rmi observing the distributed pattern. adrian german lecturer, computer science indiana university...

RMI

Observing the Distributed Pattern.

Adrian German

Lecturer, Computer Science

Indiana University Bloomington

RMI

Observing the Distributed Pattern.

Adrian German

Lecturer, Computer Science

Indiana University Bloomington

Java

registered

broadcast

broadcast

“Hello!”

broadcast( )

“Hello!”

broadcast( )“Hello!”

“Hello!”

“Hello!”“Hello!”

client

client

client

client

client

client

client

client

clientserver

client

client

clientserver (host)

client

client

clientserver (host)

The difference is that the server is listed in the phone book.

client

client

clientserver (host)

The difference is that the server is listed in the phone book (while a client isn’t).

client

client

clientserver (host)

How do we implement this?

client

client

clientserver (host)

client

server (host)

client

server (host)

class Server {

Client[] clients;

void broadcast(String message) { ... }

int register(Client client) { ... }

}

client

server (host)

class Server {

Client[] clients;



}

class Client {

void register(int index,

Client client) { ... }

void update(Message msg) { ... }

}

client

server (host)

class Server {

Client[] clients;



}

class Client {

void register(int index,

Client client) { ... }

void update(Message msg) { ... }

}

Clients call the server's broadcast method in turn, which calls the clients' update.

client

server (host)

clientserver

serverclient

serverclient

f

serverclient

ff

client.f(...) calls server.f(...)

serverclient

ff

g


which in turn calls client.g(...)

serverclient

ff

g



The question is: how do we turn this code into a distributed program?

serverclient

ff

g



The question is: how do we turn this code into a distributed program?

(Hawaii)

(Sweden)Internet

Internet

this local program

even simpler

function call

server

add()

client

fun()

value returned

function call

server

add()

client

fun()

value returned

class Server { int add(int a, int b) { return a + b; }}

class Client { void fun(Server server) { System.out.println(server.add(1, 2)); }}

class LocalProgram { public static void main(String[] args) { Server a = new Server(); Client b = new Client(); b.fun(a); }}

function call

server

add()

client

fun()

value returned


Important questions:a) who creates the server?b) who creates the client?c) does the client really initiate anything?

function call

server

add()

client

fun()

value returned

The difference between local and distributed computing is real.

Differences are impossible to ignore at least in the following areas:

a) latency, b) memory access, c) partial failure, and d) concurrency.

... that is, at least at the present time as well as in the near future.

function call

server

add()

client

fun()

value returned

abstract class NetworkPeer implements java.rmi.Remote { public void exportMethods() throws java.rmi.RemoteException { java.rmi.server.UnicastRemoteObject.exportObject(this);

} public java.rmi.Remote locatePeer(String peerHost, int peerPort, String peerName) throws Exception { return java.rmi.Naming.lookup("rmi://" + peerHost + ":" + peerPort + "/" + peerName);

} public void startAsNetworkClient(String peerHost, int peerPort, String peerName) throws Exception { this.exportMethods(); java.rmi.Remote peer = this.locatePeer(peerHost, peerPort, peerName); this.startAsClientOf(peer); // see below ... }

public abstract void startAsClientOf(java.rmi.Remote peer) throws java.rmi.RemoteException; public abstract void startAsServer(); // ... start as local server

}

function call

server

add()

client

fun()

value returned

abstract class NetworkPeer implements java.rmi.Remote { public void exportMethods() throws java.rmi.RemoteException { java.rmi.server.UnicastRemoteObject.exportObject(this);

} public java.rmi.Remote locatePeer(String peerHost, int peerPort, String peerName) throws Exception { return java.rmi.Naming.lookup("rmi://" + peerHost + ":" + peerPort + "/" + peerName);

} public void startAsNetworkClient(String peerHost, int peerPort, String peerName) throws Exception { this.exportMethods(); java.rmi.Remote peer = this.locatePeer(peerHost, peerPort, peerName); this.startAsClientOf(peer); // see below ... }

public abstract void startAsClientOf(java.rmi.Remote peer) throws java.rmi.RemoteException; public abstract void startAsServer(); // ... start as local server

}Distributed processing is a world of free agents.

