Implementing Processes, Threads, and Resources

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Copyright © 2004 Pearson Education, Inc. Operating Systems: A Modern Perspective, Chapter 6

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ImplementingProcesses, Threads,

and Resources

6

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OS AddressSpace

Implementing the Process Abstraction

ControlUnit

OS interface

…

Mac

hine

Exe

cuta

ble

Mem

ory

ALU

CPUPi Address

Space

Pi CPU

Pi ExecutableMemory

Pk AddressSpace

…

Pk CPU

Pk ExecutableMemory

Pj AddressSpace

Pj CPU

Pj ExecutableMemory

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External View of the Process Manager

Hardware

ApplicationProgram

Dev

ice

Mgr

Proc

ess M

gr

Mem

ory

Mgr

File

Mgr

UNIXD

evic

e M

gr

Proc

ess M

gr

Mem

ory

Mgr

File

Mgr

Windows

CreateThread()CreateProcess()CloseHandle()

WaitForSingleObject()

fork()

exec()wait()

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Process Manager Responsibilities• Define & implement the essential characteristics of a

process and thread– Algorithms to define the behavior– Data structures to preserve the state of the execution

• Define what “things” threads in the process can reference – the address space (most of the “things” are memory locations)

• Manage the resources used by the processes/threads• Tools to create/destroy/manipulate processes & threads• Tools to time-multiplex the CPU – Scheduling the

(Chapter 7)• Tools to allow threads to synchronization the operation

with one another (Chapters 8-9)• Mechanisms to handle deadlock (Chapter 10)• Mechanisms to handle protection (Chapter 14)

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Modern Processes and Threads

OS interface

…

…

…Pi CPU

Thrdj in Pi Thrdk in Pi

…

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Processes &Threads

Add

ress

Spa

ce

Map

Stac

k

State

Prog

ram

Stat

ic d

ata

Res

ourc

es

Stac

k

State

Map

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The Address Space

Process

AddressSpace

AddressBinding

ExecutableMemory

Other objects

Files

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Building the Address Space

• Some parts are built into the environment– Files– System services

• Some parts are imported at runtime– Mailboxes– Network connections

• Memory addresses are created at compile (and run) time

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Tracing the Hardware Process

BootstapLoader

ProcessManager

InterruptHandler P1 P,2 Pn

…

Machine isPowered up

InitializationLoad the kernel

Service an interrupt

Har

dwar

e pr

oces

s pro

gres

s

Execute a threadSchedule

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The Abstract Machine Interface

User ModeInstructions

Application Program

User ModeInstructions

Abstract Machine Instructions

TrapInstruction

Supervisor ModeInstructions

fork()

create()open()

OS

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Context Switching

ProcessManager

InterruptHandler

P1

P2

Pn

Executable Memory

Initialization1

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45

7Interrupt

8

9

6

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Process Descriptors• OS creates/manages process abstraction• Descriptor is data structure for each process

– Register values– Logical state– Type & location of resources it holds– List of resources it needs– Security keys– etc. (see Table 6.1 and the source code of your

favorite OS)

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Creating a Process in UNIX

pid = fork();

UNIX kernel

…

Process Table

Process Descriptor

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Simple State Diagram

ReadyBlocked

Running

Start

Schedule

Request

Done

Request

Allocate

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UNIX State Transition Diagram

Runnable

UninterruptibleSleep

Running

Start

Schedule

Request

Done

I/O RequestAllocate

zombie

Wait byparent

Sleeping

Traced or Stopped

Request

I/O Complete Resume

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Windows NT Thread States

Initialized

CreateThread

Ready

Activate

Sele

ct

Standby

Running

Terminated

Waiting

Transition

Reinitialize

Exit

Pree

mpt

Dispatch

WaitWait Complete

Wait Complete

Dispatch

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Resources

R = {Rj | 0 j < m} = resource typesC = {cj 0 | RjR (0 j < m)} = units of Rj available

Reusable resource: After a unit of the resource has been allocated, it must ultimately be released back to the system. E.g., CPU, primary memory, disk space, … The maximum value for cj is the number of units of that resourceConsumable resource: There is no need to release a resource after it has been acquired. E.g., a message, input data, … Notice that cj is unbounded.

Resource: Anything that a process can request, then be blocked because that thing is not available.

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Using the Model• There is a resource manager, Mgr(Rj) for every Rj

Mgr(Rj)Process

pi can only request ni cj units of reusable Rj

pi can request unbounded # of units of consumable Rj

• Process pi can request units of Rj if it is currently running

request

•Mgr(Rj) can allocate units of Rj to pi

allocate

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A Generic Resource Manager

Process

Resource Manager

ProcessProcessProcess

Blocked Processes

Resource Pool

request()

release()

Policy

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Process Hierarchies• Parent-child relationship may be significant:

parent controls children’s execution

Ready-Active

Blocked-Active

Running

StartSchedule

RequestDone

Request

AllocateReady-Suspended

Blocked-Suspended

SuspendYield

AllocateSuspend

Suspend

Activate

Activate

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Process Manager Overview

Program Process

Abstract Computing Environment

FileManager

MemoryManager

DeviceManager

ProtectionDeadlock

Synchronization

ProcessDescription

CPU Other H/W

SchedulerResourceManagerResourceManagerResourceManager

MemoryDevices

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UNIX Organization

System Call Interface

FileManager

MemoryManager

DeviceManager

ProtectionDeadlock

Synchronization

ProcessDescription

CPU Other H/W

SchedulerResourceManagerResourceManagerResourceManager

MemoryDevices

Libraries ProcessProcess

Process

Monolithic Kernel

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Windows NT Organization

Processor(s) Main Memory Devices

Libraries

ProcessProcess

Process

SubsystemUser

Subsystem Subsystem

Hardware Abstraction LayerNT Kernel

NT ExecutiveI/O Subsystem

TT

TT

TT T T

T

Implementing Processes, Threads, and Resources

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