rather than last), so we tell the validate code
336 // to use a higher index (saved from phase2) when verifying perm_gen.
337 G1CollectedHeap* g1h = G1CollectedHeap::heap();
338 Generation* pg = g1h->perm_gen();
339
340 EventMark m("4 compact heap");
341 TraceTime tm("phase 4", PrintGC && Verbose, true, gclog_or_tty);
342 GenMarkSweep::trace("4");
343
344 pg->compact();
345
346 G1SpaceCompactClosure blk;
347 g1h->heap_region_iterate(&blk);
348
349 }
350
351 // Local Variables: ***
352 // c-indentation-style: gnu ***
353 // End: ***