关于轻量级锁的一些问题

ObjectSynchronizer::inflate(THREAD, obj())->enter(THREAD);

// Try one round of spinning *before* enqueueing Self
// and before going through the awkward and expensive state
// transitions.  The following spin is strictly optional ...
// Note that if we acquire the monitor from an initial spin
// we forgo posting JVMTI events and firing DTRACE probes.
if (Knob_SpinEarly && TrySpin (Self) > 0) {
  assert (_owner == Self      , "invariant") ;
  assert (_recursions == 0    , "invariant") ;
  assert (((oop)(object()))->mark() == markOopDesc::encode(this), "invariant") ;
  Self->_Stalled = 0 ;
  return ;
}

if (mark == (markOop) Atomic::cmpxchg_ptr(lock, obj()->mark_addr(), mark)) {
    TEVENT (slow_enter: release stacklock) ;
    return ;
}

class BasicLock VALUE_OBJ_CLASS_SPEC {
  friend class VMStructs;
 private:
  volatile markOop _displaced_header;
 public:
  void         set_displaced_header(markOop header)   { _displaced_header = header; }
  ......  
};

// A BasicObjectLock associates a specific Java object with a BasicLock.
// It is currently embedded in an interpreter frame.

// Because some machines have alignment restrictions on the control stack,
// the actual space allocated by the interpreter may include padding words
// after the end of the BasicObjectLock.  Also, in order to guarantee
// alignment of the embedded BasicLock objects on such machines, we
// put the embedded BasicLock at the beginning of the struct.

class BasicObjectLock VALUE_OBJ_CLASS_SPEC {
  friend class VMStructs;
 private:
  BasicLock _lock; // the lock, must be double word aligned
  oop       _obj; // object holds the lock;

 public:
  // Manipulation
  oop      obj() const { return _obj;  }
  void set_obj(oop obj) { _obj = obj; }
  BasicLock* lock() { return &_lock; }

  // Note: Use frame::interpreter_frame_monitor_size() for the size of BasicObjectLocks
  //       in interpreter activation frames since it includes machine-specific padding.
  static int size() { return sizeof(BasicObjectLock)/wordSize; }

  // GC support
  void oops_do(OopClosure* f) { f->do_oop(&_obj); }

  static int obj_offset_in_bytes() { return offset_of(BasicObjectLock, _obj);  }
  static int lock_offset_in_bytes() { return offset_of(BasicObjectLock, _lock); }
};