Chapter 4: Threads

Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009

Chapter 4: Threads

‣ Overvie
‣ Multithreading Model
‣ Thread Librarie
‣ Threading Issue
‣ Operating System Example
‣ Windows XP Thread
‣ Linux Threads

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 Objectives

‣ To introduce the notion of a thread — a fundamental unit

of CPU utilization that forms the basis of multithreaded
computer system
‣ To discuss the APIs for the Pthreads, Win32, and Java
thread librarie
‣ To examine issues related to multithreaded
programming

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Motivation
‣ Threads run within applicatio
‣ Multiple tasks with the application can be implemented by
separate thread
✦ Update displa
✦ Fetch dat
✦ Spell checkin
✦ Answer a network reques

‣ Process creation is heavy-weight while thread creation is light-

weigh
‣ Can simplify code, increase efficienc
‣ Kernels are generally multithreaded

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 Single and Multithreaded Processes

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Multithreaded Server Architecture

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 Benefits

‣ Responsiveness

‣ Resource Sharing

‣ Economy

‣ Scalability

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Multicore Programming

‣ Multicore systems putting pressure on programmers,

challenges include
✦ Dividing activitie
✦ Balanc
✦ Data splittin
✦ Data dependenc
✦ Testing and debugging

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 Concurrent Execution on a
Single-core System

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Parallel Execution on a
Multicore System

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 User Threads

‣ Thread management done by user-level threads library

‣ Three primary thread libraries

✦ POSIX Pthreads
✦ Win32 thread
✦ Java threads

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Kernel Threads

‣ Supported by the Kernel

‣ Example
✦ Windows XP/200
✦ Solari
✦ Linu
✦ Tru64 UNI
✦ Mac OS X

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 Multithreading Models

‣ Many-to-One

‣ One-to-One

‣ Many-to-Many

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Many-to-One

‣ Many user-level threads mapped to single kernel threa

‣ Examples
✦ Solaris Green Thread
✦ GNU Portable Threads

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 Many-to-One Model

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One-to-One

‣ Each user-level thread maps to kernel threa

‣ Example
✦ Windows NT/XP/200
✦ Linu
✦ Solaris 9 and later

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 One-to-one Model

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Many-to-Many Model

‣ Allows many user level threads to be mapped to

many kernel thread

‣ Allows the operating system to create a sufficient

number of kernel thread

‣ Solaris prior to version

‣ Windows NT/2000 with the ThreadFiber package

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 Many-to-Many Model

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Two-level Model

‣ Similar to M:M, except that it allows a user thread to be

bound to kernel threa

‣ Example
✦ IRI
✦ HP-U
✦ Tru64 UNI
✦ Solaris 8 and earlier

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 Two-level Model

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Thread Libraries

‣ Thread library provides programmer with API for

creating and managing thread

‣ Two primary ways of implementin

✦ Library entirely in user spac
✦ Kernel-level library supported by the OS

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 Pthreads

‣ May be provided either as user-level or kernel-leve

‣ A POSIX standard (IEEE 1003.1c) API for thread

creation and synchronizatio

‣ API specifies behavior of the thread library,

implementation is up to development of the librar

‣ Common in UNIX operating systems (Solaris, Linux,

Mac OS X)

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Pthreads Example

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 Pthreads Example (Cont.)

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Win32 API Multithreaded C Program

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 Win32 API Multithreaded C Program (Cont.)

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Java Threads

‣ Java threads are managed by the JV

‣ Typically implemented using the threads model

provided by underlying O

‣ Java threads may be created by:

✦ Extending Thread clas

✦ Implementing the Runnable interface

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 Java Multithreaded Program

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Java Multithreaded Program (Cont.)

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 Threading Issues

‣ Semantics of fork() and exec() system call

‣ Thread cancellation of target threa

✦ Asynchronous or deferre

‣ Signal handlin
✦ Synchronous and asynchronous

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Threading Issues (Cont.)

‣ Thread pool

‣ Thread-specific dat
✦ Create Facility needed for data private to thread
‣ Scheduler activations

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 Semantics of fork() and exec()

‣ Does fork() duplicate only the calling thread or all

threads?

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Thread Cancellation

‣ Terminating a thread before it has finishe

‣ Two general approaches

✦ Asynchronous cancellation terminates the target
thread immediately
✦ Deferred cancellation allows the target thread to
periodically check if it should be cancelled.

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 Signal Handling
‣ Signals are used in UNIX systems to notify a process that a
particular event has occurred
‣ A signal handler is used to process signal
1. Signal is generated by particular even
2. Signal is delivered to a proces
3. Signal is handle

‣ Options
✦ Deliver the signal to the thread to which the signal applie
✦ Deliver the signal to every thread in the proces
✦ Deliver the signal to certain threads in the proces
✦ Assign a specific thread to receive all signals for the
process

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Thread Pools

‣ Create a number of threads in a pool where they await

wor

‣ Advantages
✦ Usually slightly faster to service a request with an
existing thread than create a new threa
✦ Allows the number of threads in the application(s) to
be bound to the size of the pool

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 Thread Specific Data

‣ Allows each thread to have its own copy of dat

‣ Useful when you do not have control over the thread

creation process (i.e., when using a thread pool)

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Scheduler Activations

‣ Both M:M and Two-level models require

communication to maintain the appropriate number of
kernel threads allocated to the applicatio

‣ Scheduler activations provide upcalls - a

communication mechanism from the kernel to the
thread librar

‣ This communication allows an application to maintain

the correct number kernel threads

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 Lightweight Processes

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Operating System Examples

‣ Windows XP Thread

‣ Linux Thread

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 Windows XP Threads
‣ Implements the one-to-one mapping, kernel-leve
‣ Each thread contain
✦ A thread i
✦ Register se
✦ Separate user and kernel stack
✦ Private data storage are

‣ The register set, stacks, and private storage area are known as
the context of the thread
‣ The primary data structures of a thread include
✦ ETHREAD (executive thread block
✦ KTHREAD (kernel thread block
✦ TEB (thread environment block)

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Windows XP Threads Data Structures

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 Linux Threads
‣ Provides fork() and clone() system call
✦ fork(): traditional functionality of duplicating a
process
✦ clone(): create thread and allows a child task to

share the address space of the parent task

(process
‣ Doesn’t distinguish between process and thread; uses
the term task —rather than process or thread
‣ Unique kernel data structure(struct task_struct)
exists for each task in the system

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Linux Threads
‣ Data of new tas
✦ fork(): new task is created; copy of all the associated data
structures of the parent process
✦ clone():new task is created and points to the data structures
of the parent task, depending on the set of flags passed to clone()
✦ if none of these flags is set: no sharing takes place, functionality
similar to that provided by the fork() system call

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 End of Chapter 4

Operating System Concepts – 8th Edition Silberschatz, Galvin and Gagne ©2009