The class above is all that an object needs to become a free agent. Any object.

function call

server

add()

client

fun()

value returned




public class ServerImplementation extends NetworkPeer implements Server { public static void main(String[] args) { String portNumber = args[0], ownName = args[1]; ServerImplementation here = new ServerImplementation(); here.startAsNetworkServer(ownName, Integer.parseInt(portNumber)); } public void startAsClientOf(java.rmi.Remote peer) { } public void startAsServer() { } public int add(int a, int b) throws java.rmi.RemoteException { System.out.println("I am adding for the audience..."); return a + b; } }public interface Server extends java.rmi.Remote { public int add(int a, int b) throws java.rmi.RemoteException; }

function call

server

add()

client

fun()

value returned

class ServerImplementation extends NetworkPeer implements Server { public int add(int a, int b) throws java.rmi.RemoteException { return a + b; } public void startAsServer() { } public void startAsClientOf(java.rmi.Remote peer) { } public static void main(String[] args) { String portNumber = args[0], ownName = args[1]; ServerImplementation here = new ServerImplementation(); here.startAsNetworkServer(ownName, Integer.parseInt(portNumber)); } }public interface Server extends java.rmi.Remote { public int add(int a, int b) throws java.rmi.RemoteException; }

public class ClientImplementation extends NetworkPeer {

public void startAsClientOf(java.rmi.Remote peer) throws java.rmi.RemoteException { this.fun((Server) peer); }

void fun(Server server) throws java.rmi.RemoteException { System.out.println(server.add(2, 3)); }

public static void main(String[] args) throws Exception { String ownName = args[0], serverHostName = args[1], serverPortNumber = args[2], serverName = args[3]; ClientImplementation client = new ClientImplementation(); client.startAsNetworkClientOf(serverHostName, Integer.parseInt(serverPortNumber), serverName); }

public void startAsServer() { }

}

class LocalSetup { public static void main(String[] args) throws java.rmi.RemoteException { ServerImplementation server = new ServerImplementation(); server.startAsServer(); ClientImplementation client = new ClientImplementation(); client.startAsClientOf(server); } }


class LocalSetup { public static void main(String[] args) throws java.rmi.RemoteException {

ServerImplementation server = new ServerImplementation(); server.startAsServer();

ClientImplementation client = new ClientImplementation(); client.startAsClientOf(server); } }




LocalSetup




LocalSetup

Server




LocalSetup

Client

Server




LocalSetup

Client

Server

So although there is no network there is already a change of attitude.

public abstract class NetworkPeer implements java.rmi.Remote {

public void exportMethods() throws java.rmi.RemoteException { java.rmi.server.UnicastRemoteObject.exportObject(this); }

public java.rmi.Remote locatePeer(String peerHost, int peerPort, String peerName) throws Exception { return java.rmi.Naming.lookup("rmi://" + peerHost + ":" + peerPort + "/" + peerName); }

public void startAsNetworkClientOf(String peerHost, int peerPort, String peerName) throws Exception { this.exportMethods(); java.rmi.Remote peer = this.locatePeer(peerHost, peerPort, peerName); this.startAsClientOf(peer); // see below ... }

public abstract void startAsClientOf(java.rmi.Remote peer) throws java.rmi.RemoteException;

public void startAsNetworkServer(String name, int port) { System.setSecurityManager(new java.rmi.RMISecurityManager()); try { this.exportMethods(); java.rmi.registry.Registry registry = java.rmi.registry.LocateRegistry.createRegistry(port); registry.bind(name, this); this.startAsServer(); // see below ... System.out.println("Server is ready ... "); } catch (Exception e) { System.out.println("Server error: " + e + " ... "); } }

public abstract void startAsServer();

}


public void exportMethods() throws java.rmi.RemoteException { ... }

public java.rmi.Remote locatePeer(String peerHost, int peerPort, String peerName) throws Exception { return java.rmi.Naming.lookup("rmi://" + peerHost + ":" + peerPort + "/" + peerName); }





}



public java.rmi.Remote locatePeer(... peerHost, ... peerPort, ... peerName) ... { ... }





