Silberschatz, Galvin and Gagne 20025.1Operating System Concepts

Chapter 5: Threads

Overview Multithreading Models Threading Issues Pthreads Solaris 2 Threads Windows 2000 Threads Linux Threads Java Threads

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PROCESS

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Single and Multithreaded Processes

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BENEFITS

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Remote Procedure Call Using Threads

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Remote Procedure Call Using Threads

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PROCESS VERSUS TREAD CONTEXT SWITCHING

PER PROCESS ITEMS PER THREAD ITEMSAddress space Program counterGlobal variables RegistersOpen files StackChild processes StatePending alarmsSignals, signal handlersAccounting info

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THREAD STATES

Spawn: New thread created

Running, Ready: As before

Block: Waiting for event. Do the mini-context switchi.e. save and restore registers, PC and SP

Unblock: Change state to Ready

Finish: Finish the thread within the process

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Relationship Between Threads and Processes

Threads:Process Description Example Systems

1:1 Each thread of execution is aunique process with its ownaddress space and resources.

Traditional UNIX implementations

M:1 A process defines an addressspace and dynamic resourceownership. Multiple threadsmay be created and executedwithin that process.

Windows NT, Solaris, OS/2,OS/390, MACH

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Relationship Between Threads and Processes

Threads:Process Description Example Systems

1:M A thread may migrate from oneprocess environment toanother. This allows a threadto be easily moved amongdistinct systems.

Ra (Clouds), Emerald

M:M Combines attributes of M:1and 1:M cases

TRIX

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USER – LEVEL THREADS

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KERNEL – LEVEL THREADS

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User Threads

Thread management done by user-level threads library

Examples

- POSIX Pthreads

- Mach C-threads

- Solaris threads

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Kernel Threads

Supported by the Kernel

Examples

- Windows 95/98/NT/2000

- Solaris

- Tru64 UNIX

- BeOS

- Linux

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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 thread.

Used on systems that do not support kernel threads.

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Many-to-One Model

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One-to-One

Each user-level thread maps to kernel thread.

Examples

- Windows 95/98/NT/2000

- OS/2

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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 threads.

Allows the operating system to create a sufficient number of kernel threads.

Solaris 2 Windows NT/2000 with the ThreadFiber package

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Many-to-Many Model

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Threading Issues

Semantics of fork() and exec() system calls. Thread cancellation. Signal handling Thread pools Thread specific data

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Pthreads

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.

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/* example – cont. */

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Solaris 2 Threads

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Solaris Process

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Solaris Thread Execution

Synchronization Suspension Preemption Yielding

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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

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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)

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Java Threads

Java threads may be created by:

Extending Thread class Implementing the Runnable interface

Java threads are managed by the JVM.

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Java Thread States