Thread Model Concept

CHAPTER 4

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Processes & ThreadsProcesses & Threads

Dr. D. M. Akbar Hussain

Department of Electronic SystemsDE5 1

Thread Model Concept Thread Model Concept

Single Thread Model

User address space Kernel Stack

g

User StackPCB


Department of Electronic SystemsDE5

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Thread Model Concept Thread Model Concept

Thread Control Thread Control

Multithread ModelThread Thread

User Stack

Kernel Stack

Thread Control Block

r add

ress

spac

ePC

B

User Stack

Kernel Stack

Thread Control Block


Department of Electronic Systems3

Kernel Stack

Use

s Kernel Stack

Thread has what ……?Thread has what ……?

Static Storage space for locals Resources, Memory Access and Privilege

State (Ready ……. Execution Stack



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Multithreading in Multithreading in Operating SystemsOperating Systems

MS DOS:UNIX:Windows:Linux:MACH:Solaris:


Department of Electronic Systems

Solaris:OS-2:

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Characteristics of a Characteristics of a Thread Thread

Asynchronous processingModular programming structureSuspension of a process suspend all threadsTermination of a process terminate all threads



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Advantages Advantages

–Less time to create a thread in a process rather than to create a new processLess time to create a thread in a process rather than to create a new process.

–In the other extreme it takes less time to terminate a thread.

–Switching between two threads of the same process is faster.

–Communication is faster between threads because they are sharing memory,normally, kernel intervention is required for two processes to communicate.

Note: Thread synchronization is required when threads of a same process are sharingdata it is basically the same level of synchronization required for processes



data,it is basically the same level of synchronization required for processes.

Thread State Tree Thread State Tree (Functionality)(Functionality)

Process

Thread

Spawn Exit/Finish



Spawn

BlockUnblock

/ s

Spawning within a Thread

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Performance Benefits using a Performance Benefits using a ThreadThreadConsider a program makes two remote procedure calls to two different hosts:

RPC 1 RPC 2 Request

PROCESS

Server 1 Server 2

Request Request



RPC requests have to be processed sequentially in a single thread program model

Performance Benefits using a Performance Benefits using a ThreadThread

RPC 2 Request

PROCESS THREAD A

Server 1

Server 2q

PROCESS THREAD B



RPC 1 Request

RPC requests are interleaved using a multi thread program model

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Kernel Kernel vsvs User Level User Level ThreadsThreads

User Level

User Space

Kernel Space

Threads Library

Threads



P

User Level ThreadsUser Level Threads

Thread 1 Thread 2

Process A is executing its Thread 2

Ready Executing

Blocked

Ready Executing

Blocked

Read

Thread 1 Thread 2

Process A



Ready Executing

Blocked

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R d R dThread 1 Thread 2

Ready Executing

Blocked

Ready Executing

Blocked

Ready Executing

Process A



Blocked

Switch to another Process


R d R dThread 1 Thread 2

Ready Executing

Blocked

Ready Executing

Blocked

Ready Executing

Process A

Mean while the



Blocked

Mean while the event has occurred so it has been moved to the ready state.

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Th d 1 Th d 2

Thread 2 needs some thing from Thread 1 so it goes to block state .Thread 1 starts

execution

Ready Executing

Blocked

Ready Executing

Blocked

Thread 1 Thread 2

Process A



Ready Executing

Blocked Again its time of execution starts

Plus & Minus Plus & Minus of User Level Threadsof User Level Threads

Less overhead as switching takes place among the user level threads.

Suitable Scheduling scheme can be made application specific.

U l l th d (ULT ) / b f i d d t f k l l l tUser level threads (ULTs) can run on any o/s because of independent of kernel level support mechanism.

One of the short coming of ULTs is that most system calls are blocking, so when ever a system call is executed by a thread, not only the executing thread but all other threads will also be blocked.

In a ULTs scheme, a multi-threaded application cannot take advantage of multi-processing, a kernel assigns one process to only one processor at a time.



Ways to over come these disadvantages, in the first place applications should be developed as multi-processes rather than multi-threaded. One can also use jacketing (which basically converts a blocking system call to non blocking system call)

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Kernel Level ThreadsKernel Level Threads

User Level Th d

User Space

Kernel Space

Threads

Kernel Level Threads



P

Combined ApproachCombined ApproachUser Level

Threads

User SpaceKernel Space

Threads Library




PP

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Plus & MinusPlus & Minus

In a pure kernel level thread scheme all thread management is performed by the kernel. API inthe application space is linked to the kernel thread facility. W2K, Linux and O/S2 areexamples of such scheme.

All threads in an application are supported within a single process.

Context information is maintained by the kernel as a whole for process and individually forthreads.

Scheduling is performed on thread basis, so the ULTs drawbacks can be solved here as kernelcan simultaneously schedule threads on different processors.



Also, if one thread of a process is blocked it can schedule another thread of the same process.The disadvantage is that transfer of control from one thread to another thread within the sameprocess requires mode switching.

Process & Thread Process & Thread EquivalenceEquivalence

System Process: Thread

UNIX 1 : 1 Each thread is a unique process having itsown address space and

resources

Windows, Solaris 1 : M Threads can be created within the

OS/2, MACH processes having address space and dynamic resource ownership



Ra (Clouds), Emerald M : 1 In this case a thread can migrate from one process to another.

