Implementing Processes, Threads, and Resources

Operating Systems: A Modern Perspective, Chapter 6

Slide 6-1

Copyright © 2004 Pearson Education, Inc.

ImplementingProcesses, Threads,

and Resources


Slide 6-2


OS AddressSpace

OS AddressSpace

Implementing the Process Abstraction

ControlUnit

OS interface

…

Mac

hine

Exe

cuta

ble

Mem

ory

ALU

CPUPi Address

Space

Pi AddressSpace

Pi CPU

Pi ExecutableMemory

Pi ExecutableMemory

Pk AddressSpace

Pk AddressSpace

…

Pk CPU

Pk ExecutableMemory

Pk ExecutableMemory

Pj AddressSpace

Pj AddressSpace

Pj CPU

Pj ExecutableMemory

Pj ExecutableMemory

Ideal Abstraction:As if using anActual machine


Slide 6-3


Modern process

“The value of the modern process model is that it enables the programmer to design software so that various parts of the computation can work together as a set of threads within a single modern process framework.”

Classic process can work together but they do not share a customized computational framework


Slide 6-4


External View of the Process Manager

Hardware

ApplicationProgram

ApplicationProgram

Dev

ice

Mgr

Pro

cess

Mgr

Mem

ory

Mgr

Fil

e M

gr

UNIXD

evic

e M

gr

Pro

cess

Mgr

Mem

ory

Mgr

Fil

e M

gr

Windows

CreateThread()CreateProcess()CloseHandle()

WaitForSingleObject()

fork()

exec()wait()


Slide 6-5


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)


Slide 6-6


Modern Processes and Threads

OS interface

…

…

…Pi CPU

Thrdj in Pi Thrdk in Pi

…


Slide 6-7


Modern Threads

User Space Threads - underlying Os implements classic processes and the user space thread library executes on top of the OS abstract machine to multiprogram the threads. (Mach C and POSIX threads)

Kernel Threads - OS time-multiplexes the execution of threads instead of processes. Therefore when one thread blocks the other threads can still execute. (Windows)


Slide 6-8


Resources

Any element of the abstract machine that a process can request and can cause the process to be blocked if not available.

If device is allocated to a process then it is configured into the abstract machine for process

Multiple resource managers - hardware devices, processor, abstract synch resources, primary memory, and files

Each resource manager must present a common behavior described by a general model


Slide 6-9


Processes &Threads

Add

ress

Spa

ceA

ddre

ss S

pace

MapMap

Sta

ck

State

Pro

gram

Sta

tic d

ata

Res

ourc

es

Sta

ck

State

MapMap


Slide 6-10


The Address Space

ProcessProcess

AddressSpace

AddressBinding

ExecutableMemory

Other objects

Files


Slide 6-11


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


Slide 6-12


The OS

• Abstract machine interface– Host hardware instruction set and set of

functions exported by OS

• Unix and Windows most widely used

• Unix - POSIX interface (standard)


Slide 6-13


Modern Process Framework

• Thread-based computation is executed within this framework

• Modern Process structure– Address space– Program– Data - shared by threads– Resources

• Threads share the resources that have been allocated to the process

– Process Id


Slide 6-14


Threads

• Active Element

• Threads– Host process environment– Thread-specific data (at least a stack)– Thread ID


Slide 6-15


Tracing the Hardware Process

Bootstap

LoaderProcessManager

InterruptHandler P1 P,2 Pn

…

Machine isPowered up

InitializationLoad the kernel

Service an interrupt

Har

dwar

e pr

oces

s pr

ogre

ss

Execute a thread

Schedule


Slide 6-16


The Abstract Machine Interface

User ModeInstructions


Application Program


Abstract Machine Instructions

TrapInstruction

Supervisor ModeInstructions

Supervisor ModeInstructions

fork()

create()open()

OS


Slide 6-17


Abstract Machine Instruction SetALU - load, store, add…Control Unit - branch, procedure_call…Trap - create_process(), open_file()…

Linux 2.4x - exports over 200 functions- 2.5 million lines of code

Windows NT/2000/XP- exports over 2,000 functions- over 25 million lines of code


Slide 6-18


Context Switching

ProcessManager

InterruptHandler

P1

P2

Pn

Executable Memory

Initialization1

23

45

7Interrupt

8

9

6


Slide 6-19


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– Process ID, parent process


Slide 6-20


Creating a Process in UNIX

pid = fork();

