Silberschatz, Galvin and Gagne ©2009Operating System Concepts – 8th Edition,
Chapter 4: Threads
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Chapter 4: Threads
OverviewMultithreading ModelsThread LibrariesThreading IssuesOperating System ExamplesWindows XP ThreadsLinux 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 systemsTo discuss the APIs for the Pthreads, Win32, and Java thread librariesTo examine issues related to multithreaded programming
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Single and Multithreaded Processes
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Benefits
Responsiveness
Resource Sharing
Economy
Scalability
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Multicore Programming
Multicore systems putting pressure on programmers, challenges includeDividing activitiesBalanceData splittingData dependencyTesting and debugging
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Multithreaded Server Architecture
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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 PthreadsWin32 threadsJava threads
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Kernel Threads
Supported by the Kernel
ExamplesWindows XP/2000SolarisLinuxTru64 UNIXMac 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 threadExamples:
Solaris Green ThreadsGNU Portable Threads
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Many-to-One Model
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One-to-One
Each user-level thread maps to kernel threadExamples
Windows NT/XP/2000LinuxSolaris 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 threadsAllows the operating system to create a sufficient number of kernel threadsSolaris prior to version 9Windows 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 threadExamples
IRIXHP-UXTru64 UNIXSolaris 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 threadsTwo primary ways of implementing
Library entirely in user spaceKernel-level library supported by the OS
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Pthreads
May be provided either as user-level or kernel-levelA POSIX standard (IEEE 1003.1c) API for thread creation and synchronizationAPI specifies behavior of the thread library, implementation is up to development of the libraryCommon in UNIX operating systems (Solaris, Linux, Mac OS X)
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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 classImplementing the Runnable interface
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Threading Issues
Semantics of fork() and exec() system callsThread cancellation of target thread
Asynchronous or deferredSignal handlingThread poolsThread-specific dataScheduler 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 finishedTwo general approaches:
Asynchronous cancellation terminates the target thread immediatelyDeferred 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 occurredA signal handler is used to process signals1. Signal is generated by particular event2. Signal is delivered to a process3. Signal is handled
Options:Deliver the signal to the thread to which the signal appliesDeliver the signal to every thread in the processDeliver the signal to certain threads in the processAssign a specific threa to receive all signals for the process
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Thread Pools
Create a number of threads in a pool where they await workAdvantages:
Usually slightly faster to service a request with an existing thread than create a new threadAllows 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 dataUseful 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 applicationScheduler activations provide upcalls - a communication mechanism from the kernel to the thread libraryThis communication allows an application to maintain the correctnumber kernel threads
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Operating System Examples
Windows XP ThreadsLinux Thread
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Windows XP Threads
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Linux Threads
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Windows XP Threads
Implements the one-to-one mapping, kernel-levelEach thread contains
A thread idRegister setSeparate user and kernel stacksPrivate data storage area
The register set, stacks, and private storage area are known as the context of the threadsThe primary data structures of a thread include:
ETHREAD (executive thread block)KTHREAD (kernel thread block)TEB (thread environment block)
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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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End of Chapter 4