Download Different Approaches to Distributed Computation - Slide Notes | CMSC 433 and more Study notes Programming Languages in PDF only on Docsity!
CMSC 433, Alan Sussman, U. Maryland (via
CMSC433, Spring 2002
Programming Language
Technology and Paradigms
Distributed Computing & RMI
Alan Sussman
March 14, 2002
CMSC 433, Spring 2002 - Alan Sussman 2
Administrivia
• Commentary for project 2 due next Wed.
• Project 4 posted
- distributed computing with RMI
• Read Ch. 15, pages 973-979, in Eckel
- Readings web page also has additional
distributed computing reading
• Return and talk about exam Tuesday
CMSC 433, Spring 2002 - Alan Sussman 3
Last time - Distributed computing
- Issues
- addressing objects
- latency
- partial failure
- concurrency
- Robustness and performance requirements call for
a non-uniform view of distributed objects
- plan for failure
- cope with latency
CMSC 433, Spring 2002 - Alan Sussman 4
Latency
• Making a call to an object on a remote
machine is much more expensive than a
local call
- several orders of magnitude
• Leading to overall system performance
problems if there are “too many” remote
calls
RMI
CMSC 433, Spring 2002 - Alan Sussman 6
Different Approaches to
Distributed Computation
• High-performance, parallel scientific apps
• Connecting via sockets
- custom protocols for each application
• RPC/DCOM/CORBA/RMI
- make what looks like a normal function call
- function is actually invoked on another machine
- Arguments are marshalled for transport
- return value is marshalled as well
CMSC 433, Alan Sussman, U. Maryland (via
CMSC 433, Spring 2002 - Alan Sussman 7
Remote Method Invocation
• Easy way to get distributed computation
• Have stub for remote object
- calls to stub get translated into network call
• Arguments and return values can be passed
over network
CMSC 433, Spring 2002 - Alan Sussman 8
Remote Objects and Interfaces
• Remote Objects are those that can be
referenced remotely
- extend java.rmi.UnicastRemoteObject
- constructor throws java.rmi.RemoteException
• Remote interfaces describe services that can
be provided remotely
- extend java.rmi.Remote interface
- all methods throw java.rmi.RemoteException
CMSC 433, Spring 2002 - Alan Sussman 9
RMIC - RMI Compiler
• Generates stub code for a class
- For 1.1, also generates skeleton class
- skeleton not needed for 1.2+
• Generates stubs for all methods declared in
remote interfaces
- other methods don’t get a stub
CMSC 433, Spring 2002 - Alan Sussman 10
Passing arguments
• Can pass arbitrary values as arguments
• Can return arbitrary values as results
• To pass a value, it must implement either
• Passing the same Serializable object in
different calls
- will materialize different objects at receiver
CMSC 433, Spring 2002 - Alan Sussman 11
Downloading code
• When you pass a reference to a remote class
- receiver (the method being called) needs stub
class code (class file generated by rmic )
• When you pass a ref to serializable class
- receiver needs class (the class file from javac )
• References to remote and serializable
classes annotated with RMI codebase
- where code can be loaded from
CMSC 433, Spring 2002 - Alan Sussman 12
SecurityManager
• Must install some Security Manager to
allow download of classes from RMI
codebase
• Can use RMISecurityManager
System.setSecurityManager(new
RMISecurityManager());
• Modify policy file to grant permissions
- example of that will be on Lectures web page
CMSC 433, Alan Sussman, U. Maryland (via
CMSC 433, Spring 2002 - Alan Sussman 19
RMI Registry on Server host
ServerImpl
Naming.rebind(“ ChatServer”, s);
Hosted Remote Objects
RMIRegistry
ChatServer
ServerImpl Stub
CMSC 433, Spring 2002 - Alan Sussman 20
Client creation on Client host
ClientImpl
Client c = new ClientImpl();
Hosted Remote Objects
c
CMSC 433, Spring 2002 - Alan Sussman 21
Server Lookup on Client host
ClientImpl
Server s = (Server) Naming.lookup(“//host/ ChatServer”);
Hosted Remote Objects
c
s
ServerImpl Stub
Hosted Remote Objects
ServerImpl CMSC 433, Spring 2002 - Alan Sussman 22
Invoke message on Server from Client host
prepare call on client
ClientImpl
Connection conn = s.logon(“Alan”, c);
Hosted Remote Objects
c
s
ServerImpl Stub
Marshalled arguments Serialized String “Alan” Serialized Stub for c
target
method: logon
CMSC 433, Spring 2002 - Alan Sussman 23
Unmarshalling arguments
on Server host
“Alan”
ClientImpl Stub
ServerImpl
Marshalled arguments Serialized String “Alan” Serialized Stub for c
target
method: logon logon
CMSC 433, Spring 2002 - Alan Sussman 24
Execution on Server host
“Alan”
ClientImpl Stub
ServerImpl
Hosted Remote Objects
name
client
conn
Connection Impl
CMSC 433, Alan Sussman, U. Maryland (via
CMSC 433, Spring 2002 - Alan Sussman 25
Marshalling return value on
Server host
“Alan”
ClientImpl Stub
ServerImpl
Hosted Remote Objects
Connection Impl
Marshalled return value:
Serialized Stub for conn
conn
CMSC 433, Spring 2002 - Alan Sussman 26
Unmarshalling return value on Client host
ClientImpl
Hosted Remote Objects
c
s
ServerImpl Stub
Marshalled return value Serialized Stub for conn
ConnImpl Stub
conn
