1 /*
2 * Copyright (c) 2001, 2018, 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/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "classfile/vmSymbols.hpp"
31 #include "code/codeCache.hpp"
32 #include "code/icBuffer.hpp"
33 #include "gc/serial/genMarkSweep.hpp"
34 #include "gc/shared/collectedHeap.inline.hpp"
35 #include "gc/shared/gcHeapSummary.hpp"
36 #include "gc/shared/gcTimer.hpp"
37 #include "gc/shared/gcTrace.hpp"
38 #include "gc/shared/gcTraceTime.inline.hpp"
39 #include "gc/shared/genCollectedHeap.hpp"
40 #include "gc/shared/generation.hpp"
41 #include "gc/shared/genOopClosures.inline.hpp"
42 #include "gc/shared/modRefBarrierSet.hpp"
43 #include "gc/shared/referencePolicy.hpp"
44 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
45 #include "gc/shared/space.hpp"
46 #include "gc/shared/strongRootsScope.hpp"
47 #include "gc/shared/weakProcessor.hpp"
48 #include "oops/instanceRefKlass.hpp"
49 #include "oops/oop.inline.hpp"
50 #include "prims/jvmtiExport.hpp"
51 #include "runtime/handles.inline.hpp"
52 #include "runtime/synchronizer.hpp"
53 #include "runtime/thread.inline.hpp"
54 #include "runtime/vmThread.hpp"
55 #include "utilities/copy.hpp"
56 #include "utilities/events.hpp"
57 #include "utilities/stack.inline.hpp"
58
59 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) {
60 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
61
62 GenCollectedHeap* gch = GenCollectedHeap::heap();
63 #ifdef ASSERT
64 if (gch->soft_ref_policy()->should_clear_all_soft_refs()) {
65 assert(clear_all_softrefs, "Policy should have been checked earlier");
66 }
67 #endif
68
69 // hook up weak ref data so it can be used during Mark-Sweep
70 assert(ref_processor() == NULL, "no stomping");
71 assert(rp != NULL, "should be non-NULL");
72 set_ref_processor(rp);
73 rp->setup_policy(clear_all_softrefs);
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 used regions for each generation that will be
85 // subject to collection, so that card table adjustments can
86 // be made intelligently (see clear / invalidate further below).
87 gch->save_used_regions();
88
89 allocate_stacks();
90
91 mark_sweep_phase1(clear_all_softrefs);
92
93 mark_sweep_phase2();
94
95 // Don't add any more derived pointers during phase3
96 #if COMPILER2_OR_JVMCI
97 assert(DerivedPointerTable::is_active(), "Sanity");
98 DerivedPointerTable::set_active(false);
99 #endif
100
101 mark_sweep_phase3();
102
103 mark_sweep_phase4();
104
105 restore_marks();
106
107 // Set saved marks for allocation profiler (and other things? -- dld)
108 // (Should this be in general part?)
109 gch->save_marks();
110
111 deallocate_stacks();
112
113 // If compaction completely evacuated the young generation then we
114 // can clear the card table. Otherwise, we must invalidate
115 // it (consider all cards dirty). In the future, we might consider doing
116 // compaction within generations only, and doing card-table sliding.
117 CardTableRS* rs = gch->rem_set();
118 Generation* old_gen = gch->old_gen();
119
120 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
121 if (gch->young_gen()->used() == 0) {
122 // We've evacuated the young generation.
123 rs->clear_into_younger(old_gen);
124 } else {
125 // Invalidate the cards corresponding to the currently used
126 // region and clear those corresponding to the evacuated region.
127 rs->invalidate_or_clear(old_gen);
128 }
129
130 CodeCache::gc_epilogue();
131 JvmtiExport::gc_epilogue();
132
133 // refs processing: clean slate
134 set_ref_processor(NULL);
135
136 // Update heap occupancy information which is used as
137 // input to soft ref clearing policy at the next gc.
138 Universe::update_heap_info_at_gc();
139
140 // Update time of last gc for all generations we collected
141 // (which currently is all the generations in the heap).
142 // We need to use a monotonically non-decreasing time in ms
143 // or we will see time-warp warnings and os::javaTimeMillis()
144 // does not guarantee monotonicity.
145 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
146 gch->update_time_of_last_gc(now);
147
148 gch->trace_heap_after_gc(_gc_tracer);
149 }
150
151 void GenMarkSweep::allocate_stacks() {
152 GenCollectedHeap* gch = GenCollectedHeap::heap();
153 // Scratch request on behalf of old generation; will do no allocation.
154 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
155
156 // $$$ To cut a corner, we'll only use the first scratch block, and then
157 // revert to malloc.
