text: /*
   * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * 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).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
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   */
  
  #ifndef SHARE_VM_OOPS_MARKOOP_HPP
  #define SHARE_VM_OOPS_MARKOOP_HPP
  
  #include "oops/oop.hpp"
  
  // The markOop describes the header of an object.
  //
  // Note that the mark is not a real oop but just a word.
  // It is placed in the oop hierarchy for historical reasons.
  //
  // 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)
  //             size:32 ------------------------------------------>| (CMS free block)
  //             PromotedObject*:29 ---------->| promo_bits:3 ----->| (CMS promoted object)
  //
  //  64 bits:
  //  --------
  //  unused:25 hash:31 -->| unused:1   age:4    biased_lock:1 lock:2 (normal object)
  //  JavaThread*:54 epoch:2 unused:1   age:4    biased_lock:1 lock:2 (biased object)
  //  PromotedObject*:61 --------------------->| promo_bits:3 ----->| (CMS promoted object)
  //  size:64 ----------------------------------------------------->| (CMS free block)
  //
  //  unused:25 hash:31 -->| cms_free:1 age:4    biased_lock:1 lock:2 (COOPs && normal object)
  //  JavaThread*:54 epoch:2 cms_free:1 age:4    biased_lock:1 lock:2 (COOPs && biased object)
  //  narrowOop:32 unused:24 cms_free:1 unused:4 promo_bits:3 ----->| (COOPs && CMS promoted object)
  //  unused:21 size:35 -->| cms_free:1 unused:7 ------------------>| (COOPs && CMS free block)
  //
  //  - 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
  //    biased locking), and for the CMS "freeness" bit in the 64bVM (+COOPs).
  //
  //    [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 markOopDesc: public oopDesc {
   private:
    // Conversion
    uintptr_t value() const { return (uintptr_t) this; }
  
   public:
    // Constants
    enum { age_bits                 = 4,
           lock_bits                = 2,
           biased_lock_bits         = 1,
           max_hash_bits            = BitsPerWord - age_bits - lock_bits - biased_lock_bits,
           hash_bits                = max_hash_bits > 31 ? 31 : max_hash_bits,
           cms_bits                 = LP64_ONLY(1) NOT_LP64(0),
           epoch_bits               = 2
    };
  
    // The biased locking code currently requires that the age bits be
    // contiguous to the lock bits.
    enum { lock_shift               = 0,
           biased_lock_shift        = lock_bits,
           age_shift                = lock_bits + biased_lock_bits,
           cms_shift                = age_shift + age_bits,
           hash_shift               = cms_shift + cms_bits,
           epoch_shift              = hash_shift
    };
  
    enum { lock_mask                = right_n_bits(lock_bits),
           lock_mask_in_place       = lock_mask << lock_shift,
           biased_lock_mask         = right_n_bits(lock_bits + biased_lock_bits),
           biased_lock_mask_in_place= biased_lock_mask << lock_shift,
           biased_lock_bit_in_place = 1 << biased_lock_shift,
           age_mask                 = right_n_bits(age_bits),
           age_mask_in_place        = age_mask << age_shift,
           epoch_mask               = right_n_bits(epoch_bits),
           epoch_mask_in_place      = epoch_mask << epoch_shift,
           cms_mask                 = right_n_bits(cms_bits),
           cms_mask_in_place        = cms_mask << cms_shift
  #ifndef _WIN64
           ,hash_mask               = right_n_bits(hash_bits),
           hash_mask_in_place       = (address_word)hash_mask << hash_shift
  #endif
    };
  
    // Alignment of JavaThread pointers encoded in object header required by biased locking
    enum { biased_lock_alignment    = 2 << (epoch_shift + epoch_bits)
    };
  
  #ifdef _WIN64
      // These values are too big for Win64
      const static uintptr_t hash_mask = right_n_bits(hash_bits);
      const static uintptr_t hash_mask_in_place  =
                              (address_word)hash_mask << hash_shift;
  #endif
  
    enum { locked_value             = 0,
           unlocked_value           = 1,
           monitor_value            = 2,
           marked_value             = 3,
           biased_lock_pattern      = 5
    };
  
    enum { no_hash                  = 0 };  // no hash value assigned
  
    enum { no_hash_in_place         = (address_word)no_hash << hash_shift,
           no_lock_in_place         = unlocked_value
    };
  
    enum { max_age                  = age_mask };
  
    enum { max_bias_epoch           = epoch_mask };
  
    // 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*) ((intptr_t) (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);
    }
    markOop set_bias_epoch(int epoch) {
      assert(has_bias_pattern(), "should not call this otherwise");
      assert((epoch & (~epoch_mask)) == 0, "epoch overflow");
      return markOop(mask_bits(value(), ~epoch_mask_in_place) | (epoch << epoch_shift));
    }
    markOop incr_bias_epoch() {
      return set_bias_epoch((1 + bias_epoch()) & epoch_mask);
    }
    // Prototype mark for initialization
    static markOop biased_locking_prototype() {
      return markOop( 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 markOop 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 markOop INFLATING() { return (markOop) 0; }    // inflate-in-progress
  
