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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

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 *

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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

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 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

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#ifndef SHARE_OOPS_MARKWORD_HPP

#define SHARE_OOPS_MARKWORD_HPP

#include "metaprogramming/integralConstant.hpp"

#include "metaprogramming/primitiveConversions.hpp"

#include "oops/oopsHierarchy.hpp"

#include "runtime/globals.hpp"

// The markWord describes the header of an object.

//

// Bit-format of an object header (most significant first, big endian layout below):

//

//  32 bits:

//  --------

//             hash:25 ------------>| age:4    biased_lock:1 lock:2 (normal object)

//             JavaThread*:23 epoch:2 age:4    biased_lock:1 lock:2 (biased object)

//

//  64 bits:

//  --------

//

//  - hash contains the identity hash value: largest value is

//    31 bits, see os::random().  Also, 64-bit vm's require

//    a hash value no bigger than 32 bits because they will not

//    properly generate a mask larger than that: see library_call.cpp

//    and c1_CodePatterns_sparc.cpp.

//

//  - the biased lock pattern is used to bias a lock toward a given

//    thread. When this pattern is set in the low three bits, the lock

//    is either biased toward a given thread or "anonymously" biased,

//    indicating that it is possible for it to be biased. When the

//    lock is biased toward a given thread, locking and unlocking can

//    be performed by that thread without using atomic operations.

//    When a lock's bias is revoked, it reverts back to the normal

//    locking scheme described below.

//

//    Note that we are overloading the meaning of the "unlocked" state

//    of the header. Because we steal a bit from the age we can

//    guarantee that the bias pattern will never be seen for a truly

//    unlocked object.

//

//    Note also that the biased state contains the age bits normally

//    contained in the object header. Large increases in scavenge

//    times were seen when these bits were absent and an arbitrary age

//    assigned to all biased objects, because they tended to consume a

//    significant fraction of the eden semispaces and were not

//    promoted promptly, causing an increase in the amount of copying

//    performed. The runtime system aligns all JavaThread* pointers to

//    a very large value (currently 128 bytes (32bVM) or 256 bytes (64bVM))

//    to make room for the age bits & the epoch bits (used in support of

//

//    [JavaThread* | epoch | age | 1 | 01]       lock is biased toward given thread

//    [0           | epoch | age | 1 | 01]       lock is anonymously biased

//

//  - the two lock bits are used to describe three states: locked/unlocked and monitor.

//

//    [ptr             | 00]  locked             ptr points to real header on stack

//    [header      | 0 | 01]  unlocked           regular object header

//    [ptr             | 10]  monitor            inflated lock (header is wapped out)

//    [ptr             | 11]  marked             used by markSweep to mark an object

//                                               not valid at any other time

//

//    We assume that stack/thread pointers have the lowest two bits cleared.

class BasicLock;

class ObjectMonitor;

class JavaThread;

class markWord {

 private:

  uintptr_t _value;

 public:

  explicit markWord(uintptr_t value) : _value(value) {}

  markWord() { /* uninitialized */}

  // It is critical for performance that this class be trivially

  // destructable, copyable, and assignable.

  static markWord from_pointer(void* ptr) {

    return markWord((uintptr_t)ptr);

  }

  void* to_pointer() const {

    return (void*)_value;

  }

  bool operator==(const markWord& other) const {

    return _value == other._value;

  }

  bool operator!=(const markWord& other) const {

    return !operator==(other);

  }

  // Conversion

  uintptr_t value() const { return _value; }

  // Constants

  static const int age_bits                       = 4;

  static const int lock_bits                      = 2;

  static const int biased_lock_bits               = 1;

  static const int max_hash_bits                  = BitsPerWord - age_bits - lock_bits - biased_lock_bits;

  static const int hash_bits                      = max_hash_bits > 31 ? 31 : max_hash_bits;

  static const int epoch_bits                     = 2;

  // The biased locking code currently requires that the age bits be

  // contiguous to the lock bits.

  static const int lock_shift                     = 0;

  static const int biased_lock_shift              = lock_bits;

  static const int age_shift                      = lock_bits + biased_lock_bits;

  static const int epoch_shift                    = hash_shift;

  static const uintptr_t lock_mask                = right_n_bits(lock_bits);

  static const uintptr_t lock_mask_in_place       = lock_mask << lock_shift;

  static const uintptr_t biased_lock_mask         = right_n_bits(lock_bits + biased_lock_bits);

  static const uintptr_t biased_lock_mask_in_place= biased_lock_mask << lock_shift;

  static const uintptr_t biased_lock_bit_in_place = 1 << biased_lock_shift;

  static const uintptr_t age_mask                 = right_n_bits(age_bits);

  static const uintptr_t age_mask_in_place        = age_mask << age_shift;

  static const uintptr_t epoch_mask               = right_n_bits(epoch_bits);

  static const uintptr_t epoch_mask_in_place      = epoch_mask << epoch_shift;

  static const uintptr_t hash_mask                = right_n_bits(hash_bits);

  static const uintptr_t hash_mask_in_place       = hash_mask << hash_shift;

