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/slidingForwarding.hpp"
49 #include "gc/shared/space.hpp"
50 #include "gc/shared/strongRootsScope.hpp"
51 #include "gc/shared/weakProcessor.hpp"
52 #include "memory/universe.hpp"
53 #include "oops/instanceRefKlass.hpp"
54 #include "oops/oop.inline.hpp"
55 #include "prims/jvmtiExport.hpp"
56 #include "runtime/handles.inline.hpp"
57 #include "runtime/synchronizer.hpp"
58 #include "runtime/thread.inline.hpp"
59 #include "runtime/vmThread.hpp"
60 #include "utilities/copy.hpp"
61 #include "utilities/events.hpp"
62 #include "utilities/stack.inline.hpp"
63 #if INCLUDE_JVMCI
64 #include "jvmci/jvmci.hpp"
65 #endif
66
67 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) {
68 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
69
70 GenCollectedHeap* gch = GenCollectedHeap::heap();
71 #ifdef ASSERT
72 if (gch->soft_ref_policy()->should_clear_all_soft_refs()) {
73 assert(clear_all_softrefs, "Policy should have been checked earlier");
74 }
75 #endif
76
77 // hook up weak ref data so it can be used during Mark-Sweep
78 assert(ref_processor() == NULL, "no stomping");
79 assert(rp != NULL, "should be non-NULL");
80 set_ref_processor(rp);
81 rp->setup_policy(clear_all_softrefs);
82
83 gch->trace_heap_before_gc(_gc_tracer);
84
85 // Increment the invocation count
86 _total_invocations++;
87
88 // Capture used regions for each generation that will be
89 // subject to collection, so that card table adjustments can
90 // be made intelligently (see clear / invalidate further below).
91 gch->save_used_regions();
92
93 allocate_stacks();
94
95 mark_sweep_phase1(clear_all_softrefs);
96
97 SlidingForwarding::begin();
98
99 mark_sweep_phase2();
100
101 // Don't add any more derived pointers during phase3
102 #if COMPILER2_OR_JVMCI
103 assert(DerivedPointerTable::is_active(), "Sanity");
104 DerivedPointerTable::set_active(false);
105 #endif
106
107 mark_sweep_phase3();
108
109 mark_sweep_phase4();
110
111 restore_marks();
112
113 // Set saved marks for allocation profiler (and other things? -- dld)
114 // (Should this be in general part?)
115 gch->save_marks();
116
117 SlidingForwarding::end();
118
119 deallocate_stacks();
120
121 // If compaction completely evacuated the young generation then we
122 // can clear the card table. Otherwise, we must invalidate
123 // it (consider all cards dirty). In the future, we might consider doing
124 // compaction within generations only, and doing card-table sliding.
125 CardTableRS* rs = gch->rem_set();
126 Generation* old_gen = gch->old_gen();
127
128 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
129 if (gch->young_gen()->used() == 0) {
130 // We've evacuated the young generation.
131 rs->clear_into_younger(old_gen);
132 } else {
133 // Invalidate the cards corresponding to the currently used
134 // region and clear those corresponding to the evacuated region.
135 rs->invalidate_or_clear(old_gen);
136 }
137
138 gch->prune_scavengable_nmethods();
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::heap()->update_capacity_and_used_at_gc();
146
147 // Signal that we have completed a visit to all live objects.
148 Universe::heap()->record_whole_heap_examined_timestamp();
149
150 gch->trace_heap_after_gc(_gc_tracer);
151 }
152
153 void GenMarkSweep::allocate_stacks() {
154 GenCollectedHeap* gch = GenCollectedHeap::heap();
155 // Scratch request on behalf of old generation; will do no allocation.
156 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
157
158 // $$$ To cut a corner, we'll only use the first scratch block, and then
159 // revert to malloc.
160 if (scratch != NULL) {
161 _preserved_count_max =
162 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
163 } else {
164 _preserved_count_max = 0;
165 }
166
167 _preserved_marks = (PreservedMark*)scratch;
168 _preserved_count = 0;
169 }
170
171
172 void GenMarkSweep::deallocate_stacks() {
173 GenCollectedHeap* gch = GenCollectedHeap::heap();
174 gch->release_scratch();
175
176 _preserved_mark_stack.clear(true);
177 _preserved_oop_stack.clear(true);
178 _marking_stack.clear();
179 _objarray_stack.clear(true);
180 }
181
182 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
183 // Recursively traverse all live objects and mark them
184 GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
185
186 GenCollectedHeap* gch = GenCollectedHeap::heap();
187
188 // Need new claim bits before marking starts.
