1. Chapters 4 & 5 Interprocess Communication
Presentation of the characteristics of protocols for communication between processes:
Client-Server or group communication, RPC, RMI, …
Communication between distributed objects and remote invocation

2. Themes 1st Part: Means of Interprocess Communication (RPC, RMI, …)
2nd Part:
Types of Interprocess Communication
(Client-Sever, Group)
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3. Means of Interprocess Communication
Introduction
Layered Protocols
RMI (Remote Method Invocation)
Readings
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4. Request-Reply Protocol Marshalling and external data representation
Introduction (1)
Applications, services
RMI, RPC and events
Middleware layers
Request-Reply Protocol
Marshalling and external data representation
UDP and TCP
Operating System
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5. Introduction (2) Characteristics of middleware layers:
Location transparency (definition)
Independent: protocols that support the middleware abstractions are independent of the underlying transport protocols (example)
Heterogeneous hardware: hide the difference due to hardware architectures (big-endian, little-endian, …) (mean)
Use of several programming languages: allow distributed applications to use more than one programming language (example)
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6. Introduction (3) Definition of remote procedure using different IDL
RPC/IDL:
program RAND_PROG {
version RAND_VERS
void INITIALIZE_RANDOM(long) = 1;
double GET_NEXT_RANDOM(void) = 2;
} = 1;
} = 0x ;
RPC/IDL :
program RAND_PROG {
version RAND_VERS
void INITIALIZE_RANDOM(long) = 1;
double GET_NEXT_RANDOM(void) = 2;
} = 1;
} = 0x ;
CORBA/IDL:
module EXAMPLES {
interface RAND_PROG
void INITIALIZE_RANDOM(in long arg);
double GET_NEXT_RANDOM(void); };
CORBA/IDL :
module EXAMPLES {
interface RAND_PROG
void INITIALIZE_RANDOM(in long arg);
double GET_NEXT_RANDOM(void); };
Definition of remote procedure using different IDL
RMI/INTERFACE:
Import java.rmi.*;
package EXAMPLES;
public interface RAND_VERS extends Remote {
public void INITIALIZE_RANDOM(long arg) throws RemoteExceptions;
public double GET_NEXT_RANDOM(void) throws RemoteExceptions; };
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7. Introduction (4) Characteristics of interprocess communication:
Types of communication:
Synchronous: the sending and receiving processes synchronize at every message
Send and Receive: blocking operations
Asynchronous: no synchronization between the sending and receiving processes
Send: non-blocking operation
Receive: non-blocking or blocking operation
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8. Introduction (5) Characteristics (continued): Message destinations:
Messages sent to <Internet address, Local port >
Processes may use multiple ports from which to receive messages
Communication reliability:
Integrity (definition)
Validity (definition)
Ordering: some applications require that messages be delivered in sender order
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9. Introduction (6) Characteristics (continued) :
Sockets: used by UDP and TCP as endpoint for communication between processes
Must be bound to a local port and one of the Internet addresses
Each socket is associated to one protocol: UDP or TCP
216 possible ports
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10. Layered Protocols (1)
Multiple layers intervene during interprocess communication
Internetwork layers (Internet)
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11. Layered Protocols (2) UDP Datagram Communication
Types of communication:
UDP Datagram Communication
TCP Stream Communication
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12. UDP Datagram Communication
Datagrams transmitted by UDP: without acknowledgments or retries
Blocking: UDP use a non-blocking send and a blocking receive
Failure model: UDP suffers from
Omission failures: messages dropped (causes)
Ordering: messages can sometimes be delivered out of sender order
UDP advantage: do not suffer from the overheads associated with guaranteed message delivery
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13. Datagram Communication: Java API (1)
Manipulating Internet addresses:
Class InetAddress: represents Internet addresses (example)
 InetAddress ( string address ): multiple forms of the constructor exist
short int  getPort () const
bool  setPort ( short int port )
string  getAddress () const
bool  setAddress ( string address )
bool  setAddress ( unsigned long int address )
string  getHostName ()
string  getHostByIP ( string ip )
string  getIPByName ( string host ) …
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14. Datagram Communication: Java API (2)
Manipulating datagrams:
Class DatagramPacket : creates packets containing data to be transmitted or received and the address of destination or source of the datagrams
Port Number
Internet Address
Message’s length
Message’s bytes
Datagram packet
Constructors:
Receiver: DatagramPacket(byte buffer[], int length)
buffer for holding the incoming datagram
Number of bytes to read
UDP Port
Data packet
Length of data packet
Destination
address
Sender:
DatagramPacket( byte buffer[], int length,
InetAddress address, int port)
