基于ReadWriteLock读写锁实现的缓存

package william.pattern; import java.util.HashMap; import java.util.Map; import java.util.concurrent.ConcurrentHashMap; import java.util.concurrent.locks.Lock; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; import java.util.function.Supplier; /** * @Author: ZhangShenao * @Date: 2019/5/22 10:22 * @Description:基于读写锁实现的简单的缓存 * 1.读操作之间可并发执行 * 2.读写、写写操作之间互斥 * 3.根据key获取不同的锁,减小锁粒度 */ public class SimpleCache<K, V> { private Map<K, V> cache = new HashMap<>(); private Map<K, ReadWriteLock> locks = new ConcurrentHashMap<>(); public V get(K key, Supplier<V> optionsWhenMiss) { V value; try { //加读锁 acquireLock(key, false); //查询缓存 value = cache.get(key); } finally { //释放读锁 releaseLock(key, false); } //如果缓存命中,则直接返回 if (value != null) { return value; } //缓存未命中,加写锁,执行optionsWhenMiss操作 try { acquireLock(key, true); //这里再进行一次缓存的查询,避免高并发场景下,多线程竞争写锁,导致数据的重复查询 value = cache.get(key); if (value == null) { value = optionsWhenMiss.get(); } } finally { //释放写锁 releaseLock(key, true); } return value; } public void put(K key, V value) { //加写锁 try { acquireLock(key, true); cache.put(key, value); } finally { //释放写锁 releaseLock(key, true); } } private void acquireLock(K key, boolean write) { Lock lock = lockForKey(key, write); lock.lock(); } private void releaseLock(K key, boolean write) { Lock lock = lockForKey(key, write); lock.unlock(); } private Lock lockForKey(K key, boolean write) { ReadWriteLock rw = locks.computeIfAbsent(key, k -> new ReentrantReadWriteLock()); return write ? rw.writeLock() : rw.readLock(); } }