rev 54621 : imported patch 8221734-v1

   1 /*
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  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).
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  24 
  25 #ifndef SHARE_OOPS_MARKOOP_HPP
  26 #define SHARE_OOPS_MARKOOP_HPP
  27 
  28 #include "oops/oop.hpp"
  29 
  30 // The markOop describes the header of an object.
  31 //
  32 // Note that the mark is not a real oop but just a word.
  33 // It is placed in the oop hierarchy for historical reasons.
  34 //
  35 // Bit-format of an object header (most significant first, big endian layout below):
  36 //
  37 //  32 bits:
  38 //  --------
  39 //             hash:25 ------------>| age:4    biased_lock:1 lock:2 (normal object)
  40 //             JavaThread*:23 epoch:2 age:4    biased_lock:1 lock:2 (biased object)
  41 //             size:32 ------------------------------------------>| (CMS free block)
  42 //             PromotedObject*:29 ---------->| promo_bits:3 ----->| (CMS promoted object)
  43 //
  44 //  64 bits:
  45 //  --------
  46 //  unused:25 hash:31 -->| unused:1   age:4    biased_lock:1 lock:2 (normal object)
  47 //  JavaThread*:54 epoch:2 unused:1   age:4    biased_lock:1 lock:2 (biased object)
  48 //  PromotedObject*:61 --------------------->| promo_bits:3 ----->| (CMS promoted object)
  49 //  size:64 ----------------------------------------------------->| (CMS free block)
  50 //
  51 //  unused:25 hash:31 -->| cms_free:1 age:4    biased_lock:1 lock:2 (COOPs && normal object)
  52 //  JavaThread*:54 epoch:2 cms_free:1 age:4    biased_lock:1 lock:2 (COOPs && biased object)
  53 //  narrowOop:32 unused:24 cms_free:1 unused:4 promo_bits:3 ----->| (COOPs && CMS promoted object)
  54 //  unused:21 size:35 -->| cms_free:1 unused:7 ------------------>| (COOPs && CMS free block)
  55 //
  56 //  - hash contains the identity hash value: largest value is
  57 //    31 bits, see os::random().  Also, 64-bit vm's require
  58 //    a hash value no bigger than 32 bits because they will not
  59 //    properly generate a mask larger than that: see library_call.cpp
  60 //    and c1_CodePatterns_sparc.cpp.
  61 //
  62 //  - the biased lock pattern is used to bias a lock toward a given
  63 //    thread. When this pattern is set in the low three bits, the lock
  64 //    is either biased toward a given thread or "anonymously" biased,
  65 //    indicating that it is possible for it to be biased. When the
  66 //    lock is biased toward a given thread, locking and unlocking can
  67 //    be performed by that thread without using atomic operations.
  68 //    When a lock's bias is revoked, it reverts back to the normal
  69 //    locking scheme described below.
  70 //
  71 //    Note that we are overloading the meaning of the "unlocked" state
  72 //    of the header. Because we steal a bit from the age we can
  73 //    guarantee that the bias pattern will never be seen for a truly
  74 //    unlocked object.
  75 //
  76 //    Note also that the biased state contains the age bits normally
  77 //    contained in the object header. Large increases in scavenge
  78 //    times were seen when these bits were absent and an arbitrary age
  79 //    assigned to all biased objects, because they tended to consume a
  80 //    significant fraction of the eden semispaces and were not
  81 //    promoted promptly, causing an increase in the amount of copying
  82 //    performed. The runtime system aligns all JavaThread* pointers to
  83 //    a very large value (currently 128 bytes (32bVM) or 256 bytes (64bVM))
  84 //    to make room for the age bits & the epoch bits (used in support of
  85 //    biased locking), and for the CMS "freeness" bit in the 64bVM (+COOPs).
  86 //
  87 //    [JavaThread* | epoch | age | 1 | 01]       lock is biased toward given thread
  88 //    [0           | epoch | age | 1 | 01]       lock is anonymously biased
  89 //
  90 //  - the two lock bits are used to describe three states: locked/unlocked and monitor.
