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,
56 bool clear_all_softrefs) {
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 guarantee(level == 1, "We always collect both old and young.");
88
89 // Capture used regions for each generation that will be
90 // subject to collection, so that card table adjustments can
91 // be made intelligently (see clear / invalidate further below).
92 gch->save_used_regions(level);
93
94 allocate_stacks();
95
96 mark_sweep_phase1(level, clear_all_softrefs);
97
98 mark_sweep_phase2();
99
100 // Don't add any more derived pointers during phase3
101 COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
102 COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
103
104 mark_sweep_phase3(level);
105
106 mark_sweep_phase4();
107
108 restore_marks();
109
110 // Set saved marks for allocation profiler (and other things? -- dld)
111 // (Should this be in general part?)
112 gch->save_marks();
113
114 deallocate_stacks();
115
116 // If compaction completely evacuated all generations younger than this
117 // one, then we can clear the card table. Otherwise, we must invalidate
118 // it (consider all cards dirty). In the future, we might consider doing
119 // compaction within generations only, and doing card-table sliding.
120 bool all_empty = true;
121 for (int i = 0; all_empty && i < level; i++) {
122 Generation* g = gch->get_gen(i);
123 all_empty = all_empty && gch->get_gen(i)->used() == 0;
124 }
125 GenRemSet* rs = gch->rem_set();
126 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
127 if (all_empty) {
128 // We've evacuated all generations below us.
129 Generation* g = gch->get_gen(level);
130 rs->clear_into_younger(g);
131 } else {
132 // Invalidate the cards corresponding to the currently used
133 // region and clear those corresponding to the evacuated region
134 // of all generations just collected.
135 rs->invalidate_or_clear(gch->get_gen(1));
136 rs->invalidate_or_clear(gch->get_gen(0));
137 }
138
139 Threads::gc_epilogue();
140 CodeCache::gc_epilogue();
141 JvmtiExport::gc_epilogue();
142
143 if (PrintGC && !PrintGCDetails) {
144 gch->print_heap_change(gch_prev_used);
145 }
146
147 // refs processing: clean slate
148 _ref_processor = NULL;
149
150 // Update heap occupancy information which is used as
151 // input to soft ref clearing policy at the next gc.
152 Universe::update_heap_info_at_gc();
153
154 // Update time of last gc for all generations we collected
155 // (which curently is all the generations in the heap).
156 // We need to use a monotonically non-deccreasing time in ms
157 // or we will see time-warp warnings and os::javaTimeMillis()
158 // does not guarantee monotonicity.
159 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
160 gch->update_time_of_last_gc(now);
161
162 gch->trace_heap_after_gc(_gc_tracer);
163 }
164
165 void GenMarkSweep::allocate_stacks() {
166 GenCollectedHeap* gch = GenCollectedHeap::heap();
167 // Scratch request on behalf of oldest generation; will do no
168 // allocation.
169 ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);
170
171 // $$$ To cut a corner, we'll only use the first scratch block, and then
172 // revert to malloc.
173 if (scratch != NULL) {
174 _preserved_count_max =
175 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
176 } else {
177 _preserved_count_max = 0;
178 }
179
180 _preserved_marks = (PreservedMark*)scratch;
181 _preserved_count = 0;
182 }
183
184
185 void GenMarkSweep::deallocate_stacks() {
186 if (!UseG1GC) {
187 GenCollectedHeap* gch = GenCollectedHeap::heap();
188 gch->release_scratch();
189 }
190
191 _preserved_mark_stack.clear(true);
192 _preserved_oop_stack.clear(true);
193 _marking_stack.clear();
194 _objarray_stack.clear(true);
195 }
196
197 void GenMarkSweep::mark_sweep_phase1(int level,
198 bool clear_all_softrefs) {
199 // Recursively traverse all live objects and mark them
200 GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer);
201 trace(" 1");
202
203 GenCollectedHeap* gch = GenCollectedHeap::heap();
204
205 // Because follow_root_closure is created statically, cannot
206 // use OopsInGenClosure constructor which takes a generation,
207 // as the Universe has not been created when the static constructors
208 // are run.
209 follow_root_closure.set_orig_generation(gch->get_gen(level));
210
211 // Need new claim bits before marking starts.
212 ClassLoaderDataGraph::clear_claimed_marks();
213
214 gch->gen_process_strong_roots(level,
215 false, // Younger gens are not roots.
