code: public static WorkQueue getWorkQueue() {
          if (singleton == null) {
              synchronized (WorkQueue.class) {
                  if (singleton == null)
                      // REMINDER: default number of threads?
                      singleton = new WorkQueue(); 
              }
          }
          return singleton;
      }
docs: Returns the canonical instance of the {@link WorkQueue} to be used in
  running concurrent tasks.