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CSS434 Interprocess Communication
Textbook Ch4
Professor: Munehiro Fukuda
CSS434 IPC
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Outline
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Java sockets
Object serialization
Blocking/non-blocking communication
Buffering
Error handling
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Idenpotency
Exactly-one semantics
CSS434 IPC
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Middleware Layers
Applic ations, services
RMI and RPC
This
c hapter
reques t-reply protocol
Middlew are
lay ers
marshalling and ex ternal data representation
UDP and TCP
CSS434 IPC
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Sockets and Ports
socket
any port
agreed port
socket
message
client
server
other ports
Internet address = 138.37.94.248
Internet address = 138.37.88.249
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Java TCP Client
import java.net.*;
import java.io.*;
public class TCPClient {
public static void main (String args[]) {
// arguments supply message and hostname of destination
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 4.3
String data = in.readUTF();
System.out.println("Received: "+ data) ;
}catch (UnknownHostException e){
System.out.println("Sock:"+e.getMessage());
}catch (EOFException e){System.out.println("EOF:"+e.getMessage());
}catch (IOException e){System.out.println("IO:"+e.getMessage());}
}finally {if(s!=null) try {s.close();}catch (IOException e){System.out.println("close:"+e.getMessage());}}
}
}
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Java TCP Server
import java.net.*;
import java.io.*;
public class TCPServer {
public static void main (String args[]) {
try{
int serverPort = 7896;
ServerSocket listenSocket = new ServerSocket(serverPort);
while(true) {
Socket clientSocket = listenSocket.accept();
Connection c = new Connection(clientSocket);
}
} catch(IOException e) {System.out.println("Listen :"+e.getMessage());}
}
}
// this figure continues on the next slide
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Java TCP Server (Cont’d)
class Connection extends Thread {
DataInputStream in;
DataOutputStream out;
Socket clientSocket;
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();
out.writeUTF(data);
} catch(EOFException e) {System.out.println("EOF:"+e.getMessage());
} catch(IOException e) {System.out.println("IO:"+e.getMessage());}
} finally{ try {clientSocket.close();}catch (IOException e){/*close failed*/}}
}
}
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Serialization
Manual Operations in C++
class SubObject {
public:
int id;
SubObject( int I ) { id = I; }
void print( ) { cout << “SubObject: id=“ << id << endl; }
};
class MainObject {
public:
int id;
SubObject *subObj;
MainObject( int I, SubObject *s ) { id = I; subObj = j; }
void print( ) { cout << “MainObject: id=“ << id << endl; }
};
MainObj
ＳｕＯｂｊ
Read/write
Int main( int argc, char** argv )
{
int f1 = create( “sample.dat”, 0744 );
MainObject *obj1 = new MainObject( 1, new SubObject( 2 ) );
write( f1, obj1, sizeof( *obj1 ) );
write( f1, obj1->subObj, sizeof( *obj1->subObj ) ); //manually write data pointed to by obj1
close( f1 );
int f2 = open( “sample.dat”, O_RDONLY );
MainObject *obj2 = new MainObject( 0, new SubObject( 0 ) );
read( f2, obj2, sizeof( MainObject ) );
read( f2, obj2->subObj, sizeof( SubObject ) );
//manually read data pointed to by obj2
close( f2 );
obj2->print( );
obj2->subObj->print( );
CSS434 IPC
}
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Serialization
Automatic Operations in Java
public class SubObject implements Serializable {
private int id;
public SubObject( int I ) { id = I; }
public void print( ) { System.out.println( “SubObject: id =“ + id ); }
}
public class MainObject implements Serializable {
public int id;
public SubObject subObj;
public MainObject( int I, SubObject s ) { id = I; subObj = s; }
public void print( ) { System.out.println( “MainObject: id =“ + id ); }
}
Public class Test {
public static void main( String args[] ) throws IOException, ClassNotFoundException {
FileOutputStream f1 = new FileOutputStream( “sample.dat” );
ObjectOutputStream o = new ObjectOutputStream( f1 );
MainObject obj1 = new MainObject( 1, new SubObject( 2 ) );
o.writeObject( obj1 );
//automatically write all objects traceable from obj1
o.flush( );
o.close( );
FileInputStream f2 = new FileInputStream( “sample.dat” );
ObjectInputStream i = new ObjectInputStream( f2 );
MainObject obj2 = (MainObject)I.readObject( );
// automatically read all object traceable from obj2
I.close( );
obj2.print( );
obj2.subObj.print( );
}
}
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Serialization
Serializable or Not Serializable

