1 /*
2 * Copyright (c) 2001, 2015, 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/systemDictionary.hpp"
29 #include "classfile/vmSymbols.hpp"
30 #include "code/codeCache.hpp"
31 #include "code/icBuffer.hpp"
32 #include "gc_implementation/shared/gcHeapSummary.hpp"
33 #include "gc_implementation/shared/gcTimer.hpp"
34 #include "gc_implementation/shared/gcTrace.hpp"
35 #include "gc_implementation/shared/gcTraceTime.hpp"
36 #include "gc_interface/collectedHeap.inline.hpp"
37 #include "memory/genCollectedHeap.hpp"
38 #include "memory/genMarkSweep.hpp"
39 #include "memory/genOopClosures.inline.hpp"
40 #include "memory/modRefBarrierSet.hpp"
41 #include "memory/referencePolicy.hpp"
42 #include "memory/space.hpp"
43 #include "oops/instanceRefKlass.hpp"
44 #include "oops/oop.inline.hpp"
45 #include "prims/jvmtiExport.hpp"
46 #include "runtime/fprofiler.hpp"
47 #include "runtime/handles.inline.hpp"
48 #include "runtime/synchronizer.hpp"
49 #include "runtime/thread.inline.hpp"
50 #include "runtime/vmThread.hpp"
51 #include "utilities/copy.hpp"
52 #include "utilities/events.hpp"
53
54 void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp, bool clear_all_softrefs) {
55 guarantee(level == 1, "We always collect both old and young.");
56 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
57
58 GenCollectedHeap* gch = GenCollectedHeap::heap();
59 #ifdef ASSERT
60 if (gch->collector_policy()->should_clear_all_soft_refs()) {
61 assert(clear_all_softrefs, "Policy should have been checked earlier");
62 }
63 #endif
64
65 // hook up weak ref data so it can be used during Mark-Sweep
66 assert(ref_processor() == NULL, "no stomping");
67 assert(rp != NULL, "should be non-NULL");
68 _ref_processor = rp;
69 rp->setup_policy(clear_all_softrefs);
70
71 GCTraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer->gc_id());
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 heap size before collection for printing.
83 size_t gch_prev_used = gch->used();
84
85 // Capture used regions for each generation that will be
86 // subject to collection, so that card table adjustments can
87 // be made intelligently (see clear / invalidate further below).
88 gch->save_used_regions(level);
89
90 allocate_stacks();
91
92 mark_sweep_phase1(level, clear_all_softrefs);
93
94 mark_sweep_phase2();
95
96 // Don't add any more derived pointers during phase3
97 COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
98 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
99
100 mark_sweep_phase3(level);
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 GenRemSet* 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 if (PrintGC && !PrintGCDetails) {
133 gch->print_heap_change(gch_prev_used);
134 }
135
136 // refs processing: clean slate
137 _ref_processor = NULL;
138
139 // Update heap occupancy information which is used as
140 // input to soft ref clearing policy at the next gc.
141 Universe::update_heap_info_at_gc();
142
143 // Update time of last gc for all generations we collected
144 // (which currently is all the generations in the heap).
145 // We need to use a monotonically non-decreasing time in ms
146 // or we will see time-warp warnings and os::javaTimeMillis()
147 // does not guarantee monotonicity.
148 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
149 gch->update_time_of_last_gc(now);
150
151 gch->trace_heap_after_gc(_gc_tracer);
152 }
153
154 void GenMarkSweep::allocate_stacks() {
155 GenCollectedHeap* gch = GenCollectedHeap::heap();
156 // Scratch request on behalf of old generation; will do no allocation.
157 ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
158
159 // $$$ To cut a corner, we'll only use the first scratch block, and then
160 // revert to malloc.
161 if (scratch != NULL) {
162 _preserved_count_max =
163 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
164 } else {
165 _preserved_count_max = 0;
166 }
167
168 _preserved_marks = (PreservedMark*)scratch;
169 _preserved_count = 0;
170 }
171
172
173 void GenMarkSweep::deallocate_stacks() {
174 if (!UseG1GC) {
175 GenCollectedHeap* gch = GenCollectedHeap::heap();
176 gch->release_scratch();
177 }
178
179 _preserved_mark_stack.clear(true);
180 _preserved_oop_stack.clear(true);
181 _marking_stack.clear();
182 _objarray_stack.clear(true);
183 }
184
185 void GenMarkSweep::mark_sweep_phase1(int level,
186 bool clear_all_softrefs) {
187 // Recursively traverse all live objects and mark them
188 GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
189 trace(" 1");
190
191 GenCollectedHeap* gch = GenCollectedHeap::heap();
192
193 // Because follow_root_closure is created statically, cannot
194 // use OopsInGenClosure constructor which takes a generation,
195 // as the Universe has not been created when the static constructors
196 // are run.
