RunnableExecutorPair(Runnable runnable, Executor executor) {
        this.runnable = runnable;
        this.executor = executor;
      }
    }
  }

  // A version of the list that uses compare and swap to manage the stack without locks.
  private static final class ExecutionListCAS {
    static final Logger log = Logger.getLogger(ExecutionListCAS.class.getName());

    private static final sun.misc.Unsafe UNSAFE;

      RunnableExecutorPair(Runnable runnable, Executor executor) {
        this.runnable = runnable;
        this.executor = executor;
      }
    }
  }

  // A version of the list that uses compare and swap to manage the stack without locks.
  private static final class ExecutionListCAS {
    static final Logger log = Logger.getLogger(ExecutionListCAS.class.getName());

    private static final sun.misc.Unsafe UNSAFE;