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 // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
125 if (all_empty) {
126 // We've evacuated all generations below us.
127 Generation* g = gch->get_gen(level);
128 rs->clear_into_younger(g);
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(gch->get_gen(1));
134 rs->invalidate_or_clear(gch->get_gen(0));
135 }
136
137 Threads::gc_epilogue();
138 CodeCache::gc_epilogue();
139 JvmtiExport::gc_epilogue();
140
141 if (PrintGC && !PrintGCDetails) {
142 gch->print_heap_change(gch_prev_used);
143 }
144
145 // refs processing: clean slate
146 _ref_processor = NULL;
147
148 // Update heap occupancy information which is used as
149 // input to soft ref clearing policy at the next gc.
150 Universe::update_heap_info_at_gc();
151
152 // Update time of last gc for all generations we collected
153 // (which curently is all the generations in the heap).
154 // We need to use a monotonically non-deccreasing time in ms
155 // or we will see time-warp warnings and os::javaTimeMillis()
156 // does not guarantee monotonicity.
157 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
158 gch->update_time_of_last_gc(now);
159
160 gch->trace_heap_after_gc(_gc_tracer);
161 }
162
163 void GenMarkSweep::allocate_stacks() {
164 GenCollectedHeap* gch = GenCollectedHeap::heap();
165 // Scratch request on behalf of oldest generation; will do no
166 // allocation.
167 ScratchBlock* scratch = gch->gather_scratch(gch->_gens[gch->_n_gens-1], 0);
168
169 // $$$ To cut a corner, we'll only use the first scratch block, and then
170 // revert to malloc.
171 if (scratch != NULL) {
172 _preserved_count_max =
173 scratch->num_words * HeapWordSize / sizeof(PreservedMark);
174 } else {
175 _preserved_count_max = 0;
176 }
177
178 _preserved_marks = (PreservedMark*)scratch;
179 _preserved_count = 0;
180 }
181
182
183 void GenMarkSweep::deallocate_stacks() {
184 if (!UseG1GC) {
185 GenCollectedHeap* gch = GenCollectedHeap::heap();
186 gch->release_scratch();
187 }
188
189 _preserved_mark_stack.clear(true);
190 _preserved_oop_stack.clear(true);
191 _marking_stack.clear();
192 _objarray_stack.clear(true);
193 }
194
195 void GenMarkSweep::mark_sweep_phase1(int level,
196 bool clear_all_softrefs) {
197 // Recursively traverse all live objects and mark them
198 GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer);
199 trace(" 1");
200
201 GenCollectedHeap* gch = GenCollectedHeap::heap();
202
203 // Because follow_root_closure is created statically, cannot
204 // use OopsInGenClosure constructor which takes a generation,
205 // as the Universe has not been created when the static constructors
206 // are run.
207 follow_root_closure.set_orig_generation(gch->get_gen(level));
208
209 // Need new claim bits before marking starts.
210 ClassLoaderDataGraph::clear_claimed_marks();
211
212 gch->gen_process_strong_roots(level,
213 false, // Younger gens are not roots.
214 true, // activate StrongRootsScope
215 false, // not scavenging
216 SharedHeap::SO_SystemClasses,
217 &follow_root_closure,
218 true, // walk code active on stacks
219 &follow_root_closure,
220 &follow_klass_closure);
221
222 // Process reference objects found during marking
223 {
224 ref_processor()->setup_policy(clear_all_softrefs);
225 const ReferenceProcessorStats& stats =
226 ref_processor()->process_discovered_references(
227 &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer);
228 gc_tracer()->report_gc_reference_stats(stats);
229 }
230
231 // This is the point where the entire marking should have completed.
232 assert(_marking_stack.is_empty(), "Marking should have completed");
233
234 // Unload classes and purge the SystemDictionary.
235 bool purged_class = SystemDictionary::do_unloading(&is_alive);
236
237 // Unload nmethods.
