0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 1 301 601 901 1201 1501 1801
Figura 6.2: Dettaglio dei tempi rilevati per l'invio di messaggi di Heartbeat dal peer2
dal 150-esimo messaggio inviato no alla ne della prova.
(WirePipe e RendezvousService). Il binding diretto tra i peer endpoint comporta maggiore velocità nella consegna dei messaggi; inoltre l'eliminazione di due elementi nei messaggi (header dovuti ai protocolli wire e rendezvous) comporta un minore overhead per la gestione.
6.2 Avviare la piattaforma JXTA
Il codice Java riportato di seguito mostra come avviare la piattaforma JXTA: Con gurazione del peer attraverso i metodi della classe net.jxta.platform
.NetworkConfigurator.
Inizializzazione del gruppo di default netPeerGroup. Utilizzo dei servizi relativi al gruppo netPeerGroup.
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 1 301 601 901 1201 1501 1801 2101 2401
Figura 6.3: Tempi rilevati per l'invio di messaggi di Heartbeat dal peer3 per tutta
la durata del test.
import java.util.Enumeration; import java.io.File; import java.io.IOException; import java.net.URI; import net.jxta.endpoint.EndpointAddress; import net.jxta.exception.PeerGroupException; import net.jxta.platform.NetworkConfigurator; import net.jxta.peer.PeerID; import net.jxta.peergroup.PeerGroup; import net.jxta.peergroup.NetPeerGroupFactory; import net.jxta.protocol.ConfigParams; import net.jxta.rendezvous.RendezvousEvent; import net.jxta.rendezvous.RendezvousListener; import net.jxta.rendezvous.RendezVousService; /**
6.2. AVVIARE LA PIATTAFORMA JXTA 141 *
* @author Mohamed Abdelaziz (hamada)
* JXTA tutorial http://jxta.org modified by Silvia Ciotti *
*/
public class NetworkManager implements RendezvousListener { /**
* Gruppo di default di JXTA */
private PeerGroup netPeerGroup = null;
// flags to indicate the state of the jxta platform private boolean started = false;
private boolean stopped = false; private RendezVousService rendezvous; private Enumeration connRVP;
private final String connectLock = new String("connectLock"); private String instanceName = "NA";
/**
* Posizione del file system della cache JXTA ottenuta leggendo la property "JXTA_HOME" */
private final File home = new File(System.getProperty("JXTA_HOME", ".cache")); /**
*
* @param instanceName Node name
* @param home Cache storage home directory
*/
public NetworkManager(String instanceName) { this.instanceName = instanceName; // cancella la cache
clearCache(home); }
public void setAutoRendezvous(RendezVousService rendezvous) {
rendezvous.setAutoStart(true, 100); // wait a bit before go on
try{ Thread.sleep(4000); }catch(Exception e){ e.printStackTrace(); } } /**
* Stampa a video alcune informazione rigurdanti il rendezvous service passato come argomento *
* @param rendezvous Il Rendezvous Serivice del gruppo di cui di vogliono ottenere info */
public void stat(RendezVousService rendezvous){ System.out.println();
System.out.println(" -- Statistiche -- "); System.out.println("Stato del peer");
System.out.println(" Peer Mode: "+rendezvous.getRendezVousStatus().toString());
System.out.println(" E' connesso a un rendez-vous?: "+ rendezvous.isConnectedToRendezVous()); System.out.println(" Il peer e' un nodo Rendezvous? " + rendezvous.isRendezVous());
System.out.println("Lista dei rendezvous a cui e' connesso il peer:"); PeerID peerid= null;
connRVP = rendezvous.getConnectedRendezVous(); if (connRVP != null) {
System.out.println("--inzio--"); while (connRVP.hasMoreElements()) {
peerid = (PeerID) connRVP.nextElement(); System.out.println(" -- peer id: " +peerid); }
System.out.println("--fine--"); }
System.out.println(" -- Fine Statistiche -- "); System.out.println();
} /**
* Creates and starts the JXTA NetPeerGroup using a platform configuration * template. This class also registers a listener for rendezvous events *
* @param principal principal used the generate the self signed peer root cert * @param password the root cert password
6.2. AVVIARE LA PIATTAFORMA JXTA 143 * @param rvp if true the peer is Rendezvous, else id edge
*/
public synchronized void start(String principal, String password, boolean rvp, String ip) { if (started) {
return; }
try {
//clearCache(home);
