groupmgmt.impl
Class SafeDistanceDetector

java.lang.Object
  groupmgmt.MemberDetector
      groupmgmt.impl.SafeDistanceDetector

All Implemented Interfaces:

BeaconListener, java.util.EventListener, GroupChangedListener, LocationListener

public class SafeDistanceDetector

extends MemberDetector

implements BeaconListener, LocationListener, GroupChangedListener

The SafeDistanceDetector class; Detects members based on beacons, using a BeaconServer. If a new beacon is received, we check the distance, and if it is within a safe range, reportChange is called and it passes the change on to the Disseminator. If a beacon is received with 'stopping' set or if a beacon moves beyond the safe distance, then reportChange is called to remove the member. This class is also in charge of multicasting beacons to its neighbors.

Everything here is done locally, there is no need for a MemberDetector leader because all Members act the same. (It would be possible to implement a less chatty [fewer beacons] and thus more scalable model by designating a MemberDetector leader.)

Uses: MemberBeacon, BeaconEvent, BeaconListener, BeaconServer. also uses Location and LocationGenerator from the location package.

Version:

July 2003

Author:

Christine Julien, Tom Elgin

Field Summary

private BeaconServer	beaconServer The BeaconServer for this host.
private boolean	debugging Determines whether to output log messages.
private Location	location The physical location of this Member.
private LocationGenerator	locationGenerator The LocationGenerator - the object that updates our location (via LocationChangedEvents).
private java.util.Hashtable	neighborBeacons The neighbors table.
private double	safeDistance The safe distance for this host, calculated based on the provided input parameters.
private java.lang.Boolean	stopping Object to use for waiting to exit the Group after I set my beacon to stopping.

Fields inherited from class groupmgmt.MemberDetector

disseminator

Constructor Summary

SafeDistanceDetector(int beaconPort, java.lang.String beaconAddress, int beaconPeriod, double range, double maxSpeed, double networkLatency, LocationGenerator locationGenerator)
Constructor.

Method Summary

void	groupChanged(GroupChangedEvent evt) Implements the GroupChangedListener interface.
void	locationChanged(LocationEvent event) Implements the LocationListener interface.
private void	log(java.lang.String msg) For testing.
void	newMemberBeacon(BeaconEvent memberBeaconEvent) Implements the BeaconListener interface.
private void	reportArriving(Member member) Private utility method to report an arriving Member to the Disseminator.
private void	reportDeparting(Member member) Private utility method to report a departing Member to the Disseminator.
void	setDebug(boolean debugging) Determine whether to output logging messages.
protected void	start() Begin looking for changes in the group (hosts to engage/disengage with) and start sending beacons.
protected void	stop() Stop reporting changes in the group, stop looking for beacons, and stop sending beacons.

Methods inherited from class groupmgmt.MemberDetector

isActive, reportChange

Methods inherited from class java.lang.Object

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

Field Detail

beaconServer

private BeaconServer beaconServer

The BeaconServer for this host. It is the object responsible for sending and listening for beacons. Part of the beacon package.

neighborBeacons

private java.util.Hashtable neighborBeacons

The neighbors table. Contains a MemberBeacon object corresponding to every neighbor of this Member (everyone we are connected to). SafeDistanceDetector beacons include location information, used for safe distance calculations. The table is keyed by Member and contains the most recent MemberBeacon.

location

private Location location

The physical location of this Member.

locationGenerator

private LocationGenerator locationGenerator

The LocationGenerator - the object that updates our location (via LocationChangedEvents). The location info is incorporated into the broadcasted beacons.

safeDistance

private double safeDistance

The safe distance for this host, calculated based on the provided input parameters. We only connect with Members that are within safe distance of us. (The location package reports distance in meters, so this should be in meters.)

stopping

private java.lang.Boolean stopping

Object to use for waiting to exit the Group after I set my beacon to stopping.

debugging

private boolean debugging

Determines whether to output log messages.

Constructor Detail

SafeDistanceDetector

public SafeDistanceDetector(int beaconPort,
                            java.lang.String beaconAddress,
                            int beaconPeriod,
                            double range,
                            double maxSpeed,
                            double networkLatency,
                            LocationGenerator locationGenerator)

Constructor. Sets the beaconing parameters and initializes the BeaconServer. This does NOT start the BeaconServer, activate() must be called.

Parameters:

beaconPort - The port to multicast beacons to.

beaconAddress - The multicast address to send beacons to.

beaconPeriod - How often to send beacons (milliseconds).

range - The transmission range of the network (meters).

maxSpeed - The maximum speed of the host (meters/second).

networkLatency - Lag in the network (milliseconds).

locationGenerator - Where to receive locationChanged events from.

Method Detail

setDebug

public void setDebug(boolean debugging)

Determine whether to output logging messages.

Parameters:

debugging - Outputs messages if true.

start

protected void start()

Begin looking for changes in the group (hosts to engage/disengage with) and start sending beacons.

Specified by:

start in class MemberDetector

stop

protected void stop()

Stop reporting changes in the group, stop looking for beacons, and stop sending beacons. Blocks until we have been removed from the group.

Specified by:

stop in class MemberDetector

locationChanged

public void locationChanged(LocationEvent event)

Implements the LocationListener interface. Updates the current location and changes the beacon.

Specified by:

locationChanged in interface LocationListener

Parameters:

event - The LocationEvent containing the new Location.

groupChanged

public void groupChanged(GroupChangedEvent evt)

Implements the GroupChangedListener interface. Only used while stopping. If the new group I'm in is just me, then I've successfully stopped.

Specified by:

groupChanged in interface GroupChangedListener

Parameters:

evt - The GroupChangedEvent.

newMemberBeacon

public void newMemberBeacon(BeaconEvent memberBeaconEvent)

Implements the BeaconListener interface. Updates the neighbors table and adds or removes neighbors based on location and stopping information.

Specified by:

newMemberBeacon in interface BeaconListener

Parameters:

memberBeaconEvent - The event generated by the receipt of the new beacon.

reportArriving

private void reportArriving(Member member)

Private utility method to report an arriving Member to the Disseminator.

Parameters:

member - The member that's arriving.

reportDeparting

private void reportDeparting(Member member)

Private utility method to report a departing Member to the Disseminator.

Parameters:

member - The member that's departing.

log

private void log(java.lang.String msg)

For testing. Output a message to the command line.