1 /*
2 * Copyright (c) 2001, 2013, 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/symbolTable.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/generation.inline.hpp"
41 #include "memory/modRefBarrierSet.hpp"
42 #include "memory/referencePolicy.hpp"
43 #include "memory/space.hpp"
44 #include "oops/instanceRefKlass.hpp"
45 #include "oops/oop.inline.hpp"
46 #include "prims/jvmtiExport.hpp"
47 #include "runtime/fprofiler.hpp"
48 #include "runtime/handles.inline.hpp"
49 #include "runtime/synchronizer.hpp"
50 #include "runtime/thread.inline.hpp"
51 #include "runtime/vmThread.hpp"
52 #include "utilities/copy.hpp"
53 #include "utilities/events.hpp"
54
55 void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp, bool clear_all_softrefs) {
56 guarantee(level == 1, "We always collect both old and young.");
57 assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
58
59 GenCollectedHeap* gch = GenCollectedHeap::heap();
60 #ifdef ASSERT
61 if (gch->collector_policy()->should_clear_all_soft_refs()) {
62 assert(clear_all_softrefs, "Policy should have been checked earlier");
63 }
64 #endif
65
66 // hook up weak ref data so it can be used during Mark-Sweep
67 assert(ref_processor() == NULL, "no stomping");
68 assert(rp != NULL, "should be non-NULL");
69 _ref_processor = rp;
70 rp->setup_policy(clear_all_softrefs);
71
72 GCTraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL);
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 Threads::gc_prologue();
80
81 // Increment the invocation count
82 _total_invocations++;
83
84 // Capture heap size before collection for printing.
85 size_t gch_prev_used = gch->used();
86
87 // Capture used regions for each generation that will be
88 // subject to collection, so that card table adjustments can
89 // be made intelligently (see clear / invalidate further below).
90 gch->save_used_regions(level);
91
92 allocate_stacks();
93
94 mark_sweep_phase1(level, clear_all_softrefs);
95
96 mark_sweep_phase2();
97
98 // Don't add any more derived pointers during phase3
99 COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
100 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
101
102 mark_sweep_phase3(level);
103
104 mark_sweep_phase4();
105
106 restore_marks();
107
108 // Set saved marks for allocation profiler (and other things? -- dld)
109 // (Should this be in general part?)
110 gch->save_marks();
111
112 deallocate_stacks();
113
114 // If compaction completely evacuated all generations younger than this
115 // one, then we can clear the card table. Otherwise, we must invalidate
116 // it (consider all cards dirty). In the future, we might consider doing
117 // compaction within generations only, and doing card-table sliding.
118 bool all_empty = true;
119 for (int i = 0; all_empty && i < level; i++) {
120 Generation* g = gch->get_gen(i);
121 all_empty = all_empty && gch->get_gen(i)->used() == 0;
122 }
123 GenRemSet* rs = gch->rem_set();
124 Generation* old_gen = gch->get_gen(level);
125 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
126 if (all_empty) {
127 // We've evacuated all generations below us.
128 rs->clear_into_younger(old_gen);
129 } else {
130 // Invalidate the cards corresponding to the currently used
131 // region and clear those corresponding to the evacuated region
132 // of all generations just collected.
133 rs->invalidate_or_clear(old_gen);
134 }
135
136 Threads::gc_epilogue();
137 CodeCache::gc_epilogue();
138 JvmtiExport::gc_epilogue();
139
140 if (PrintGC && !PrintGCDetails) {
141 gch->print_heap_change(gch_prev_used);
142 }
143
144 // refs processing: clean slate
145 _ref_processor = NULL;
146
147 // Update heap occupancy information which is used as
148 // input to soft ref clearing policy at the next gc.
149 Universe::update_heap_info_at_gc();
150
151 // Update time of last gc for all generations we collected
152 // (which curently is all the generations in the heap).
153 // We need to use a monotonically non-deccreasing time in ms
154 // or we will see time-warp warnings and os::javaTimeMillis()
155 // does not guarantee monotonicity.
156 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
157 gch->update_time_of_last_gc(now);
158
159 gch->trace_heap_after_gc(_gc_tracer);
160 }
161
162 void GenMarkSweep::allocate_stacks() {
163 GenCollectedHeap* gch = GenCollectedHeap::heap();
164 // Scratch request on behalf of oldest generation; will do no
165 // allocation.
166 ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);
167
168 // $$$ To cut a corner, we'll only use the first scratch block, and then
169 // revert to malloc.
