code: private void addWorkerFailed(Worker w) {
          final ReentrantLock mainLock = this.mainLock;
          mainLock.lock();
          try {
              if (w != null)
                  workers.remove(w);
              decrementWorkerCount();
              tryTerminate();
          } finally {
              mainLock.unlock();
          }
      }
docs: Rolls back the worker thread creation.
  - removes worker from workers, if present
  - decrements worker count
  - rechecks for termination, in case the existence of this
  worker was holding up termination