自旋锁

参考这里，自旋锁是不释放 CPU 的，而一般的锁，会让进程进入睡眠状态，让出控制机，等待条件满足，被内核唤醒。

参考

https://stackoverflow.com/questions/1957398/what-exactly-are-spin-locks
https://stackoverflow.com/questions/26709471/how-to-implement-a-spinlock-to-avoid-blocking Java 对于自旋锁的实现
https://stackoverflow.com/questions/6325824/does-any-jvm-implement-blocking-with-spin-waiting Java 对于自旋锁的实现
http://tutorials.jenkov.com/java-concurrency/locks.html Java 对于锁的使用