Mon, 09 Jun 2008 11:51:19 -0400
6687581: Make CMS work with compressed oops
Summary: Make FreeChunk read markword instead of LSB in _klass pointer to indicate that it's a FreeChunk for compressed oops.
Reviewed-by: ysr, jmasa
1 /*
2 * Copyright 1997-2006 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.
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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
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23 */
25 // The markOop describes the header of an object.
26 //
27 // Note that the mark is not a real oop but just a word.
28 // It is placed in the oop hierarchy for historical reasons.
29 //
30 // Bit-format of an object header (most significant first):
31 //
32 // 32 bits: unused:0 hash:25 age:4 biased_lock:1 lock:2
33 // 64 bits: unused:24 hash:31 cms:2 age:4 biased_lock:1 lock:2
34 // unused:20 size:35 cms:2 age:4 biased_lock:1 lock:2 (if cms
35 // free chunk)
36 //
37 // - hash contains the identity hash value: largest value is
38 // 31 bits, see os::random(). Also, 64-bit vm's require
39 // a hash value no bigger than 32 bits because they will not
40 // properly generate a mask larger than that: see library_call.cpp
41 // and c1_CodePatterns_sparc.cpp.
42 //
43 // - the biased lock pattern is used to bias a lock toward a given
44 // thread. When this pattern is set in the low three bits, the lock
45 // is either biased toward a given thread or "anonymously" biased,
46 // indicating that it is possible for it to be biased. When the
47 // lock is biased toward a given thread, locking and unlocking can
48 // be performed by that thread without using atomic operations.
49 // When a lock's bias is revoked, it reverts back to the normal
50 // locking scheme described below.
51 //
52 // Note that we are overloading the meaning of the "unlocked" state
53 // of the header. Because we steal a bit from the age we can
54 // guarantee that the bias pattern will never be seen for a truly
55 // unlocked object.
56 //
57 // Note also that the biased state contains the age bits normally
58 // contained in the object header. Large increases in scavenge
59 // times were seen when these bits were absent and an arbitrary age
60 // assigned to all biased objects, because they tended to consume a
61 // significant fraction of the eden semispaces and were not
62 // promoted promptly, causing an increase in the amount of copying
63 // performed. The runtime system aligns all JavaThread* pointers to
64 // a very large value (currently 128 bytes) to make room for the
65 // age bits when biased locking is enabled.
66 //
67 // [JavaThread* | epoch | age | 1 | 01] lock is biased toward given thread
68 // [0 | epoch | age | 1 | 01] lock is anonymously biased
69 //
70 // - the two lock bits are used to describe three states: locked/unlocked and monitor.
71 //
72 // [ptr | 00] locked ptr points to real header on stack
73 // [header | 0 | 01] unlocked regular object header
74 // [ptr | 10] monitor inflated lock (header is wapped out)
75 // [ptr | 11] marked used by markSweep to mark an object
76 // not valid at any other time
77 //
78 // We assume that stack/thread pointers have the lowest two bits cleared.
80 class BasicLock;
81 class ObjectMonitor;
82 class JavaThread;
84 class markOopDesc: public oopDesc {
85 private:
86 // Conversion
87 uintptr_t value() const { return (uintptr_t) this; }
89 public:
90 // Constants
91 enum { age_bits = 4,
92 lock_bits = 2,
93 biased_lock_bits = 1,
94 max_hash_bits = BitsPerWord - age_bits - lock_bits - biased_lock_bits,
95 hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits,
96 cms_bits = LP64_ONLY(1) NOT_LP64(0),
97 epoch_bits = 2
98 };
100 // The biased locking code currently requires that the age bits be
101 // contiguous to the lock bits. Class data sharing would prefer the
102 // hash bits to be lower down to provide more random hash codes for
103 // shared read-only symbolOop objects, because these objects' mark
104 // words are set to their own address with marked_value in the lock
105 // bit, and using lower bits would make their identity hash values
106 // more random. However, the performance decision was made in favor
107 // of the biased locking code.
