Operating Systems

1
Operating Systems

• Distributed Computing
• 12/11/00
• Shawn Cooper

2
Distributed Computing

• What is Distributed Computing?
• Remote Procedure Call (RPC)
• Components and Component Architectures
• MS COM, EJB/J2EE
• Whats Next
• SOAP, .NET

3
Distributed Computing What?

• Computing in which components comprising an
  application can be located on different computers
  connected to a network
• Examples WEB applications, n-tiered
  architectures

4
Distributed Computing Why?

• Goal Make things faster! More efficient!
• Scale up vs. Scale out
• Parallel Computing

5
Distributed Computing How?

• Message passing mechanisms are the basis for
  distributed computing
• Similar to a mailbox
• RPC as the plumbing for distributed computing

6
Remote Procedure Call
7
RPC - Overview

• Goal Should be able to execute code on a
  remote computer exactly the same as on the local
  computer
• When making a remote procedure call
• The calling environment is suspended, procedure
  parameters are transferred across the network to
  the environment where the procedure is to
  execute, and the procedure is executed there.
• When the procedure finishes and produces its
  results, its results are transferred back to the
  calling environment, where execution resumes as
  if returning from a regular procedure call.

8
What happens during RPC

• The following steps take place during an RPC
• A client invokes a client stub procedure, passing
  parameters in the usual way. The client stub
  resides within the client's own address space.
• The client stub marshalls the parameters into a
  message. Marshalling includes converting the
  representation of the parameters into a standard
  format, and copying each parameter into the
  message.
• The client stub passes the message to the
  transport layer, which sends it to the remote
  server machine.
• On the server, the transport layer passes the
  message to a server stub, which demarshalls the
  parameters and calls the desired server routine
  using the regular procedure call mechanism.

9
RPC (cont)

• When the server procedure completes, it returns
  to the server stub (e.g., via a normal procedure
  call return), which marshalls the return values
  into a message. The server stub then hands the
  message to the transport layer.
• The transport layer sends the result message back
  to the client transport layer, which hands the
  message back to the client stub.
• The client stub demarshalls the return parameters
  and execution returns to the caller.

10
Issues with RPC

• Data Format
• Sun RPC uses XDR
• Call By Reference
• Global Variables

11
Components
12
Software Development

• Goals of Software Development
• Easier, Reusable, Robust
• Evolution Procedural, Object Oriented,
  Components
• Components were developed because object oriented
  languages, while helpful, have not yet achieved
  their goals of reuse

13
Components

• What is a component?
• Reusable, self contained building block that can
  be combined with other building blocks to form an
  application
• Examples
• Interface and implementation

14
Component Architectures

• What is a component architecture
• Eases distributed software development
• Services
• Transactions
• Security
• Object lifetime and Thread Management
• others...
• Examples of component architectures
• Microsofts COM
• Suns EJB/J2EE
• CORBA

15
COM

• Specification and implementation of a component
  architecture built by Microsoft
• Components are called COM objects
• Each COM object has a globally unique CLSID
• Based on DCE RPC (ORPC)
• MTS, MSMQ, DCOM

16
DCOM

• DCOM is simply COM with a longer wire
• How does DCOM work?

17
EJB and J2EE

• J2EE is a specification put forth by Sun and
  implemented by external vendors
• BEA Weblogic, IBM Websphere, Bluestones
  Total-e-Server
• Components are called Java Beans and Enterprise
  Java Beans
• EJBs reside inside an EJB Container which manage
  every aspect of the bean (access, security,
  persistence, transactions, concurrency, etc.).
  Clients never access the Bean directly.

18
EJB

• Locate objects across the network with Java
  Naming and Directory Interface (JNDI) and
  communicate with remote objects using Remote
  Method Invocation (RMI)
• JNDI allows objects to search for other objects
  by name
• RMI is specific to Java, not compatible with RPC

19
(No Transcript)
20
Comparison

• COM
• MS Only
• Windows Only
• One Standard, One implementation
• Fast moving

• J2EE
• Open Standards
• Multiple Platforms
• Incompatible Implementations
• Standard Committees

21
Whats Next?
22
SOAP

• Simple Object Access Protocol (SOAP)
  specification put forth by MS, IBM, Developmentor
• Lightweight protocol for exchange of information
  in a distributed environment.
• Based on Open Standards
• An XML based protocol consisting of
• An envelope that that defines a framework for
  describing what is in a message and how to
  process it
• a set of encoding rules for expressing instances
  of application-defined data types
• a convention for representing remote procedure
  calls and responses
• Can be used over HTTP

23
QA