*/
class DaemonsState {
    final int busy
    final int idle

    DaemonsState(int busy, int idle) {
        this.busy = Math.max(busy, 0)
        this.idle = Math.max(idle, 0)
    }

    static getWildcardState() {
        new DaemonsState()
    }

    private DaemonsState() {
        this.busy = -1
        this.idle = -1
    }

 * actions to perform when the checkpoint is reached.
 */
class DaemonsStateCheckpoint {

    final DaemonsState expectedState
    private final Runnable[] actions

    DaemonsStateCheckpoint(DaemonsState expectedState, Runnable... actions) {
        this.expectedState = expectedState
        this.actions = actions
    }

    String toString() {

    private final List<DaemonsStateCheckpoint> allCheckpoints
    private final List<DaemonsStateCheckpoint> remainingCheckpoints

    private DaemonsState lastDaemonsState = new DaemonsState(0, 0)
    private final Map<Long, DaemonsState> pastStateChanges = new LinkedHashMap<Long, DaemonsState>() // processed changes
    private final Queue<Holder> changeQueue = new LinkedBlockingQueue() // unprocessed changes

        state(numDaemons - idle, idle)
    }

    void stopped() {
        numDaemons = 0
        state(0, 0)
    }

    void state(int busy, int idle) {
        state(new DaemonsState(busy, idle))
    }

    void state(DaemonsState checkpointState) {
        finishCheckpoint()
        currentState = checkpointState
    }

    void numDaemons(int numDaemons) {
        this.numDaemons = numDaemons
    }