File instanceHome = new File(home, instanceName); NetworkConfigurator config = new NetworkConfigurator(); config.setHome(instanceHome); if (!config.exists()) { //config.setPeerID(IDFactory.newPeerID(PeerGroupID.defaultNetPeerGroupID)); config.setName(instanceName); config.setDescription(" "); if (rvp){ config.setMode(NetworkConfigurator.RDV_NODE); } config.setPrincipal(principal); config.setPassword(password); try {
// rendezvous pubblici messi a disposizione dalla Sun
config.addRdvSeedingURI(new URI("http://rdv.jxtahosts.net/cgi-bin/rendezvous.cgi?2")); config.addRelaySeedingURI(new URI("http://rdv.jxtahosts.net/cgi-bin/relays.cgi?2")); // è possibile aggiungere altri seed rendezvous e relay
// config.addRdvSeedingURI(new URI(new URI("131.114...."))); // config.addRelaySeedingURI(new URI("131.114...."));
} catch (java.net.URISyntaxException use) { use.printStackTrace();
} try {
config.save();
} catch (IOException io) { io.printStackTrace(); }
}
NetPeerGroupFactory factory = new NetPeerGroupFactory((ConfigParams) config.getPlatformConfig(), instanceHome.toURI());
netPeerGroup = factory.getInterface();
System.out.println("Node PeerID : "+netPeerGroup.getPeerID().getUniqueValue().toString()); // estraggo il servizio RendezVous da netpeergroup
rendezvous = netPeerGroup.getRendezVousService(); // registra il listener per eventi rendezvous rendezvous.addListener(this);
started = true;
} catch (PeerGroupException e) {
// could not instantiate the group, print the stack and exit System.out.println("fatal error : group creation failure"); e.printStackTrace();
System.exit(1); }
} /**
* Stops and unrefrences the NetPeerGroup */
public synchronized void stop() { if (stopped && !started) {
return; } rendezvous.removeListener(this); netPeerGroup.stopApp(); netPeerGroup.unref(); netPeerGroup = null; stopped = true; return; } /**
* Gets the netPeerGroup object *
* @return The netPeerGroup value */
public PeerGroup getNetPeerGroup() { return netPeerGroup;
6.2. AVVIARE LA PIATTAFORMA JXTA 145 /**
* Metodo che restituisce i RendezVous peer a cui il peer e' connesso * @return
*/
public Enumeration getRVP(){ return connRVP;
} /**
* Blocks if not connected to a rendezvous, or * until a connection to rendezvous node occurs *
* @param rendezvous Il rendezvous service del gruppo per cui si vuole * attende la connesione a un peer RV
* @param timeout timeout in milliseconds di attesa della connessione a un RVP * @param block attesa infinita oppure no
* @param ipAddress indirizzo ip del rendezvous peer a cui il peer vuole connettersi * nella forma http://131.114.111.111:9700 (indicare la porta)
*/
public void waitForRendezvousConnection(RendezVousService rendezvous, long timeout, boolean block, String ipAddress ){
if (ipAddress != null){ try {
rendezvous.connectToRendezVous(new EndpointAddress(new URI(ipAddress))); } catch (Exception e) {
// TODO Auto-generated catch block e.printStackTrace();
} }
// se non e' connesso a nessun rendezvous OPPURE se lui stesso non e' Rendezvous if (!rendezvous.isConnectedToRendezVous() || !rendezvous.isRendezVous()) {
System.out.println("Waiting for Rendezvous Connection"); try { if (!rendezvous.isConnectedToRendezVous()) { synchronized (connectLock) { if (block) connectLock.wait(); else connectLock.wait(timeout);
} }
if (block)
System.out.println("Connesso a un Rendezvous Peer"); else {
// Se scade il timeout, il metodo prosegue stampando la riga sotto // quindi va avanti anche se non e' connesso a nessun rendez vous System.out.println("Timeout expired");
System.out.println("Vedere gli eventuali eventi RendezvousEvent ricevuti"); }
} catch (InterruptedException e) {} }
} /**
* RendezvousEvent che si riceve *
* @param event rendezvousEvent */
public void rendezvousEvent(RendezvousEvent event) { System.out.println(" --> EVENTO rendezvous ricevuto"); if (event.getType() == event.RDVCONNECT ||
event.getType() == event.RDVRECONNECT || event.getType() == event.BECAMERDV) { switch(event.getType()) {
case RendezvousEvent.RDVCONNECT :
System.out.println("Tipo evento: Connected to rendezvous peer :"+event.getPeerID()); break;
case RendezvousEvent.RDVRECONNECT :
System.out.println("Tipo evento: Reconnected to rendezvous peer :"+event.getPeerID()); break;
case RendezvousEvent.BECAMERDV :
System.out.println("Tipo evento: Became a Rendezvous"); break; } synchronized (connectLock) { connectLock.notify(); } } }