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15. Datagram Communication: Java API (3)
Manipulating datagrams (continued): main methods of the class DatagramPacket
InetAddress getAddress ()
int getPort ()
void setAddress(InetAddress iaddr)
byte[] getData ()
void setData(byte ibuf[])
void setPort(int iport)
int getLength ()
void setLength(int ilength)
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16. Datagram Communication: Java API (4)
Manipulating sockets:
Class DatagramSocket: represents a socket for sending and receiving datagram packets
Constructors:
DatagramSocket () throws SocketException
DatagramSocket (int port) throws SocketException
DatagramSocket(int port, InetAddress laddr) throws SocketException
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17. Datagram Communication: Java API (5)
Manipulating sockets (continued): main methods of the class DatagramSocket
void send(DatagramPacket data) throws IOException
void receive(DatagramPacket data) throws IOException
void setSoTimeout(int timeout) throws SocketException
Enable/disable SO_TIMEOUT with the specified timeout. 0 = no timeout
void close ()
int getLocalPort ()
int getSoTimeout() throws SocketException
void connect (InetAddress address, int port)
void disconnect()
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18. Datagram Communication: Java API (6)
Example: Client sends a request
import java.net.*; import java.io.*;
public class UDPClient{
public static void main(String args[]) {
// args[0] = message to be sent to the server; args[1] = IP address of the server
DatagramSocket aSocket = null;
try {
aSocket = new DatagramSocket();
byte [] m = args[0].getBytes();
InetAddress aHost = InetAddress.getByName(args[1]);
int serverPort = 6789;
DatagramPacket request = new DatagramPacket(m, args[0].length(), aHost, serverPort);
aSocket.send(request);
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19. Datagram Communication: Java API (7)
Example (continued): Client waits for a reply
byte[] buffer = new byte[1000];
DatagramPacket reply = new DatagramPacket(buffer, buffer.length);
aSocket.receive(reply);
System.out.println("Reply: " + new String(reply.getData()));
}catch (SocketException e){System.out.println("Socket: " e.getMessage());
}catch (IOException e){System.out.println("IO: " e.getMessage());
}finally {if(aSocket != null) aSocket.close();}}}
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20. Datagram Communication: Java API (8)
Example (continued): Server waits continually for a request
import java.net.*; import java.io.*;
public class UDPServer{
public static void main(String args[]) {
DatagramSocket aSocket = null;
try{
aSocket = new DatagramSocket(6789);
byte[] buffer = new byte[1000];
while(true){
DatagramPacket request = new DatagramPacket(buffer,
buffer.length);
aSocket.receive(request);
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21. Datagram Communication: Java API (9)
Example (continued): Server sends the response to the client
DatagramPacket reply = new DatagramPacket( request.getData(),
request.getLength(),
request.getAddress(),
request.getPort());
aSocket.send(reply);}
}catch (SocketException e){System.out.println("Socket: " e.getMessage());
}catch (IOException e) {System.out.println("IO: " + e.getMessage());
}finally {if(aSocket != null) aSocket.close();}}}
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22. TCP Stream Communication (1)
Use of input or output streams
Characteristics:
Message sizes (size)
Lost messages: use of an acknowledgment scheme
Flow control: TCP protocol attempts to match the speeds of the processes that read and write to a stream (how?)
Message duplication and ordering: (How?)
Message destinations: (how?)
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23. TCP Stream Communication (2)
Characteristics (continued):
Matching of data items: processes need to agree as to the contents of the data transmitted over a stream (example)
Blocking: (When?)
Use of threads: (How?)
Server: accepts a connection
A thread is created for the new client
CSI408-Distributed Information Systems
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24. TCP Stream Communication (3)
Failure model: must satisfy
Integrity property: (How?)
Validity property: (How?)
TCP limits: does not guarantee to deliver messages in the face of all possible difficulties
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25. Stream Communication: Java API (1)
Client:
Class Socket: used by a client to establish a connection with the server
Constructors: creates a TCP socket by specifying the DNS hostname and a port of a server
public Socket (String Host, int Port) throws UnknownHost…
public Socket (InetAddress Host, int Port) throws Unknown…
public Socket (InetAddress Host, int Port, InetAddress LocalAddress, int LocalPort) throws UnknownHost… …
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26. Stream Communication: Java API (2)
Client (continued): main methods of class Socket
close() throws IOException
InetAddress getInetAddress ()
int getPort ()
InetAddress getLocalAddress ()
int getLocalPort ()
int getSoTimeout() throws SocketException
void setSoTimeout(int timeout) throws SocketException
InputStream getInputStream() throws IOException
OutputStream getOutputStream() throws IOException …
