21,Feb,Tue

Module name: Operating Systems Concepts

Teacher: Xin Huang Email: [email protected] Room: SD461

Assessment

  1. Final Exam 80%
  2. Assessment1 10% (Week8)
  3. Assessment2 10% (Week 14)

Essential Textbook Operating System Concepts 9th

Overview PPT

How a Modern Computer Works

Symmetric Multiprocessing Architecture

Cluster Systems

A view of Operating System Services

Memory Layout for Multiprogrammed System pic for MS-DOS

Operating System Structure

  • Various ways to Structure on
    • Simple structrue- MS-DOS
    • More complex -- UNIX
    • Layered -- an abstraction
    • Solaris Modular Apporach
    • Microkernel (funtion limited)
    • Hybrid (nowadays use to bulid system)

What Operating Systems Do

Transition from User to Kernel Mode

API - System Call - OS Relationship

Parameter Passing via Table

Standard C Library Example

Storage-Device Hierarchy layer higher, price increase, speed increase, volumn decrease

Computer System Organization Connected using buses

Migration of data "A" from Disk to Register

Interrupt I/O tranfer done, CPU interrupt

Processes PPT

  • notation of a Process
  • various features of processess
    • Scheduling
    • Creation
    • Termination
  • explore interprocess communication
    • Shared Memory
    • Message Passing

      all these charpter are in book

Process Concept

  • Process

    • a program in execution
    • process execution must progress in sequential fashion(cpu only handle sequential requeset)
    • Process in Memory

    • Process state

    • Process Control Block(PCB)

    • Diagram showing CPU switch from process to Processes

Process Scheduling

  • Process scheduler

    • Selects among available processes for next execution on CPU
    • Maintains scheduling queues of Processes
      • Job queue - set of all processes in the System
      • Ready queue - set of all processes residing in main memory, ready and waiting to execute
      • Device queues - set of processes waiting for an I/O device

  • The ready queue and various I/O device queues

  • Queueing-diagram representation of process Scheduling

  • Short-term scheduler (or CPU scheduler) - selects which porcess should be executed next and allocates CPU
  • Long-term scheduler (or job scheduler) - selects which processes should be brought into the ready queue
  • I/O-bound process - spends more time doing I/O than computations, many short CPU bursts

  • CPU-bound process - spends more time doing computations; few very long CPU bursts

  • Addition of medium-term scheduling to the queueing diagram

  • 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 via a context switch
    • Context of a process represented in the PCB

Operations on Process

  • Process Creation

    • Parent process Creatione children processes, which, in turn create other processes, forming a tree of processes

    • C Program Forking Separate Processes

Process Termination

  • Process executes last statement and then asks the operating system to delete it using the exit() system call.

    • Returns status data from child to parent (via wait())
    • Process' resources are deallocated by operating system

Interprocess Communication Communications Models

Producer-Consumer Problem

  • Paradigm for cooperating processes, producer process produces information that is consumed by a consumer process

Bounded-Buffer - Shared -Memory Solution

Bounded-Buffer -Producer

Bounde-Buffer -Consumer

Interprocess Communication - Message Passing

  • IPC facility provides two opertions:
    • send(message)
    • receive(message)

Direct Communication

  • Processes much name each other explicitly:
    • send(P,message) - send a message to process P
    • recevie(Q,message) - receive a message from process Q

Indirect Communication

  • create a new mailbox (port)
  • send and receive messages through mailbox
    • send(A, message) - send a message to mailbox A
    • receive(A, message) - receive a message from mailbox A
  • destroy a mailbox

Synchronization

Threads PPT

Objectives

  • notion of a Threads
  • APIs

Threads

  • Thread -- a fundamental unit of CPU utilization that forms the basis of multithreaded computer Systems

Single and Multithreaded Processes

Multithreaded Server Architecture

Benefits

  • Resopnsiveness - many allow continued execution if part of process is blocked, especially important for user inter faces
  • Resource Sharing - threads share resources of process, easier than shared memory or message Passing
  • Economy - cheaper than process creation, thread switching lower overhead than context switching
  • Scalability - process can take advantage of multiprocessor architectures

Multithreading Models User Threads and Kernel Threads

  • User threads - management done by user-level threads library
  • Kernel threads - Supported by the Kernel

many-to-One

  • Many user-level threads mapped to single kernel Thread
  • One thread blocking causes all to block
  • Multiple threads may not run in parallel on muticore system because only one may be in kernel at a time

One-to-One

  • Each user-level thread maps to kernel Thread
  • More concurrency than many-to-one
  • Number of threads per process sometimes restricted due to overhead

Many-to-Many

  • Allows many user level threads to be mapped to many kernel threads
  • Allows the operating system to create a sufficient number of kernel threads

Two-level Model

  • Similar to M:M, except that it allows a user thread to be bound to kernel thread

Thread Libraries

  • Thread library provides programmer with API for creating and managing threads Pthreads
  • May be provided either as user-level or kernel-level
  • API specifies behavior of the thread library, implementation is up to development of the Library
  • Common in UNIX operating Systems

Pthreads Code for Joining 10 Threads

Implict Threading

  • Growing in populrity as numbers of threads increase, program correctness more difficult with explicit threads
  • Creation and management of threads done by compilers and run-tim libraries rather than programmers

Q&A

  • What are the three main purposes of an operating system?
  1. Provide an environment for a computer user to execute programs on computer hardware in a convenient and efficient manner
  2. To allocate the separate resources of the computer as needed to solve the problem given. The allocation process should be as fair and efficient as possible
  3. As a control program it serves two major functions:
    • Supervision of the execution of user programs to prevent errors and improper use of the computer
    • Management of the operation and control of I/O devices

  • What is the purpose of system calls?

    System call allow user-level processes to request services of the operating system

  • Including the initial parentprocess,how many processesarecreated by the program？

    8

  • Provide two programming examplesin which multithreadingprovides better performance than a single-threaded solution.

    a. A web server that services each request in a separate thread b. A parallelized application such as matrix multiplication where different parts of the matrix may be work on in parallel c. An interactive GUI program such as a debugger where a thread is used to monitor user input, another thread represents the running application.

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