1 /*
2 * Copyright (c) 2001, 2015, 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 "precompiled.hpp"
26 #include "classfile/javaClasses.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "classfile/vmSymbols.hpp"
30 #include "code/codeCache.hpp"
31 #include "code/icBuffer.hpp"
32 #include "gc/serial/genMarkSweep.hpp"
33 #include "gc/shared/collectedHeap.inline.hpp"
34 #include "gc/shared/gcHeapSummary.hpp"
35 #include "gc/shared/gcTimer.hpp"
36 #include "gc/shared/gcTrace.hpp"
37 #include "gc/shared/gcTraceTime.hpp"
38 #include "gc/shared/genCollectedHeap.hpp"
39 #include "gc/shared/generation.hpp"
40 #include "gc/shared/genOopClosures.inline.hpp"
41 #include "gc/shared/modRefBarrierSet.hpp"
42 #include "gc/shared/referencePolicy.hpp"
43 #include "gc/shared/space.hpp"
44 #include "gc/shared/strongRootsScope.hpp"
45 #include "oops/instanceRefKlass.hpp"
46 #include "oops/oop.inline.hpp"
47 #include "prims/jvmtiExport.hpp"
48 #include "runtime/fprofiler.hpp"
49 #include "runtime/handles.inline.hpp"
50 #include "runtime/synchronizer.hpp"
51 #include "runtime/thread.inline.hpp"
52 #include "runtime/vmThread.hpp"
53 #include "utilities/copy.hpp"
54 #include "utilities/events.hpp"
55 #include "utilities/stack.inline.hpp"
56
57 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) {
58 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
59
60 GenCollectedHeap* gch = GenCollectedHeap::heap();
61 #ifdef ASSERT
62 if (gch->collector_policy()->should_clear_all_soft_refs()) {
63 assert(clear_all_softrefs, "Policy should have been checked earlier");
64 }
65 #endif
66
67 // hook up weak ref data so it can be used during Mark-Sweep
68 assert(ref_processor() == NULL, "no stomping");
69 assert(rp != NULL, "should be non-NULL");
70 set_ref_processor(rp);
71 rp->setup_policy(clear_all_softrefs);
72
73 GCTraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer->gc_id());
74
75 gch->trace_heap_before_gc(_gc_tracer);
76
77 // When collecting the permanent generation Method*s may be moving,
78 // so we either have to flush all bcp data or convert it into bci.
79 CodeCache::gc_prologue();
80
81 // Increment the invocation count
82 _total_invocations++;
83
84 // Capture heap size before collection for printing.
85 size_t gch_prev_used = gch->used();
86
87 // Capture used regions for each generation that will be
88 // subject to collection, so that card table adjustments can
89 // be made intelligently (see clear / invalidate further below).
90 gch->save_used_regions();
91
92 allocate_stacks();
93
94 mark_sweep_phase1(clear_all_softrefs);
95
96 mark_sweep_phase2();
97
98 // Don't add any more derived pointers during phase3
99 #if defined(COMPILER2) || INCLUDE_JVMCI
100 assert(DerivedPointerTable::is_active(), "Sanity");
101 DerivedPointerTable::set_active(false);
102 #endif
103
104 mark_sweep_phase3();
105
106 mark_sweep_phase4();
107
108 restore_marks();
109
110 // Set saved marks for allocation profiler (and other things? -- dld)
111 // (Should this be in general part?)
112 gch->save_marks();
113
114 deallocate_stacks();
115
116 // If compaction completely evacuated the young generation then we
117 // can clear the card table. Otherwise, we must invalidate
118 // it (consider all cards dirty). In the future, we might consider doing
119 // compaction within generations only, and doing card-table sliding.
120 GenRemSet* rs = gch->rem_set();
121 Generation* old_gen = gch->old_gen();
122
123 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
124 if (gch->young_gen()->used() == 0) {
125 // We've evacuated the young generation.
126 rs->clear_into_younger(old_gen);
127 } else {
128 // Invalidate the cards corresponding to the currently used
129 // region and clear those corresponding to the evacuated region.
130 rs->invalidate_or_clear(old_gen);
131 }
132
133 CodeCache::gc_epilogue();
134 JvmtiExport::gc_epilogue();
135
136 if (PrintGC && !PrintGCDetails) {
137 gch->print_heap_change(gch_prev_used);
138 }
139
140 // refs processing: clean slate
141 set_ref_processor(NULL);
142
143 // Update heap occupancy information which is used as
144 // input to soft ref clearing policy at the next gc.
145 Universe::update_heap_info_at_gc();
146
147 // Update time of last gc for all generations we collected
148 // (which currently is all the generations in the heap).
149 // We need to use a monotonically non-decreasing time in ms
150 // or we will see time-warp warnings and os::javaTimeMillis()
151 // does not guarantee monotonicity.
152 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
153 gch->update_time_of_last_gc(now);
154
155 gch->trace_heap_after_gc(_gc_tracer);
156 }
157
158 void GenMarkSweep::allocate_stacks() {
159 GenCollectedHeap* gch = GenCollectedHeap::heap();
160 // Scratch request on behalf of old generation; will do no allocation.
161 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
162
163 // $$$ To cut a corner, we'll only use the first scratch block, and then
164 // revert to malloc.