CSI408-Distributed Information Systems
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27. Stream Communication: Java API (3)
Example 1: list all services of ports on a local machine
arlequin{elhadef}102: java Ports1
Server attached to port 7
Server attached to port 9
Server attached to port 13
Server attached to port 19
Server attached to port 22
Server attached to port 23
Server attached to port 37
Server attached to port 79
Server attached to port 111
Server attached to port 512
Server attached to port 513
Server attached to port 514
Server attached to port 515
Execution results:
import java.net.*; import java.io.*;
public class Ports1 {
public static void main(String[] args) {
Socket s;
String host = "localhost";
if(args.length > 0) host=args[0] ;
for(int i = 0 ; i < 1024; i++) {
try { s=new Socket(host,i);
System.out.println("Server " +
" attached to port "+ i);
} catch (ConnectException e) { ;
} catch (UnknownHostException e) {
System.err.println(e+" --> "+i) ;
} catch (IOException e)
{ System.err.println(e); }}}}
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28. Stream Communication: Java API (4)
Example 2: manipulating InetAddress addresses
import java.net.*; import java.io.*;
public class Ports2 {
public static void main(String[] args) {
Socket s;
String host = "
if(args.length > 0) hote=args[0] ;
try {
InetAddress address = InetAddress.getByName(host);
for(int i = 1 ; i < 1024; i++) {
try { s=new Socket(address,i);
System.out.println("Server attached to port "+
i + " of " + address);
} catch (ConnectException e) { ;
} catch (IOException e) { System.err.println(e); }}
} catch (UnknownHostException e) { System.err.println(e) ;
}}}
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29. Stream Communication: Java API (4)
Example 2: manipulating InetAddress addresses
arlequin{elhadef}120: java Ports2
Server attached to port 7 of
Server attached to port 9 of
Server attached to port 13 of
Server attached to port 15 of
Server attached to port 19 of
Server attached to port 25 of
Server attached to port 37 of
Server attached to port 53 of
Server attached to port 79 of
Server attached to port 80 of
Server attached to port 109 of
Server attached to port 110 of
Server attached to port 111 of
Server attached to port 113 of
Server attached to port 143 of
Execution results
CSI408-Distributed Information Systems
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30. Stream Communication: Java API (5)
Example 3: manipulating socket’s attributes
import java.net.*;
import java.io.*;
public class Attributes {
public static void main(String[] args) {
Socket s;
for(int i = 0 ; i < args.length ; i++) {
try {
s=new Socket(args[i],80);
System.out.println("\nConnect to "+ s.getInetAddress() +
" on port " + s.getPort() +
"\nfrom port "+ s.getLocalPort() +
" of "+ s.getLocalAddress()) ;
} catch (ConnectException e) { ;
} catch (IOException e) { System.err.println(e); } } }}
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31. Stream Communication: Java API (5)
Example 3: manipulating socket’s attributes
import java.net.*;
import java.io.*;
public class Attributes {
public static void main(String[] args) {
Socket s;
for(int i = 0 ; i < args.length ; i++) {
try {
s=new Socket(args[i],80);
System.out.println("\nConnect to "+ s.getInetAddress() +
" on port " + s.getPort() +
"\nfrom port "+ s.getLocalPort() +
" of "+ s.getLocalAddress()) ;
} catch (ConnectException e) { ;
} catch (IOException e) { System.err.println(e); } } }}
CSI408-Distributed Information Systems
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32. Stream Communication: Java API (6)
Manipulating data streams:
Get I/O stream: functions
public InputStream getInputStream() throws IOException
publi OutputStream getOutputStream() throws IOException
Manipulate streams with the following classes that offer many functionalities
DataInputStream
DataOutputStream
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33. Stream Communication: Java API (7)
Example 4: read the date and the time from the Unix’ daytime server (port 13) on the host arlequin.dmi.usherb.ca
import java.net.*; import java.io.*;
public class DateAndTime {
public static void main(String[] args) {
Socket s;
String host;
DataInputStream timeStream;
host="arlequin.dmi.usherb.ca";
try { InetAddress address = InetAddress.getByName(host);
try { s=new Socket(address,13);
timeStream = new DataInputStream(s.getInputStream());
String DateTime= timeStream.readLine();
System.out.println("Date and time on: "+host+" are "+DateTime);
} catch (ConnectException e) { System.err.println(e);
} catch (IOException e) { System.err.println(e); }
} catch (UnknownHostException e) { System.err.println(e); } }}
arlequin{elhadef}131: java DateAndTime.java
Date and time on: arlequin.dmi.usherb.ca are Sun Sep 22 17:18:
Execution results:
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34. Stream Communication: Java API (8)
Server:
Class ServerSocket: used by a server to establish a connection with a client
Constructors: create a TCP socket at a server port for listening for connect requests from clients
public ServerSocket(int port) throws IOException, …
public ServerSocket(int port, int backlog) throws IOExcept…
public ServerSocket(int port, int backlog, InetAddress bindAddr) throws IOException, …
