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 "gc/shared/weakProcessor.hpp"
47 #include "oops/instanceRefKlass.hpp"
48 #include "oops/oop.inline.hpp"
49 #include "prims/jvmtiExport.hpp"
50 #include "runtime/handles.inline.hpp"
51 #include "runtime/synchronizer.hpp"
52 #include "runtime/thread.inline.hpp"
53 #include "runtime/vmThread.hpp"
54 #include "utilities/copy.hpp"
55 #include "utilities/events.hpp"
56 #include "utilities/stack.inline.hpp"
57
58 void GenMarkSweep::invoke_at_safepoint(ReferenceProcessor* rp, bool clear_all_softrefs) {
59 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
60
61 GenCollectedHeap* gch = GenCollectedHeap::heap();
62 #ifdef ASSERT
63 if (gch->soft_ref_policy()->should_clear_all_soft_refs()) {
64 assert(clear_all_softrefs, "Policy should have been checked earlier");
65 }
66 #endif
67
68 // hook up weak ref data so it can be used during Mark-Sweep
69 assert(ref_processor() == NULL, "no stomping");
70 assert(rp != NULL, "should be non-NULL");
71 set_ref_processor(rp);
72 rp->setup_policy(clear_all_softrefs);
73
74 gch->trace_heap_before_gc(_gc_tracer);
75
76 // When collecting the permanent generation Method*s may be moving,
77 // so we either have to flush all bcp data or convert it into bci.
78 CodeCache::gc_prologue();
79
80 // Increment the invocation count
81 _total_invocations++;
82
83 // Capture used regions for each generation that will be
84 // subject to collection, so that card table adjustments can
85 // be made intelligently (see clear / invalidate further below).
86 gch->save_used_regions();
87
88 allocate_stacks();
89
90 mark_sweep_phase1(clear_all_softrefs);
91
92 mark_sweep_phase2();
93
94 // Don't add any more derived pointers during phase3
95 #if COMPILER2_OR_JVMCI
96 assert(DerivedPointerTable::is_active(), "Sanity");
97 DerivedPointerTable::set_active(false);
98 #endif
99
100 mark_sweep_phase3();
101
102 mark_sweep_phase4();
103
104 restore_marks();
105
106 // Set saved marks for allocation profiler (and other things? -- dld)
107 // (Should this be in general part?)
108 gch->save_marks();
109
110 deallocate_stacks();
111
112 // If compaction completely evacuated the young generation then we
113 // can clear the card table. Otherwise, we must invalidate
114 // it (consider all cards dirty). In the future, we might consider doing
115 // compaction within generations only, and doing card-table sliding.
116 CardTableRS* rs = gch->rem_set();
117 Generation* old_gen = gch->old_gen();
118
119 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
120 if (gch->young_gen()->used() == 0) {
121 // We've evacuated the young generation.
122 rs->clear_into_younger(old_gen);
123 } else {
124 // Invalidate the cards corresponding to the currently used
125 // region and clear those corresponding to the evacuated region.
126 rs->invalidate_or_clear(old_gen);
127 }
128
129 CodeCache::gc_epilogue();
130 JvmtiExport::gc_epilogue();
131
132 // refs processing: clean slate
133 set_ref_processor(NULL);
134
135 // Update heap occupancy information which is used as
136 // input to soft ref clearing policy at the next gc.
137 Universe::update_heap_info_at_gc();
138
139 // Update time of last gc for all generations we collected
140 // (which currently is all the generations in the heap).
141 // We need to use a monotonically non-decreasing time in ms
142 // or we will see time-warp warnings and os::javaTimeMillis()
143 // does not guarantee monotonicity.
144 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
145 gch->update_time_of_last_gc(now);
146
147 gch->trace_heap_after_gc(_gc_tracer);
148 }
149
150 void GenMarkSweep::allocate_stacks() {
151 GenCollectedHeap* gch = GenCollectedHeap::heap();
152 // Scratch request on behalf of old generation; will do no allocation.
153 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
154
155 // $$$ To cut a corner, we'll only use the first scratch block, and then
156 // revert to malloc.
157 if (scratch != NULL) {
158 _preserved_count_max =
159 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
160 } else {
161 _preserved_count_max = 0;
162 }
163
164 _preserved_marks = (PreservedMark*)scratch;
165 _preserved_count = 0;
166 }
167
168
169 void GenMarkSweep::deallocate_stacks() {
170 GenCollectedHeap* gch = GenCollectedHeap::heap();
171 gch->release_scratch();
172
173 _preserved_mark_stack.clear(true);
174 _preserved_oop_stack.clear(true);
175 _marking_stack.clear();
176 _objarray_stack.clear(true);
177 }
178
179 void GenMarkSweep::mark_sweep_phase1(bool clear_all_softrefs) {
180 // Recursively traverse all live objects and mark them
181 GCTraceTime(Info, gc, phases) tm("Phase 1: Mark live objects", _gc_timer);
182
183 GenCollectedHeap* gch = GenCollectedHeap::heap();
184
185 // Because follow_root_closure is created statically, cannot
186 // use OopsInGenClosure constructor which takes a generation,
187 // as the Universe has not been created when the static constructors
188 // are run.
189 follow_root_closure.set_orig_generation(gch->old_gen());
190
191 // Need new claim bits before marking starts.