6.2. AVVIARE LA PIATTAFORMA JXTA 147
/**
* Svuota la cache di JXTA */
public void clearCache(){ clearCache(home); }
private void clearCache(final File rootDir) { try {
if (rootDir.exists()) {
File[] list = rootDir.listFiles(); for (File aList : list) {
if (aList.isDirectory()) { clearCache(aList); } else { aList.delete(); } } } rootDir.delete();
System.out.println("Cache component " + rootDir.toString() + " cleared."); }
catch (Throwable t) {
System.out.println("Unable to clear " + rootDir.toString()); t.printStackTrace();
} } /**
* Main method per alcune prove *
* @param args */
public static void main(String args[]) {
NetworkManager manager = new NetworkManager("Network Manager"); System.out.println("Starting Peer Configuration ....");
// nel metodo start ottengo il servizio rendezvous da netpeergroup //boolean isRVP = Boolean.parseBoolean(args[0]);
PeerGroup netPG = manager.getNetPeerGroup(); String ipAdd = null;
// aspetto la connessione al RVP per 10 secondi
System.out.println("Waiting for RVP connection for 10 seconds...");
manager.waitForRendezvousConnection(netPG.getRendezVousService(), 10000, false, ipAdd); System.out.println("Print out some statistics");
manager.stat(netPG.getRendezVousService());
System.out.println("Prova metodo setAutoStart per diventare dinamicamente RendezvousPeer"); manager.setAutoRendezvous(netPG.getRendezVousService()); manager.stat(netPG.getRendezVousService()); System.out.println("Stopping JXTA...."); manager.stop(); } }
Capitolo 7
Conclusioni
Numerose scelte che hanno determinato lo sviluppo del supporto JaDE sono state guidate dal necessità di trovare un compromesso tra consistenza e grado di distri- buzione: negli ambienti virtuali distribuiti possiamo aermare che più lo stato è replicato tra i peer e più sarà alta la probabilità che si veri chino inconsistenze.
In contesti molto dinamici la manutenzione della overlay network si realizza attraverso la collaborazione reciproca dei peer del sistema: la loro coordinazione richiede di sostenere un numero elevato di messaggi, che quindi va a aumentare il tra co di rete, contribuendo alla congestione della stessa.
L'architettura proposta in JaDE risponde proprio a questa esigenza introducendo però delle situazioni particolari, e a nostro avviso rare, in cui possono veri carsi inconsistenze oppure perdita parziale dello stato, inevitabili in questo contesto.
La scelta di utilizzare aree di interesse sse per l'invio dei messaggi di posizione è stata guidata dalla semplicità di gestione che questo metodo comporta e anche da- gli strumenti forniti dalla piattaforma JXTA che ci ha permesso l'implementazione del supporto. Tuttavia abbiamo dimostrato che è possibile introdurre aree di inte- resse dinamiche con una delle soluzioni proposte per il recupero di oggetti passivi. Un possibile sviluppo futuro potrebbe indagare l'estensione di questa soluzione per implementare aree mobili anche per le posizioni dei peer.
L'utilizzo di JXTA ci ha permesso di sviluppare il supporto avendo a disposizione molti servizi base ed ha fornito un insieme di protocolli per gestire gli aspetti di coor- dinazione tra peer (peer group e servizi associati, pipe come canali di comunicazione,
etc.).
Un ulteriore sviluppo futuro riguarda la possibilità di ottimizzare le comunicazioni sulla overlay network utilizzando l'approccio basato sui diagrammi di Voronoi. L'uso di questi permette di stabilire dinamicamente connessioni di tipo uno a uno tra i peer che si trovano sicamente vicini. Una soluzione possibile è anche quella di combinare il modello ibrido di JXTA con l'uso dei diagrammi di Voronoi.
Ringraziamenti
I miei ringraziamenti vanno in primo luogo alla Prof.ssa Laura Ricci per i preziosi suggerimenti e per il costante supporto durante lo svolgimento della tesi. Ringrazio inoltre il Dott. Luca Genovali che ha fornito spunti e consigli nell'arontare i vari problemi incontrati nella realizzazione del mio lavoro.
Ringrazio tutta la mia famiglia e in modo particolare i miei genitori per avermi sempre supportato in tutte scelte di questi anni di università. In ne ringrazio tutti gli amici con cui ho condiviso tante di coltà ma anche tanti momenti felici della vita universitaria.
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