port: the specified port, or 0 to use any free port
bindAddr: the local InetAddress the server will bind to
backlog: the maximum length of the queue
Method used to establish the communication: accept a connection
socket accept() throws IOException
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35. Stream Communication: Java API (9)
Example 5: TCP Client connects to a server, sends a request and waits for a response
import java.net.*; import java.io.*;
public class TCPClient {
public static void main (String args[]) { // arguments supply message and hostname
Socket s = null;
try{
int serverPort = 7896;
s = new Socket(args[1], serverPort);
DataInputStream in = new DataInputStream( s.getInputStream());
DataOutputStream out =new DataOutputStream( s.getOutputStream());
out.writeUTF(args[0]); // UTF is a string encoding see Sn. 4.4
String data = in.readUTF(); // read a line of data from the stream
System.out.println("Received: "+ data) ;
}catch (UnknownHostException e) {System.out.println("Socket:"+e.getMessage());
}catch (EOFException e){System.out.println("EOF:"+e.getMessage());
}catch (IOException e){System.out.println("readline:"+e.getMessage());
}finally {if(s!=null) try {s.close();
}catch (IOException e) {System.out.println ("close:" e.getMessage());}}}}
CSI408-Distributed Information Systems
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36. Stream Communication: Java API (10)
Example 5 (continued): TCP Server establishes a connection with each client and displays its request
import java.net.*;
import java.io.*;
public class TCPServer {
public static void main (String args[]) {
try{
int serverPort = 7896; // the server port
ServerSocket listenSocket = new ServerSocket(serverPort);
while(true) {
Socket clientSocket = listenSocket.accept();
Connection c = new Connection(clientSocket); }
} catch(IOException e) {System.out.println("Listen socket:"+e.getMessage());} }}
class Connection extends Thread {
DataInputStream in;
DataOutputStream out;
Socket clientSocket;
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37. Stream Communication: Java API (11)
public Connection (Socket aClientSocket) {
try {
clientSocket = aClientSocket;
in = new DataInputStream( clientSocket.getInputStream());
out =new DataOutputStream( clientSocket.getOutputStream());
this.start();
} catch(IOException e) {System.out.println("Connection:"+e.getMessage());} }
public void run(){
try { // an echo server
String data = in.readUTF(); // read a line of data from the stream
out.writeUTF(data);
}catch (EOFException e){System.out.println("EOF:"+e.getMessage());
} catch(IOException e) {System.out.println("readline:"+e.getMessage());
} finally{ try {clientSocket.close();}catch (IOException e){/*close failed*/}} }}
CSI408-Distributed Information Systems
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38. RMI (Remote Method Invocation) (1)
Distributed object model: allow objects at different processes to communicate with each other using calls to remote methods
C must have a reference to object E so that it can invoke one of its methods
B and F: distant objects
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39. Before Studying RMI External Data Representation CORBA’s CDR
JAVA’s Object Serialization
Remote Object Reference
Remote Interface
RMI (continued)
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40. External Data Representation and Marshalling (1)
Different representations:
Floating-point numbers: different ways
Different coding to represent characters
Different formats: Little-endian, big-endian
converted into sequences of bytes
Receiving process
Rebuild the data structures
Sending process
Information to be transmitted = data structures (set of interconnected objects)
External data Representation
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41. External Data Representation and Marshalling (2)
Form suitable for transmission into a message (binary, ASCII, e.g., HTTP)
Data collection
Carried out by a middleware layer
Unmarshalling
Different tools:
CORBA’s Common Data Representation (CDR)
JAVA’s Object Serialization
SUN’s XDR Standard: exchange of messages between clients et servers SUN NFS (Network File System)
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42. CORBA’s CDR (1) Defined with CORBA 2.0 [Object Management Group, 1998]
Binary format: arguments and results of the invocations
Can represent all data types: short, long, unsigned short, unsigned long, float, double, char, boolean, octet, any (tout type simple or composed : string, array, struct, enumerated, union, …)
CDR (CORBA) & XDR (SUN): types not included, suppose that the sender and the receiver both know the order and the field types
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43. CORBA’s CDR (2) Example:
{‘Smith’, ‘London’, 1934}  struct Person { string name;
string place;
long year;};
unsigned long (32 bits)
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44. JAVA’s Object Serialization (1)
Java RMI: objects are passed as parameters or results to method invocations
Binary format: messages are build from an object or hierarchy of objects
Class ObjectOutputStream: writing the contents of the instance variables
Class ObjectInputStream: reconstructing the original message
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