238 CodeCache::do_unloading(&is_alive, purged_class);
239
240 // Prune dead klasses from subklass/sibling/implementor lists.
241 Klass::clean_weak_klass_links(&is_alive);
242
243 // Delete entries for dead interned strings.
244 StringTable::unlink(&is_alive);
245
246 // Clean up unreferenced symbols in symbol table.
247 SymbolTable::unlink();
248
249 gc_tracer()->report_object_count_after_gc(&is_alive);
250 }
251
252
253 void GenMarkSweep::mark_sweep_phase2() {
254 // Now all live objects are marked, compute the new object addresses.
255
256 // It is imperative that we traverse perm_gen LAST. If dead space is
257 // allowed a range of dead object may get overwritten by a dead int
258 // array. If perm_gen is not traversed last a Klass* may get
259 // overwritten. This is fine since it is dead, but if the class has dead
260 // instances we have to skip them, and in order to find their size we
261 // need the Klass*!
262 //
263 // It is not required that we traverse spaces in the same order in
264 // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
265 // tracking expects us to do so. See comment under phase4.
266
267 GenCollectedHeap* gch = GenCollectedHeap::heap();
268
269 GCTraceTime tm("phase 2", PrintGC && Verbose, true, _gc_timer);
270 trace("2");
271
272 gch->prepare_for_compaction();
273 }
274
275 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
276 public:
277 void do_generation(Generation* gen) {
278 gen->adjust_pointers();
279 }
280 };
281
282 void GenMarkSweep::mark_sweep_phase3(int level) {
283 GenCollectedHeap* gch = GenCollectedHeap::heap();
284
285 // Adjust the pointers to reflect the new locations
286 GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer);
287 trace("3");
288
289 // Need new claim bits for the pointer adjustment tracing.
290 ClassLoaderDataGraph::clear_claimed_marks();
291
292 // Because the closure below is created statically, we cannot
293 // use OopsInGenClosure constructor which takes a generation,
294 // as the Universe has not been created when the static constructors
295 // are run.
296 adjust_pointer_closure.set_orig_generation(gch->get_gen(level));
297
298 gch->gen_process_strong_roots(level,
299 false, // Younger gens are not roots.
300 true, // activate StrongRootsScope
301 false, // not scavenging
302 SharedHeap::SO_AllClasses,
303 &adjust_pointer_closure,
304 false, // do not walk code
305 &adjust_pointer_closure,
306 &adjust_klass_closure);
307
308 // Now adjust pointers in remaining weak roots. (All of which should
309 // have been cleared if they pointed to non-surviving objects.)
310 CodeBlobToOopClosure adjust_code_pointer_closure(&adjust_pointer_closure,
311 /*do_marking=*/ false);
312 gch->gen_process_weak_roots(&adjust_pointer_closure,
313 &adjust_code_pointer_closure);
314
315 adjust_marks();
316 GenAdjustPointersClosure blk;
317 gch->generation_iterate(&blk, true);
318 }
319
320 class GenCompactClosure: public GenCollectedHeap::GenClosure {
321 public:
322 void do_generation(Generation* gen) {
323 gen->compact();
324 }
325 };
326
327 void GenMarkSweep::mark_sweep_phase4() {
328 // All pointers are now adjusted, move objects accordingly
329
330 // It is imperative that we traverse perm_gen first in phase4. All
331 // classes must be allocated earlier than their instances, and traversing
332 // perm_gen first makes sure that all Klass*s have moved to their new
333 // location before any instance does a dispatch through it's klass!
334
335 // The ValidateMarkSweep live oops tracking expects us to traverse spaces
336 // in the same order in phase2, phase3 and phase4. We don't quite do that
337 // here (perm_gen first rather than last), so we tell the validate code
338 // to use a higher index (saved from phase2) when verifying perm_gen.
339 GenCollectedHeap* gch = GenCollectedHeap::heap();
340
341 GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer);
342 trace("4");
343
344 GenCompactClosure blk;
345 gch->generation_iterate(&blk, true);
346 }