chapter 4: threads. 2 overview multithreading models thread libraries threading issues operating...

Chapter 4: Chapter 4: ThreadsThreads

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Chapter 4: ThreadsChapter 4: Threads

OverviewOverview

Multithreading ModelsMultithreading Models

Thread LibrariesThread Libraries

Threading IssuesThreading Issues

Operating System ExamplesOperating System Examples

Windows XP ThreadsWindows XP Threads

Linux ThreadsLinux Threads

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ObjectivesObjectives

To introduce the notion of a thread — a To introduce the notion of a thread — a fundamental unit of CPU utilization that fundamental unit of CPU utilization that forms the basis of multithreaded computer forms the basis of multithreaded computer systemssystems

To discuss the APIs for the Pthreads, To discuss the APIs for the Pthreads, Win32, and Java thread librariesWin32, and Java thread libraries

To examine issues related to To examine issues related to multithreaded programmingmultithreaded programming

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Single and Multithreaded Single and Multithreaded ProcessesProcesses

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BenefitsBenefits

ResponsivenessResponsiveness

Resource SharingResource Sharing

EconomyEconomy

ScalabilityScalability

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Multicore ProgrammingMulticore Programming

Multicore systems are putting pressure on Multicore systems are putting pressure on programmersprogrammers

Challenges includeChallenges include Dividing activitiesDividing activities BalanceBalance Data splittingData splitting Data dependencyData dependency Testing and debuggingTesting and debugging

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Multithreaded Server Multithreaded Server ArchitectureArchitecture

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Concurrent Execution on a Single-core Concurrent Execution on a Single-core SystemSystem

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Parallel Execution on a Multicore Parallel Execution on a Multicore SystemSystem

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User ThreadsUser Threads

Thread management done by user-level Thread management done by user-level threads librarythreads library

Three primary thread libraries:Three primary thread libraries: POSIX POSIX PthreadsPthreads Win32 threadsWin32 threads Java threadsJava threads

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Kernel ThreadsKernel Threads

Supported by the KernelSupported by the Kernel

ExamplesExamples Windows XP/2000Windows XP/2000 SolarisSolaris LinuxLinux Tru64 UNIXTru64 UNIX Mac OS XMac OS X

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OverviewOverview







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Many-to-OneMany-to-One

One-to-OneOne-to-One

Many-to-ManyMany-to-Many

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Many-to-OneMany-to-One

Many user-level threads mapped to single Many user-level threads mapped to single kernel threadkernel thread

Examples:Examples: Solaris Green ThreadsSolaris Green Threads GNU Portable ThreadsGNU Portable Threads

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Many-to-One ModelMany-to-One Model

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One-to-OneOne-to-One

Each user-level thread maps to kernel Each user-level thread maps to kernel threadthread

ExamplesExamples Windows NT/XP/2000Windows NT/XP/2000 LinuxLinux Solaris 9 and laterSolaris 9 and later

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One-to-one ModelOne-to-one Model

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Many-to-Many ModelMany-to-Many Model

Allows many user level threads to Allows many user level threads to be mapped to many kernel threadsbe mapped to many kernel threads

Allows the operating system to Allows the operating system to create a sufficient number of kernel create a sufficient number of kernel threadsthreads

Solaris prior to version 9Solaris prior to version 9

Windows NT/2000 with the Windows NT/2000 with the ThreadFiberThreadFiber package package

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Many-to-Many ModelMany-to-Many Model

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Two-level ModelTwo-level ModelSimilar to M:M, except that it Similar to M:M, except that it allows a user thread to be allows a user thread to be boundbound to kernel thread to kernel thread

ExamplesExamples IRIXIRIX HP-UXHP-UX Tru64 UNIXTru64 UNIX Solaris 8 and earlierSolaris 8 and earlier

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Two-level ModelTwo-level Model

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OverviewOverview







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A A tthread hread librarylibrary provides programmer with provides programmer with an API for creating and managing threadsan API for creating and managing threads

Two primary ways of implementingTwo primary ways of implementing Library entirely in user spaceLibrary entirely in user space Kernel-level library supported by the OSKernel-level library supported by the OS

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PthreadsPthreads

May be provided either as user-level or kernel-May be provided either as user-level or kernel-levellevel

A POSIX standard (IEEE 1003.1c) API for A POSIX standard (IEEE 1003.1c) API for thread creation and synchronizationthread creation and synchronization

API specifies behavior of the thread library, API specifies behavior of the thread library, implementation is up to development of the implementation is up to development of the librarylibrary

Common in UNIX operating systems (Solaris, Common in UNIX operating systems (Solaris, Linux, Mac OS X)Linux, Mac OS X)

