我的线程获取读锁定，但在尝试释放它时抛出IllegalMonitorStateException

Question

我的应用程序部署在Weblogic 10.3.5上，带有java 6 update 30.我在执行此代码行时遇到以下错误：

    lock.readLock().lock();
    try {
        holder = cache.get(configName);
        // If it exists in the cache, return it
        if (holder != null)
            return holder;
    } finally {
        lock.readLock().unlock();
    }

虽然在类加载期间初始化了锁：

private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();

缓存是：

private Map<String, ConfigurationHolder> cache = new HashMap<String,ConfigurationHolder>();

突然抛出了IllegalMonitorStateException：

Caused by: java.lang.IllegalMonitorStateException
    at java.util.concurrent.locks.ReentrantReadWriteLock$Sync.tryReleaseShared(ReentrantReadWriteLock.java:363)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer.releaseShared(AbstractQueuedSynchronizer.java:1317)
    at java.util.concurrent.locks.ReentrantReadWriteLock$ReadLock.unlock(ReentrantReadWriteLock.java:745) 

我在这种情况下阅读了here类似的描述。

任何人都知道为什么会这样？