197 assert(level == 1, "We don't use mark-sweep on young generations");
198 follow_root_closure.set_orig_generation(gch->old_gen());
199
200 // Need new claim bits before marking starts.
201 ClassLoaderDataGraph::clear_claimed_marks();
202
203 gch->gen_process_roots(level,
204 false, // Younger gens are not roots.
205 true, // activate StrongRootsScope
206 GenCollectedHeap::SO_None,
207 GenCollectedHeap::StrongRootsOnly,
208 &follow_root_closure,
209 &follow_root_closure,
210 &follow_cld_closure);
211
212 // Process reference objects found during marking
213 {
214 ref_processor()->setup_policy(clear_all_softrefs);
215 const ReferenceProcessorStats& stats =
216 ref_processor()->process_discovered_references(
217 &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer, _gc_tracer->gc_id());
218 gc_tracer()->report_gc_reference_stats(stats);
219 }
220
221 // This is the point where the entire marking should have completed.
222 assert(_marking_stack.is_empty(), "Marking should have completed");
223
224 // Unload classes and purge the SystemDictionary.
225 bool purged_class = SystemDictionary::do_unloading(&is_alive);
226
227 // Unload nmethods.
228 CodeCache::do_unloading(&is_alive, purged_class);
229
230 // Prune dead klasses from subklass/sibling/implementor lists.
231 Klass::clean_weak_klass_links(&is_alive);
232
233 // Delete entries for dead interned strings.
234 StringTable::unlink(&is_alive);
235
236 // Clean up unreferenced symbols in symbol table.
237 SymbolTable::unlink();
238
239 gc_tracer()->report_object_count_after_gc(&is_alive);
240 }
241
242
243 void GenMarkSweep::mark_sweep_phase2() {
244 // Now all live objects are marked, compute the new object addresses.
245
246 // It is imperative that we traverse perm_gen LAST. If dead space is
247 // allowed a range of dead object may get overwritten by a dead int
248 // array. If perm_gen is not traversed last a Klass* may get
249 // overwritten. This is fine since it is dead, but if the class has dead
250 // instances we have to skip them, and in order to find their size we
251 // need the Klass*!
252 //
253 // It is not required that we traverse spaces in the same order in
254 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
255 // tracking expects us to do so. See comment under phase4.
256
257 GenCollectedHeap* gch = GenCollectedHeap::heap();
258
259 GCTraceTime tm("phase 2", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
260 trace("2");
261
262 gch->prepare_for_compaction();
263 }
264
265 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
266 public:
267 void do_generation(Generation* gen) {
268 gen->adjust_pointers();
269 }
270 };
271
272 void GenMarkSweep::mark_sweep_phase3(int level) {
273 GenCollectedHeap* gch = GenCollectedHeap::heap();
274
275 // Adjust the pointers to reflect the new locations
276 GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
277 trace("3");
278
279 // Need new claim bits for the pointer adjustment tracing.
280 ClassLoaderDataGraph::clear_claimed_marks();
281
282 // Because the closure below is created statically, we cannot
283 // use OopsInGenClosure constructor which takes a generation,
284 // as the Universe has not been created when the static constructors
285 // are run.
286 assert(level == 1, "We don't use mark-sweep on young generations.");
287 adjust_pointer_closure.set_orig_generation(gch->old_gen());
288
289 gch->gen_process_roots(level,
290 false, // Younger gens are not roots.
291 true, // activate StrongRootsScope
292 GenCollectedHeap::SO_AllCodeCache,
293 GenCollectedHeap::StrongAndWeakRoots,
294 &adjust_pointer_closure,
295 &adjust_pointer_closure,
296 &adjust_cld_closure);
297
298 gch->gen_process_weak_roots(&adjust_pointer_closure);
299
300 adjust_marks();
301 GenAdjustPointersClosure blk;
302 gch->generation_iterate(&blk, true);
303 }
304
305 class GenCompactClosure: public GenCollectedHeap::GenClosure {
306 public:
307 void do_generation(Generation* gen) {
308 gen->compact();
309 }
310 };
311
312 void GenMarkSweep::mark_sweep_phase4() {
313 // All pointers are now adjusted, move objects accordingly
314
315 // It is imperative that we traverse perm_gen first in phase4. All
316 // classes must be allocated earlier than their instances, and traversing
317 // perm_gen first makes sure that all Klass*s have moved to their new
318 // location before any instance does a dispatch through it's klass!
319
320 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
321 // in the same order in phase2, phase3 and phase4. We don't quite do that
322 // here (perm_gen first rather than last), so we tell the validate code
323 // to use a higher index (saved from phase2) when verifying perm_gen.
324 GenCollectedHeap* gch = GenCollectedHeap::heap();
325
326 GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
327 trace("4");
328
329 GenCompactClosure blk;
330 gch->generation_iterate(&blk, true);
331 }