DISTRIBUTED

OPERATING SYSTEMS

Sandeep Kumar PooniaHead Of Dept. CS/IT

B.E., M.Tech., UGC-NET

LM-IAENG, LM-IACSIT,LM-CSTA, LM-AIRCC, LM-SCIEI, AM-UACEE

1 MCS 5.1 DISTRIBUTED OPERATING SYSTEMSCOURSE OUTLINE

BROAD COVERAGE: Introduction to distributed computing systems (DCS)

DCS design goals, Transparencies, Fundamental issues

Distributed Coordination

Process synchronization

Inter-process communication

Deadlocks in distributed systems

Load scheduling and balancing techniques

Case Study: Amoeba, Mach, Chorus, DCE

PREREQUISITES Operating Systems

Computer Networks

Database System

REFERENCE BOOKS:

Distributed Operating Systems Concepts and

Design, Pradeep K. Sinha, PHI

Distributed Operating Systems by Andrew S

Tannebaum, PHI

Distributed Operating Systems and Algorithm

Analysis by Randy Chow, Pearson Education.

INTRODUCTION TO OPERATING

SYSTEM

What is an Operating System?

Mainframe Systems

Desktop Systems

Multiprocessor Systems

Distributed Systems

Clustered System

Real -Time Systems

Handheld Systems

Computing Environments

WHAT IS AN OPERATING SYSTEM?

A program that acts as an intermediary

between a user of a computer and the

computer hardware.

Operating system goals:

Execute user programs and make solving user

problems easier.

Make the computer system convenient to use.

Use the computer hardware in an efficient

manner.

COMPUTER SYSTEM COMPONENTS

1.Hardware – provides basic computing resources

(CPU, memory, I/O devices).

2.Operating system – controls and coordinates the

use of the hardware among the various

application programs for the various users.

3.Applications programs – define the ways in

which the system resources are used to solve the

computing problems of the users (compilers,

database systems, video games, business

programs).

4.Users (people, machines, other computers).

Program Interface

Humans

User Programs

O.S. Interface

O.S.

Hardware Interface/

Privileged Instructions

Disk/Tape/Memory

ABSTRACT VIEW OF SYSTEM COMPONENTS

OPERATING SYSTEM DEFINITIONS

Resource allocator – manages and allocates

resources.

Control program – controls the execution of user

programs and operations of I/O devices .

Kernel – the one program running at all times (all

else being application programs).

MAINFRAME SYSTEMS Reduce setup time by batching similar jobs

Automatic job sequencing – automatically

transfers control from one job to another.

First rudimentary operating system.

Resident monitor

initial control in monitor

control transfers to job

when job completes control transfers pack to

monitor

MEMORY LAYOUT FOR A SIMPLE BATCH SYSTEM

MULTIPROGRAMMED BATCH SYSTEMS

Several jobs are kept in main memory at the same time, and the

CPU is multiplexed among them.

OS FEATURES NEEDED FOR

MULTIPROGRAMMING

I/O routine supplied by the system.

Memory management – the system must

allocate the memory to several jobs.

CPU scheduling – the system must choose

among several jobs ready to run.

Allocation of devices.

TIME-SHARING SYSTEMS–INTERACTIVE COMPUTING

The CPU is multiplexed among several jobs that

are kept in memory and on disk (the CPU is

allocated to a job only if the job is in memory).

A job swapped in and out of memory to the disk.

On-line communication between the user and the

system is provided; when the operating system

finishes the execution of one command, it seeks

the next “control statement” from the user’s

keyboard.

On-line system must be available for users to

access data and code.

DESKTOP SYSTEMS Personal computers – computer system

dedicated to a single user.

I/O devices – keyboards, mice, display screens, small printers.

User convenience and responsiveness.

Can adopt technology developed for larger operating system’ often individuals have sole use of computer and do not need advanced CPU utilization of protection features.

May run several different types of operating systems (Windows, MacOS, UNIX, Linux)

PARALLEL SYSTEMS

Multiprocessor systems with more than on CPU

in close communication.

Tightly coupled system – processors share

memory and a clock; communication usually

takes place through the shared memory.