    // Should this header be preserved during GC?
    inline bool must_be_preserved(oop obj_containing_mark) const;
    inline bool must_be_preserved_with_bias(oop obj_containing_mark) 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.
    inline bool must_be_preserved_for_promotion_failure(oop obj_containing_mark) const;
    inline bool must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const;
  
    // Should this header be preserved during a scavenge where CMS is
    // the old generation?
    // (This is basically the same body as must_be_preserved_for_promotion_failure(),
    // but takes the Klass* as argument instead)
    inline bool must_be_preserved_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
    inline bool must_be_preserved_with_bias_for_cms_scavenge(Klass* klass_of_obj_containing_mark) const;
  
    // WARNING: The following routines are used EXCLUSIVELY by
    // synchronization functions. They are not really gc safe.
    // They must get updated if markOop layout get changed.
    markOop set_unlocked() const {
      return markOop(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);
    }
    markOop displaced_mark_helper() const {
      assert(has_displaced_mark_helper(), "check");
      intptr_t ptr = (value() & ~monitor_value);
      return *(markOop*)ptr;
    }
    void set_displaced_mark_helper(markOop m) const {
      assert(has_displaced_mark_helper(), "check");
      intptr_t ptr = (value() & ~monitor_value);
      *(markOop*)ptr = m;
    }
    markOop copy_set_hash(intptr_t hash) const {
      intptr_t tmp = value() & (~hash_mask_in_place);
      tmp |= ((hash & hash_mask) << hash_shift);
      return (markOop)tmp;
    }
    // it is only used to be stored into BasicLock as the
    // indicator that the lock is using heavyweight monitor
    static markOop unused_mark() {
      return (markOop) marked_value;
    }
    // the following two functions create the markOop to be
    // stored into object header, it encodes monitor info
    static markOop encode(BasicLock* lock) {
      return (markOop) lock;
    }
    static markOop encode(ObjectMonitor* monitor) {
      intptr_t tmp = (intptr_t) monitor;
      return (markOop) (tmp | monitor_value);
    }
    static markOop encode(JavaThread* thread, uint age, int bias_epoch) {
      intptr_t tmp = (intptr_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 (markOop) (tmp | (bias_epoch << epoch_shift) | (age << age_shift) | biased_lock_pattern);
    }
  
    // used to encode pointers during GC
    markOop clear_lock_bits() { return markOop(value() & ~lock_mask_in_place); }
  
    // age operations
    markOop set_marked()   { return markOop((value() & ~lock_mask_in_place) | marked_value); }
    markOop set_unmarked() { return markOop((value() & ~lock_mask_in_place) | unlocked_value); }
  
    uint    age()               const { return mask_bits(value() >> age_shift, age_mask); }
    markOop set_age(uint v) const {
      assert((v & ~age_mask) == 0, "shouldn't overflow age field");
      return markOop((value() & ~age_mask_in_place) | (((uintptr_t)v & age_mask) << age_shift));
    }
    markOop incr_age()          const { return age() == max_age ? markOop(this) : 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 markOop prototype() {
      return markOop( no_hash_in_place | no_lock_in_place );
    }
  
    // Helper function for restoration of unmarked mark oops during GC
    static inline markOop prototype_for_object(oop obj);
  
    // Debugging
    void print_on(outputStream* st) const;
  
    // Prepare address of oop for placement into mark
    inline static markOop encode_pointer_as_mark(void* p) { return markOop(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 clear_lock_bits(); }
  
    // These markOops indicate cms free chunk blocks and not objects.
    // In 64 bit, the markOop is set to distinguish them from oops.
    // These are defined in 32 bit mode for vmStructs.
    const static uintptr_t cms_free_chunk_pattern  = 0x1;
  
    // Constants for the size field.
    enum { size_shift                = cms_shift + cms_bits,
           size_bits                 = 35    // need for compressed oops 32G
         };
    // These values are too big for Win64
    const static uintptr_t size_mask = LP64_ONLY(right_n_bits(size_bits))
                                       NOT_LP64(0);
    const static uintptr_t size_mask_in_place =
                                       (address_word)size_mask << size_shift;
  
  #ifdef _LP64
    static markOop cms_free_prototype() {
      return markOop(((intptr_t)prototype() & ~cms_mask_in_place) |
                     ((cms_free_chunk_pattern & cms_mask) << cms_shift));
    }
    uintptr_t cms_encoding() const {
      return mask_bits(value() >> cms_shift, cms_mask);
    }
    bool is_cms_free_chunk() const {
      return is_neutral() &&
             (cms_encoding() & cms_free_chunk_pattern) == cms_free_chunk_pattern;
    }
  
    size_t get_size() const       { return (size_t)(value() >> size_shift); }
    static markOop set_size_and_free(size_t size) {
      assert((size & ~size_mask) == 0, "shouldn't overflow size field");
      return markOop(((intptr_t)cms_free_prototype() & ~size_mask_in_place) |
                     (((intptr_t)size & size_mask) << size_shift));
    }
  #endif // _LP64
  };
  
  #endif // SHARE_VM_OOPS_MARKOOP_HPP
  