1 /*
2 * Copyright (c) 1997, 2009, 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 class ReferenceProcessor;
26 class DataLayout;
27
28 // MarkSweep takes care of global mark-compact garbage collection for a
29 // GenCollectedHeap using a four-phase pointer forwarding algorithm. All
30 // generations are assumed to support marking; those that can also support
31 // compaction.
32 //
33 // Class unloading will only occur when a full gc is invoked.
34
35 // If VALIDATE_MARK_SWEEP is defined, the -XX:+ValidateMarkSweep flag will
36 // be operational, and will provide slow but comprehensive self-checks within
37 // the GC. This is not enabled by default in product or release builds,
38 // since the extra call to track_adjusted_pointer() in _adjust_pointer()
39 // would be too much overhead, and would disturb performance measurement.
40 // However, debug builds are sometimes way too slow to run GC tests!
41 #ifdef ASSERT
42 #define VALIDATE_MARK_SWEEP 1
43 #endif
44 #ifdef VALIDATE_MARK_SWEEP
45 #define VALIDATE_MARK_SWEEP_ONLY(code) code
46 #else
47 #define VALIDATE_MARK_SWEEP_ONLY(code)
48 #endif
49
50 // declared at end
51 class PreservedMark;
52
53 class MarkSweep : AllStatic {
54 //
55 // Inline closure decls
56 //
57 class FollowRootClosure: public OopsInGenClosure {
58 public:
59 virtual void do_oop(oop* p);
60 virtual void do_oop(narrowOop* p);
61 };
62
63 class MarkAndPushClosure: public OopClosure {
64 public:
65 virtual void do_oop(oop* p);
66 virtual void do_oop(narrowOop* p);
67 virtual const bool should_remember_mdo() const { return true; }
68 virtual void remember_mdo(DataLayout* p) { MarkSweep::revisit_mdo(p); }
69 };
70
71 class FollowStackClosure: public VoidClosure {
72 public:
73 virtual void do_void();
74 };
75
76 class AdjustPointerClosure: public OopsInGenClosure {
77 private:
78 bool _is_root;
79 public:
80 AdjustPointerClosure(bool is_root) : _is_root(is_root) {}
81 virtual void do_oop(oop* p);
82 virtual void do_oop(narrowOop* p);
83 };
84
85 // Used for java/lang/ref handling
86 class IsAliveClosure: public BoolObjectClosure {
87 public:
88 virtual void do_object(oop p);
89 virtual bool do_object_b(oop p);
90 };
91
92 class KeepAliveClosure: public OopClosure {
93 protected:
94 template <class T> void do_oop_work(T* p);
95 public:
96 virtual void do_oop(oop* p);
97 virtual void do_oop(narrowOop* p);
98 };
99
100 //
101 // Friend decls
102 //
103 friend class AdjustPointerClosure;
104 friend class KeepAliveClosure;
105 friend class VM_MarkSweep;
106 friend void marksweep_init();
107
108 //
109 // Vars
110 //
111 protected:
112 // Traversal stacks used during phase1
113 static Stack<oop> _marking_stack;
114 static Stack<ObjArrayTask> _objarray_stack;
115 // Stack for live klasses to revisit at end of marking phase
116 static Stack<Klass*> _revisit_klass_stack;
117 // Set (stack) of MDO's to revisit at end of marking phase
118 static Stack<DataLayout*> _revisit_mdo_stack;
119
120 // Space for storing/restoring mark word
121 static Stack<markOop> _preserved_mark_stack;
122 static Stack<oop> _preserved_oop_stack;
123 static size_t _preserved_count;
124 static size_t _preserved_count_max;
125 static PreservedMark* _preserved_marks;
126
127 // Reference processing (used in ...follow_contents)
128 static ReferenceProcessor* _ref_processor;
129
130 #ifdef VALIDATE_MARK_SWEEP
131 static GrowableArray<void*>* _root_refs_stack;
132 static GrowableArray<oop> * _live_oops;
133 static GrowableArray<oop> * _live_oops_moved_to;
134 static GrowableArray<size_t>* _live_oops_size;
135 static size_t _live_oops_index;
136 static size_t _live_oops_index_at_perm;
137 static GrowableArray<void*>* _other_refs_stack;
138 static GrowableArray<void*>* _adjusted_pointers;
139 static bool _pointer_tracking;
140 static bool _root_tracking;
141
142 // The following arrays are saved since the time of the last GC and
143 // assist in tracking down problems where someone has done an errant
144 // store into the heap, usually to an oop that wasn't properly
145 // handleized across a GC. If we crash or otherwise fail before the
146 // next GC, we can query these arrays to find out the object we had
147 // intended to do the store to (assuming it is still alive) and the
148 // offset within that object. Covered under RecordMarkSweepCompaction.
