Memory Slots

The slots are used to memorize data for different skills. A slot has a key which uniquely identifies the slot within the skill in use.

Skills define the data type of the slot and can read and write data into it.

Note

Data already stored in a slot will be overwritten once another skill writes data into it.

A skill can request slots from the Skill Configurator. The configurator tries to find the slot definition inside the robot behavior control (SCXML) with the key and state and configures the slot with the corresponding xpath.

Note

The slot keys are only unique within the skill itself. Other skills can have slots with the same ID. The robot behavior control needs to make sure to correctly configure the slots.

Slot Types

There are three different kind of slots:

Slot Types

Slot Type	Explanation
ReadSlot	Used to only read from a slot
WriteSlot	Used to write into a slot
ReadWriteSlot	Used to read and write from and into a slot

Usage

Memory slots are created using the MemoryFactory class. This will create instances of ObjectSlots which inherit from the MemorySlot interface (both implemented in the bonsai_core repository).

Slots have several functions that you can use:

Slot Functions

Function	Explanation
recall()	Used to read from the slot (which allows reading)
memorize()	Used to write to a slot (if allowed to write)
forget()	Removes the data from the slot

Within a skill, using the SkillConfigurator the skill can request slots from which it can read or write from. The skill can define the key used to reference the slot. The slot location for the skill is defined within the SCXML.

Example

In this example we want to:

• Read from a slot containing an int

• Write a String to a slot

• Read and Write data of the type Type from a slot

public class ExampleSkill implements AbstractSkill {

     // define here the keys of everything we want to get from the configurator
     private static final String KEY_CLASS_SLOT = "ClassSlot";
     private static final String KEY_INT_SLOT = "IntSlot";
     private static final String KEY_STRING_SLOT = "StringSlot";

     // Declare the Actuators, Sensors, Slots and parameters
     private Slot<String> stringSlot;
     private Slot<Integer> intSlot;
     private Slot<Type> classSlot;

     private String stringData = "example";
     private int intData;
     private Type classData;

    /*
    * This function uses the Skillconfigurator to get the configured objects and initialize everything
    * that has been declared above
    */
    @Override
    public void configure(ISkillConfigurator conf) {
        this.intSlot = conf.getReadSlot(KEY_INT_SLOT)           // read slot
        this.stringSlot = conf.getWriteSlot(KEY_STRING_SLOT);   // write slot
        this.classSlot = conf.getReadWriteSlot(KEY_CLASS_SLOT); // read and write slot
    }

    /*
     * This function will return the ExitToken Fatal when the slots are null
     */
    @Override
    public boolean init(){
        // Check if slots have been configured
        if (this.intSlot == null || this.stringSlot == null || this.classSlot == null)
            return false

        // read from a ReadSlot
        this.intData = this.intSlot.recall();
        // read from the ReadWriteSlot
        this.classData = this.classSlot.recall();
    }

    @Override
    public ExitToken execute() {
        // write to the WriteSlot
        this.stringSlot.memorize(this.stringData);
        // write to the ReadWriteSlot
        this.classData.doSomeChanges();
        this.classSlot.memorize(this.classData);
    }

    ...

}

Note

The skill defines by which key (SlotID) it wants to request its slot. Other parameters need to define slots are provided using the robotic behavior control.