code: private void interruptWorkers() {
          final ReentrantLock mainLock = this.mainLock;
          mainLock.lock();
          try {
              for (Worker w : workers)
                  w.interruptIfStarted();
          } finally {
              mainLock.unlock();
          }
      }
docs: Interrupts all threads, even if active. Ignores SecurityExceptions
  (in which case some threads may remain uninterrupted).