Package lejos.robotics.subsumption

Class Arbitrator

java.lang.Object

lejos.robotics.subsumption.Arbitrator

public class Arbitrator
extends java.lang.Object

An Arbitrator object manages a behavior control system by starting and stopping individual behaviors
by the calling the action() and suppress() methods on them.
These Behavior objects are stored in an array, in order of increasing priority.
Arbitrator has three major responsibilities:
1. Determine the highest priority behavior among those that returns true to takeControl() .
2. Suppress the active behavior if its priority is less than highest priority. These two taska are performed the Arbitrator's internal Monitor thread.
3. When the action() method exits, call action() on the Behavior of highest priority.
This task is performed by the Arbitrator main thread.
The Arbitrator assumes that a Behavior is no longer active when action() exits,
therefore it will only call suppress() on the active Behavior i.e. whose action() method is running.
It can make consecutive calls of action() on the same Behavior.
Requirements for a Behavior:
When suppress() is called, terminate action() immediately.
When action() exits, the robot is in a safe state (e.g. motors stopped)
When the behavior should take control, the takeControl() should continue to return true
until its action starts.
After your code instantiates the Arbitrator, it should call go() to start it running.

See Also:

Behavior

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
private class	Arbitrator.Monitor Finds the highest priority behavior that returns true to takeControl(); If this priority is higher than the active behavior, it calls active.suppress().

Field Summary

Fields

Modifier and Type	Field and Description
private int	_active
private Behavior[]	_behavior
private int	_highestPriority
private boolean	_returnWhenInactive
boolean	keepRunning
private Arbitrator.Monitor	monitor Monitor is an inner class.
private int	NONE

Constructor Summary

Constructors

Constructor and Description
Arbitrator(Behavior[] behaviorList) Same as Arbitrator(behaviorList, false) Arbitrator start() never exits
Arbitrator(Behavior[] behaviorList, boolean returnWhenInactive) Allocates an Arbitrator object and initializes it with an array of Behavior objects.

Method Summary

Modifier and Type	Method and Description
void	go() This method starts the arbitration of Behaviors and runs an endless loop.
void	stop()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

NONE

private final int NONE

See Also:

Constant Field Values

_behavior

private Behavior[] _behavior

_highestPriority

private int _highestPriority

_active

private int _active

_returnWhenInactive

private boolean _returnWhenInactive

keepRunning

public boolean keepRunning

monitor

private Arbitrator.Monitor monitor

Monitor is an inner class. It polls the behavior array to find the behavior of hightst priority. If higher than the active behavior, it calls active.suppress()

Constructor Detail

Arbitrator

public Arbitrator(Behavior[] behaviorList,
                  boolean returnWhenInactive)

Allocates an Arbitrator object and initializes it with an array of Behavior objects. The index of a behavior in this array is its priority level, so the behavior of the largest index has the highest the priority level. The behaviors in an Arbitrator can not be changed once the arbitrator is initialized.
NOTE: Once the Arbitrator is initialized, the method go() must be called to begin the arbitration.

Parameters:

behaviorList - an array of Behavior objects.

returnWhenInactive - if true, the go() method returns when no Behavior is active.

Arbitrator

public Arbitrator(Behavior[] behaviorList)

Same as Arbitrator(behaviorList, false) Arbitrator start() never exits

Parameters:

behaviorList - An array of Behavior objects.

Method Detail

go

public void go()

This method starts the arbitration of Behaviors and runs an endless loop.
Note: Arbitrator does not run in a separate thread. The go() method will not return unless
1. no action() method is running and
2. no behavior takeControl() returns true and
3. the returnWhenInacative flag is true,

stop

public void stop()