ReadWriteLock §

ReadWriteLock是一种比ReentrantLock更宽松的锁，它：

• 只允许一个线程写入（在写入时其他线程既不能写入也不能读取）
• 没有写入时，允许多个线程同时进行读取操作

public class Counter {
    private final ReadWriteLock rwlock = new ReentrantReadWriteLock();
    private final Lock rlock = rwlock.readLock();
    private final Lock wlock = rwlock.writeLock();
    private int[] counts = new int[10];
 
    public void inc(int index) {
        wlock.lock(); // 加写锁
        try {
            counts[index] += 1;
        } finally {
            wlock.unlock(); // 释放写锁
        }
    }
 
    public int[] get() {
        rlock.lock(); // 加读锁
        try {
            return Arrays.copyOf(counts, counts.length);
        } finally {
            rlock.unlock(); // 释放读锁
        }
    }
}