code: int getNumberOfReferenceHolders(JobID jobId) {
  		synchronized (lockObject) {
  			LibraryCacheEntry entry = cacheEntries.get(jobId);
  			return entry == null ? 0 : entry.getNumberOfReferenceHolders();
  		}
  	}
docs: Gets the number of tasks holding {@link ClassLoader} references for the given job.
  
  @param jobId ID of a job
  
  @return number of reference holders