Threads, SMP, and Threads, SMP, and MicrokernelsMicrokernelsChapter 4

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ProcessProcessResource ownership - process

includes a virtual address space to hold the process image

Scheduling/execution- follows an execution path that may be interleaved with other processes

These two characteristics are treated independently by the operating system

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ProcessProcessDispatching is referred to as a

thread or lightweight processResource of ownership is referred

to as a process or task

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MultithreadingMultithreadingOperating system supports

multiple threads of execution within a single process

MS-DOS supports a single threadUNIX supports multiple user

processes but only supports one thread per process

Windows, Solaris, Linux, Mach, and OS/2 support multiple threads

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ProcessProcessHave a virtual address space

which holds the process imageProtected access to processors,

other processes, files, and I/O resources

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ThreadThreadAn execution state (running, ready,

etc.)Saved thread context when not

runningHas an execution stackSome per-thread static storage for

local variablesAccess to the memory and

resources of its process◦all threads of a process share this

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Benefits of ThreadsBenefits of ThreadsTakes less time to create a new thread

than a processLess time to terminate a thread than a

processLess time to switch between two

threads within the same processSince threads within the same process

share memory and files, they can communicate with each other without invoking the kernel

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Uses of Threads in a Single-Uses of Threads in a Single-User Multiprocessing SystemUser Multiprocessing SystemForeground to background workAsynchronous processingSpeed of executionModular program structure

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ThreadsThreadsSuspending a process involves

suspending all threads of the process since all threads share the same address space

Termination of a process, terminates all threads within the process

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Thread StatesThread StatesStates associated with a change

in thread state◦Spawn

Spawn another thread

◦Block◦Unblock◦Finish

Deallocate register context and stacks

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Remote Procedure Call Remote Procedure Call Using Single ThreadUsing Single Thread

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Remote Procedure Call Remote Procedure Call Using ThreadsUsing Threads

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MultithreadingMultithreading

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Adobe PageMakerAdobe PageMaker

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User-Level ThreadsUser-Level ThreadsAll thread management is done

by the applicationThe kernel is not aware of the

existence of threads

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User-Level ThreadsUser-Level Threads

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Kernel-Level ThreadsKernel-Level ThreadsWindows is an example of this

approachKernel maintains context

information for the process and the threads

Scheduling is done on a thread basis

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Kernel-Level ThreadsKernel-Level Threads

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VAX Running UNIX-Like VAX Running UNIX-Like Operating SystemOperating System

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Combined ApproachesCombined ApproachesExample is SolarisThread creation done in the user

spaceBulk of scheduling and

synchronization of threads within application

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Combined ApproachesCombined Approaches

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Relationship Between Relationship Between Threads and ProcessesThreads and Processes

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Categories of Computer Categories of Computer SystemsSystemsSingle Instruction Single Data

(SISD) stream◦Single processor executes a single

instruction stream to operate on data stored in a single memory

Single Instruction Multiple Data (SIMD) stream◦Each instruction is executed on a

different set of data by the different processors

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Categories of Computer Categories of Computer SystemsSystemsMultiple Instruction Single Data (MISD)

stream◦ A sequence of data is transmitted to a set

of processors, each of which executes a different instruction sequence. Never implemented

Multiple Instruction Multiple Data (MIMD)◦ A set of processors simultaneously execute

different instruction sequences on different data sets

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Symmetric Symmetric MultiprocessingMultiprocessingKernel can execute on any

processorTypically each processor does

self-scheduling form the pool of available process or threads

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Multiprocessor Operating Multiprocessor Operating System Design System Design ConsiderationsConsiderationsSimultaneous concurrent

processes or threadsSchedulingSynchronizationMemory managementReliability and fault tolerance

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MicrokernelsMicrokernelsSmall operating system coreContains only essential core operating

systems functionsMany services traditionally included in

the operating system are now external subsystems◦ Device drivers◦ File systems◦ Virtual memory manager◦ Windowing system◦ Security services

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Benefits of a Microkernel Benefits of a Microkernel OrganizationOrganizationUniform interface on request made by

a process◦ Don’t distinguish between kernel-level and

user-level services◦ All services are provided by means of

message passingExtensibility

◦ Allows the addition of new servicesFlexibility

◦ New features added◦ Existing features can be subtracted

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Benefits of a Microkernel Benefits of a Microkernel OrganizationOrganizationPortability

◦Changes needed to port the system to a new processor is changed in the microkernel - not in the other services

Reliability◦Modular design◦Small microkernel can be rigorously

tested

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Benefits of Microkernel Benefits of Microkernel OrganizationOrganizationDistributed system support

◦Message are sent without knowing what the target machine is

Object-oriented operating system◦Components are objects with clearly

defined interfaces that can be interconnected to form software

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Microkernel DesignMicrokernel Design

Low-level memory management◦ Mapping each virtual page to a physical

page frame

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Microkernel DesignMicrokernel DesignInterprocess communicationI/O and interrupt management

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Windows ProcessesWindows ProcessesImplemented as objectsAn executable process may

contain one or more threadsBoth processes and thread

objects have built-in synchronization capabilities

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Windows Process ObjectWindows Process Object

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Windows Thread ObjectWindows Thread Object

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Windows 2000Windows 2000Thread StatesThread StatesReadyStandbyRunningWaitingTransitionTerminated

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SolarisSolarisProcess includes the user’s

address space, stack, and process control block

User-level threadsLightweight processes (LWP)Kernel threads

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Solaris Lightweight Data Solaris Lightweight Data StructureStructureIdentifierPrioritySignal maskSaved values of user-level registersKernel stackResource usage and profiling dataPointer to the corresponding kernel

threadPointer to the process structure

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Linux Task Data StructureLinux Task Data StructureStateScheduling informationIdentifiersInterprocess communicationLinksTimes and timersFile systemAddress spaceProcessor-specific context

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Linux States of a ProcessLinux States of a ProcessRunningInterruptableUninterruptableStoppedZombie

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