3. Object超类
wait(), wait(time), notify(), notifyAll()
2. Thread类
sleep()
3. LockSupport工具
park(), parkNanos(), parkUntil(), unpark()
4. Condition接口
await(), signal(), signalAll()
wait()会释放锁,而sleep()并不释放锁
wait()一般用于Synchronized中,而await()只能用于ReentrantLock锁中