149 static GrowableArray<HeapWord*> * _cur_gc_live_oops;
150 static GrowableArray<HeapWord*> * _cur_gc_live_oops_moved_to;
151 static GrowableArray<size_t>* _cur_gc_live_oops_size;
152 static GrowableArray<HeapWord*> * _last_gc_live_oops;
153 static GrowableArray<HeapWord*> * _last_gc_live_oops_moved_to;
154 static GrowableArray<size_t>* _last_gc_live_oops_size;
155 #endif
156
157 // Non public closures
158 static IsAliveClosure is_alive;
159 static KeepAliveClosure keep_alive;
160
161 // Class unloading. Update subklass/sibling/implementor links at end of marking phase.
162 static void follow_weak_klass_links();
163
164 // Class unloading. Clear weak refs in MDO's (ProfileData)
165 // at the end of the marking phase.
166 static void follow_mdo_weak_refs();
167
168 // Debugging
169 static void trace(const char* msg) PRODUCT_RETURN;
170
171 public:
172 // Public closures
173 static FollowRootClosure follow_root_closure;
174 static CodeBlobToOopClosure follow_code_root_closure; // => follow_root_closure
175 static MarkAndPushClosure mark_and_push_closure;
176 static FollowStackClosure follow_stack_closure;
177 static AdjustPointerClosure adjust_root_pointer_closure;
178 static AdjustPointerClosure adjust_pointer_closure;
179
180 // Reference Processing
181 static ReferenceProcessor* const ref_processor() { return _ref_processor; }
182
183 // Call backs for marking
184 static void mark_object(oop obj);
185 // Mark pointer and follow contents. Empty marking stack afterwards.
186 template <class T> static inline void follow_root(T* p);
187 // Mark pointer and follow contents.
188 template <class T> static inline void mark_and_follow(T* p);
189 // Check mark and maybe push on marking stack
190 template <class T> static inline void mark_and_push(T* p);
191 static inline void push_objarray(oop obj, size_t index);
192
193 static void follow_stack(); // Empty marking stack.
194
195 static void preserve_mark(oop p, markOop mark);
196 // Save the mark word so it can be restored later
197 static void adjust_marks(); // Adjust the pointers in the preserved marks table
198 static void restore_marks(); // Restore the marks that we saved in preserve_mark
199
200 template <class T> static inline void adjust_pointer(T* p, bool isroot);
201
202 static void adjust_root_pointer(oop* p) { adjust_pointer(p, true); }
203 static void adjust_pointer(oop* p) { adjust_pointer(p, false); }
204 static void adjust_pointer(narrowOop* p) { adjust_pointer(p, false); }
205
206 #ifdef VALIDATE_MARK_SWEEP
207 static void track_adjusted_pointer(void* p, bool isroot);
208 static void check_adjust_pointer(void* p);
209 static void track_interior_pointers(oop obj);
210 static void check_interior_pointers();
211
212 static void reset_live_oop_tracking(bool at_perm);
213 static void register_live_oop(oop p, size_t size);
214 static void validate_live_oop(oop p, size_t size);
215 static void live_oop_moved_to(HeapWord* q, size_t size, HeapWord* compaction_top);
216 static void compaction_complete();
217
218 // Querying operation of RecordMarkSweepCompaction results.
219 // Finds and prints the current base oop and offset for a word
220 // within an oop that was live during the last GC. Helpful for
221 // tracking down heap stomps.
222 static void print_new_location_of_heap_address(HeapWord* q);
223 #endif
224
225 // Call backs for class unloading
226 // Update subklass/sibling/implementor links at end of marking.
227 static void revisit_weak_klass_link(Klass* k);
228 // For weak refs clearing in MDO's
229 static void revisit_mdo(DataLayout* p);
230 };
231
232 class PreservedMark VALUE_OBJ_CLASS_SPEC {
233 private:
234 oop _obj;
235 markOop _mark;
236
237 public:
238 void init(oop obj, markOop mark) {
239 _obj = obj;
240 _mark = mark;
241 }
242
243 void adjust_pointer() {
244 MarkSweep::adjust_pointer(&_obj);
245 }
246
247 void restore() {
248 _obj->set_mark(_mark);
249 }
250 };