158 if (scratch != NULL) {
159 _preserved_count_max =
160 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
161 } else {
162 _preserved_count_max = 0;
163 }
164
165 _preserved_marks = (PreservedMark*)scratch;
166 _preserved_count = 0;
167 }
168
169
170 void GenMarkSweep::deallocate_stacks() {
171 GenCollectedHeap* gch = GenCollectedHeap::heap();
172 gch->release_scratch();
173
174 _preserved_mark_stack.clear(true);
175 _preserved_oop_stack.clear(true);
176 _marking_stack.clear();
177 _objarray_stack.clear(true);
178 }
179
180 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
181 // Recursively traverse all live objects and mark them
182 GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
183
184 GenCollectedHeap* gch = GenCollectedHeap::heap();
185
186 // Because follow_root_closure is created statically, cannot
187 // use OopsInGenClosure constructor which takes a generation,
188 // as the Universe has not been created when the static constructors
189 // are run.
190 follow_root_closure.set_orig_generation(gch->old_gen());
191
192 // Need new claim bits before marking starts.
193 ClassLoaderDataGraph::clear_claimed_marks();
194
195 {
196 StrongRootsScope srs(1);
197
198 gch->full_process_roots(&srs,
199 false, // not the adjust phase
200 GenCollectedHeap::SO_None,
201 ClassUnloading, // only strong roots if ClassUnloading
202 // is enabled
203 &follow_root_closure,
204 &follow_cld_closure);
205 }
206
207 // Process reference objects found during marking
208 {
209 GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer());
210
211 ref_processor()->setup_policy(clear_all_softrefs);
212 ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->max_num_queues());
213 const ReferenceProcessorStats& stats =
214 ref_processor()->process_discovered_references(
215 &is_alive, &keep_alive, &follow_stack_closure, NULL, &pt);
216 pt.print_all_references();
217 gc_tracer()->report_gc_reference_stats(stats);
218 }
219
220 // This is the point where the entire marking should have completed.
221 assert(_marking_stack.is_empty(), "Marking should have completed");
222
223 {
224 GCTraceTime(Debug, gc, phases) tm_m("Weak Processing", gc_timer());
225 WeakProcessor::weak_oops_do(&is_alive, &do_nothing_cl);
226 }
227
228 {
229 GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer());
230
231 // Unload classes and purge the SystemDictionary.
232 bool purged_class = SystemDictionary::do_unloading(gc_timer());
233
234 // Unload nmethods.
235 CodeCache::do_unloading(&is_alive, purged_class);
236
237 // Prune dead klasses from subklass/sibling/implementor lists.
238 Klass::clean_weak_klass_links(purged_class);
239 }
240
241 {
242 GCTraceTime(Debug, gc, phases) t("Scrub String Table", gc_timer());
243 // Delete entries for dead interned strings.
244 StringTable::unlink(&is_alive);
245 }
246
247 {
248 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", gc_timer());
249 // Clean up unreferenced symbols in symbol table.
250 SymbolTable::unlink();
251 }
252
253 gc_tracer()->report_object_count_after_gc(&is_alive);
254 }
255
256
257 void GenMarkSweep::mark_sweep_phase2() {
258 // Now all live objects are marked, compute the new object addresses.
259
260 // It is imperative that we traverse perm_gen LAST. If dead space is
261 // allowed a range of dead object may get overwritten by a dead int
262 // array. If perm_gen is not traversed last a Klass* may get
263 // overwritten. This is fine since it is dead, but if the class has dead
264 // instances we have to skip them, and in order to find their size we
265 // need the Klass*!
266 //
267 // It is not required that we traverse spaces in the same order in
268 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
269 // tracking expects us to do so. See comment under phase4.
270
271 GenCollectedHeap* gch = GenCollectedHeap::heap();
272
273 GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
274
275 gch->prepare_for_compaction();
276 }
277
278 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
279 public:
280 void do_generation(Generation* gen) {
281 gen->adjust_pointers();
282 }
283 };
284
285 void GenMarkSweep::mark_sweep_phase3() {
286 GenCollectedHeap* gch = GenCollectedHeap::heap();
287
288 // Adjust the pointers to reflect the new locations
289 GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
290
291 // Need new claim bits for the pointer adjustment tracing.
292 ClassLoaderDataGraph::clear_claimed_marks();
293
294 // Because the closure below is created statically, we cannot
295 // use OopsInGenClosure constructor which takes a generation,
296 // as the Universe has not been created when the static constructors
297 // are run.
298 adjust_pointer_closure.set_orig_generation(gch->old_gen());
299
300 {
301 StrongRootsScope srs(1);
302
303 gch->full_process_roots(&srs,
304 true, // this is the adjust phase
305 GenCollectedHeap::SO_AllCodeCache,
306 false, // all roots
307 &adjust_pointer_closure,
308 &adjust_cld_closure);
309 }
310
311 gch->gen_process_weak_roots(&adjust_pointer_closure);
312
313 adjust_marks();
314 GenAdjustPointersClosure blk;
315 gch->generation_iterate(&blk, true);
316 }
317
318 class GenCompactClosure: public GenCollectedHeap::GenClosure {
319 public:
320 void do_generation(Generation* gen) {
321 gen->compact();
322 }
323 };
324
325 void GenMarkSweep::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 Klass*s 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 GenCollectedHeap* gch = GenCollectedHeap::heap();
338
339 GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
340
341 GenCompactClosure blk;
342 gch->generation_iterate(&blk, true);
343 }