1 /*
2 * Copyright (c) 2001, 2021, 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/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 "compiler/oopMap.hpp"
35 #include "gc/serial/genMarkSweep.hpp"
36 #include "gc/serial/serialGcRefProcProxyTask.hpp"
37 #include "gc/shared/collectedHeap.inline.hpp"
38 #include "gc/shared/gcHeapSummary.hpp"
39 #include "gc/shared/gcTimer.hpp"
40 #include "gc/shared/gcTrace.hpp"
41 #include "gc/shared/gcTraceTime.inline.hpp"
42 #include "gc/shared/genCollectedHeap.hpp"
43 #include "gc/shared/generation.hpp"
44 #include "gc/shared/genOopClosures.inline.hpp"
45 #include "gc/shared/modRefBarrierSet.hpp"
46 #include "gc/shared/referencePolicy.hpp"
47 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
48 #include "gc/shared/space.hpp"
49 #include "gc/shared/strongRootsScope.hpp"
50 #include "gc/shared/weakProcessor.hpp"
51 #include "memory/universe.hpp"
52 #include "oops/instanceRefKlass.hpp"
53 #include "oops/oop.inline.hpp"
54 #include "prims/jvmtiExport.hpp"
55 #include "runtime/handles.inline.hpp"
56 #include "runtime/synchronizer.hpp"
57 #include "runtime/thread.inline.hpp"
58 #include "runtime/vmThread.hpp"
59 #include "utilities/copy.hpp"
60 #include "utilities/events.hpp"
61 #include "utilities/stack.inline.hpp"
62 #if INCLUDE_JVMCI
63 #include "jvmci/jvmci.hpp"
64 #endif
65
66 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) {
67 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
68
69 GenCollectedHeap* gch = GenCollectedHeap::heap();
70 #ifdef ASSERT
71 if (gch->soft_ref_policy()->should_clear_all_soft_refs()) {
72 assert(clear_all_softrefs, "Policy should have been checked earlier");
73 }
74 #endif
75
76 // hook up weak ref data so it can be used during Mark-Sweep
77 assert(ref_processor() == NULL, "no stomping");
78 assert(rp != NULL, "should be non-NULL");
79 set_ref_processor(rp);
80 rp->setup_policy(clear_all_softrefs);
81
82 gch->trace_heap_before_gc(_gc_tracer);
83
84 // Increment the invocation count
85 _total_invocations++;
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 COMPILER2_OR_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 CardTableRS* 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 gch->prune_scavengable_nmethods();
134
135 // refs processing: clean slate
136 set_ref_processor(NULL);
137
138 // Update heap occupancy information which is used as
139 // input to soft ref clearing policy at the next gc.
140 Universe::heap()->update_capacity_and_used_at_gc();
141
142 // Signal that we have completed a visit to all live objects.
143 Universe::heap()->record_whole_heap_examined_timestamp();
144
145 gch->trace_heap_after_gc(_gc_tracer);
146 }
147
148 void GenMarkSweep::allocate_stacks() {
149 GenCollectedHeap* gch = GenCollectedHeap::heap();
150 // Scratch request on behalf of old generation; will do no allocation.
151 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
152
153 // $$$ To cut a corner, we'll only use the first scratch block, and then
154 // revert to malloc.
155 if (scratch != NULL) {
156 _preserved_count_max =
157 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
158 } else {
159 _preserved_count_max = 0;
160 }
161
162 _preserved_marks = (PreservedMark*)scratch;
163 _preserved_count = 0;
164 }
165
166
167 void GenMarkSweep::deallocate_stacks() {
168 GenCollectedHeap* gch = GenCollectedHeap::heap();
169 gch->release_scratch();
170
171 _preserved_mark_stack.clear(true);
172 _preserved_oop_stack.clear(true);
173 _marking_stack.clear();
174 _objarray_stack.clear(true);
175 }
176
177 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
178 // Recursively traverse all live objects and mark them
179 GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
180
181 GenCollectedHeap* gch = GenCollectedHeap::heap();
182
183 // Need new claim bits before marking starts.