  91 //
  92 //    [ptr             | 00]  locked             ptr points to real header on stack
  93 //    [header      | 0 | 01]  unlocked           regular object header
  94 //    [ptr             | 10]  monitor            inflated lock (header is wapped out)
  95 //    [ptr             | 11]  marked             used by markSweep to mark an object
  96 //                                               not valid at any other time
  97 //
  98 //    We assume that stack/thread pointers have the lowest two bits cleared.
  99 
 100 class BasicLock;
 101 class ObjectMonitor;
 102 class JavaThread;
 103 
 104 class markOopDesc: public oopDesc {
 105  private:
 106   // Conversion
 107   uintptr_t value() const { return (uintptr_t) this; }
 108 
 109  public:
 110   // Constants
 111   enum { age_bits                 = 4,
 112          lock_bits                = 2,
 113          biased_lock_bits         = 1,
 114          max_hash_bits            = BitsPerWord - age_bits - lock_bits - biased_lock_bits,
 115          hash_bits                = max_hash_bits > 31 ? 31 : max_hash_bits,
 116          cms_bits                 = LP64_ONLY(1) NOT_LP64(0),
 117          epoch_bits               = 2
 118   };
 119 
 120   // The biased locking code currently requires that the age bits be
 121   // contiguous to the lock bits.
 122   enum { lock_shift               = 0,
 123          biased_lock_shift        = lock_bits,
 124          age_shift                = lock_bits + biased_lock_bits,
 125          cms_shift                = age_shift + age_bits,
 126          hash_shift               = cms_shift + cms_bits,
 127          epoch_shift              = hash_shift
 128   };
 129 
 130   enum { lock_mask                = right_n_bits(lock_bits),
 131          lock_mask_in_place       = lock_mask << lock_shift,
 132          biased_lock_mask         = right_n_bits(lock_bits + biased_lock_bits),
 133          biased_lock_mask_in_place= biased_lock_mask << lock_shift,
 134          biased_lock_bit_in_place = 1 << biased_lock_shift,
 135          age_mask                 = right_n_bits(age_bits),
 136          age_mask_in_place        = age_mask << age_shift,
 137          epoch_mask               = right_n_bits(epoch_bits),
 138          epoch_mask_in_place      = epoch_mask << epoch_shift,
 139          cms_mask                 = right_n_bits(cms_bits),
 140          cms_mask_in_place        = cms_mask << cms_shift
 141   };
 142 
 143   const static uintptr_t hash_mask = right_n_bits(hash_bits);
 144   const static uintptr_t hash_mask_in_place = hash_mask << hash_shift;
 145 
 146   // Alignment of JavaThread pointers encoded in object header required by biased locking
 147   enum { biased_lock_alignment    = 2 << (epoch_shift + epoch_bits)
 148   };
 149 
 150   enum { locked_value             = 0,
 151          unlocked_value           = 1,
 152          monitor_value            = 2,
 153          marked_value             = 3,
 154          biased_lock_pattern      = 5
 155   };
 156 
 157   enum { no_hash                  = 0 };  // no hash value assigned
 158 
 159   enum { no_hash_in_place         = (address_word)no_hash << hash_shift,
 160          no_lock_in_place         = unlocked_value
 161   };
 162 
 163   enum { max_age                  = age_mask };
 164 
 165   enum { max_bias_epoch           = epoch_mask };
 166 
 167   // Biased Locking accessors.
 168   // These must be checked by all code which calls into the
 169   // ObjectSynchronizer and other code. The biasing is not understood
 170   // by the lower-level CAS-based locking code, although the runtime
 171   // fixes up biased locks to be compatible with it when a bias is
 172   // revoked.
 173   bool has_bias_pattern() const {
 174     return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern);
 175   }
 176   JavaThread* biased_locker() const {
 177     assert(has_bias_pattern(), "should not call this otherwise");
 178     return (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place))));
 179   }
 180   bool biased_locker_is(JavaThread* thread) const {
 181     if (!has_bias_pattern()) {
 182       return false;
 183     }
 184     // If current thread is not the owner it can be unbiased at anytime.