}



public java.rmi.Remote locatePeer(... peerHost, ... peerPort, ... peerName) ... { ... }

public void startAsNetworkClientOf(... peerHost, ... peerPort, ... peerName) ... { ... }




}

tucotuco.cs.indiana.edu% pwd/nfs/paca/san/r1a0l1/dgerman/october-21tucotuco.cs.indiana.edu% ls -ld *.java-rw-r--r-- 1 dgerman faculty 761 Oct 21 00:59 ClientImplementation.java-rw-r--r-- 1 dgerman faculty 293 Oct 21 00:57 LocalSetup.java-rw-r--r-- 1 dgerman faculty 1524 Oct 21 00:54 NetworkPeer.java-rw-r--r-- 1 dgerman faculty 117 Oct 21 00:59 Server.java-rw-r--r-- 1 dgerman faculty 551 Oct 21 01:06 ServerImplementation.javatucotuco.cs.indiana.edu% javac *.javatucotuco.cs.indiana.edu% rmic NetworkPeertucotuco.cs.indiana.edu% rmic ServerImplementationtucotuco.cs.indiana.edu% java ServerImplementation 16450 Dirac

burrowww.cs.indiana.edu% pwd/nfs/paca/san/r1a0l1/dgerman/october-21burrowww.cs.indiana.edu% ls -ld *-rw-r--r-- 1 dgerman faculty 975 Oct 21 01:34 ClientImplementation.class-rw-r--r-- 1 dgerman faculty 761 Oct 21 00:59 ClientImplementation.java-rw-r--r-- 1 dgerman faculty 498 Oct 21 01:34 LocalSetup.class-rw-r--r-- 1 dgerman faculty 293 Oct 21 00:57 LocalSetup.java-rw-r--r-- 1 dgerman faculty 1938 Oct 21 01:34 NetworkPeer.class-rw-r--r-- 1 dgerman faculty 1524 Oct 21 00:54 NetworkPeer.java-rw-r--r-- 1 dgerman faculty 908 Oct 21 01:34 NetworkPeer_Skel.class-rw-r--r-- 1 dgerman faculty 482 Oct 21 01:34 NetworkPeer_Stub.class-rw-r--r-- 1 dgerman faculty 191 Oct 21 01:34 Server.class-rw-r--r-- 1 dgerman faculty 117 Oct 21 00:59 Server.java-rw-r--r-- 1 dgerman faculty 886 Oct 21 01:34 ServerImplementation.class-rw-r--r-- 1 dgerman faculty 551 Oct 21 01:06 ServerImplementation.java-rw-r--r-- 1 dgerman faculty 1611 Oct 21 01:34 ServerImplementation_Skel.class-rw-r--r-- 1 dgerman faculty 3134 Oct 21 01:34 ServerImplementation_Stub.classburrowww.cs.indiana.edu% java ClientImplementation Larry tucotuco.cs.indiana.edu 16450 Dirac

burrowww.cs.indiana.edu% java LocalSetupI am adding for the audience...5

burrowww.cs.indiana.edu% java ServerImplementation 16450 DiracServer is ready ... I am adding for the audience...

tucotuco.cs.indiana.edu% java ClientImplementation Larry burrowww.cs.indiana.edu 16450 Dirac5

12

3

4

5

More sophisticated example:

In this last example topology was more general.

Clients were also acting as servers.

The only difference is that they still need a moderator to start participating.

Conclusions

1. The NetworkPeer abstraction successfully summarizes the "RMI recipe".

2. The LocalSetup program allows for the local development and testing.

3. The use of this pattern is similar to the use of the MVC pattern.

4. Clients need to be implemented as Threads. Their synchronization rules must be as simple as possible. As "decentralized" as possible, so as to not assume the existence of the OS.

5. Using the programmer's API the application can run both ways.

6. This approach is good when few developers and use of Java is preferred.

7. Further work will address the question:

does an extremely unreliable network breaks any of the above?

Unreliable means: lost references, exceptions are actually the rule, etc.

rmi observing the distributed pattern. adrian german lecturer, computer science indiana university...

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