Download Figure 5.01 - Ceng Anadolu

Chapter 4: Threads
Operating System Concepts – 8th Edition
Silberschatz, Galvin and Gagne ©2009
Objectives

To introduce the notion of a thread — a fundamental unit of CPU utilization that forms the basis of
multithreaded computer systems

To discuss the APIs for the Pthreads, Win32, and Java thread libraries

To examine issues related to multithreaded programming
Operating System Concepts – 8th Edition
4.2
Silberschatz, Galvin and Gagne ©2009
Motivation

Threads run within application

Multiple tasks with the application can be implemented by separate threads

Update display

Fetch data

Spell checking

Answer a network request

Process creation is heavy-weight while thread creation is light-weight

Can simplify code, increase efficiency

Kernels are generally multithreaded
Operating System Concepts – 8th Edition
4.3
Silberschatz, Galvin and Gagne ©2009
Single and Multithreaded Processes
Operating System Concepts – 8th Edition
4.4
Silberschatz, Galvin and Gagne ©2009
Recall a process’s address space
0xFFFFFFFF
stack
(dynamic allocated mem)
SP
heap
(dynamic allocated mem)
static data
(data segment)
0x00000000
Operating System Concepts – 8th Edition
code
(text segment)
4.5
PC
Silberschatz, Galvin and Gagne ©2009
A process’s address space with threads
thread 1 stack
0xFFFFFFFF
SP
thread 2 stack
thread 3 stack
SP (T1)
SP (T2)
SP (T3)
address space
heap
(dynamic allocated mem)
static data
(data segment)
0x00000000
Operating System Concepts – 8th Edition
PC
code
(text segment)
4.6
PC (T2)
PC (T1)
PC (T3)
Silberschatz, Galvin and Gagne ©2009
Benefits

Responsiveness

Resource Sharing

Economy

Scalability
Operating System Concepts – 8th Edition
4.7
Silberschatz, Galvin and Gagne ©2009
Multithreaded Server Architecture
Operating System Concepts – 8th Edition
4.8
Silberschatz, Galvin and Gagne ©2009
Concurrent Execution on a
Single-core System
Operating System Concepts – 8th Edition
4.9
Silberschatz, Galvin and Gagne ©2009
Parallel Execution on a
Multicore System
Operating System Concepts – 8th Edition
4.10
Silberschatz, Galvin and Gagne ©2009
User Threads

Thread management done by user-level threads library: the user-level process (user-level threads) a library linked
into the program manages the threads.

To make threads cheap and fast, they need to be implemented at the user level



managed entirely by user-level library, e.g. libpthreads.a
each process keeps track of its own threads in a thread table
Three primary thread libraries:

POSIX Pthreads

Win32 threads

Java threads
Operating System Concepts – 8th Edition
4.11
Silberschatz, Galvin and Gagne ©2009
Kernel Threads

Supported by the Kernel

all thread operations are implemented in the kernel

OS schedules all of the threads in a system

if one thread in a process blocks (e.g. on I/O), the OS knows about it, and can run other threads from that
process

possible to overlap I/O and computation inside a process
Operating System Concepts – 8th Edition
4.12
Silberschatz, Galvin and Gagne ©2009
Multithreading Models

Many-to-One

One-to-One

Many-to-Many
Operating System Concepts – 8th Edition
4.13
Silberschatz, Galvin and Gagne ©2009
Many-to-One

Many user-level threads mapped to single kernel thread

Examples:

Solaris Green Threads

GNU Portable Threads
Operating System Concepts – 8th Edition
4.14
Silberschatz, Galvin and Gagne ©2009
Many-to-One Model
Operating System Concepts – 8th Edition
4.15
Silberschatz, Galvin and Gagne ©2009
One-to-One

Each user-level thread maps to kernel thread

Examples

Windows NT/XP/2000

Linux

Solaris 9 and later
Operating System Concepts – 8th Edition
4.16
Silberschatz, Galvin and Gagne ©2009
One-to-one Model
Operating System Concepts – 8th Edition
4.17
Silberschatz, Galvin and Gagne ©2009
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 prior to version 9

