code: private int incrementReferenceCounter(final JobID jobID) {
  
  		while (true) {
  
  			AtomicInteger ai = this.libraryReferenceCounter.get(jobID);
  			if (ai == null) {
  
  				ai = new AtomicInteger(1);
  				if (this.libraryReferenceCounter.putIfAbsent(jobID, ai) == null) {
  					return 1;
  				}
  
  				// We had a race, try again
  			} else {
  				return ai.incrementAndGet();
  			}
  		}
  	}
docs: Increments the reference counter for the library manager entry with the given job ID.
  
  @param jobID
  the job ID identifying the library manager entry
  @return the increased reference counter