 185     JavaThread* jt = (JavaThread*) ((intptr_t) (mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place))));
 186     return jt == thread;
 187   }
 188 
 189   // Indicates that the mark has the bias bit set but that it has not
 190   // yet been biased toward a particular thread
 191   bool is_biased_anonymously() const {
 192     return (has_bias_pattern() && (biased_locker() == NULL));
 193   }
 194   // Indicates epoch in which this bias was acquired. If the epoch
 195   // changes due to too many bias revocations occurring, the biases
 196   // from the previous epochs are all considered invalid.
 197   int bias_epoch() const {
 198     assert(has_bias_pattern(), "should not call this otherwise");
 199     return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift);
 200   }
 201   markOop set_bias_epoch(int epoch) {
 202     assert(has_bias_pattern(), "should not call this otherwise");
 203     assert((epoch & (~epoch_mask)) == 0, "epoch overflow");
 204     return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift));
 205   }
 206   markOop incr_bias_epoch() {
 207     return set_bias_epoch((1 + bias_epoch()) & epoch_mask);
 208   }
 209   // Prototype mark for initialization
 210   static markOop biased_locking_prototype() {
 211     return markOop( biased_lock_pattern );
 212   }
 213 
 214   // lock accessors (note that these assume lock_shift == 0)
 215   bool is_locked()   const {
 216     return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
 217   }
 218   bool is_unlocked() const {
 219     return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value);
 220   }
 221   bool is_marked()   const {
 222     return (mask_bits(value(), lock_mask_in_place) == marked_value);
 223   }
 224   bool is_neutral()  const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); }
 225 
 226   // Special temporary state of the markOop while being inflated.
 227   // Code that looks at mark outside a lock need to take this into account.
 228   bool is_being_inflated() const { return (value() == 0); }
 229 
 230   // Distinguished markword value - used when inflating over
 231   // an existing stacklock.  0 indicates the markword is "BUSY".
 232   // Lockword mutators that use a LD...CAS idiom should always
 233   // check for and avoid overwriting a 0 value installed by some
 234   // other thread.  (They should spin or block instead.  The 0 value
 235   // is transient and *should* be short-lived).
 236   static markOop INFLATING() { return (markOop) 0; }    // inflate-in-progress
 237 
 238   // Should this header be preserved during GC?
 239   inline bool must_be_preserved(oop obj_containing_mark) const;
 240   inline bool must_be_preserved_with_bias(oop obj_containing_mark) const;
 241 
 242   // Should this header (including its age bits) be preserved in the
 243   // case of a promotion failure during scavenge?
 244   // Note that we special case this situation. We want to avoid
 245   // calling BiasedLocking::preserve_marks()/restore_marks() (which
 246   // decrease the number of mark words that need to be preserved
 247   // during GC) during each scavenge. During scavenges in which there
 248   // is no promotion failure, we actually don't need to call the above
 249   // routines at all, since we don't mutate and re-initialize the
 250   // marks of promoted objects using init_mark(). However, during
 251   // scavenges which result in promotion failure, we do re-initialize
 252   // the mark words of objects, meaning that we should have called
 253   // these mark word preservation routines. Currently there's no good
 254   // place in which to call them in any of the scavengers (although
 255   // guarded by appropriate locks we could make one), but the
 256   // observation is that promotion failures are quite rare and
 257   // reducing the number of mark words preserved during them isn't a
 258   // high priority.
 259   inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const;
 260   inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const;
 261 
 262   // Should this header be preserved during a scavenge where CMS is
 263   // the old generation?
 264   // (This is basically the same body as must_be_preserved_for_promotion_failure(),
 265   // but takes the Klass* as argument instead)
 266   inline bool must_be_preserved_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
 267   inline bool must_be_preserved_with_bias_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
 268 
 269   // WARNING: The following routines are used EXCLUSIVELY by
 270   // synchronization functions. They are not really gc safe.
 271   // They must get updated if markOop layout get changed.