109 enum { lock_shift = 0,
110 biased_lock_shift = lock_bits,
111 age_shift = lock_bits + biased_lock_bits,
112 cms_shift = age_shift + age_bits,
113 hash_shift = cms_shift + cms_bits,
114 epoch_shift = hash_shift
115 };
117 enum { lock_mask = right_n_bits(lock_bits),
118 lock_mask_in_place = lock_mask << lock_shift,
119 biased_lock_mask = right_n_bits(lock_bits + biased_lock_bits),
120 biased_lock_mask_in_place= biased_lock_mask << lock_shift,
121 biased_lock_bit_in_place = 1 << biased_lock_shift,
122 age_mask = right_n_bits(age_bits),
123 age_mask_in_place = age_mask << age_shift,
124 epoch_mask = right_n_bits(epoch_bits),
125 epoch_mask_in_place = epoch_mask << epoch_shift,
126 cms_mask = right_n_bits(cms_bits),
127 cms_mask_in_place = cms_mask << cms_shift
128 #ifndef _WIN64
129 ,hash_mask = right_n_bits(hash_bits),
130 hash_mask_in_place = (address_word)hash_mask << hash_shift
131 #endif
132 };
134 // Alignment of JavaThread pointers encoded in object header required by biased locking
135 enum { biased_lock_alignment = 2 << (epoch_shift + epoch_bits)
136 };
138 #ifdef _WIN64
139 // These values are too big for Win64
140 const static uintptr_t hash_mask = right_n_bits(hash_bits);
141 const static uintptr_t hash_mask_in_place =
142 (address_word)hash_mask << hash_shift;
143 #endif
145 enum { locked_value = 0,
146 unlocked_value = 1,
147 monitor_value = 2,
148 marked_value = 3,
149 biased_lock_pattern = 5
150 };
152 enum { no_hash = 0 }; // no hash value assigned
154 enum { no_hash_in_place = (address_word)no_hash << hash_shift,
155 no_lock_in_place = unlocked_value
156 };
158 enum { max_age = age_mask };
160 enum { max_bias_epoch = epoch_mask };
162 // Biased Locking accessors.
163 // These must be checked by all code which calls into the
164 // ObjectSynchronizer and other code. The biasing is not understood
165 // by the lower-level CAS-based locking code, although the runtime
166 // fixes up biased locks to be compatible with it when a bias is
167 // revoked.
168 bool has_bias_pattern() const {
169 return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern);
170 }
171 JavaThread* biased_locker() const {
172 assert(has_bias_pattern(), "should not call this otherwise");
173 return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place))));
174 }
175 // Indicates that the mark has the bias bit set but that it has not
176 // yet been biased toward a particular thread
177 bool is_biased_anonymously() const {
178 return (has_bias_pattern() && (biased_locker() == NULL));
179 }
180 // Indicates epoch in which this bias was acquired. If the epoch
181 // changes due to too many bias revocations occurring, the biases
182 // from the previous epochs are all considered invalid.
183 int bias_epoch() const {
184 assert(has_bias_pattern(), "should not call this otherwise");
185 return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift);
186 }
187 markOop set_bias_epoch(int epoch) {
188 assert(has_bias_pattern(), "should not call this otherwise");
189 assert((epoch & (~epoch_mask)) == 0, "epoch overflow");
190 return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift));
191 }
192 markOop incr_bias_epoch() {
193 return set_bias_epoch((1 + bias_epoch()) & epoch_mask);
194 }
195 // Prototype mark for initialization
196 static markOop biased_locking_prototype() {
197 return markOop( biased_lock_pattern );
198 }
200 // lock accessors (note that these assume lock_shift == 0)
201 bool is_locked() const {
202 return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
203 }
204 bool is_unlocked() const {
205 return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value);
206 }
207 bool is_marked() const {
208 return (mask_bits(value(), lock_mask_in_place) == marked_value);
209 }
210 bool is_neutral() const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); }
212 // Special temporary state of the markOop while being inflated.
