code: @Override
  	public void clear() {
  		final String sourceMethod = "clear"; //$NON-NLS-1$
  		SignalUtil.lock(cloneLock.readLock(), sourceClass, sourceMethod);
  		try {
  			cacheMap.clear();
  			layerBuildMap.clear();
  		} finally {
  			cloneLock.readLock().unlock();
  		}
  	}
docs: /* (non-Javadoc)
  @see java.util.concurrent.ConcurrentHashMap#clear()