Created
June 26, 2020 09:29
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| class CacheData { | |
| Object data; | |
| volatile boolean isCacheValid; | |
| final ReadWriteLock rwl = new ReentrantReadWriteLock(); | |
| // 读锁 | |
| final Lock r = rwl.readLock(); | |
| // 写锁 | |
| final Lock w = rwl.writeLock(); | |
| void processCacheData() { | |
| // 获取读锁 | |
| r.lock(); | |
| if (!isCacheValid) { | |
| // 缓存无效，释放读锁，因为不允许锁的升级 | |
| r.unlock(); | |
| // 获取写锁 | |
| w.lock(); | |
| try { | |
| // 再次检查缓存 | |
| if (!isCacheValid) { | |
| data = ...; | |
| isCacheValid = true; | |
| } | |
| // 释放写锁前，降级为读锁，降级是支持的 | |
| r.lock(); | |
| } finally { | |
| // 释放写锁 | |
| w.unlock(); | |
| } | |
| // 此处仍然持有读锁 | |
| try { | |
| use(data); | |
| } finally { | |
| r.unlock(); | |
| } | |
| } |
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