213 // Code that looks at mark outside a lock need to take this into account.
214 bool is_being_inflated() const { return (value() == 0); }
216 // Distinguished markword value - used when inflating over
217 // an existing stacklock. 0 indicates the markword is "BUSY".
218 // Lockword mutators that use a LD...CAS idiom should always
219 // check for and avoid overwriting a 0 value installed by some
220 // other thread. (They should spin or block instead. The 0 value
221 // is transient and *should* be short-lived).
222 static markOop INFLATING() { return (markOop) 0; } // inflate-in-progress
224 // Should this header be preserved during GC?
225 bool must_be_preserved(oop obj_containing_mark) const {
226 if (!UseBiasedLocking)
227 return (!is_unlocked() || !has_no_hash());
228 return must_be_preserved_with_bias(obj_containing_mark);
229 }
230 inline bool must_be_preserved_with_bias(oop obj_containing_mark) const;
232 // Should this header (including its age bits) be preserved in the
233 // case of a promotion failure during scavenge?
234 // Note that we special case this situation. We want to avoid
235 // calling BiasedLocking::preserve_marks()/restore_marks() (which
236 // decrease the number of mark words that need to be preserved
237 // during GC) during each scavenge. During scavenges in which there
238 // is no promotion failure, we actually don't need to call the above
239 // routines at all, since we don't mutate and re-initialize the
240 // marks of promoted objects using init_mark(). However, during
241 // scavenges which result in promotion failure, we do re-initialize
242 // the mark words of objects, meaning that we should have called
243 // these mark word preservation routines. Currently there's no good
244 // place in which to call them in any of the scavengers (although
245 // guarded by appropriate locks we could make one), but the
246 // observation is that promotion failures are quite rare and
247 // reducing the number of mark words preserved during them isn't a
248 // high priority.
249 bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const {
250 if (!UseBiasedLocking)
251 return (this != prototype());
252 return must_be_preserved_with_bias_for_promotion_failure(obj_containing_mark);
253 }
254 inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const;
256 // Should this header be preserved during a scavenge where CMS is
257 // the old generation?
258 // (This is basically the same body as must_be_preserved_for_promotion_failure(),
259 // but takes the klassOop as argument instead)
260 bool must_be_preserved_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const {
261 if (!UseBiasedLocking)
262 return (this != prototype());
263 return must_be_preserved_with_bias_for_cms_scavenge(klass_of_obj_containing_mark);
264 }
265 inline bool must_be_preserved_with_bias_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const;
267 // WARNING: The following routines are used EXCLUSIVELY by
268 // synchronization functions. They are not really gc safe.
269 // They must get updated if markOop layout get changed.
270 markOop set_unlocked() const {
271 return markOop(value() | unlocked_value);
272 }
273 bool has_locker() const {
274 return ((value() & lock_mask_in_place) == locked_value);
275 }
276 BasicLock* locker() const {
277 assert(has_locker(), "check");
278 return (BasicLock*) value();
279 }
280 bool has_monitor() const {
281 return ((value() & monitor_value) != 0);
282 }
283 ObjectMonitor* monitor() const {
284 assert(has_monitor(), "check");
285 // Use xor instead of &~ to provide one extra tag-bit check.