TRIX M : N Combination of M:1 & 1:M

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Computer System CategoriesComputer System Categories

1. SISD Single Instruction Single Data:g g

2. SIMD Single Instruction Multiple Data:

3. MISD Multiple Instruction Single Data:

4 MIMD Multiple Instruction Multiple Data:



4. MIMD Multiple Instruction Multiple Data:

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Symmetric ProcessingSymmetric Processing

Parallel Processing

SIMD MIMD

g

Shared Memory

Tightly Coupled

Loosely CoupledDistributed

Memory



Master-Slave SMP Clusters

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Symmetric Symmetric vsvsMaster/Slave ProcessingMaster/Slave Processing



SMP Conceptual ViewSMP Conceptual View

ProcessorProcessor

C hC h

ProcessorProcessor

C hC h

ProcessorProcessor

C hC hCacheCache CacheCache CacheCache

Main

Memory

Main

Memory

I/OI/O



MemoryMemoryI/OI/O

I/OI/O

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SMP Design ConsiderationSMP Design Consideration

• Simultaneous concurrent processes or threads• Simultaneous concurrent processes or threads.

• Scheduling

• Synchronization

• Memory Management

Reliabilit & Fa lt Tolerance



• Reliability & Fault Tolerance

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MicroMicro--kernelskernels

Question: How to qualify, meaning how small the core shouldbe to qualify for a micro kernel.



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Kernel ArchitecturesKernel Architectures

ss ryry rsrs rr

Process ManagementProcess Management

Virtual MemoryVirtual Memory

I/O ManagementI/O Management

Inter Process Com.Inter Process Com.

File SystemFile System

ApplicationsApplications

Clie

nt P

roce

ssC

lient

Pro

cess

Virt

ual M

emor

Virt

ual M

emor

Dev

ice

Driv

erD

evic

e D

river

File

Ser

ver

File

Ser

ver

Proc

ess S

erve

Proc

ess S

erve

Micro KernelMicro Kernel

Ker

nel

Mod

e

Kernel Mode

Use

r M

odeUser Mode



HardwareHardware HardwareHardware

Microkernel Advantages Microkernel Advantages

Uniform InterfaceUniform Interface

Extensibility

Flexibility

Portability

Reliability

Distributed System Support



y pp

Object Oriented Operating System (OOOS)

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Windows 2000 Thread & Windows 2000 Thread & SMPSMP

Processes implemented on different operating systems maydiffer in many ways ?differ in many ways ?

• Characteristics ofW2K Processes

Processes are implemented as objects

Process may have one or more threads

P d th d h b ilt i bilit f h i ti



Processes and threads have built in capability for synchronization

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W2K Process & ResourcesW2K Process & Resources

Access Token

Object Table

Handle 1

Process

Thread x

Virtual Address Space

Available Objects



Handle 2

Handle 3

File y

Section z

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Windows 2000 Process & Thread ObjectsWindows 2000 Process & Thread Objects

ibut

es Process ID

Security Descriptor

Base Priority

Process

bute

s Process ID

Thread Context

Dynamic Priority

Threades

Obj

ect B

ody

Attr Default Processor affinity

Quota Limits

Execution Time

I/O Counters

VM Operational Counters

Exception Debugging Port

Exit Status

Create Process

Open Process

Query Process Information

Set Process Information

C P sO

bjec

t Bod

y A

ttrib

Base Priority

Thread Processor affinity

Thread Execution Time

Alert Status

Suspension Count

Impersonation Token

Termination Port

Thread Exit Status

Create Thread

Open Thread

Query Thread Information

S Th d I f i



Serv

ice Current Process

Terminate Process

Allocate Virtual Memory

Read/Write Virtual Memory

Protect Virtual Memory

Lock/Unlock virtual Memory

Query Virtual Memory

Flush Virtual Memory

Serv

ices Set Thread Information

Current Thread

Terminate Thread

Get Context

Set Context

Resume

Alert Thread

Test Thread Alert

Register Termination Port

W2K Processes StatesW2K Processes States

Standby Executing Terminated

Initialized

Ready Waiting

Initialize



TransitionPaged Out

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W2K Thread StatesW2K Thread StatesRunable

Pick to Run SwitchStandby

Resource Unblock (Resource Available) Block Terminate

Available

PreemptedReady Executing



Available

Unblock (Resource Not Available)

Not Runable

TransitionWaiting

Terminated

LINUX Process / Thread LINUX Process / Thread ModelModel



Hardware Condition

I/O Operation, Signal from another Process or Resource not available

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SOLARIS Thread StatesSOLARIS Thread States



Process & Threads in Process & Threads in SOLARISSOLARIS



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Solaris MultiSolaris Multi--threaded threaded ArchitectureArchitecture

Process 1 Process 2 Process 3 Process 4

Kernel Space

User Space

LWP LWPLWPLWPLWPLWPLWPLWP

Threads LibraryThreads LibraryThreads LibraryThreads Library



P


P P P P

Process Image for Process Image for referencereference



Thread Model Concept

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