45. JAVA’s Object Serialization (2)
Example: Class Person
Public class Person implements Serializable {
private String name;
private String place;
private int year;
public Person (String aName,
String a Place, int aYear) {
name = aName;
place = aPlace;
year = aYear;
} … }
Person p= new Person("Smith",
"London",
1934);
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

46. JAVA’s Object Serialization (3)
Class ObjectOutputStream
ObjectOutputStream(OutputStream)
ObjectOutputStream(void)
write(byte[])
write(int)
writeByte(int)
writeChar(int)
writeFloat(float)
writeLong(long)
writeShort(int)
writeUTF(String)
writeBytes(String)
writeObject(Object)
writeDouble(double)
writeBoolean(boolean) …
Person p= new Person("Smith", "London", 1934);
// Serialization
ObjectOutputStream SP = new ObjectOutputStream();
SP.writeObject(p);
// Deserialization
ObjectInputStream DSP = new ObjectInputStream();
Person aPerson = DSP.readObject();
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

47. Remote Object Reference
Client Process
Invokes one method
of a remote object
Invocation
message
Server Process
Remote Object Reference: remote object identifier valid in a distributed system
Unicity: time
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
Unique identifier
of the process
(local) incremented when the process creates an object
Unicity: space
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48. Remote Interface (1) Specify which method can be remotely invoked
Local object: can invoke all methods m1-m6
Remote object: can invoke only the methods m1-m3 published in the remote interface
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

49. Remote Interface (2)
Example: CORBA’s Interface Definition Language (IDL)
// In file Person.idl
struct Person {
string name;
string place;
long year;
} ;
interface PersonList {
readonly attribute string listname;
void addPerson(in Person p) ;
void getPerson(in string name, out Person p);
long number(); };
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