286 return (ObjectMonitor*) (value() ^ monitor_value);
287 }
288 bool has_displaced_mark_helper() const {
289 return ((value() & unlocked_value) == 0);
290 }
291 markOop displaced_mark_helper() const {
292 assert(has_displaced_mark_helper(), "check");
293 intptr_t ptr = (value() & ~monitor_value);
294 return *(markOop*)ptr;
295 }
296 void set_displaced_mark_helper(markOop m) const {
297 assert(has_displaced_mark_helper(), "check");
298 intptr_t ptr = (value() & ~monitor_value);
299 *(markOop*)ptr = m;
300 }
301 markOop copy_set_hash(intptr_t hash) const {
302 intptr_t tmp = value() & (~hash_mask_in_place);
303 tmp |= ((hash & hash_mask) << hash_shift);
304 return (markOop)tmp;
305 }
306 // it is only used to be stored into BasicLock as the
307 // indicator that the lock is using heavyweight monitor
308 static markOop unused_mark() {
309 return (markOop) marked_value;
310 }
311 // the following two functions create the markOop to be
312 // stored into object header, it encodes monitor info
313 static markOop encode(BasicLock* lock) {
314 return (markOop) lock;
315 }
316 static markOop encode(ObjectMonitor* monitor) {
317 intptr_t tmp = (intptr_t) monitor;
318 return (markOop) (tmp | monitor_value);
319 }
320 static markOop encode(JavaThread* thread, int age, int bias_epoch) {
321 intptr_t tmp = (intptr_t) thread;
322 assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer");
323 assert(age <= max_age, "age too large");
324 assert(bias_epoch <= max_bias_epoch, "bias epoch too large");
325 return (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);
326 }
328 // used to encode pointers during GC
329 markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); }
331 // age operations
332 markOop set_marked() { return markOop((value() & ~lock_mask_in_place) | marked_value); }
334 int age() const { return mask_bits(value() >> age_shift, age_mask); }
335 markOop set_age(int v) const {
336 assert((v & ~age_mask) == 0, "shouldn't overflow age field");
337 return markOop((value() & ~age_mask_in_place) | (((intptr_t)v & age_mask) << age_shift));
338 }
339 markOop incr_age() const { return age() == max_age ? markOop(this) : set_age(age() + 1); }
341 // hash operations
342 intptr_t hash() const {
343 return mask_bits(value() >> hash_shift, hash_mask);
344 }
346 bool has_no_hash() const {
347 return hash() == no_hash;
348 }
350 // Prototype mark for initialization
351 static markOop prototype() {
352 return markOop( no_hash_in_place | no_lock_in_place );
353 }
355 // Helper function for restoration of unmarked mark oops during GC
356 static inline markOop prototype_for_object(oop obj);
358 // Debugging
359 void print_on(outputStream* st) const;
361 // Prepare address of oop for placement into mark
362 inline static markOop encode_pointer_as_mark(void* p) { return markOop(p)->set_marked(); }
364 // Recover address of oop from encoded form used in mark
365 inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return clear_lock_bits(); }
367 // see the definition in markOop.cpp for the gory details
368 bool should_not_be_cached() const;
370 // These markOops indicate cms free chunk blocks and not objects.
371 // In 64 bit, the markOop is set to distinguish them from oops.
372 // These are defined in 32 bit mode for vmStructs.
373 const static uintptr_t cms_free_chunk_pattern = 0x1;
375 // Constants for the size field.
376 enum { size_shift = cms_shift + cms_bits,
377 size_bits = 35 // need for compressed oops 32G
378 };
379 // These values are too big for Win64
380 const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits))
381 NOT_LP64(0);
382 const static uintptr_t size_mask_in_place =
383 (address_word)size_mask << size_shift;
385 #ifdef _LP64
386 static markOop cms_free_prototype() {
387 return markOop(((intptr_t)prototype() & ~cms_mask_in_place) |
388 ((cms_free_chunk_pattern & cms_mask) << cms_shift));
389 }
390 uintptr_t cms_encoding() const {
391 return mask_bits(value() >> cms_shift, cms_mask);
392 }
393 bool is_cms_free_chunk() const {
394 return is_neutral() &&
395 (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern;
396 }
398 size_t get_size() const { return (size_t)(value() >> size_shift); }
399 static markOop set_size_and_free(size_t size) {
400 assert((size & ~size_mask) == 0, "shouldn't overflow size field");
401 return markOop(((intptr_t)cms_free_prototype() & ~size_mask_in_place) |
402 (((intptr_t)size & size_mask) << size_shift));
403 }
404 #endif // _LP64
405 };