192 ClassLoaderDataGraph::clear_claimed_marks();
193
194 {
195 StrongRootsScope srs(1);
196
197 gch->full_process_roots(&srs,
198 false, // not the adjust phase
199 GenCollectedHeap::SO_None,
200 ClassUnloading, // only strong roots if ClassUnloading
201 // is enabled
202 &follow_root_closure,
203 &follow_cld_closure);
204 }
205
206 // Process reference objects found during marking
207 {
208 GCTraceTime(Debug, gc, phases) tm_m("Reference Processing", gc_timer());
209
210 ref_processor()->setup_policy(clear_all_softrefs);
211 ReferenceProcessorPhaseTimes pt(_gc_timer, ref_processor()->num_q());
212 const ReferenceProcessorStats& stats =
213 ref_processor()->process_discovered_references(
214 &is_alive, &keep_alive, &follow_stack_closure, NULL, &pt);
215 pt.print_all_references();
216 gc_tracer()->report_gc_reference_stats(stats);
217 }
218
219 // This is the point where the entire marking should have completed.
220 assert(_marking_stack.is_empty(), "Marking should have completed");
221
222 {
223 GCTraceTime(Debug, gc, phases) tm_m("Weak Processing", gc_timer());
224 WeakProcessor::weak_oops_do(&is_alive, &do_nothing_cl);
225 }
226
227 {
228 GCTraceTime(Debug, gc, phases) tm_m("Class Unloading", gc_timer());
229
230 // Unload classes and purge the SystemDictionary.
231 bool purged_class = SystemDictionary::do_unloading(&is_alive, gc_timer());
232
233 // Unload nmethods.
234 CodeCache::do_unloading(&is_alive, purged_class);
235
236 // Prune dead klasses from subklass/sibling/implementor lists.
237 Klass::clean_weak_klass_links(&is_alive);
238 }
239
240 {
241 GCTraceTime(Debug, gc, phases) t("Scrub String Table", gc_timer());
242 // Delete entries for dead interned strings.
243 StringTable::unlink(&is_alive);
244 }
245
246 {
247 GCTraceTime(Debug, gc, phases) t("Scrub Symbol Table", gc_timer());
248 // Clean up unreferenced symbols in symbol table.
249 SymbolTable::unlink();
250 }
251
252 gc_tracer()->report_object_count_after_gc(&is_alive);
253 }
254
255
256 void GenMarkSweep::mark_sweep_phase2() {
257 // Now all live objects are marked, compute the new object addresses.
258
259 // It is imperative that we traverse perm_gen LAST. If dead space is
260 // allowed a range of dead object may get overwritten by a dead int
261 // array. If perm_gen is not traversed last a Klass* may get
262 // overwritten. This is fine since it is dead, but if the class has dead
263 // instances we have to skip them, and in order to find their size we
264 // need the Klass*!
265 //
266 // It is not required that we traverse spaces in the same order in
267 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
268 // tracking expects us to do so. See comment under phase4.
269
270 GenCollectedHeap* gch = GenCollectedHeap::heap();
271
272 GCTraceTime(Info, gc, phases) tm("Phase 2: Compute new object addresses", _gc_timer);
273
274 gch->prepare_for_compaction();
275 }
276
277 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
278 public:
279 void do_generation(Generation* gen) {
280 gen->adjust_pointers();
281 }
282 };
283
284 void GenMarkSweep::mark_sweep_phase3() {
285 GenCollectedHeap* gch = GenCollectedHeap::heap();
286
287 // Adjust the pointers to reflect the new locations
288 GCTraceTime(Info, gc, phases) tm("Phase 3: Adjust pointers", gc_timer());
289
290 // Need new claim bits for the pointer adjustment tracing.
291 ClassLoaderDataGraph::clear_claimed_marks();
292
293 // Because the closure below is created statically, we cannot
294 // use OopsInGenClosure constructor which takes a generation,
295 // as the Universe has not been created when the static constructors
296 // are run.
297 adjust_pointer_closure.set_orig_generation(gch->old_gen());
298
299 {
300 StrongRootsScope srs(1);
301
302 gch->full_process_roots(&srs,
303 true, // this is the adjust phase
304 GenCollectedHeap::SO_AllCodeCache,
305 false, // all roots
306 &adjust_pointer_closure,
307 &adjust_cld_closure);
308 }
309
310 gch->gen_process_weak_roots(&adjust_pointer_closure);
311
312 adjust_marks();
313 GenAdjustPointersClosure blk;
314 gch->generation_iterate(&blk, true);
315 }
316
317 class GenCompactClosure: public GenCollectedHeap::GenClosure {
318 public:
319 void do_generation(Generation* gen) {
320 gen->compact();
321 }
322 };
323
324 void GenMarkSweep::mark_sweep_phase4() {
325 // All pointers are now adjusted, move objects accordingly
326
327 // It is imperative that we traverse perm_gen first in phase4. All
328 // classes must be allocated earlier than their instances, and traversing
329 // perm_gen first makes sure that all Klass*s have moved to their new
330 // location before any instance does a dispatch through it's klass!
331
332 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
333 // in the same order in phase2, phase3 and phase4. We don't quite do that
334 // here (perm_gen first rather than last), so we tell the validate code
335 // to use a higher index (saved from phase2) when verifying perm_gen.
336 GenCollectedHeap* gch = GenCollectedHeap::heap();
337
338 GCTraceTime(Info, gc, phases) tm("Phase 4: Move objects", _gc_timer);
339
340 GenCompactClosure blk;
341 gch->generation_iterate(&blk, true);
342 }