distributed operating system, Lecture notes of Computer Engineering and Programming

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Distributed OperatingSystems - Introduction

Prof. NaliniVenkatasubramanian(

includes slides from Prof. Petru Eles and Profs.

textbook slides by Kshemkalyani/Singhal

Process/Thread Management

Scheduling

Communication

Synchronization

Memory Management

Storage Management

FileSystems Management

Protection and Security

Networking

What does an OS do?

Hardware Architectures

Multiprocessors

Tightly coupled

Shared memory

Cache

CPU

Cache

CPU

Memory

Parallel Architecture

Hardware Architectures

Multicomputers

Loosely coupled

Private memory

Autonomous

Memory

CPU

Memory

CPU

Memory

CPU

Distributed Architecture

Distributed Operating System(DOS)

Distributed Computing Systems commonly use twotypes of Operating Systems.



Network Operating Systems



Distributed Operating System

Differences between the two types



System Image



Autonomy



Fault Tolerance Capability

Operating System Types

Multiprocessor OS

Looks like a virtual uniprocessor, contains only one copy of the OS, communicates via sharedmemory, single run queue

Network OS

Does not look like a virtual uniprocessor, contains n copies of the OS, communicates via shared files,n run queues

Distributed OS

Looks like a virtual uniprocessor (more or less), contains n copies of the OS, communicates via messages, n run queues

Transparency

Location transparency

processes, cpu’s and other devices, files

Replication transparency (of files)

Concurrency transparency

(user unaware of the existence of others)

Parallelism

User writes serial program, compiler and OS

do the rest

Performance

Throughput - response time

Load Balancing (static, dynamic)

Communication is slow compared tocomputation speed

fine grain, coarse grain parallelism

Remote Procedure Call

A convenient way to construct a client-server connectionwithout explicitly writing send/ receive type programs(helps maintain transparency).

Remote Procedure Calls (RPC)

General message passing model. Providesprogrammers with a familiar mechanism for buildingdistributed applications/systems

Familiar semantics (similar to LPC)



Simple syntax, well defined interface, ease of use, generalityand IPC between processes on same/different machines.

It is generally synchronous

Can be made asynchronous by using multi-threading

RPC continued…

Transparency of RPC



Syntactic Transparency



Semantic Transparency

Unfortunately achieving exactly the same semantics for RPCs and LPCs isclose to impossible



Disjoint address spaces



More vulnerable to failure



Consume more time (mostly due to communication delays)

Implementing RPC Mechanism

Uses the concept of stubs; A perfectly normal LPCabstraction by concealing from programs the interfaceto the underlying RPC

Involves the following elements



The client



The client stub



The RPC runtime



The server stub



The server

RPC servers and protocols…

RPC Messages (call and reply messages)

Server Implementation



Stateful servers



Stateless servers

Communication Protocols



Request(R)Protocol



Request/Reply(RR) Protocol



Request/Reply/Ack(RRA) Protocol

RPC NG: DCOM & CORBA

Object models allow services and functionality to becalled from distinct processes

DCOM/COM+(Win2000) and CORBA IIOP extend this toallow calling services and objects on different machines

More OS features (authentication,resourcemanagement,process creation,…) are being moved todistributed objects.