Advantages of parallel system:

Increased throughput

Economical

Increased reliability

graceful degradation

fail-soft systems

PARALLEL SYSTEMS (CONT.) Symmetric multiprocessing (SMP)

Each processor runs and identical copy of the

operating system.

Many processes can run at once without

performance deterioration.

Most modern operating systems support SMP

Asymmetric multiprocessing

Each processor is assigned a specific task; master

processor schedules and allocated work to slave

processors.

More common in extremely large systems

SYMMETRIC MULTIPROCESSING ARCHITECTURE

DISTRIBUTED SYSTEMS Distribute the computation among several

physical processors.

Loosely coupled system – each processor has its

own local memory; processors communicate with

one another through various communications

lines, such as high-speed buses or telephone lines.

Advantages of distributed systems.

Resources Sharing

Computation speed up – load sharing

Reliability

Communications

DISTRIBUTED SYSTEMS (CONT) Requires networking infrastructure.

Local area networks (LAN) or Wide area

networks (WAN)

May be either client-server or peer-to-peer

systems.

GENERAL STRUCTURE OF CLIENT-SERVER

CLUSTERED SYSTEMS

Clustering allows two or more systems to share

storage.

Provides high reliability.

Asymmetric clustering: one server runs the

application while other servers standby.

Symmetric clustering: all N hosts are running the

application.

REAL-TIME SYSTEMS Often used as a control device in a dedicated

application such as controlling scientific

experiments, medical imaging systems,

industrial control systems, and some display

systems.

Well-defined fixed-time constraints.

Real-Time systems may be either hard or soft

real-time.

REAL-TIME SYSTEMS (CONT.)

Hard real-time:

Secondary storage limited or absent, data stored in

short term memory, or read-only memory (ROM)

Conflicts with time-sharing systems, not supported by

general-purpose operating systems.

Soft real-time

Limited utility in industrial control of robotics

Useful in applications (multimedia, virtual reality)

requiring advanced operating-system features.

HANDHELD SYSTEMS

Personal Digital Assistants (PDAs)

Cellular telephones

Issues:

Limited memory

Slow processors

Small display screens.

Very fast storage is very expensive. So the OperatingSystem manages a hierarchy of storage devices in order tomake the best use of resources. In fact, considerableeffort goes into this support.

OPERATING SYSTEM

OVERVIEW

Storage

Hierarchy

Fast and Expensive

Slow an Cheap

COMPUTER-SYSTEM STRUCTURES

Computer System Operation

I/O Structure

Storage Structure

Storage Hierarchy

Hardware Protection

General System Architecture

COMPUTER-SYSTEM ARCHITECTURE

COMPUTER-SYSTEM OPERATION I/O devices and the CPU can execute concurrently.

Each device controller is in charge of a particular device

type.

Each device controller has a local buffer.

CPU moves data from/to main memory to/from local

buffers

I/O is from the device to local buffer of controller.

Device controller informs CPU that it has finished its

operation by causing an interrupt.

COMMON FUNCTIONS OF INTERRUPTS

Interrupt transfers control to the interrupt service

routine generally, through the interrupt vector, which

contains the addresses of all the service routines.

Interrupt architecture must save the address of the

interrupted instruction.

Incoming interrupts are disabled while another interrupt

is being processed to prevent a lost interrupt.

A trap is a software-generated interrupt caused either by

an error or a user request.

An operating system is interrupt driven.

I/O STRUCTURE

After I/O starts, control returns to user program only upon I/O completion.

Wait instruction idles the CPU until the next interrupt

Wait loop (contention for memory access).

At most one I/O request is outstanding at a time, no simultaneous I/O processing.

After I/O starts, control returns to user program without waiting for I/O completion.

System call – request to the operating system to allow user to wait for I/O completion.

Device-status table contains entry for each I/O device indicating its type, address, and state.

Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt.

DIRECT MEMORY ACCESS STRUCTURE

Used for high-speed I/O devices able to transmit

information at close to memory speeds.

Device controller transfers blocks of data from

buffer storage directly to main memory without

CPU intervention.

Only one interrupt is generated per block, rather

than the one interrupt per byte.

STORAGE STRUCTURE

Main memory – only large storage media that the

CPU can access directly.

Secondary storage – extension of main memory

that provides large nonvolatile storage capacity.