184 ClassLoaderDataGraph::clear_claimed_marks();
185
186 {
187 StrongRootsScope srs(0);
188
189 gch->full_process_roots(false, // not the adjust phase
190 GenCollectedHeap::SO_None,
191 ClassUnloading, // only strong roots if ClassUnloading
192 // is enabled
193 &follow_root_closure,
194 &follow_cld_closure);
195 }
196
197 // Process reference objects found during marking
198 {
199 GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer());
200
201 ref_processor()->setup_policy(clear_all_softrefs);
202 ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues());
203 SerialGCRefProcProxyTask task(is_alive, keep_alive, follow_stack_closure);
204 const ReferenceProcessorStats& stats = ref_processor()->process_discovered_references(task, pt);
205 pt.print_all_references();
206 gc_tracer()->report_gc_reference_stats(stats);
207 }
208
209 // This is the point where the entire marking should have completed.
210 assert(_marking_stack.is_empty(), "Marking should have completed");
211
212 {
213 GCTraceTime(Debug, gc, phases) tm_m("Weak Processing", gc_timer());
214 WeakProcessor::weak_oops_do(&is_alive, &do_nothing_cl);
215 }
216
217 {
218 GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer());
219
220 // Unload classes and purge the SystemDictionary.
221 bool purged_class = SystemDictionary::do_unloading(gc_timer());
222
223 // Unload nmethods.
224 CodeCache::do_unloading(&is_alive, purged_class);
225
226 // Prune dead klasses from subklass/sibling/implementor lists.
227 Klass::clean_weak_klass_links(purged_class);
228
229 // Clean JVMCI metadata handles.
230 JVMCI_ONLY(JVMCI::do_unloading(purged_class));
231 }
232
233 {
234 GCTraceTime(Debug, gc, phases) tm_m("Report Object Count", gc_timer());
235 gc_tracer()->report_object_count_after_gc(&is_alive, nullptr);
236 }
237 }
238
239
240 void GenMarkSweep::mark_sweep_phase2() {
241 // Now all live objects are marked, compute the new object addresses.
242
243 // It is imperative that we traverse perm_gen LAST. If dead space is
244 // allowed a range of dead object may get overwritten by a dead int
245 // array. If perm_gen is not traversed last a Klass* may get
246 // overwritten. This is fine since it is dead, but if the class has dead
247 // instances we have to skip them, and in order to find their size we
248 // need the Klass*!
249 //
250 // It is not required that we traverse spaces in the same order in
251 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
252 // tracking expects us to do so. See comment under phase4.
253
254 GenCollectedHeap* gch = GenCollectedHeap::heap();
255
256 GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
257
258 gch->prepare_for_compaction();
259 }
260
261 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
262 public:
263 void do_generation(Generation* gen) {
264 gen->adjust_pointers();
265 }
266 };
267
268 void GenMarkSweep::mark_sweep_phase3() {
269 GenCollectedHeap* gch = GenCollectedHeap::heap();
270
271 // Adjust the pointers to reflect the new locations
272 GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
273
274 // Need new claim bits for the pointer adjustment tracing.
275 ClassLoaderDataGraph::clear_claimed_marks();
276
277 {
278 StrongRootsScope srs(0);
279
280 gch->full_process_roots(true, // this is the adjust phase
281 GenCollectedHeap::SO_AllCodeCache,
282 false, // all roots
283 &adjust_pointer_closure,
284 &adjust_cld_closure);
285 }
286
287 gch->gen_process_weak_roots(&adjust_pointer_closure);
288
289 adjust_marks();
290 GenAdjustPointersClosure blk;
291 gch->generation_iterate(&blk, true);
292 }
293
294 class GenCompactClosure: public GenCollectedHeap::GenClosure {
295 public:
296 void do_generation(Generation* gen) {
297 gen->compact();
298 }
299 };
300
301 void GenMarkSweep::mark_sweep_phase4() {
302 // All pointers are now adjusted, move objects accordingly
303
304 // It is imperative that we traverse perm_gen first in phase4. All
305 // classes must be allocated earlier than their instances, and traversing
306 // perm_gen first makes sure that all Klass*s have moved to their new
307 // location before any instance does a dispatch through it's klass!
308
309 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
310 // in the same order in phase2, phase3 and phase4. We don't quite do that
311 // here (perm_gen first rather than last), so we tell the validate code
312 // to use a higher index (saved from phase2) when verifying perm_gen.
313 GenCollectedHeap* gch = GenCollectedHeap::heap();
314
315 GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
316
317 GenCompactClosure blk;
318 gch->generation_iterate(&blk, true);
319 }