Tue, 13 Apr 2010 13:52:10 -0700
6858496: Clear all SoftReferences before an out-of-memory due to GC overhead limit.
Summary: Ensure a full GC that clears SoftReferences before throwing an out-of-memory
Reviewed-by: ysr, jcoomes
1 /*
2 * Copyright 1997-2009 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
20 * CA 95054 USA or visit www.sun.com if you need additional information or
21 * have any questions.
22 *
23 */
25 class ReferenceProcessor;
26 class DataLayout;
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.
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
50 // declared at end
51 class PreservedMark;
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 };
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 };
71 class FollowStackClosure: public VoidClosure {
72 public:
73 virtual void do_void();
74 };
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 };
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 };
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 };
100 //
101 // Friend decls
102 //
103 friend class AdjustPointerClosure;
104 friend class KeepAliveClosure;
105 friend class VM_MarkSweep;
106 friend void marksweep_init();
107 friend class DataLayout;
109 //
110 // Vars
111 //
112 protected:
113 // Traversal stacks used during phase1
114 static GrowableArray<oop>* _marking_stack;
115 static GrowableArray<ObjArrayTask>* _objarray_stack;
116 // Stack for live klasses to revisit at end of marking phase
117 static GrowableArray<Klass*>* _revisit_klass_stack;
118 // Set (stack) of MDO's to revisit at end of marking phase
119 static GrowableArray<DataLayout*>* _revisit_mdo_stack;
121 // Space for storing/restoring mark word
122 static GrowableArray<markOop>* _preserved_mark_stack;
123 static GrowableArray<oop>* _preserved_oop_stack;
124 static size_t _preserved_count;
125 static size_t _preserved_count_max;
126 static PreservedMark* _preserved_marks;
128 // Reference processing (used in ...follow_contents)
129 static ReferenceProcessor* _ref_processor;
131 #ifdef VALIDATE_MARK_SWEEP
132 static GrowableArray<void*>* _root_refs_stack;
133 static GrowableArray<oop> * _live_oops;
134 static GrowableArray<oop> * _live_oops_moved_to;
135 static GrowableArray<size_t>* _live_oops_size;
136 static size_t _live_oops_index;
137 static size_t _live_oops_index_at_perm;
138 static GrowableArray<void*>* _other_refs_stack;
139 static GrowableArray<void*>* _adjusted_pointers;
140 static bool _pointer_tracking;
141 static bool _root_tracking;
143 // The following arrays are saved since the time of the last GC and
144 // assist in tracking down problems where someone has done an errant
145 // store into the heap, usually to an oop that wasn't properly
146 // handleized across a GC. If we crash or otherwise fail before the
147 // next GC, we can query these arrays to find out the object we had
148 // intended to do the store to (assuming it is still alive) and the
149 // offset within that object. Covered under RecordMarkSweepCompaction.
150 static GrowableArray<HeapWord*> * _cur_gc_live_oops;
151 static GrowableArray<HeapWord*> * _cur_gc_live_oops_moved_to;
152 static GrowableArray<size_t>* _cur_gc_live_oops_size;
153 static GrowableArray<HeapWord*> * _last_gc_live_oops;
154 static GrowableArray<HeapWord*> * _last_gc_live_oops_moved_to;
155 static GrowableArray<size_t>* _last_gc_live_oops_size;
156 #endif
158 // Non public closures
159 static IsAliveClosure is_alive;
160 static KeepAliveClosure keep_alive;
162 // Class unloading. Update subklass/sibling/implementor links at end of marking phase.
163 static void follow_weak_klass_links();
165 // Class unloading. Clear weak refs in MDO's (ProfileData)
166 // at the end of the marking phase.
167 static void follow_mdo_weak_refs();
169 // Debugging
170 static void trace(const char* msg) PRODUCT_RETURN;
172 public:
173 // Public closures
174 static FollowRootClosure follow_root_closure;
175 static CodeBlobToOopClosure follow_code_root_closure; // => follow_root_closure
176 static MarkAndPushClosure mark_and_push_closure;
177 static FollowStackClosure follow_stack_closure;
178 static AdjustPointerClosure adjust_root_pointer_closure;
179 static AdjustPointerClosure adjust_pointer_closure;
181 // Reference Processing
182 static ReferenceProcessor* const ref_processor() { return _ref_processor; }
184 // Call backs for marking
185 static void mark_object(oop obj);
186 // Mark pointer and follow contents. Empty marking stack afterwards.
187 template <class T> static inline void follow_root(T* p);
188 // Mark pointer and follow contents.
189 template <class T> static inline void mark_and_follow(T* p);
190 // Check mark and maybe push on marking stack
191 template <class T> static inline void mark_and_push(T* p);
192 static inline void push_objarray(oop obj, size_t index);
194 static void follow_stack(); // Empty marking stack.
196 static void preserve_mark(oop p, markOop mark);
197 // Save the mark word so it can be restored later
198 static void adjust_marks(); // Adjust the pointers in the preserved marks table
199 static void restore_marks(); // Restore the marks that we saved in preserve_mark
201 template <class T> static inline void adjust_pointer(T* p, bool isroot);
203 static void adjust_root_pointer(oop* p) { adjust_pointer(p, true); }
204 static void adjust_pointer(oop* p) { adjust_pointer(p, false); }
205 static void adjust_pointer(narrowOop* p) { adjust_pointer(p, false); }
207 #ifdef VALIDATE_MARK_SWEEP
208 static void track_adjusted_pointer(void* p, bool isroot);
209 static void check_adjust_pointer(void* p);
210 static void track_interior_pointers(oop obj);
211 static void check_interior_pointers();
213 static void reset_live_oop_tracking(bool at_perm);
214 static void register_live_oop(oop p, size_t size);
215 static void validate_live_oop(oop p, size_t size);
216 static void live_oop_moved_to(HeapWord* q, size_t size, HeapWord* compaction_top);
217 static void compaction_complete();
219 // Querying operation of RecordMarkSweepCompaction results.
220 // Finds and prints the current base oop and offset for a word
221 // within an oop that was live during the last GC. Helpful for
222 // tracking down heap stomps.
223 static void print_new_location_of_heap_address(HeapWord* q);
224 #endif
226 // Call backs for class unloading
227 // Update subklass/sibling/implementor links at end of marking.
228 static void revisit_weak_klass_link(Klass* k);
229 // For weak refs clearing in MDO's
230 static void revisit_mdo(DataLayout* p);
231 };
233 class PreservedMark VALUE_OBJ_CLASS_SPEC {
234 private:
235 oop _obj;
236 markOop _mark;
238 public:
239 void init(oop obj, markOop mark) {
240 _obj = obj;
241 _mark = mark;
242 }
244 void adjust_pointer() {
245 MarkSweep::adjust_pointer(&_obj);
246 }
248 void restore() {
249 _obj->set_mark(_mark);
250 }
251 };