1. Read-write lock divides access to a resource (such as a file) into two locks, one read-write lock.
2. Because of read-write locks, read and write operations between multiple threads will not conflict.
3. ReadWriteLock is a read-write lock. It is an interface. RentrantReadWriteLock implements this interface.
Example
public class CacheDemo { private Map<String, Object> cache = new HashMap<>(); private ReadWriteLock readWriteLock = new ReentrantReadWriteLock(); public static void main(String[] args) { } public Object getData(String key) { Object value = null; //首先开启读锁,从缓存中去取 readWriteLock.readLock().lock(); try { value = cache.get(key); //如果缓存中没有释放读锁,上写锁 if (value == null) { //对应queryDB() readWriteLock.readLock().unlock(); //读锁必须unlock之后才能获取写锁 readWriteLock.writeLock().lock(); try { //对应queryDB() value = queryDB(); } finally { //释放写锁 readWriteLock.writeLock().unlock(); } //然后再上读锁 readWriteLock.readLock().lock(); } } finally { //最后释放读锁 readWriteLock.readLock().unlock(); } return value; } public Object queryDB() { return "aaaa"; } }
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