50. RMI (Remote Method Invocation) (2)
RMI invocation semantics:
Fault tolerance measures
Retransmit request message
Duplicate filtering
Re-execute procedure or retransmit reply
Invocation semantics No
Not applicable
Maybe
CORBA
Yes No
Re-execute procedure
At-least-one
SUN/RPC
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
Yes
retransmit reply
At-most-one
Java RMI, CORBA
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51. RMI (Remote Method Invocation) (3)
Architecture:
RMI Client
RMI Server    
Stub
Skeleton
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
Remote Reference
Layer (RRL)
Remote Reference
Layer (RRL)
Transport Layer
Transport Layer
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52. RMI (Remote Method Invocation) (4)
Programming with RMI: steps to follow
Define the interfaces of all distant classes
Create and compile the implementations of these classes
Create stub and skeleton classes: RMIC
Create and compile a server application
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
Start RMIREGISTRY and execute the server application
Create and compile a client program that invokes the distant methods
Start client application
CSI408-Distributed Information Systems
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53. RMI (Remote Method Invocation) (5)
Case study:
A bank’s application capable of managing multiples accounts
It’ll be placed on a distant machine, interrogated and manipulated by clients
Define the interfaces of all distant classes
Class CreditManager : search or create a bank account
Class CreditCard: make purchases, set up signature, or get the account’s state
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

54. RMI (Remote Method Invocation) (6)
Class CreditManager:
package credit;
import credit.*;
import java.rmi.*;
public interface CreditManager extends Remote {
public CreditCard findCreditAccount(String Customer)
throws UnknownAccountException, RemoteException;
public CreditCard newCreditAccount(String newCustomer)
throws DuplicateAccountException, RemoteException; }
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

55. RMI (Remote Method Invocation) (7)
Class CreditCard:
package credit;
import credit.*;
import java.rmi.*;
public interface CreditCard extends Remote {
public float getCreditLine() throws RemoteException;
public void makePurchase(float amount, int signature)
throws InvalidSignatureException, RemoteException,
CreditLineExceededException;
public void setSignature(int pin) throws RemoteException; }
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

56. RMI (Remote Method Invocation) (8)
Create and compile the implementations of these classes
package credit;
import java.rmi.*;
import java.rmi.server.*;
import java.util.Hashtable;
public class CreditManagerImpl extends UnicastRemoteObject
implements CreditManager {
private static transient Hashtable accounts = new Hashtable();
public CreditManagerImpl() throws RemoteException { } …
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

57. RMI (Remote Method Invocation) (9)
Create and compile the implementations of these classes (continued)
public CreditCard newCreditAccount(String customerName)
throws DuplicateAccountException, RemoteException {
CreditCardImpl newCard = null;
if (accounts.get(customerName) == null)
newCard = new CreditCardImpl(customerName);
else throw new DuplicateAccountException();
accounts.put(customerName, newCard);
return newCard; } …
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

58. RMI (Remote Method Invocation) (9)
Create and compile the implementations of these classes (continued)
public CreditCard findCreditAccount(String customer)
throws UnknownAccountException, RemoteException {
CreditCardImpl
account = (CreditCardImpl)accounts.get(customer);
if (account == null)
throw new UnknownAccountException();
else
return account; }
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

59. RMI (Remote Method Invocation) (10)
Create and compile the implementations of these classes (continued)
package credit;
import java.rmi.*;
import java.rmi.server.*;
import java.io.Serializable;
public class CreditCardImpl extends UnicastRemoteObject
implements CreditCard, Serializable {
private float creditLine = 5000f;
private int signature = 0;
private String accountName; …
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

60. RMI (Remote Method Invocation) (11)
Create and compile the implementations of these classes (continued)
public CreditCardImpl(String customer)
throws RemoteException {
accountName = customer; }
public float getCreditLine() throws RemoteException {
return creditLine;
public void setSignature(int pin) throws RemoteException {
signature = pin; …
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