170 if (scratch != NULL) {
171 _preserved_count_max =
172 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
173 } else {
174 _preserved_count_max = 0;
175 }
176
177 _preserved_marks = (PreservedMark*)scratch;
178 _preserved_count = 0;
179 }
180
181
182 void GenMarkSweep::deallocate_stacks() {
183 if (!UseG1GC) {
184 GenCollectedHeap* gch = GenCollectedHeap::heap();
185 gch->release_scratch();
186 }
187
188 _preserved_mark_stack.clear(true);
189 _preserved_oop_stack.clear(true);
190 _marking_stack.clear();
191 _objarray_stack.clear(true);
192 }
193
194 void GenMarkSweep::mark_sweep_phase1(int level,
195 bool clear_all_softrefs) {
196 // Recursively traverse all live objects and mark them
197 GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer);
198 trace(" 1");
199
200 GenCollectedHeap* gch = GenCollectedHeap::heap();
201
202 // Because follow_root_closure is created statically, cannot
203 // use OopsInGenClosure constructor which takes a generation,
204 // as the Universe has not been created when the static constructors
205 // are run.
206 follow_root_closure.set_orig_generation(gch->get_gen(level));
207
208 // Need new claim bits before marking starts.
209 ClassLoaderDataGraph::clear_claimed_marks();
210
211 gch->gen_process_strong_roots(level,
212 false, // Younger gens are not roots.
213 true, // activate StrongRootsScope
214 false, // not scavenging
215 SharedHeap::SO_SystemClasses,
216 &follow_root_closure,
217 true, // walk code active on stacks
218 &follow_root_closure,
219 &follow_klass_closure);
220
221 // Process reference objects found during marking
222 {
223 ref_processor()->setup_policy(clear_all_softrefs);
224 const ReferenceProcessorStats& stats =
225 ref_processor()->process_discovered_references(
226 &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer);
227 gc_tracer()->report_gc_reference_stats(stats);
228 }
229
230 // This is the point where the entire marking should have completed.
231 assert(_marking_stack.is_empty(), "Marking should have completed");
232
233 // Unload classes and purge the SystemDictionary.
234 bool purged_class = SystemDictionary::do_unloading(&is_alive);
235
236 // Unload nmethods.
237 CodeCache::do_unloading(&is_alive, purged_class);
238
239 // Prune dead klasses from subklass/sibling/implementor lists.
240 Klass::clean_weak_klass_links(&is_alive);
241
242 // Delete entries for dead interned strings.
243 StringTable::unlink(&is_alive);
244
245 // Clean up unreferenced symbols in symbol table.
246 SymbolTable::unlink();
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 tm("phase 2", PrintGC && Verbose, true, _gc_timer);
269 trace("2");
270
271 gch->prepare_for_compaction();
272 }
273
274 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
275 public:
276 void do_generation(Generation* gen) {
277 gen->adjust_pointers();
278 }
279 };
280
281 void GenMarkSweep::mark_sweep_phase3(int level) {
282 GenCollectedHeap* gch = GenCollectedHeap::heap();
283
284 // Adjust the pointers to reflect the new locations
285 GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer);
286 trace("3");
287
288 // Need new claim bits for the pointer adjustment tracing.
289 ClassLoaderDataGraph::clear_claimed_marks();
290
291 // Because the closure below is created statically, we cannot
292 // use OopsInGenClosure constructor which takes a generation,
293 // as the Universe has not been created when the static constructors
294 // are run.
295 adjust_pointer_closure.set_orig_generation(gch->get_gen(level));
296
297 gch->gen_process_strong_roots(level,
298 false, // Younger gens are not roots.
299 true, // activate StrongRootsScope
300 false, // not scavenging
301 SharedHeap::SO_AllClasses,
302 &adjust_pointer_closure,
303 false, // do not walk code
304 &adjust_pointer_closure,
305 &adjust_klass_closure);
306
307 // Now adjust pointers in remaining weak roots. (All of which should
308 // have been cleared if they pointed to non-surviving objects.)
309 CodeBlobToOopClosure adjust_code_pointer_closure(&adjust_pointer_closure,
310 /*do_marking=*/ false);
311 gch->gen_process_weak_roots(&adjust_pointer_closure,
312 &adjust_code_pointer_closure);
313
314 adjust_marks();
315 GenAdjustPointersClosure blk;
316 gch->generation_iterate(&blk, true);
317 }
318
319 class GenCompactClosure: public GenCollectedHeap::GenClosure {
320 public:
321 void do_generation(Generation* gen) {
322 gen->compact();
323 }
324 };
325
326 void GenMarkSweep::mark_sweep_phase4() {
327 // All pointers are now adjusted, move objects accordingly
328
329 // It is imperative that we traverse perm_gen first in phase4. All
330 // classes must be allocated earlier than their instances, and traversing
331 // perm_gen first makes sure that all Klass*s have moved to their new
332 // location before any instance does a dispatch through it's klass!
333
334 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
335 // in the same order in phase2, phase3 and phase4. We don't quite do that
336 // here (perm_gen first rather than last), so we tell the validate code
337 // to use a higher index (saved from phase2) when verifying perm_gen.
338 GenCollectedHeap* gch = GenCollectedHeap::heap();
339
340 GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer);
341 trace("4");
342
343 GenCompactClosure blk;
344 gch->generation_iterate(&blk, true);
345 }