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Java ThreadsJava ThreadsJava threads are managed by the JVMJava threads are managed by the JVM

Typically implemented using the threads model Typically implemented using the threads model provided by underlying OSprovided by underlying OS

Java threads may be created by:Java threads may be created by: Extending Thread classExtending Thread class Implementing the Runnable interfaceImplementing the Runnable interface

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OverviewOverview







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Threading IssuesThreading IssuesSemantics of Semantics of fork()fork() and and exec()exec() system callssystem calls

Thread cancellation Thread cancellation of of target threadtarget thread Asynchronous or deferredAsynchronous or deferred

Signal Signal handlinghandling

Thread poolsThread pools

Thread-specific dataThread-specific data

Scheduler activationsScheduler activations

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Semantics of fork() and exec()Semantics of fork() and exec()

Does Does fork()fork() duplicate only the calling duplicate only the calling thread or all threads?thread or all threads?

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Thread CancellationThread CancellationTerminating a thread before it has Terminating a thread before it has finishedfinished

Two general approaches:Two general approaches: Asynchronous cancellationAsynchronous cancellation

terminates the target thread terminates the target thread immediatelyimmediately

Deferred cancellationDeferred cancellation allows the allows the target thread to periodically check if target thread to periodically check if it should be cancelledit should be cancelled

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Signal HandlingSignal HandlingSignals are used in UNIX systems to notify a Signals are used in UNIX systems to notify a process that a particular event has occurredprocess that a particular event has occurred

A A signal handler signal handler is used to process signalsis used to process signals1.1. Signal is generated by particular eventSignal is generated by particular event

2.2. Signal is delivered to a processSignal is delivered to a process

3.3. Signal is handledSignal is handled

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Signal HandlingSignal Handling

Options for the signal handler:Options for the signal handler: Deliver the signal to the thread to which the Deliver the signal to the thread to which the

signal appliessignal applies Deliver the signal to every thread in the Deliver the signal to every thread in the

processprocess Deliver the signal to certain threads in the Deliver the signal to certain threads in the

processprocess Assign a specific thread to receive all signals Assign a specific thread to receive all signals

for the processfor the process

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Thread PoolsThread Pools

Create a number of threads in a pool Create a number of threads in a pool where they await workwhere they await work

Advantages:Advantages: Usually slightly faster to service a request Usually slightly faster to service a request

with an existing thread than create a new with an existing thread than create a new threadthread

Allows the number of threads in the Allows the number of threads in the application(s) to be bound to the size of application(s) to be bound to the size of the poolthe pool

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Thread Specific DataThread Specific Data

Allows each thread to have its own Allows each thread to have its own copy of datacopy of data

Useful when you do not have Useful when you do not have control over the thread creation control over the thread creation process (i.e., when using a thread process (i.e., when using a thread pool)pool)

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Scheduler ActivationsScheduler ActivationsBoth M:M and Two-level models require Both M:M and Two-level models require communication to maintain the appropriate communication to maintain the appropriate number of kernel threads allocated to the number of kernel threads allocated to the applicationapplication

Scheduler activations provide Scheduler activations provide upcalls upcalls - a - a communication mechanism from the kernel communication mechanism from the kernel to the thread libraryto the thread library

This communication allows an application This communication allows an application to maintain the correct number kernel to maintain the correct number kernel threadsthreads

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OverviewOverview







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Linux ThreadLinux Thread

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OverviewOverview







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Windows XP ThreadsWindows XP ThreadsImplements the one-to-one mapping, kernel-Implements the one-to-one mapping, kernel-levellevel

Each thread containsEach thread contains A thread idA thread id Register setRegister set Separate user and kernel stacksSeparate user and kernel stacks Private data storage areaPrivate data storage area

The register set, stacks, and private storage The register set, stacks, and private storage area are known as the area are known as the context context of the threadsof the threads

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The primary data structures of a thread The primary data structures of a thread include:include: ETHREAD (executive thread block)ETHREAD (executive thread block) KTHREAD (kernel thread block)KTHREAD (kernel thread block) TEB (thread environment block)TEB (thread environment block)

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OverviewOverview







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Linux ThreadsLinux ThreadsLinux refers to them as Linux refers to them as taskstasks rather than rather than threadsthreads

Thread creation is done through Thread creation is done through clone()clone() system call system call

clone()clone() allows a child task to allows a child task to share the address space of the share the address space of the parent task (process)parent task (process)

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End of Chapter 4End of Chapter 4

chapter 4: threads. 2 overview multithreading models thread libraries threading issues operating...

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