61. RMI (Remote Method Invocation) (12)
Create and compile the implementations of these classes (continued)
public void makePurchase(float amount, int signature)
throws InvalidSignatureException, RemoteException,
CreditLineExceededException {
if (signature != this.signature)
throw new InvalidSignatureException();
if (amount > creditLine)
throw new CreditLineExceededException();
else
creditLine -= amount; }
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

62. RMI (Remote Method Invocation) (13)
Create and compile a server application
RMIregistry (binder): maintains a table containing mapping from textual names to remote object references
class Naming
void rebind (String name, Remote obj)
void bind (String name, Remote obj)
void unbind (String name, Remote obj)
Remote lookup(String name)
String [] list()
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
//computerName:port/objectName
Where to find RMIregistry
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

63. RMI (Remote Method Invocation) (13)
Create and compile a server application
package credit;
import java.util.*;
import java.rmi.*;
public class ServerBank {
public static void main (String args[]) {
System.setSecurityManager(new RMISecurityManager());
try {
CreditManagerImpl cmi = new CreditManagerImpl();
Naming.rebind("cardManager", cmi);
} catch (Exception e) {
System.out.println(e.getMessage());
}}}
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

64. RMI (Remote Method Invocation) (14)
Create and compile a client program that invokes the distant methods
package credit;
import java.rmi.*;
public class ClientBank {
public static void main(String args[]) {
CreditManager cm = null;
CreditCard account = null;
if (args.length < 3) {
System.err.println("Usage : java ClientBank" +
" <server> <name1> <name2>");
System.exit (1); } …
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

65. RMI (Remote Method Invocation) (15)
Create and compile a client program that invokes the distant methods (continued)
System.setSecurityManager(new RMISecurityManager());
try {
String url = new String ("rmi://" + args[0] + "/cardManager");
cm = (CreditManager)Naming.lookup(url);
} catch (Exception e) {
System.out.println(“ Error while accessing the bank manager" + e); }
account = cm.newCreditAccount(args[1]);
System.out.println(“ Error during creation " + args[1] + " : " + e);
} …
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

66. RMI (Remote Method Invocation) (16)
Create and compile a client program that invokes the distant methods (continued)
try {
System.out.println(" Avail credit : " + account.getCreditLine());
account.setSignature(1234);
account.makePurchase(100.00f, 1234);
System.out.println(" Avail. credit : " + account.getCreditLine());
account.makePurchase(160.00f, 1234);
System.out.println(" Avail. credit : "+ account.getCreditLine());
} catch (Exception e) { System.out.println("Error " + args[1]);}
account = cm.findCreditAccount(args[2]);
} catch (Exception e) {
System.out.println(“ Error while seeking for" + args[2] + e);}}
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

67. RMI (Remote Method Invocation) (17)
Start client application
javac -d . -classpath . *.java
rmic -d . -classpath . credit.CreditCardImpl credit.CreditManagerImpl
CreditCardImpl_Skel.class
CreditCardImpl_Stub.class
CreditManagerImpl_Skel.class
CreditManagerImpl_Stub.class
start rmiregistry
start java -Djava.security.policy=c:\BankRMI\permit.policy
-Djava.rmi.server.codebase=file:///c:/BankRMI/ - classpath . credit.ServerBank
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
java -Djava.security.policy=c:\BankRMI\permit.policy
-Djava.rmi.server.codebase=file:///c:/BankRMI/
-classpath .
credit.ClientBank Pierre Marie
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

68. RMI (Remote Method Invocation) (17)
Start client application
Execution results:
Avail. credit:
Setting up signature
First purchase of 100 $
Avail. credit:
Second purchase of 160 $
Avail. credit:
Error while seeking for Marie
credit.UnknownAccountException
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

69. Readings
Tutorial: Getting Started Using RMI,
Jim  Waldo, Remote procedure calls and Java Remote Method Invocation, IEEE Concurrency, 6(3), pages 5-7, Sept 1998
A.D. Birrell and B.J. Nelson, Implementing Remote Procedure Calls (RPC), ACM Trans. on Computer Systems, 1984, pp 39-54
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

70. Types of Interprocess Communication
Client-Server Communication
Group Communication
Readings
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