Magnetic disks – rigid metal or glass platters

covered with magnetic recording material

Disk surface is logically divided into tracks, which

are subdivided into sectors.

The disk controller determines the logical interaction

between the device and the computer.

STORAGE HIERARCHY

Storage systems organized in hierarchy.

Speed

Cost

Volatility

Caching – copying information into faster storage

system; main memory can be viewed as a last

cache for secondary storage.

STORAGE-DEVICE HIERARCHY

CACHING

Use of high-speed memory to hold recently-

accessed data.

Requires a cache management policy.

Caching introduces another level in storage

hierarchy. This requires data that is

simultaneously stored in more than one level to

be consistent.

MIGRATION OF A FROM DISK TO

REGISTER

OPERATING-SYSTEM STRUCTURES

System Components

Operating System Services

System Calls

System Programs

System Structure

Virtual Machines

System Design and Implementation

System Generation

COMMON SYSTEM COMPONENTS Process Management

Main Memory Management

File Management

I/O System Management

Secondary Management

Networking

Protection System

Command-Interpreter System

PROCESS MANAGEMENT

A process is a program in execution. A process

needs certain resources, including CPU time,

memory, files, and I/O devices, to accomplish its

task.

The operating system is responsible for the

following activities in connection with process

management.

Process creation and deletion.

process suspension and resumption.

Provision of mechanisms for:

process synchronization

process communication

MAIN-MEMORY MANAGEMENT

Memory is a large array of words or bytes, each

with its own address. It is a repository of quickly

accessible data shared by the CPU and I/O devices.

Main memory is a volatile storage device. It loses

its contents in the case of system failure.

The operating system is responsible for the

following activities in connections with memory

management:

Keep track of which parts of memory are currently

being used and by whom.

Decide which processes to load when memory space

becomes available.

Allocate and deallocate memory space as needed.

FILE MANAGEMENT

A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data.

The operating system is responsible for the following activities in connections with file management:

File creation and deletion.

Directory creation and deletion.

Support of primitives for manipulating files and directories.

Mapping files onto secondary storage.

File backup on stable (nonvolatile) storage media.

I/O SYSTEM MANAGEMENT

The I/O system consists of:

A buffer-caching system

A general device-driver interface

Drivers for specific hardware devices

SECONDARY-STORAGE MANAGEMENT Since main memory (primary storage) is volatile

and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory.

Most modern computer systems use disks as the principle on-line storage medium, for both programs and data.

The operating system is responsible for the following activities in connection with disk management: Free space management

Storage allocation

Disk scheduling

NETWORKING (DISTRIBUTED SYSTEMS)

A distributed system is a collection processors

that do not share memory or a clock. Each

processor has its own local memory.

The processors in the system are connected

through a communication network.

Communication takes place using a protocol.

A distributed system provides user access to

various system resources.

Access to a shared resource allows:

Computation speed-up

Increased data availability

Enhanced reliability

OPERATING SYSTEM SERVICES Program execution – system capability to load a program into

memory and to run it.

I/O operations – since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O.

File-system manipulation – program capability to read, write, create, and delete files.

Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing.

Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs.

ADDITIONAL OPERATING SYSTEM FUNCTIONS

Additional functions exist not for helping the user,

but rather for ensuring efficient system operations.

•Resource allocation – allocating resources to multiple

users or multiple jobs running at the same time.

•Accounting – keep track of and record which users

use how much and what kinds of computer resources

for account billing or for accumulating usage

statistics.

•Protection – ensuring that all access to system

resources is controlled.

SYSTEM DESIGN GOALS

User goals – operating system should be

convenient to use, easy to learn, reliable, safe,

and fast.

System goals – operating system should be easy

to design, implement, and maintain, as well as

flexible, reliable, error-free, and efficient.

MECHANISMS AND POLICIES

Mechanisms determine how to do something,

policies decide what will be done.

The separation of policy from mechanism is a

very important principle, it allows maximum

flexibility if policy decisions are to be changed

later.

PROCESSES

Process Concept

Process Scheduling

Operations on Processes

Cooperating Processes

Interprocess Communication

Communication in Client-Server Systems

PROCESS CONCEPT

An operating system executes a variety of

programs:

Batch system – jobs

Time-shared systems – user programs or tasks

Textbook uses the terms job and process almost

interchangeably.

