code: public final void removeExpired() {
  		mapLock.lock();
  		Iterator<Entry<String, TimestampedCacheEntry<DOReader>>> entries = cacheMap.entrySet().iterator();
  		if (entries.hasNext()) {
  		    long now = System.currentTimeMillis();
  		    while (entries.hasNext()) {
  		        Entry<String, TimestampedCacheEntry<DOReader>> entry = entries.next();
  		        TimestampedCacheEntry<DOReader> e = entry.getValue();
  		        long age = e.ageAt(now);
  		        if (age > (maxSeconds * 1000)) {
  		            entries.remove();
  		            String pid = entry.getKey();
  		            LOG.debug("removing entry {} after {} milliseconds",
  		                    pid, age);
  		        }
  
  		    }
  		}
  		mapLock.unlock();
  	}
docs: remove expired entries from the cache