 272   markOop set_unlocked() const {
 273     return markOop(value() | unlocked_value);
 274   }
 275   bool has_locker() const {
 276     return ((value() & lock_mask_in_place) == locked_value);
 277   }
 278   BasicLock* locker() const {
 279     assert(has_locker(), "check");
 280     return (BasicLock*) value();
 281   }
 282   bool has_monitor() const {
 283     return ((value() & monitor_value) != 0);
 284   }
 285   ObjectMonitor* monitor() const {
 286     assert(has_monitor(), "check");
 287     // Use xor instead of &~ to provide one extra tag-bit check.
 288     return (ObjectMonitor*) (value() ^ monitor_value);
 289   }
 290   bool has_displaced_mark_helper() const {
 291     return ((value() & unlocked_value) == 0);
 292   }
 293   markOop displaced_mark_helper() const {
 294     assert(has_displaced_mark_helper(), "check");
 295     intptr_t ptr = (value() & ~monitor_value);
 296     return *(markOop*)ptr;
 297   }
 298   void set_displaced_mark_helper(markOop m) const {
 299     assert(has_displaced_mark_helper(), "check");
 300     intptr_t ptr = (value() & ~monitor_value);
 301     *(markOop*)ptr = m;
 302   }
 303   markOop copy_set_hash(intptr_t hash) const {
 304     intptr_t tmp = value() & (~hash_mask_in_place);
 305     tmp |= ((hash & hash_mask) << hash_shift);
 306     return (markOop)tmp;
 307   }
 308   // it is only used to be stored into BasicLock as the
 309   // indicator that the lock is using heavyweight monitor
 310   static markOop unused_mark() {
 311     return (markOop) marked_value;
 312   }
 313   // the following two functions create the markOop to be
 314   // stored into object header, it encodes monitor info
 315   static markOop encode(BasicLock* lock) {
 316     return (markOop) lock;
 317   }
 318   static markOop encode(ObjectMonitor* monitor) {
 319     intptr_t tmp = (intptr_t) monitor;
 320     return (markOop) (tmp | monitor_value);
 321   }
 322   static markOop encode(JavaThread* thread, uint age, int bias_epoch) {
 323     intptr_t tmp = (intptr_t) thread;
 324     assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer");
 325     assert(age <= max_age, "age too large");
 326     assert(bias_epoch <= max_bias_epoch, "bias epoch too large");
 327     return (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);
 328   }
 329 
 330   // used to encode pointers during GC
 331   markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); }
 332 
 333   // age operations
 334   markOop set_marked()   { return markOop((value() & ~lock_mask_in_place) | marked_value); }
 335   markOop set_unmarked() { return markOop((value() & ~lock_mask_in_place) | unlocked_value); }
 336 
 337   uint    age()               const { return mask_bits(value() >> age_shift, age_mask); }
 338   markOop set_age(uint v) const {
 339     assert((v & ~age_mask) == 0, "shouldn't overflow age field");
 340     return markOop((value() & ~age_mask_in_place) | (((uintptr_t)v & age_mask) << age_shift));
 341   }
 342   markOop incr_age()          const { return age() == max_age ? markOop(this) : set_age(age() + 1); }
 343 
 344   // hash operations
 345   intptr_t hash() const {
 346     return mask_bits(value() >> hash_shift, hash_mask);
 347   }
 348 
 349   bool has_no_hash() const {
 350     return hash() == no_hash;
 351   }
 352 
 353   // Prototype mark for initialization
 354   static markOop prototype() {
 355     return markOop( no_hash_in_place | no_lock_in_place );
 356   }
 357 
 358   // Helper function for restoration of unmarked mark oops during GC
 359   static inline markOop prototype_for_object(oop obj);
 360 
 361   // Debugging
 362   void print_on(outputStream* st) const;
 363 
 364   // Prepare address of oop for placement into mark
 365   inline static markOop encode_pointer_as_mark(void* p) { return markOop(p)->set_marked(); }
 366 
 367   // Recover address of oop from encoded form used in mark
 368   inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return clear_lock_bits(); }
 369 
 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;
 374 
 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;
 384 
 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   }
 397 
 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 };
 406 
 407 #endif // SHARE_OOPS_MARKOOP_HPP
--- EOF ---