Sequences and AsyncActionNode

下面例子将展示SequenceNode和ReactiveSequence的不同

一个异步行为有它自己的线程；允许用户使用阻塞函数，但是要将执行流返回给到树；

//Custom type
struct Pose2D
{
  double x, y, theta;
};

class MoveBaseAction : public AsyncActionNode
{
  public:
    MoveBaseAction(const std::string& name, const NodeConfiguration& config)
      : AsyncActionNode(name, config)
    { }

    static PortsList providedPorts()
    {
        return{ InputPort<Pose2D>("goal") };
    }

    NodeStatus tick() override;

    // This overloaded method is used to stop the execution of this node.
  void halt() override
 {
  _halt_requested.store(true);
 }
private:
  std::atomic_bool_halt_requested;
};

//-------------------------

NodeStatus MoveBaseAction::tick()
{
    Pose2D goal;
    if ( !getInput<Pose2D>("goal", goal))
    {
        throw RuntimeError("missing required input [goal]");
    }

    printf("[ MoveBase: STARTED ]. goal: x=%.f y=%.1f theta=%.2f
", 
           goal.x, goal.y, goal.theta);

    _halt_requested.store(false);
    int count = 0;

    // Pretend that "computing" takes 250 milliseconds.
    // It is up to you to check periodicall _halt_requested and interrupt
    // this tick() if it is true.
    while (!_halt_requested && count++ < 25)
    {
        SleepMS(10);
    }

    std::cout << "[ MoveBase: FINISHED ]" << std::endl;
    return _halt_requested ? NodeStatus::FAILURE : NodeStatus::SUCCESS;
}

方法MoveBaseAction::tick()在不主线程不同的线程中执行，主线程唤醒的MoveBaseAction::executeTick().

自己需要实现一个有效的halt()函数；

也需要实现一个函数convertFromString<Pose2D>(StringView)；

Sequence与ReactiveSequence比较

下面是一个简单的SequenceNode

 <root>
     <BehaviorTree>
        <Sequence>
            <BatteryOK/>
            <SaySomething   message="mission started..." />
            <MoveBase       goal="1;2;3"/>
            <SaySomething   message="mission completed!" />
        </Sequence>
     </BehaviorTree>
 </root>

int main()
{
    using namespace DummyNodes;

    BehaviorTreeFactory factory;
    factory.registerSimpleCondition("BatteryOK", std::bind(CheckBattery));
    factory.registerNodeType<MoveBaseAction>("MoveBase");
    factory.registerNodeType<SaySomething>("SaySomething");

    auto tree = factory.createTreeFromText(xml_text);

    NodeStatus status;

    std::cout << "
--- 1st executeTick() ---" << std::endl;
    status = tree.tickRoot();

    SleepMS(150);
    std::cout << "
--- 2nd executeTick() ---" << std::endl;
    status = tree.tickRoot();

    SleepMS(150);
    std::cout << "
--- 3rd executeTick() ---" << std::endl;
    status = tree.tickRoot();

    std::cout << std::endl;

    return 0;
}

Expected output:

    --- 1st executeTick() ---
    [ Battery: OK ]
    Robot says: "mission started..."
    [ MoveBase: STARTED ]. goal: x=1 y=2.0 theta=3.00

    --- 2nd executeTick() ---
    [ MoveBase: FINISHED ]

    --- 3rd executeTick() ---
    Robot says: "mission completed!"

注意到当executeTick()被执行的时候，MoveBase返回RUNNING，在第一次和第二次，第三次最后成功；

BatteryOK只执行了一次；

如果使用ReactiveSequence,MoveBase返回RUNNING,序列sequence重新开始从BatteryOK开始执行，这样比较合理

 <root>
     <BehaviorTree>
        <ReactiveSequence>
            <BatteryOK/>
            <Sequence>
                <SaySomething   message="mission started..." />
                <MoveBase       goal="1;2;3"/>
                <SaySomething   message="mission completed!" />
            </Sequence>
        </ReactiveSequence>
     </BehaviorTree>
 </root>

Expected output:
  --- 1st executeTick() ---
    [ Battery: OK ]
    Robot says: "mission started..."
    [ MoveBase: STARTED ]. goal: x=1 y=2.0 theta=3.00

    --- 2nd executeTick() ---
    [ Battery: OK ]
    [ MoveBase: FINISHED ]

    --- 3rd executeTick() ---
    [ Battery: OK ]
    Robot says: "mission completed!"