ValueLock

根据值进行加锁

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public enum ValueLock {
    MediaIdLock;

    ValueLock() {
        for (int i = 0; i < concurrencyLevel; i++) {
            locks[i] = new ReentrantLock();
        }
    }

    private int concurrencyLevel = 1 << 8; // 256locks
    private Lock[] locks = new Lock[concurrencyLevel];

    public Lock getLock(Object key) {
        return locks[key.hashCode() & (concurrencyLevel-1)]; // select one of 256 locks
    }

//    public static void main(String[] args) {
//        Lock mediaIdLock = ValueLock.MediaIdLock.getLock(11);
//        try {
//            mediaIdLock.lock();
//            // do something
//        } finally {
//            mediaIdLock.unlock();
//        }
//    }
}

• lock-unlock-based-on-value
• 单例模式
• 按位与操作，负数时用的补码(取反末尾+1)