Process – a program in execution; process

execution must progress in sequential fashion.

A process includes:

program counter

stack

data section

PROCESS STATE

As a process executes, it changes state

new: The process is being created.

running: Instructions are being executed.

waiting: The process is waiting for some event to occur.

ready: The process is waiting to be assigned to a process.

terminated: The process has finished execution.

DIAGRAM OF PROCESS STATE

PROCESS CONTROL BLOCK (PCB)Information associated with each process.

Process state

Program counter

CPU registers

CPU scheduling information

Memory-management information

Accounting information

I/O status information

PROCESS CONTROL BLOCK (PCB)

CPU SWITCH FROM PROCESS TO PROCESS

CONTEXT SWITCH

When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process.

Context-switch time is overhead; the system does no useful work while switching.

Time dependent on hardware support.

PROCESS CREATION

Parent process create children processes, which,

in turn create other processes, forming a tree of

processes.

Resource sharing

Parent and children share all resources.

Children share subset of parent’s resources.

Parent and child share no resources.

Execution

Parent and children execute concurrently.

Parent waits until children terminate.

PROCESS TERMINATION

Process executes last statement and asks the

operating system to decide it (exit).

Output data from child to parent (via wait).

Process’ resources are deallocated by operating

system.

Parent may terminate execution of children

processes (abort).

Child has exceeded allocated resources.

Task assigned to child is no longer required.

Parent is exiting.

Operating system does not allow child to continue if its

parent terminates.

Cascading termination.

COOPERATING PROCESSES

Independent process cannot affect or be affected

by the execution of another process.

Cooperating process can affect or be affected by

the execution of another process

Advantages of process cooperation

Information sharing

Computation speed-up

Modularity

Convenience

PRODUCER-CONSUMER PROBLEM

Paradigm for cooperating processes, producer

process produces information that is consumed

by a consumer process.

unbounded-buffer places no practical limit on the size

of the buffer.

bounded-buffer assumes that there is a fixed buffer

size.

REMOTE PROCEDURE CALLS

Remote procedure call (RPC) abstracts procedure

calls between processes on networked systems.

Stubs – client-side proxy for the actual procedure

on the server.

The client-side stub locates the server and

marshalls the parameters.

The server-side stub receives this message,

unpacks the marshalled parameters, and peforms

the procedure on the server.

REMOTE METHOD INVOCATION

Remote Method Invocation (RMI) is a Java

mechanism similar to RPCs.

RMI allows a Java program on one machine to

invoke a method on a remote object.

THREADS

Overview

Multithreading Models

Threading Issues

Windows 2000 Threads

Linux Threads

Java Threads

SINGLE AND MULTITHREADED PROCESSES

BENEFITS

Responsiveness

Resource Sharing

Economy

Utilization of MP Architectures

USER THREADS

Thread management done by user-level threads

library

Examples

- POSIX Pthreads

- Mach C-threads

- Solaris threads

KERNEL THREADS

Supported by the Kernel

Examples

- Windows 95/98/NT/2000

- Solaris

- Tru64 UNIX

- BeOS

- Linux

MULTITHREADING MODELS

Many-to-One

One-to-One

Many-to-Many

MANY-TO-ONE

Many user-level threads mapped to single kernel

thread.

Used on systems that do not support kernel

threads.

MANY-TO-ONE MODEL

ONE-TO-ONE

Each user-level thread maps to kernel thread.

Examples

- Windows 95/98/NT/2000

- OS/2

ONE-TO-ONE MODEL

MANY-TO-MANY MODEL

Allows many user level threads to be mapped to

many kernel threads.

Allows the operating system to create a

sufficient number of kernel threads.

Solaris 2

Windows NT/2000 with the ThreadFiber package

MANY-TO-MANY MODEL

WINDOWS 2000 THREADS

Implements the one-to-one mapping.

Each thread contains

- a thread id

- register set

- separate user and kernel stacks

- private data storage area

LINUX THREADS

Linux refers to them as tasks rather than

threads.

Thread creation is done through clone() system

call.

Clone() allows a child task to share the address

space of the parent task (process)

JAVA THREADS

Java threads may be created by:

Extending Thread class

Implementing the Runnable interface

Java threads are managed by the JVM.