1/*
2 * Copyright (c) 2001, 2019, 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.
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23 */
24
25#include "precompiled.hpp"
26#include "classfile/classLoaderDataGraph.hpp"
27#include "classfile/javaClasses.hpp"
28#include "classfile/stringTable.hpp"
29#include "classfile/symbolTable.hpp"
30#include "classfile/systemDictionary.hpp"
31#include "classfile/vmSymbols.hpp"
32#include "code/codeCache.hpp"
33#include "code/icBuffer.hpp"
34#include "gc/serial/genMarkSweep.hpp"
35#include "gc/shared/collectedHeap.inline.hpp"
36#include "gc/shared/gcHeapSummary.hpp"
37#include "gc/shared/gcTimer.hpp"
38#include "gc/shared/gcTrace.hpp"
39#include "gc/shared/gcTraceTime.inline.hpp"
40#include "gc/shared/genCollectedHeap.hpp"
41#include "gc/shared/generation.hpp"
42#include "gc/shared/genOopClosures.inline.hpp"
43#include "gc/shared/modRefBarrierSet.hpp"
44#include "gc/shared/referencePolicy.hpp"
45#include "gc/shared/referenceProcessorPhaseTimes.hpp"
46#include "gc/shared/space.hpp"
47#include "gc/shared/strongRootsScope.hpp"
48#include "gc/shared/weakProcessor.hpp"
49#include "memory/universe.hpp"
50#include "oops/instanceRefKlass.hpp"
51#include "oops/oop.inline.hpp"
52#include "prims/jvmtiExport.hpp"
53#include "runtime/handles.inline.hpp"
54#include "runtime/synchronizer.hpp"
55#include "runtime/thread.inline.hpp"
56#include "runtime/vmThread.hpp"
57#include "utilities/copy.hpp"
58#include "utilities/events.hpp"
59#include "utilities/stack.inline.hpp"
60#if INCLUDE_JVMCI
61#include "jvmci/jvmci.hpp"
62#endif
63
64void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) {
65 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
66
67 GenCollectedHeap* gch = GenCollectedHeap::heap();
68#ifdef ASSERT
69 if (gch->soft_ref_policy()->should_clear_all_soft_refs()) {
70 assert(clear_all_softrefs, "Policy should have been checked earlier");
71 }
72#endif
73
74 // hook up weak ref data so it can be used during Mark-Sweep
75 assert(ref_processor() == NULL, "no stomping");
76 assert(rp != NULL, "should be non-NULL");
77 set_ref_processor(rp);
78 rp->setup_policy(clear_all_softrefs);
79
80 gch->trace_heap_before_gc(_gc_tracer);
81
82 // Increment the invocation count
83 _total_invocations++;
84
85 // Capture used regions for each generation that will be
86 // subject to collection, so that card table adjustments can
87 // be made intelligently (see clear / invalidate further below).
88 gch->save_used_regions();
89
90 allocate_stacks();
91
92 mark_sweep_phase1(clear_all_softrefs);
93
94 mark_sweep_phase2();
95
96 // Don't add any more derived pointers during phase3
97#if COMPILER2_OR_JVMCI
98 assert(DerivedPointerTable::is_active(), "Sanity");
99 DerivedPointerTable::set_active(false);
100#endif
101
102 mark_sweep_phase3();
103
104 mark_sweep_phase4();
105
106 restore_marks();
107
108 // Set saved marks for allocation profiler (and other things? -- dld)
109 // (Should this be in general part?)
110 gch->save_marks();
111
112 deallocate_stacks();
113
114 // If compaction completely evacuated the young generation then we
115 // can clear the card table. Otherwise, we must invalidate
116 // it (consider all cards dirty). In the future, we might consider doing
117 // compaction within generations only, and doing card-table sliding.
118 CardTableRS* rs = gch->rem_set();
119 Generation* old_gen = gch->old_gen();
120
121 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
122 if (gch->young_gen()->used() == 0) {
123 // We've evacuated the young generation.
124 rs->clear_into_younger(old_gen);
125 } else {
126 // Invalidate the cards corresponding to the currently used
127 // region and clear those corresponding to the evacuated region.
128 rs->invalidate_or_clear(old_gen);
129 }
130
131 gch->prune_scavengable_nmethods();
132 JvmtiExport::gc_epilogue();
133
134 // refs processing: clean slate
135 set_ref_processor(NULL);
136
137 // Update heap occupancy information which is used as
138 // input to soft ref clearing policy at the next gc.
139 Universe::update_heap_info_at_gc();
140
141 // Update time of last gc for all generations we collected
142 // (which currently is all the generations in the heap).
143 // We need to use a monotonically non-decreasing time in ms
144 // or we will see time-warp warnings and os::javaTimeMillis()
145 // does not guarantee monotonicity.
146 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
147 gch->update_time_of_last_gc(now);
148
149 gch->trace_heap_after_gc(_gc_tracer);
150}
151
152void GenMarkSweep::allocate_stacks() {
153 GenCollectedHeap* gch = GenCollectedHeap::heap();
154 // Scratch request on behalf of old generation; will do no allocation.
155 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
156
157 // $$$ To cut a corner, we'll only use the first scratch block, and then
158 // revert to malloc.