165 if (scratch != NULL) {
166 _preserved_count_max =
167 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
168 } else {
169 _preserved_count_max = 0;
170 }
171
172 _preserved_marks = (PreservedMark*)scratch;
173 _preserved_count = 0;
174 }
175
176
177 void GenMarkSweep::deallocate_stacks() {
178 if (!UseG1GC) {
179 GenCollectedHeap* gch = GenCollectedHeap::heap();
180 gch->release_scratch();
181 }
182
183 _preserved_mark_stack.clear(true);
184 _preserved_oop_stack.clear(true);
185 _marking_stack.clear();
186 _objarray_stack.clear(true);
187 }
188
189 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
190 // Recursively traverse all live objects and mark them
191 GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
192
193 GenCollectedHeap* gch = GenCollectedHeap::heap();
194
195 // Because follow_root_closure is created statically, cannot
196 // use OopsInGenClosure constructor which takes a generation,
197 // as the Universe has not been created when the static constructors
198 // are run.
199 follow_root_closure.set_orig_generation(gch->old_gen());
200
201 // Need new claim bits before marking starts.
202 ClassLoaderDataGraph::clear_claimed_marks();
203
204 {
205 StrongRootsScope srs(1);
206
207 gch->gen_process_roots(&srs,
208 GenCollectedHeap::OldGen,
209 false, // Younger gens are not roots.
210 GenCollectedHeap::SO_None,
211 ClassUnloading,
212 &follow_root_closure,
213 &follow_root_closure,
214 &follow_cld_closure);
215 }
216
217 // Process reference objects found during marking
218 {
219 ref_processor()->setup_policy(clear_all_softrefs);
220 const ReferenceProcessorStats& stats =
221 ref_processor()->process_discovered_references(
222 &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer, _gc_tracer->gc_id());
223 gc_tracer()->report_gc_reference_stats(stats);
224 }
225
226 // This is the point where the entire marking should have completed.
227 assert(_marking_stack.is_empty(), "Marking should have completed");
228
229 // Unload classes and purge the SystemDictionary.
230 bool purged_class = SystemDictionary::do_unloading(&is_alive);
231
232 // Unload nmethods.
233 CodeCache::do_unloading(&is_alive, purged_class);
234
235 // Prune dead klasses from subklass/sibling/implementor lists.
236 Klass::clean_weak_klass_links(&is_alive);
237
238 // Delete entries for dead interned strings.
239 StringTable::unlink(&is_alive);
240
241 // Clean up unreferenced symbols in symbol table.
242 SymbolTable::unlink();
243
244 gc_tracer()->report_object_count_after_gc(&is_alive);
245 }
246
247
248 void GenMarkSweep::mark_sweep_phase2() {
249 // Now all live objects are marked, compute the new object addresses.
250
251 // It is imperative that we traverse perm_gen LAST. If dead space is
252 // allowed a range of dead object may get overwritten by a dead int
253 // array. If perm_gen is not traversed last a Klass* may get
254 // overwritten. This is fine since it is dead, but if the class has dead
255 // instances we have to skip them, and in order to find their size we
256 // need the Klass*!
257 //
258 // It is not required that we traverse spaces in the same order in
259 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
260 // tracking expects us to do so. See comment under phase4.
261
262 GenCollectedHeap* gch = GenCollectedHeap::heap();
263
264 GCTraceTime tm("phase 2", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
265
266 gch->prepare_for_compaction();
267 }
268
269 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
270 public:
271 void do_generation(Generation* gen) {
272 gen->adjust_pointers();
273 }
274 };
275
276 void GenMarkSweep::mark_sweep_phase3() {
277 GenCollectedHeap* gch = GenCollectedHeap::heap();
278
279 // Adjust the pointers to reflect the new locations
280 GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
281
282 // Need new claim bits for the pointer adjustment tracing.
283 ClassLoaderDataGraph::clear_claimed_marks();
284
285 // Because the closure below is created statically, we cannot
286 // use OopsInGenClosure constructor which takes a generation,
287 // as the Universe has not been created when the static constructors
288 // are run.
289 adjust_pointer_closure.set_orig_generation(gch->old_gen());
290
291 {
292 StrongRootsScope srs(1);
293
294 gch->gen_process_roots(&srs,
295 GenCollectedHeap::OldGen,
296 false, // Younger gens are not roots.
297 GenCollectedHeap::SO_AllCodeCache,
298 GenCollectedHeap::StrongAndWeakRoots,
299 &adjust_pointer_closure,
300 &adjust_pointer_closure,
301 &adjust_cld_closure);
302 }
303
304 gch->gen_process_weak_roots(&adjust_pointer_closure);
305
306 adjust_marks();
307 GenAdjustPointersClosure blk;
308 gch->generation_iterate(&blk, true);
309 }
310
311 class GenCompactClosure: public GenCollectedHeap::GenClosure {
312 public:
313 void do_generation(Generation* gen) {
314 gen->compact();
315 }
316 };
317
318 void GenMarkSweep::mark_sweep_phase4() {
319 // All pointers are now adjusted, move objects accordingly
320
321 // It is imperative that we traverse perm_gen first in phase4. All
322 // classes must be allocated earlier than their instances, and traversing
323 // perm_gen first makes sure that all Klass*s have moved to their new
324 // location before any instance does a dispatch through it's klass!
325
326 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
327 // in the same order in phase2, phase3 and phase4. We don't quite do that
328 // here (perm_gen first rather than last), so we tell the validate code
329 // to use a higher index (saved from phase2) when verifying perm_gen.
330 GenCollectedHeap* gch = GenCollectedHeap::heap();
331
332 GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
333
334 GenCompactClosure blk;
335 gch->generation_iterate(&blk, true);
336 }