  // Alignment of JavaThread pointers encoded in object header required by biased locking

  static const size_t biased_lock_alignment       = 2 << (epoch_shift + epoch_bits);

  static const uintptr_t locked_value             = 0;

  static const uintptr_t unlocked_value           = 1;

  static const uintptr_t monitor_value            = 2;

  static const uintptr_t marked_value             = 3;

  static const uintptr_t biased_lock_pattern      = 5;

  static const uintptr_t no_hash                  = 0 ;  // no hash value assigned

  static const uintptr_t no_hash_in_place         = (address_word)no_hash << hash_shift;

  static const uintptr_t no_lock_in_place         = unlocked_value;

  static const uint max_age                       = age_mask;

  static const int max_bias_epoch                 = epoch_mask;

  // Creates a markWord with all bits set to zero.

  static markWord zero() { return markWord(uintptr_t(0)); }

  // Biased Locking accessors.

  // These must be checked by all code which calls into the

  // ObjectSynchronizer and other code. The biasing is not understood

  // by the lower-level CAS-based locking code, although the runtime

  // fixes up biased locks to be compatible with it when a bias is

  // revoked.

  bool has_bias_pattern() const {

    return (mask_bits(value(), biased_lock_mask_in_place) == biased_lock_pattern);

  }

  JavaThread* biased_locker() const {

    assert(has_bias_pattern(), "should not call this otherwise");

    return (JavaThread*) mask_bits(value(), ~(biased_lock_mask_in_place | age_mask_in_place | epoch_mask_in_place));

  }

  // Indicates that the mark has the bias bit set but that it has not

  // yet been biased toward a particular thread

  bool is_biased_anonymously() const {

    return (has_bias_pattern() && (biased_locker() == NULL));

  }

  // Indicates epoch in which this bias was acquired. If the epoch

  // changes due to too many bias revocations occurring, the biases

  // from the previous epochs are all considered invalid.

  int bias_epoch() const {

    assert(has_bias_pattern(), "should not call this otherwise");

    return (mask_bits(value(), epoch_mask_in_place) >> epoch_shift);

  }

  markWord set_bias_epoch(int epoch) {

    assert(has_bias_pattern(), "should not call this otherwise");

    assert((epoch & (~epoch_mask)) == 0, "epoch overflow");

    return markWord(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift));

  }

  markWord incr_bias_epoch() {

    return set_bias_epoch((1 + bias_epoch()) & epoch_mask);

  }

  // Prototype mark for initialization

  static markWord biased_locking_prototype() {

    return markWord( biased_lock_pattern );

  }

  // lock accessors (note that these assume lock_shift == 0)

  bool is_locked()   const {

    return (mask_bits(value(), lock_mask_in_place) != unlocked_value);

  }

  bool is_unlocked() const {

    return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value);

  }

  bool is_marked()   const {

    return (mask_bits(value(), lock_mask_in_place) == marked_value);

  }

  bool is_neutral()  const { return (mask_bits(value(), biased_lock_mask_in_place) == unlocked_value); }

  // Special temporary state of the markWord while being inflated.

  // Code that looks at mark outside a lock need to take this into account.

  bool is_being_inflated() const { return (value() == 0); }

  // Distinguished markword value - used when inflating over

  // an existing stacklock.  0 indicates the markword is "BUSY".

  // Lockword mutators that use a LD...CAS idiom should always

  // check for and avoid overwriting a 0 value installed by some

  // other thread.  (They should spin or block instead.  The 0 value

  // is transient and *should* be short-lived).

  static markWord INFLATING() { return zero(); }    // inflate-in-progress

  // Should this header be preserved during GC?

  template <typename KlassProxy>

  inline bool must_be_preserved(KlassProxy klass) const;

  // Should this header (including its age bits) be preserved in the

  // case of a promotion failure during scavenge?