UNIX kernelUNIX kernel

…

Process Table

Process Descriptor


Slide 6-21


Linux Process Descriptor


Slide 6-22




Slide 6-23




Slide 6-24


EPROCESS

…void *UniqueProcessId;…

NT Executive

Windows NT Process Descriptor

KPROCESS…uint32 KernelTime;uint32 UserTime;…Byte state;

NT Kernel

NT Kernel handles object management, interrupt handing, thread scheduling

NT Executive handles all other aspect of a process


Slide 6-25


Windows NT Process Descriptor (2)

Kernel process object includes: Pointer to the page directory Kernel & user time Process base priority Process state List of the Kernel thread descriptors that are

using this process


Slide 6-26


Windows NT Process Descriptor (3)

Parent identification Exit status Creation and termination times. Memory status Security information executable image Process priority class used by the thread scheduler. A list of handles used by this process A pointer to Win32-specific information


Slide 6-27


ETHREAD

Windows NT Thread Descriptor

EPROCESS

KPROCESS

NT KernelKTHREAD

NT Executive


Slide 6-28


Creating a Process in NT

CreateProcess(…);

Win32 SubsystemWin32 Subsystem

ntCreateProcess(…);…ntCreateThread(…);

NT ExecutiveNT Executive

NT KernelNT Kernel…

Handle Table

Process Descriptor


Slide 6-29


Windows NT Handles

Application

KernelObject

Executive Object

User Space

Supervisor Space

NT Executive

NT Kernel

Handle


Slide 6-30


Thread AbstractionProcess Manager has algorithms to control threads and thread descriptor (data structure) to keep track of threads.

Management Tasks- Create/destroy thread- Allocate thread-specific resources- Manage thread context switching

Thread Descriptor- state- execution stats- process (reference to associated process)- list of related threads- stack (reference to stack)- thread-specific resources


Slide 6-31


State of a Process/Thread

State Variable - summary status of the process/thread which is located in descriptor

ReadyBlocked

Running

Start

Schedule

Request

Done

Request

Allocate

Simple State Diagram


Slide 6-32


UNIX State Transition Diagram

Runnable

UninterruptibleSleep

Running

Start

Schedule

Request

Done

I/O Request

Allocate

zombie

Wait byparent

Sleeping

Traced or Stopped

Request

I/O Complete Resume


Slide 6-33


Windows NT Thread States

Initialized

CreateThread

Ready

Activate

Sele

ct

Standby

Running

Terminated

Waiting

Transition

Reinitialize

Exit

Pre

empt

Dispatch

WaitWait Complete

Wait Complete

Dispatch


Slide 6-34


Resources

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

Resource Descriptors- Internal resource name- Total Units- Available Units- List of available units- List of Blocked processes


Slide 6-35


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 resource

Consumable 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.


Slide 6-36


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

Mgr(Rj)ProcessProcess

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


Slide 6-37


A Generic Resource Manager

ProcessProcess

Resource Manager

ProcessProcessProcessProcessProcessProcess

Blocked Processes

Resource Pool

request()

release()

Policy


Slide 6-38


Process Hierarchies

Initial Process

System Process

System Process

Other Processes


Slide 6-39


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


Slide 6-40


Process Manager Overview

ProgramProgram ProcessProcess

Abstract Computing Environment

FileManager

MemoryManager

DeviceManager

ProtectionProtectionDeadlockDeadlock

SynchronizationSynchronization

ProcessDescription

ProcessDescription

CPUCPU Other H/WOther H/W

SchedulerScheduler ResourceManager

ResourceManagerResource

Manager


Manager

ResourceManager

MemoryMemoryDevicesDevices


Slide 6-41


UNIX Organization

System Call InterfaceSystem Call Interface

FileManager

MemoryManager

DeviceManager

ProtectionProtectionDeadlockDeadlock

SynchronizationSynchronization

ProcessDescription

ProcessDescription

CPUCPU Other H/WOther H/W

SchedulerScheduler ResourceManager


Manager


Manager

ResourceManager

MemoryMemoryDevicesDevices

LibrariesLibraries ProcessProcess

ProcessProcess

ProcessProcess

Monolithic Kernel


Slide 6-42


Windows NT Organization

Processor(s) Main Memory Devices

LibrariesLibraries

ProcessProcess

ProcessProcess

ProcessProcess

SubsystemSubsystemUser

SubsystemSubsystem SubsystemSubsystem

Hardware Abstraction LayerHardware Abstraction LayerNT Kernel

NT ExecutiveI/O SubsystemI/O Subsystem

TT

TT

TT T T

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Implementing Processes, Threads, and Resources

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