Operating System Principles

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Operating System Principles

• Ku-Yaw Chang
• canseco_at_mail.dyu.edu.tw
• Assistant Professor, Department of Computer
  Science and Information Engineering
• Da-Yeh University

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Chapter 4Multithreaded Programming

• A process
• With a single thread of control
• With multiple threads of control
• Multithreaded computer systems
• Pthreads
• Windows 32 threads
• Java thread libraries
• Windows XP and Linux
• Support at the kernel level

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Chapter 4Multithreaded Programming

1. Overview
2. Multithreading Models
3. Thread Libraries
4. Threading Issues
5. Operating-System Examples
6. Summary
7. Exercises

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4.1 Overview

• A thread
• A basic unit of CPU utilization
• A thread ID
• A program counter
• A register set
• A stack
• Called a lightweight process (LWP)
• A traditional process has a single thread of
  control, called a heavyweight process (HWP)

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Single-threaded and Multithreaded processes
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4.1.1 Motivation

• A web browser
• One thread display images or text
• Another thread retrieves data from the network
• A word processor
• One thread for displaying graphics
• Another thread for reading keystrokes
• Third thread for performing spelling and grammar
  checking

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4.1.1 Motivation

• If new process will perform the same tasks as the
  existing process, why incur all that overhead?
• Process creation is very time-consuming and
  resource intensive.
• Have the server run as a single process that
  accepts requests.

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4.1.2 Benefits

• Responsiveness
• Allow a program to continue even if part of it is
  blocked or is performing a lengthy operation
• Resource sharing
• Memory
• Different threads all within the same address
  space
• Resources
• Economy
• More economical to create and context switch
  threads
• Utilization of multiprocessor architectures
• Increase concurrency

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Chapter 4Multithreaded Programming

1. Overview
2. Multithreading Models
3. Thread Libraries
4. Threading Issues
5. Operating-System Examples
6. Summary
7. Exercises

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4.2 Multithreading Models

• User threads
• Implemented by a thread library at the user level
• Supported above the kernel
• Advantage
• Fast to create and manage
• Disadvantage
• A thread may cause the entire process to block
• Examples
• POSIX Pthreads
• Win32 threads
• Java threads

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4.2 Multithreading Models

• Kernel threads
• The kernel performs thread creation, scheduling,
  and management
• Supported directly by OS
• Advantage
• Kernel can schedule another thread when a thread
  is blocked
• Disadvantage
• Slow to create and manage
• Examples
• Windows XP
• Linux
• Max OS X

• Solaris
• Tru64 Unix

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4.2 Multithreading Models

• Many systems provide support for both user and
  kernel threads
• Different multithreading models
• Many-to-one model
• One-to-one model
• Many-to-many model

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4.2.1 Many-to-One Model

• Many user-level threads mapped to one kernel
  thread

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4.2.1 Many-to-One Model

• Advantage
• Efficient
• Disadvantage
• Entire process may block if a thread makes a
  blocking system call
• Unable to run in parallel on multiprocessors
• Used on systems that do not support kernel
  threads
• Green threads a thread library available for
  Solaris
• GNU Portable Threads

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4.2.2 One-to-One Model

• Each user thread mapped to one kernel thread

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4.2.2 One-to-One Model

• Advantage
• More concurrency
• Disadvantage
• Overhead of creating kernel threads can burden
  the performance of an application
• Restrict the number of threads
• Example
• Linux
• Windows operating systems
• Windows 95, 98, NT, 2000, and XP

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4.2.3 Many-to-Many Model

• Multiplex many user-level threads to a small or
  equal number of kernel threads two-level model

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4.2.3 Many-to-Many Model

• Advantage
• Developers can create as many as user threads as
  wish
• More concurrency
• Example
• IRIX
• HP-UX
• Tru64 Unix
• Solaris prior to version 9

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Chapter 4Multithreaded Programming

1. Overview
2. Multithreading Models
3. Thread Libraries
4. Threading Issues
5. Operating-System Examples
6. Summary
7. Exercises

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4.3 Thread Libraries

• A thread library
• Provide the programmer an API for creating and
  managing threads
• Two primary approaches
• A user-level library
• Entirely in user space, with no kernel support
• A local function call in user space
• A kernel-level library
• Supported by the operating system
• A system call to the kernel

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4.3 Thread Libraries

• Three main thread libraries in use
• POSIX Pthreads
• A specification for thread behavior
• not an implementation
• Win32
• Java

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Chapter 4Multithreaded Programming

1. Overview
2. Multithreading Models
3. Thread Libraries
4. Threading Issues
5. Operating-System Examples
6. Summary
7. Exercises

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• Be skipped

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Chapter 4Multithreaded Programming

1. Overview
2. Multithreading Models
3. Thread Libraries
4. Threading Issues
5. Operating-System Examples
6. Summary
7. Exercises

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Summary

• P.141 to P.142

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Chapter 4Multithreaded Programming

1. Overview
2. Multithreading Models
3. Thread Libraries
4. Threading Issues
5. Operating-System Examples
6. Summary
7. Exercises

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Exercises

• 4.3
• 4.4

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The End