code: @Exported
      public int getIdleExecutors() {
          int r=0;
          for (Node n : getNodes()) {
              Computer c = n.toComputer();
              if(c!=null && (c.isOnline() || c.isConnecting()) && c.isAcceptingTasks())
                  r += c.countIdle();
          }
          return r;
      }
docs: Number of idle {@link Executor}s that can start working immediately.