1 /*
2 * Copyright (c) 2001, 2017, 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/space.hpp"
45 #include "gc/shared/strongRootsScope.hpp"
46 #include "oops/instanceRefKlass.hpp"
47 #include "oops/oop.inline.hpp"
48 #include "prims/jvmtiExport.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 gch->trace_heap_before_gc(_gc_tracer);
74
75 // When collecting the permanent generation Method*s may be moving,
76 // so we either have to flush all bcp data or convert it into bci.
77 CodeCache::gc_prologue();
78
79 // Increment the invocation count
80 _total_invocations++;
81
82 // Capture used regions for each generation that will be
83 // subject to collection, so that card table adjustments can
84 // be made intelligently (see clear / invalidate further below).
85 gch->save_used_regions();
86
87 allocate_stacks();
88
89 mark_sweep_phase1(clear_all_softrefs);
90
91 mark_sweep_phase2();
92
93 // Don't add any more derived pointers during phase3
94 #if defined(COMPILER2) || INCLUDE_JVMCI
95 assert(DerivedPointerTable::is_active(), "Sanity");
96 DerivedPointerTable::set_active(false);
97 #endif
98
99 mark_sweep_phase3();
100
101 mark_sweep_phase4();
102
103 restore_marks();
104
105 // Set saved marks for allocation profiler (and other things? -- dld)
106 // (Should this be in general part?)
107 gch->save_marks();
108
109 deallocate_stacks();
110
111 // If compaction completely evacuated the young generation then we
112 // can clear the card table. Otherwise, we must invalidate
113 // it (consider all cards dirty). In the future, we might consider doing
114 // compaction within generations only, and doing card-table sliding.
115 CardTableRS* rs = gch->rem_set();
116 Generation* old_gen = gch->old_gen();
117
118 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
119 if (gch->young_gen()->used() == 0) {
120 // We've evacuated the young generation.
121 rs->clear_into_younger(old_gen);
122 } else {
123 // Invalidate the cards corresponding to the currently used
124 // region and clear those corresponding to the evacuated region.
125 rs->invalidate_or_clear(old_gen);
126 }
127
128 CodeCache::gc_epilogue();
129 JvmtiExport::gc_epilogue();
130
131 // refs processing: clean slate
132 set_ref_processor(NULL);
133
134 // Update heap occupancy information which is used as
135 // input to soft ref clearing policy at the next gc.
136 Universe::update_heap_info_at_gc();
137
138 // Update time of last gc for all generations we collected
139 // (which currently is all the generations in the heap).
140 // We need to use a monotonically non-decreasing time in ms
141 // or we will see time-warp warnings and os::javaTimeMillis()
142 // does not guarantee monotonicity.
143 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
144 gch->update_time_of_last_gc(now);
145
146 gch->trace_heap_after_gc(_gc_tracer);
147 }
148
149 void GenMarkSweep::allocate_stacks() {
150 GenCollectedHeap* gch = GenCollectedHeap::heap();
151 // Scratch request on behalf of old generation; will do no allocation.
152 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
153
154 // $$$ To cut a corner, we'll only use the first scratch block, and then
155 // revert to malloc.
156 if (scratch != NULL) {
157 _preserved_count_max =
158 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
159 } else {
160 _preserved_count_max = 0;
161 }
162
163 _preserved_marks = (PreservedMark*)scratch;
164 _preserved_count = 0;
165 }
166
167
168 void GenMarkSweep::deallocate_stacks() {
169 if (!UseG1GC) {
170 GenCollectedHeap* gch = GenCollectedHeap::heap();
171 gch->release_scratch();
172 }
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()->num_q());
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("Class Unloading", gc_timer());
225
226 // Unload classes and purge the SystemDictionary.
227 bool purged_class = SystemDictionary::do_unloading(&is_alive, gc_timer());
228
229 // Unload nmethods.
230 CodeCache::do_unloading(&is_alive, purged_class);
231
232 // Prune dead klasses from subklass/sibling/implementor lists.
233 Klass::clean_weak_klass_links(&is_alive);
234 }
235
236 {
237 GCTraceTime(Debug, gc, phases) t("Scrub String Table", gc_timer());
238 // Delete entries for dead interned strings.
239 StringTable::unlink(&is_alive);
240 }
241
242 {
243 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", gc_timer());
244 // Clean up unreferenced symbols in symbol table.
245 SymbolTable::unlink();
246 }
247
248 gc_tracer()->report_object_count_after_gc(&is_alive);
249 }
250
251
252 void GenMarkSweep::mark_sweep_phase2() {
253 // Now all live objects are marked, compute the new object addresses.
254
255 // It is imperative that we traverse perm_gen LAST. If dead space is
256 // allowed a range of dead object may get overwritten by a dead int
257 // array. If perm_gen is not traversed last a Klass* may get
258 // overwritten. This is fine since it is dead, but if the class has dead
259 // instances we have to skip them, and in order to find their size we
260 // need the Klass*!
261 //
262 // It is not required that we traverse spaces in the same order in
263 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
264 // tracking expects us to do so. See comment under phase4.
265
266 GenCollectedHeap* gch = GenCollectedHeap::heap();
267
268 GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
269
270 gch->prepare_for_compaction();
271 }
272
273 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
274 public:
275 void do_generation(Generation* gen) {
276 gen->adjust_pointers();
277 }
278 };
279
280 void GenMarkSweep::mark_sweep_phase3() {
281 GenCollectedHeap* gch = GenCollectedHeap::heap();
282
283 // Adjust the pointers to reflect the new locations
284 GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
285
286 // Need new claim bits for the pointer adjustment tracing.
287 ClassLoaderDataGraph::clear_claimed_marks();
288
289 // Because the closure below is created statically, we cannot
290 // use OopsInGenClosure constructor which takes a generation,
291 // as the Universe has not been created when the static constructors
292 // are run.
293 adjust_pointer_closure.set_orig_generation(gch->old_gen());
294
295 {
296 StrongRootsScope srs(1);
297
298 gch->full_process_roots(&srs,
299 true, // this is the adjust phase
300 GenCollectedHeap::SO_AllCodeCache,
301 false, // all roots
302 &adjust_pointer_closure,
303 &adjust_cld_closure);
304 }
305
306 gch->gen_process_weak_roots(&adjust_pointer_closure);
307
308 adjust_marks();
309 GenAdjustPointersClosure blk;
310 gch->generation_iterate(&blk, true);
311 }
312
313 class GenCompactClosure: public GenCollectedHeap::GenClosure {
314 public:
315 void do_generation(Generation* gen) {
316 gen->compact();
317 }
318 };
319
320 void GenMarkSweep::mark_sweep_phase4() {
321 // All pointers are now adjusted, move objects accordingly
322
323 // It is imperative that we traverse perm_gen first in phase4. All
324 // classes must be allocated earlier than their instances, and traversing
325 // perm_gen first makes sure that all Klass*s have moved to their new
326 // location before any instance does a dispatch through it's klass!
327
328 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
329 // in the same order in phase2, phase3 and phase4. We don't quite do that
330 // here (perm_gen first rather than last), so we tell the validate code
331 // to use a higher index (saved from phase2) when verifying perm_gen.
332 GenCollectedHeap* gch = GenCollectedHeap::heap();
333
334 GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
335
336 GenCompactClosure blk;
337 gch->generation_iterate(&blk, true);
338 }