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 all generations younger than this
113 // one, then we 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 bool all_empty = true;
117 for (int i = 0; all_empty && i < level; i++) {
118 Generation* g = gch->get_gen(i);
119 all_empty = all_empty && gch->get_gen(i)->used() == 0;
120 }
121 GenRemSet* rs = gch->rem_set();
122 Generation* old_gen = gch->get_gen(level);
123 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
124 if (all_empty) {
125 // We've evacuated all generations below us.
126 rs->clear_into_younger(old_gen);
127 } else {
128 // Invalidate the cards corresponding to the currently used
129 // region and clear those corresponding to the evacuated region.
130 rs->invalidate_or_clear(old_gen);
131 }
132
133 CodeCache::gc_epilogue();
134 JvmtiExport::gc_epilogue();
135
136 if (PrintGC && !PrintGCDetails) {
137 gch->print_heap_change(gch_prev_used);
138 }
139
140 // refs processing: clean slate
141 _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::update_heap_info_at_gc();
146
147 // Update time of last gc for all generations we collected
148 // (which currently is all the generations in the heap).
149 // We need to use a monotonically non-decreasing time in ms
150 // or we will see time-warp warnings and os::javaTimeMillis()
151 // does not guarantee monotonicity.
152 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
153 gch->update_time_of_last_gc(now);
154
155 gch->trace_heap_after_gc(_gc_tracer);
156 }
157
158 void GenMarkSweep::allocate_stacks() {
159 GenCollectedHeap* gch = GenCollectedHeap::heap();
160 // Scratch request on behalf of oldest generation; will do no
161 // allocation.
162 ScratchBlock* scratch = gch->gather_scratch(gch->get_gen(gch->_n_gens-1), 0);
163
164 // $$$ To cut a corner, we'll only use the first scratch block, and then
165 // revert to malloc.
166 if (scratch != NULL) {
167 _preserved_count_max =
168 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
169 } else {
170 _preserved_count_max = 0;
171 }
172
173 _preserved_marks = (PreservedMark*)scratch;
174 _preserved_count = 0;
175 }
176
177
178 void GenMarkSweep::deallocate_stacks() {
179 if (!UseG1GC) {
180 GenCollectedHeap* gch = GenCollectedHeap::heap();
181 gch->release_scratch();
182 }
183
184 _preserved_mark_stack.clear(true);
185 _preserved_oop_stack.clear(true);
186 _marking_stack.clear();
187 _objarray_stack.clear(true);
188 }
189
190 void GenMarkSweep::mark_sweep_phase1(int level,
191 bool clear_all_softrefs) {
192 // Recursively traverse all live objects and mark them
193 GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
194 trace(" 1");
195
196 GenCollectedHeap* gch = GenCollectedHeap::heap();
197
198 // Because follow_root_closure is created statically, cannot
199 // use OopsInGenClosure constructor which takes a generation,
200 // as the Universe has not been created when the static constructors
201 // are run.
202 follow_root_closure.set_orig_generation(gch->get_gen(level));
203
204 // Need new claim bits before marking starts.
205 ClassLoaderDataGraph::clear_claimed_marks();
206
207 gch->gen_process_roots(level,
208 false, // Younger gens are not roots.
209 true, // activate StrongRootsScope
210 GenCollectedHeap::SO_None,
211 GenCollectedHeap::StrongRootsOnly,
212 &follow_root_closure,
213 &follow_root_closure,
214 &follow_cld_closure);
215
216 // Process reference objects found during marking
217 {
218 ref_processor()->setup_policy(clear_all_softrefs);
219 const ReferenceProcessorStats& stats =
220 ref_processor()->process_discovered_references(
221 &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer, _gc_tracer->gc_id());
222 gc_tracer()->report_gc_reference_stats(stats);
223 }
224
225 // This is the point where the entire marking should have completed.
226 assert(_marking_stack.is_empty(), "Marking should have completed");
227
228 // Unload classes and purge the SystemDictionary.
229 bool purged_class = SystemDictionary::do_unloading(&is_alive);
230
231 // Unload nmethods.
232 CodeCache::do_unloading(&is_alive, purged_class);
233
234 // Prune dead klasses from subklass/sibling/implementor lists.
235 Klass::clean_weak_klass_links(&is_alive);
236
237 // Delete entries for dead interned strings.
238 StringTable::unlink(&is_alive);
239
240 // Clean up unreferenced symbols in symbol table.
241 SymbolTable::unlink();
242
243 gc_tracer()->report_object_count_after_gc(&is_alive);
244 }
245
246
247 void GenMarkSweep::mark_sweep_phase2() {
248 // Now all live objects are marked, compute the new object addresses.
249
250 // It is imperative that we traverse perm_gen LAST. If dead space is
251 // allowed a range of dead object may get overwritten by a dead int
252 // array. If perm_gen is not traversed last a Klass* may get
253 // overwritten. This is fine since it is dead, but if the class has dead
254 // instances we have to skip them, and in order to find their size we
255 // need the Klass*!
256 //
257 // It is not required that we traverse spaces in the same order in
258 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
259 // tracking expects us to do so. See comment under phase4.
260
261 GenCollectedHeap* gch = GenCollectedHeap::heap();
262
263 GCTraceTime tm("phase 2", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
264 trace("2");
265
266 gch->prepare_for_compaction();
267 }
268
269 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
270 public:
271 void do_generation(Generation* gen) {
272 gen->adjust_pointers();
273 }
274 };
275
276 void GenMarkSweep::mark_sweep_phase3(int level) {
277 GenCollectedHeap* gch = GenCollectedHeap::heap();
278
279 // Adjust the pointers to reflect the new locations
280 GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
281 trace("3");
282
283 // Need new claim bits for the pointer adjustment tracing.
284 ClassLoaderDataGraph::clear_claimed_marks();
285
286 // Because the closure below is created statically, we cannot
287 // use OopsInGenClosure constructor which takes a generation,
288 // as the Universe has not been created when the static constructors
289 // are run.
290 adjust_pointer_closure.set_orig_generation(gch->get_gen(level));
291
292 gch->gen_process_roots(level,
293 false, // Younger gens are not roots.
294 true, // activate StrongRootsScope
295 GenCollectedHeap::SO_AllCodeCache,
296 GenCollectedHeap::StrongAndWeakRoots,
297 &adjust_pointer_closure,
298 &adjust_pointer_closure,
299 &adjust_cld_closure);
300
301 gch->gen_process_weak_roots(&adjust_pointer_closure);
302
303 adjust_marks();
304 GenAdjustPointersClosure blk;
305 gch->generation_iterate(&blk, true);
306 }
307
308 class GenCompactClosure: public GenCollectedHeap::GenClosure {
309 public:
310 void do_generation(Generation* gen) {
311 gen->compact();
312 }
313 };
314
315 void GenMarkSweep::mark_sweep_phase4() {
316 // All pointers are now adjusted, move objects accordingly
317
318 // It is imperative that we traverse perm_gen first in phase4. All
319 // classes must be allocated earlier than their instances, and traversing
320 // perm_gen first makes sure that all Klass*s have moved to their new
321 // location before any instance does a dispatch through it's klass!
322
323 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
324 // in the same order in phase2, phase3 and phase4. We don't quite do that
325 // here (perm_gen first rather than last), so we tell the validate code
326 // to use a higher index (saved from phase2) when verifying perm_gen.
327 GenCollectedHeap* gch = GenCollectedHeap::heap();
328
329 GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
330 trace("4");
331
332 GenCompactClosure blk;
333 gch->generation_iterate(&blk, true);
334 }