Serializable

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Classes implementing the Serializable interface
Primitive data types such as int and double and their
arrays
Not Serializable

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Image and Thread classes
Static variables
Variables quantified with Transient

Zero or null initialized upon a de-serialization
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Blocking/Non-Blocking
Communication

Blocking communication

TCP, UDP, and other communication packages

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Rendezvous
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Client: blocked only when the destination buffer is full
Server: blocked if no message has arrived from the client.
Client: blocked for a server to receive a message
Server: blocked if no message has arrived from the client.
Non-blocking communication

Server does not want to be blocked when



It may receive a message from a different client.
It has another jobs to be done such as computation or
message transmission.
Some synchronization is necessary later.
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Non-Blocking Communication
C/C++ Example

Polling

Periodically check if a socket is ready to read data:

Example:
sd = socket( AF_INET, SOCKET_STREAM, 0);
set_fl(sd, O_NONBLOCK);
// set the socket as non-blocking
struct pollfd pfd;
pfd.fd = sd;
poll( &pfd, 1, timeout )
// poll the socket status

Interrupt

Notified from the system when a socket is ready to read data;

Example:
sd = socket(AF_INET, SOCKET_STREAM, 0);
signal(SIGIO, sigio_func);
// set a future interrupt to call
sigio_func( )
fcntl(sd, F_SETOWN, getpid( ));
// ask OS to deliver this fd
interrupt to me
fcntl(sd, F_SETFL, FASYNC);
// set this fd asynchronous
int sigio_func( ) { // invoked upon an interrupt }
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Non-Blocking Communication
Java Example

Polling

Periodically check if a socket is ready to read data:

Example 1:
socket = new Socket( server, port );
rawIn = socket.getInputStream( );
in = new DataInputStream( rawIn );
if ( rawIn.available( ) > 0 ) {
String str = in.readUTF( );
System.out.println( str );
}

Example 2:
ServerSocket server = new ServerSocket( port );
server.setSoTimeout( 500 ); //will be blocked for 500ms upon accept
Socket client = null;
try {
client = server.accept( );
} catch ( SocketTimeoutException e ) { }

Interrupt

Difficult to implement asynchronous/interruptible communication in Java
 Reason 1: There are no methods corresponding to fctl( ).
 Reason 2: JVM itself receives external interrupts.
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Buffering

message

message

message
message
message
message
No Buffering

A message remains on the sender until the
receiver issues receive( ).

Rendezvous

Performance drawback
Single Message Buffer

The sender can send at most one message
even if the receiver has not issued receive( ).

Stop-and-wait protocol
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A message can be kept read in advance.
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What if the sender has multiple messages?
Finite-Bound Buffer

Unsuccessful communication
Go-Back-N Technique

Flow-controlled communication - sliding
window in TCP

Socket: capable of changing its buffer size with
setsockopt( )
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Failure Handling
client
server
request
ack
server
client

request
timeout
request 2
response
response

timeout

response 2
request
request
ack
response

ack
timeout
request 2
CSS434 IPC
Loss of request
message
Loss of response
message
Unsuccessful
execution of request
Do we really need
acknowledgment
messages?
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Idempotency
client
server
request
server
request
client

Timeout
request 2
response

Timeout
A pair of request and
response is enough to
handle faults
Idempotency assumed:

request 3

Timeout
At-least one semantics
Last-one semantics
response
request 4
reesponse 2
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Exactly-One Semantics

Withdraw $100
Withdraw995 $100
$1000-$100
= $900
Not received
Withdraw $100
$100 received
$1000-$100

= $900 for Trans995
Not received
Withdraw995 $100
Trans995 completed
No subtraction
$900-$100
=$800!
$100 received
CSS434 IPC
What if errors in
the banking
system
New semantics
required:
 Exactly-one
semantics
 Server must
keep track of
the request
sequence
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Exercises (No turn-in)
1.
2.
3.
Consider the pros and cons of polling and interrupt in nonblocking communication.
Consider an example inducing an accidental system hangup (named a deadlock) in no-buffering communication.
Which of the following operations are idempotent?
1.
cin >> data;
2.
ifstream infile(“input.txt”); infile.seek( );
3.
cout << data;
4.
int a = 1, b = 2, c; c = a + b;
5.
int c = 1; c++;
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