Java中的鎖機制：
- API層面：Synchronized，AQS（CLH）: ReentrantLock，ReentrantReadWriteLock，StampedLock(Ordered RW locks)
- JVM層面(Hotspot): SpinLock,Biased,Stack-Locked(輕量級鎖), Inflated(重量級鎖)
- Neutral: Unlocked
- Biased: Locked/Unlocked + Unshared
- Stack-Locked: Locked + Shared but uncontended，The mark points to displaced mark word on the owner thread's stack.
- Inflated: Locked/Unlocked + Shared and contended，Threads are blocked in monitorenter or wait().，The mark points to heavy-weight "objectmonitor" structure.
參考：
http://openjdk.java.net/groups/hotspot/docs/RuntimeOverview.html
AbstractQueuedLongSynchronizer,StampedLock源碼
http://cs.rochester.edu/research/synchronization/pseudocode/ss.html