  // Note that we special case this situation. We want to avoid

  // calling BiasedLocking::preserve_marks()/restore_marks() (which

  // decrease the number of mark words that need to be preserved

  // during GC) during each scavenge. During scavenges in which there

  // is no promotion failure, we actually don't need to call the above

  // routines at all, since we don't mutate and re-initialize the

  // marks of promoted objects using init_mark(). However, during

  // scavenges which result in promotion failure, we do re-initialize

  // the mark words of objects, meaning that we should have called

  // these mark word preservation routines. Currently there's no good

  // place in which to call them in any of the scavengers (although

  // guarded by appropriate locks we could make one), but the

  // observation is that promotion failures are quite rare and

  // reducing the number of mark words preserved during them isn't a

  // high priority.

  template <typename KlassProxy>

  inline bool must_be_preserved_for_promotion_failure(KlassProxy klass) const;

  // WARNING: The following routines are used EXCLUSIVELY by

  // synchronization functions. They are not really gc safe.

  // They must get updated if markWord layout get changed.

  markWord set_unlocked() const {

    return markWord(value() | unlocked_value);

  }

  bool has_locker() const {

    return ((value() & lock_mask_in_place) == locked_value);

  }

  BasicLock* locker() const {

    assert(has_locker(), "check");

    return (BasicLock*) value();

  }

  bool has_monitor() const {

    return ((value() & monitor_value) != 0);

  }

  ObjectMonitor* monitor() const {

    assert(has_monitor(), "check");

    // Use xor instead of &~ to provide one extra tag-bit check.

    return (ObjectMonitor*) (value() ^ monitor_value);

  }

  bool has_displaced_mark_helper() const {

    return ((value() & unlocked_value) == 0);

  }

  markWord displaced_mark_helper() const {

    assert(has_displaced_mark_helper(), "check");

    uintptr_t ptr = (value() & ~monitor_value);

    return *(markWord*)ptr;

  }

  void set_displaced_mark_helper(markWord m) const {

    assert(has_displaced_mark_helper(), "check");

    uintptr_t ptr = (value() & ~monitor_value);

    ((markWord*)ptr)->_value = m._value;

  }

  markWord copy_set_hash(intptr_t hash) const {

    uintptr_t tmp = value() & (~hash_mask_in_place);

    tmp |= ((hash & hash_mask) << hash_shift);

    return markWord(tmp);

  }

  // it is only used to be stored into BasicLock as the

  // indicator that the lock is using heavyweight monitor

  static markWord unused_mark() {

    return markWord(marked_value);

  }

  // the following two functions create the markWord to be

  // stored into object header, it encodes monitor info

  static markWord encode(BasicLock* lock) {

    return from_pointer(lock);

  }

  static markWord encode(ObjectMonitor* monitor) {

    uintptr_t tmp = (uintptr_t) monitor;

    return markWord(tmp | monitor_value);

  }

  static markWord encode(JavaThread* thread, uint age, int bias_epoch) {

    uintptr_t tmp = (uintptr_t) thread;

    assert(UseBiasedLocking && ((tmp & (epoch_mask_in_place | age_mask_in_place | biased_lock_mask_in_place)) == 0), "misaligned JavaThread pointer");

    assert(age <= max_age, "age too large");

    assert(bias_epoch <= max_bias_epoch, "bias epoch too large");

    return markWord(tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);

  }

  // used to encode pointers during GC

  markWord clear_lock_bits() { return markWord(value() & ~lock_mask_in_place); }

  // age operations

  markWord set_marked()   { return markWord((value() & ~lock_mask_in_place) | marked_value); }

  markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) | unlocked_value); }

  uint     age()           const { return mask_bits(value() >> age_shift, age_mask); }

  markWord set_age(uint v) const {

    assert((v & ~age_mask) == 0, "shouldn't overflow age field");

    return markWord((value() & ~age_mask_in_place) | ((v & age_mask) << age_shift));

  }

  markWord incr_age()      const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }

  // hash operations

  intptr_t hash() const {

    return mask_bits(value() >> hash_shift, hash_mask);

  }

  bool has_no_hash() const {

    return hash() == no_hash;

  }

  // Prototype mark for initialization

  static markWord prototype() {

    return markWord( no_hash_in_place | no_lock_in_place );

  }

  // Helper function for restoration of unmarked mark oops during GC

  static inline markWord prototype_for_klass(const Klass* klass);

  // Debugging

  void print_on(outputStream* st) const;

  // Prepare address of oop for placement into mark

  inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }

  // Recover address of oop from encoded form used in mark

  inline void* decode_pointer() { if (UseBiasedLocking && has_bias_pattern()) return NULL; return (void*)clear_lock_bits().value(); }

};

// Support atomic operations.

template<>

struct PrimitiveConversions::Translate<markWord> : public TrueType {

  typedef markWord Value;

  typedef uintptr_t Decayed;

  static Decayed decay(const Value& x) { return x.value(); }

  static Value recover(Decayed x) { return Value(x); }

};

#endif // SHARE_OOPS_MARKWORD_HPP