71. Client-Server Communication(1)
Synchronous communication: Client process is blocked until the response is received from the server
Reliable: Server’s reply = acknowledgment
Client
Server
Request
getRequest
doOperation
(Wait) .
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
Select object
Execute method
Reply
sendReply .
(continuation)
Request-Reply Communication
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

72. Client-Server Communication(2)
Request-Reply message structure:
messageType
Int (0=Request, 1=Reply)
Int : generated by doOperation and copied by the server (message number + address + port)
requestId
RemoteObjectRef : a reference to a remote object encapsulated in a packet
objectReference
methodId
Int or Method
arguments
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
Array of bytes
Internet Address
Port Number
Time
Object Number
Interface of remote object
32 bits
32 bits
32 bits
32 bits
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

73. Client-Server Communication(3)
Primitives:
public byte [] doOperation (RemoteObjectRef o, int methodId, byte[] arguments);
public byte[] getRequest();
public void sendReply(byte[] reply, InetAddress clientHost, int clientPort);
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

74. Client-Server Communication(4)
Failure model for the RR protocol: primitives doOperation, getRequest and sendReply suffer from
Omission Faults
Message delivery not guaranteed
Solutions:
Timeouts
Enable servers to recognize two identical messages
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
Lost reply messages: the server re-execute only idempotent operations
History: save the results of the last executed request of each client
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

75. Client-Server Communication(5)
RPC exchange Protocols:
Messages sent by
Client
Server R
Request RR
Request
Reply
RRA
Request
Reply
Acknowledgment reply
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
Depends on the application, one of these protocols will be used
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

76. Group Communication (1)
Multicast communication: sends one message to each member of the group
Applications types: (examples)
Multicast messages provide a useful infrastructure for distributed systems with the following characteristics:
Fault tolerance based on replicated services
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
Replicated data: data are replicated to increase the performance of service
Propagation of event notifications (example)
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

77. Group Communication (2)
IP multicast:
IP multicast
UDP
In practice only UDP is used for multicast IP
Packet
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
Group
(details)
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

78. Group Communication (3)
API Java : class MulticastSocket
MulticastSocket()
MulticastSocket(int port)
void joinGroup(InetAddress groupe)
void leaveGroup(InetAddress groupe)
synchronized void send(DatagramPacket dp, byte TTL)
(TTL : definition)
synchronized void receive(DatagramPacket dp)
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
byte getTTL()
void setTTL(byte TTL)
InetAddress getInterface() Retrieve the address of the network interface used for multicast packets
setInterface(InetAddress nt) Set the outgoing network interface for multicast packets on this socket, to other than the system default
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

79. Group Communication (4)
Example : a member joins the group, sends and receives datagrams
import java.net.*; import java.io.*; public class MulticastPeer{ public static void main(String args[]){ // args[0] = message to multicast to the group // args[1] = IP address of the group (e.g. " ") MulticastSocket s =null; try { InetAddress group = InetAddress.getByName(args[1]); s = new MulticastSocket(6789); s.joinGroup(group);
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

80. Group Communication (5)
Example (continued):
byte [] m = args[0].getBytes(); DatagramPacket msgOut = new DatagramPacket(m,
m.length, group, 6789); s.send(msgOut);
byte[] buffer = new byte[1000]; // get messages from others in group for(int i=0; i< 3;i++) {
DatagramPacket msgIn = new DatagramPacket(buffer,
buffer.length); s.receive(msgIn); System.out.println("Rec. :" + new String(msgIn.getData())); }
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

81. Group Communication (6)
Example (suite):
s.leaveGroup(group); } catch (SocketException e){System.out.println("Socket: " +
e.getMessage()); } catch (IOException e){System.out.println("IO: " e.getMessage()); } finally {if(s != null) s.close();} }}
Processus émetteur peut s’exécuter dès que le message est copié dans le buffer local.
La transmission du message se fait en parallèle avec l’exécution du processus expéditeur
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.

82. Readings
MBone and Multicast Informations,
Ian Brown et al., Internet Multicast Tomorrow, Internet Protocol Journal, Vol 5(4), Dec
CSI408-Distributed Information Systems
© Mourad Elhadef, Ph. D.