216 true, // activate StrongRootsScope
217 false, // not scavenging
218 SharedHeap::SO_SystemClasses,
219 &follow_root_closure,
220 true, // walk code active on stacks
221 &follow_root_closure,
222 &follow_klass_closure);
223
224 // Process reference objects found during marking
225 {
226 ref_processor()->setup_policy(clear_all_softrefs);
227 const ReferenceProcessorStats& stats =
228 ref_processor()->process_discovered_references(
229 &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer);
230 gc_tracer()->report_gc_reference_stats(stats);
231 }
232
233 // This is the point where the entire marking should have completed.
234 assert(_marking_stack.is_empty(), "Marking should have completed");
235
236 // Unload classes and purge the SystemDictionary.
237 bool purged_class = SystemDictionary::do_unloading(&is_alive);
238
239 // Unload nmethods.
240 CodeCache::do_unloading(&is_alive, purged_class);
241
242 // Prune dead klasses from subklass/sibling/implementor lists.
243 Klass::clean_weak_klass_links(&is_alive);
244
245 // Delete entries for dead interned strings.
246 StringTable::unlink(&is_alive);
247
248 // Clean up unreferenced symbols in symbol table.
249 SymbolTable::unlink();
250
251 gc_tracer()->report_object_count_after_gc(&is_alive);
252 }
253
254
255 void GenMarkSweep::mark_sweep_phase2() {
256 // Now all live objects are marked, compute the new object addresses.
257
258 // It is imperative that we traverse perm_gen LAST. If dead space is
259 // allowed a range of dead object may get overwritten by a dead int
260 // array. If perm_gen is not traversed last a Klass* may get
261 // overwritten. This is fine since it is dead, but if the class has dead
262 // instances we have to skip them, and in order to find their size we
263 // need the Klass*!
264 //
265 // It is not required that we traverse spaces in the same order in
266 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
267 // tracking expects us to do so. See comment under phase4.
268
269 GenCollectedHeap* gch = GenCollectedHeap::heap();
270
271 GCTraceTime tm("phase 2", PrintGC && Verbose, true, _gc_timer);
272 trace("2");
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(int level) {
285 GenCollectedHeap* gch = GenCollectedHeap::heap();
286
287 // Adjust the pointers to reflect the new locations
288 GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer);
289 trace("3");
290
291 // Need new claim bits for the pointer adjustment tracing.
292 ClassLoaderDataGraph::clear_claimed_marks();
293
294 // Because the closure below is created statically, we cannot
295 // use OopsInGenClosure constructor which takes a generation,
296 // as the Universe has not been created when the static constructors
297 // are run.
298 adjust_pointer_closure.set_orig_generation(gch->get_gen(level));
299
300 gch->gen_process_strong_roots(level,
301 false, // Younger gens are not roots.
302 true, // activate StrongRootsScope
303 false, // not scavenging
304 SharedHeap::SO_AllClasses,
305 &adjust_pointer_closure,
306 false, // do not walk code
307 &adjust_pointer_closure,
308 &adjust_klass_closure);
309
310 // Now adjust pointers in remaining weak roots. (All of which should
311 // have been cleared if they pointed to non-surviving objects.)
312 CodeBlobToOopClosure adjust_code_pointer_closure(&adjust_pointer_closure,
313 /*do_marking=*/ false);
314 gch->gen_process_weak_roots(&adjust_pointer_closure,
315 &adjust_code_pointer_closure);
316
317 adjust_marks();
318 GenAdjustPointersClosure blk;
319 gch->generation_iterate(&blk, true);
320 }
321
322 class GenCompactClosure: public GenCollectedHeap::GenClosure {
323 public:
324 void do_generation(Generation* gen) {
325 gen->compact();
326 }
327 };
328
329 void GenMarkSweep::mark_sweep_phase4() {
330 // All pointers are now adjusted, move objects accordingly
331
332 // It is imperative that we traverse perm_gen first in phase4. All
333 // classes must be allocated earlier than their instances, and traversing
334 // perm_gen first makes sure that all Klass*s have moved to their new
335 // location before any instance does a dispatch through it's klass!
336
337 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
338 // in the same order in phase2, phase3 and phase4. We don't quite do that
339 // here (perm_gen first rather than last), so we tell the validate code
340 // to use a higher index (saved from phase2) when verifying perm_gen.
341 GenCollectedHeap* gch = GenCollectedHeap::heap();
342
343 GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer);
344 trace("4");
345
346 GenCompactClosure blk;
347 gch->generation_iterate(&blk, true);
348 }