159 if (scratch != NULL) {
160 _preserved_count_max =
161 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
162 } else {
163 _preserved_count_max = 0;
164 }
165
166 _preserved_marks = (PreservedMark*)scratch;
167 _preserved_count = 0;
168}
169
170
171void GenMarkSweep::deallocate_stacks() {
172 GenCollectedHeap* gch = GenCollectedHeap::heap();
173 gch->release_scratch();
174
175 _preserved_mark_stack.clear(true);
176 _preserved_oop_stack.clear(true);
177 _marking_stack.clear();
178 _objarray_stack.clear(true);
179}
180
181void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
182 // Recursively traverse all live objects and mark them
183 GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
184
185 GenCollectedHeap* gch = GenCollectedHeap::heap();
186
187 // Because follow_root_closure is created statically, cannot
188 // use OopsInGenClosure constructor which takes a generation,
189 // as the Universe has not been created when the static constructors
190 // are run.
191 follow_root_closure.set_orig_generation(gch->old_gen());
192
193 // Need new claim bits before marking starts.
194 ClassLoaderDataGraph::clear_claimed_marks();
195
196 {
197 StrongRootsScope srs(1);
198
199 gch->full_process_roots(&srs,
200 false, // not the adjust phase
201 GenCollectedHeap::SO_None,
202 ClassUnloading, // only strong roots if ClassUnloading
203 // is enabled
204 &follow_root_closure,
205 &follow_cld_closure);
206 }
207
208 // Process reference objects found during marking
209 {
210 GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer());
211
212 ref_processor()->setup_policy(clear_all_softrefs);
213 ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues());
214 const ReferenceProcessorStats& stats =
215 ref_processor()->process_discovered_references(
216 &is_alive, &keep_alive, &follow_stack_closure, NULL, &pt);
217 pt.print_all_references();
218 gc_tracer()->report_gc_reference_stats(stats);
219 }
220
221 // This is the point where the entire marking should have completed.
222 assert(_marking_stack.is_empty(), "Marking should have completed");
223
224 {
225 GCTraceTime(Debug, gc, phases) tm_m("Weak Processing", gc_timer());
226 WeakProcessor::weak_oops_do(&is_alive, &do_nothing_cl);
227 }
228
229 {
230 GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer());
231
232 // Unload classes and purge the SystemDictionary.
233 bool purged_class = SystemDictionary::do_unloading(gc_timer());
234
235 // Unload nmethods.
236 CodeCache::do_unloading(&is_alive, purged_class);
237
238 // Prune dead klasses from subklass/sibling/implementor lists.
239 Klass::clean_weak_klass_links(purged_class);
240
241 // Clean JVMCI metadata handles.
242 JVMCI_ONLY(JVMCI::do_unloading(purged_class));
243 }
244
245 gc_tracer()->report_object_count_after_gc(&is_alive);
246}
247
248
249void GenMarkSweep::mark_sweep_phase2() {
250 // Now all live objects are marked, compute the new object addresses.
251
252 // It is imperative that we traverse perm_gen LAST. If dead space is
253 // allowed a range of dead object may get overwritten by a dead int
254 // array. If perm_gen is not traversed last a Klass* may get
255 // overwritten. This is fine since it is dead, but if the class has dead
256 // instances we have to skip them, and in order to find their size we
257 // need the Klass*!
258 //
259 // It is not required that we traverse spaces in the same order in
260 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
261 // tracking expects us to do so. See comment under phase4.
262
263 GenCollectedHeap* gch = GenCollectedHeap::heap();
264
265 GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
266
267 gch->prepare_for_compaction();
268}
269
270class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
271public:
272 void do_generation(Generation* gen) {
273 gen->adjust_pointers();
274 }
275};
276
277void GenMarkSweep::mark_sweep_phase3() {
278 GenCollectedHeap* gch = GenCollectedHeap::heap();
279
280 // Adjust the pointers to reflect the new locations
281 GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
282
283 // Need new claim bits for the pointer adjustment tracing.
284 ClassLoaderDataGraph::clear_claimed_marks();
285
286 // Because the closure below is created statically, we cannot
287 // use OopsInGenClosure constructor which takes a generation,
288 // as the Universe has not been created when the static constructors
289 // are run.
290 adjust_pointer_closure.set_orig_generation(gch->old_gen());
291
292 {
293 StrongRootsScope srs(1);
294
295 gch->full_process_roots(&srs,
296 true, // this is the adjust phase
297 GenCollectedHeap::SO_AllCodeCache,
298 false, // all roots
299 &adjust_pointer_closure,
300 &adjust_cld_closure);
301 }
302
303 gch->gen_process_weak_roots(&adjust_pointer_closure);
304
305 adjust_marks();
306 GenAdjustPointersClosure blk;
307 gch->generation_iterate(&blk, true);
308}
309
310class GenCompactClosure: public GenCollectedHeap::GenClosure {
311public:
312 void do_generation(Generation* gen) {
313 gen->compact();
314 }
315};
316
317void GenMarkSweep::mark_sweep_phase4() {
318 // All pointers are now adjusted, move objects accordingly
319
320 // It is imperative that we traverse perm_gen first in phase4. All
321 // classes must be allocated earlier than their instances, and traversing
322 // perm_gen first makes sure that all Klass*s have moved to their new
323 // location before any instance does a dispatch through it's klass!
324
325 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
326 // in the same order in phase2, phase3 and phase4. We don't quite do that
327 // here (perm_gen first rather than last), so we tell the validate code
328 // to use a higher index (saved from phase2) when verifying perm_gen.
329 GenCollectedHeap* gch = GenCollectedHeap::heap();
330
331 GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
332
333 GenCompactClosure blk;
334 gch->generation_iterate(&blk, true);
335}
336