Windows NT/2000 with the ThreadFiber package
Operating System Concepts – 8th Edition
4.18
Silberschatz, Galvin and Gagne ©2009
Many-to-Many Model
Operating System Concepts – 8th Edition
4.19
Silberschatz, Galvin and Gagne ©2009
Two-level Model

Similar to M:M, except that it allows a user thread to be bound to kernel thread

Examples

IRIX

HP-UX

Tru64 UNIX

Solaris 8 and earlier
Operating System Concepts – 8th Edition
4.20
Silberschatz, Galvin and Gagne ©2009
Two-level Model
Operating System Concepts – 8th Edition
4.21
Silberschatz, Galvin and Gagne ©2009
Thread Libraries

Thread library provides programmer with API for creating and managing threads

Two primary ways of implementing

Library entirely in user space

Kernel-level library supported by the OS
Operating System Concepts – 8th Edition
4.22
Silberschatz, Galvin and Gagne ©2009
Pthreads

May be provided either as user-level or kernel-level

A POSIX standard (IEEE 1003.1c) API for thread creation and synchronization

API specifies behavior of the thread library, implementation is up to development of the library

Common in UNIX operating systems (Solaris, Linux, Mac OS X)
Operating System Concepts – 8th Edition
4.23
Silberschatz, Galvin and Gagne ©2009
Pthreads Example
Operating System Concepts – 8th Edition
4.24
Silberschatz, Galvin and Gagne ©2009
Pthreads Example (Cont.)
Operating System Concepts – 8th Edition
4.25
Silberschatz, Galvin and Gagne ©2009
Win32 API Multithreaded C Program
Operating System Concepts – 8th Edition
4.26
Silberschatz, Galvin and Gagne ©2009
Win32 API Multithreaded C Program (Cont.)
Operating System Concepts – 8th Edition
4.27
Silberschatz, Galvin and Gagne ©2009
Java Threads

Java threads are managed by the JVM

Typically implemented using the threads model provided by underlying OS

Java threads may be created by:

Extending Thread class

Implementing the Runnable interface
Operating System Concepts – 8th Edition
4.28
Silberschatz, Galvin and Gagne ©2009
Java Multithreaded Program
Operating System Concepts – 8th Edition
4.29
Silberschatz, Galvin and Gagne ©2009
Java Multithreaded Program (Cont.)
Operating System Concepts – 8th Edition
4.30
Silberschatz, Galvin and Gagne ©2009
Semantics of fork() and exec()

Does fork() duplicate only the calling thread or all threads?
Operating System Concepts – 8th Edition
4.31
Silberschatz, Galvin and Gagne ©2009
Thread Cancellation

Terminating a thread before it has finished

Two general approaches:

Asynchronous cancellation terminates the target thread immediately.

Deferred cancellation allows the target thread to periodically check if it should be cancelled.
Operating System Concepts – 8th Edition
4.32
Silberschatz, Galvin and Gagne ©2009
Thread Pools

Create a number of threads in a pool where they await work

Advantages:

Usually slightly faster to service a request with an existing thread than create a new thread

Allows the number of threads in the application(s) to be bound to the size of the pool
Operating System Concepts – 8th Edition
4.33
Silberschatz, Galvin and Gagne ©2009
Scheduler Activations

Both M:M and Two-level models require communication to maintain the appropriate number of kernel
threads allocated to the application

Scheduler activations provide upcalls - a communication mechanism from the kernel to the thread
library

This communication allows an application to maintain the correct number kernel threads
Operating System Concepts – 8th Edition
4.34
Silberschatz, Galvin and Gagne ©2009
Lightweight Processes
Operating System Concepts – 8th Edition
4.35
Silberschatz, Galvin and Gagne ©2009
End of Chapter 4
Operating System Concepts – 8th Edition
Silberschatz, Galvin and Gagne ©2009