189 ClassLoaderDataGraph::clear_claimed_marks();
190
191 {
192 StrongRootsScope srs(0);
193
194 gch->full_process_roots(false, // not the adjust phase
195 GenCollectedHeap::SO_None,
196 ClassUnloading, // only strong roots if ClassUnloading
197 // is enabled
198 &follow_root_closure,
199 &follow_cld_closure);
200 }
201
202 // Process reference objects found during marking
203 {
204 GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer());
205
206 ref_processor()->setup_policy(clear_all_softrefs);
207 ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues());
208 SerialGCRefProcProxyTask task(is_alive, keep_alive, follow_stack_closure);
209 const ReferenceProcessorStats& stats = ref_processor()->process_discovered_references(task, pt);
210 pt.print_all_references();
211 gc_tracer()->report_gc_reference_stats(stats);
212 }
213
214 // This is the point where the entire marking should have completed.
215 assert(_marking_stack.is_empty(), "Marking should have completed");
216
217 {
218 GCTraceTime(Debug, gc, phases) tm_m("Weak Processing", gc_timer());
219 WeakProcessor::weak_oops_do(&is_alive, &do_nothing_cl);
220 }
221
222 {
223 GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer());
224
225 // Unload classes and purge the SystemDictionary.
226 bool purged_class = SystemDictionary::do_unloading(gc_timer());
227
228 // Unload nmethods.
229 CodeCache::do_unloading(&is_alive, purged_class);
230
231 // Prune dead klasses from subklass/sibling/implementor lists.
232 Klass::clean_weak_klass_links(purged_class);
233
234 // Clean JVMCI metadata handles.
235 JVMCI_ONLY(JVMCI::do_unloading(purged_class));
236 }
237
238 {
239 GCTraceTime(Debug, gc, phases) tm_m("Report Object Count", gc_timer());
240 gc_tracer()->report_object_count_after_gc(&is_alive, nullptr);
241 }
242 }
243
244
245 void GenMarkSweep::mark_sweep_phase2() {
246 // Now all live objects are marked, compute the new object addresses.
247
248 // It is imperative that we traverse perm_gen LAST. If dead space is
249 // allowed a range of dead object may get overwritten by a dead int
250 // array. If perm_gen is not traversed last a Klass* may get
251 // overwritten. This is fine since it is dead, but if the class has dead
252 // instances we have to skip them, and in order to find their size we
253 // need the Klass*!
254 //
255 // It is not required that we traverse spaces in the same order in
256 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
257 // tracking expects us to do so. See comment under phase4.
258
259 GenCollectedHeap* gch = GenCollectedHeap::heap();
260
261 GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
262
263 gch->prepare_for_compaction();
264 }
265
266 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
267 public:
268 void do_generation(Generation* gen) {
269 gen->adjust_pointers();
270 }
271 };
272
273 void GenMarkSweep::mark_sweep_phase3() {
274 GenCollectedHeap* gch = GenCollectedHeap::heap();
275
276 // Adjust the pointers to reflect the new locations
277 GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
278
279 // Need new claim bits for the pointer adjustment tracing.
280 ClassLoaderDataGraph::clear_claimed_marks();
281
282 if (UseAltGCForwarding) {
283 AdjustPointerClosure<true> adjust_pointer_closure;
284 CLDToOopClosure adjust_cld_closure(&adjust_pointer_closure, ClassLoaderData::_claim_strong);
285 {
286 StrongRootsScope srs(0);
287 gch->full_process_roots(true, // this is the adjust phase
288 GenCollectedHeap::SO_AllCodeCache,
289 false, // all roots
290 &adjust_pointer_closure,
291 &adjust_cld_closure);
292 }
293 gch->gen_process_weak_roots(&adjust_pointer_closure);
294 } else {
295 AdjustPointerClosure<false> adjust_pointer_closure;
296 CLDToOopClosure adjust_cld_closure(&adjust_pointer_closure, ClassLoaderData::_claim_strong);
297 {
298 StrongRootsScope srs(0);
299 gch->full_process_roots(true, // this is the adjust phase
300 GenCollectedHeap::SO_AllCodeCache,
301 false, // all roots
302 &adjust_pointer_closure,
303 &adjust_cld_closure);
304 }
305 gch->gen_process_weak_roots(&adjust_pointer_closure);
306 }
307 adjust_marks();
308 GenAdjustPointersClosure blk;
309 gch->generation_iterate(&blk, true);
310 }
311
312 class GenCompactClosure: public GenCollectedHeap::GenClosure {
313 public:
314 void do_generation(Generation* gen) {
315 gen->compact();
316 }
317 };
318
319 void GenMarkSweep::mark_sweep_phase4() {
320 // All pointers are now adjusted, move objects accordingly
321
322 // It is imperative that we traverse perm_gen first in phase4. All
323 // classes must be allocated earlier than their instances, and traversing
324 // perm_gen first makes sure that all Klass*s have moved to their new
325 // location before any instance does a dispatch through it's klass!
326
327 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
328 // in the same order in phase2, phase3 and phase4. We don't quite do that
329 // here (perm_gen first rather than last), so we tell the validate code
330 // to use a higher index (saved from phase2) when verifying perm_gen.
331 GenCollectedHeap* gch = GenCollectedHeap::heap();
332
333 GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
334
335 GenCompactClosure blk;
336 gch->generation_iterate(&blk, true);
337 }