Transcript Introduction to Operating Systems

Introduction to Operating Systems
CS-2301, System Programming
for Non-Majors
(Slides include materials from The C Programming Language, 2nd edition, by Kernighan and Ritchie and
from C: How to Program, 5th and 6th editions, by Deitel and Deitel)
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Introduction to Operating
Systems
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Why an Intro to Operating Systems?
• This is a System Programming Course
• For people who are not CS majors
• (Nearly) every programming task in reallife includes working with an OS
• Inevitably will have to deal with principle
OS features
• Even if not knowledgeable in their designs
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Class Discussion
What is an Operating System?
(Laptops closed, please!)
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Introduction to Operating
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What Operating Systems
have you Used?
(Other than Windows, Linux,
Mac-OS, Unix)
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What is an Operating System?
• Characteristics
• Functions
– Large, complex set of
programs
– Long-lived, evolving
– Worked on by many
people for many years
CS-2301, B-Term 2009
Introduction to Operating
Systems
– Creates abstractions
– Multiplexes concurrent
activities
– Manages resources
– Mediates access to
hardware devices
– Provides a variety of
services to users and
applications
– …
5
Definition – Abstraction
• The distillation of a complex mechanism
into a simple, conceptual model
• User of abstraction does not need to worry
about details
• Implementer of abstraction does not need to
worry about how user will use it
• within limits
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Systems
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What is an Operating System?
• Characteristics
• Functions
– Large, complex set of
programs
– Long-lived, evolving
– Worked on by many
people for many years
CS-2301, B-Term 2009
Introduction to Operating
Systems
– Creates abstractions
– Multiplexes concurrent
activities
– Manages resources
– Mediates access to
hardware devices
– Provides a variety of
services to users and
applications
– …
7
Operating Systems
• Typically
–
–
–
–
Long-lived
Frequently extended and updated
Worked on by many developers
Used and, maybe, abused by a variety of users with
varying expertise and expectations
• Essential to create an acceptable computing
environment to create and execute other programs
that achieve business or personal goals
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Systems
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Kinds of operating systems
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Mainframe Operating Systems
Server Operating Systems
Multiprocessor Operating Systems
Personal Computer Operating Systems
Mobile Phone Operating Systems
Handheld Computer Operating Systems
Embedded Operating Systems
Sensor Node Operating Systems
Real-time Operating Systems
Smart-card Operating Systems
…
CS-2301, B-Term 2009
Introduction to Operating
Systems
E.g.:– Windows
Linux
Unix
Important new category
9
Some operating systems you may
(or may not) have heard about
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•
•
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•
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•
•
z/OS
VMS/Open VMS
VxWorks
RT Linux
QNX Neutrino
eCOS
BrickOS/LeJos
TinyOS
Arduino
…
CS-2301, B-Term 2009
•
•
•
•
•
•
•
iPhone OS
Android
Symbian
Blackberry OS
PalmOS/Garnet
Windows Mobile
…
Introduction to Operating
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OS and Hardware
• OS mediates programs’ access to hardware
– Computation – CPU
– Storage – volatile (memory) and persistent
(disk)
– Networks – NIC, protocols
– I/O devices – sound cards, keyboards, displays
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Four Fundamental Abstractions
• Processes & threads
• Multiplexing of processor(s) to create the illusion of
many of them
• Virtual memory
• Multiplexing of physical memory and disk blocks to
create illusion of own memory per process
• Files – i.e., persistent storage
• Organizing principles about long-term data storage
• Sockets & Connections
• Organizing principles about network communication
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Systems
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Four Fundamental Abstractions
• Processes & threads
• Multiplexing of processor(s) to create the illusion of
many of them
• Virtual memory
• Multiplexing of physical memory and disk blocks to
create illusion of own memory per process
• Files – i.e., persistent storage
• Organizing principles about long-term data storage
• Sockets & Connections
• Organizing principles about network communication
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Systems
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Definition – Process
• A particular execution of a program
• Different from all other executions of that program
• Different from executions of other programs
• The OS uses one or more CPUs to make it
seem like each process has its own CPU
• Can execute at same time!
• Uses interrupts to manage and enforce multiplexing
of CPU
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Definition – Interrupt
• A mechanism by which the processor
suspends execution of the current, running
program and gives control to the OS
• OS saves the state of the interrupted
program so that it can be restarted later
• OS then takes appropriate action
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Why Processes?
• Enables programmers
– to completely disengage from issues of
concurrent execution of independent programs
– to build applications with more than one
concurrent activity
• Enables independent applications to share a
computing system
– Safely!
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Why Processes (continued)?
• Exploit modern processors
– Capable of executing multiple, simultaneous,
program executions
– Interleaved at instruction level or even memory
access level
• Moore’s Law:–
– Integrated circuit components shrink in size by
50% every 18 months
– Double in speed every 18 months
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Resources Assigned to a Process
• Memory
• Virtual or real
• Processor time
• Priorities
• Deadlines for real-time activities
• Privileges
• Security, authentication, etc.
• Files and file space
• For long-term storage, temporary storage
• Devices
• For input and output activity, sensors, etc.
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Resources (continued)
• Managed by OS
• Protection and isolation from other
processes
• Allocation according to defined policies
• Enforcement of limits, etc.
• …
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Shell / Command Prompt
• Linux Shell is a process
• Windows Command Prompt is a process
• Created when
• you log on or connect to system (e.g., via PuTTY)
• Open Command Prompt, konsole, xterm , etc., window
–
–
–
–
Reads what you type (and displays it in your window)
Interprets lines as commands and arguments
Creates a process for each command, passes args
(Typically) waits for process to complete before
interpreting next line
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Window Manager
• Window Manager is a process
• Tracks mouse movements, key clicks, menu actions
• “Open” an application means …
• Create process for that application; give it a window
• “Open” a document means …
• If application is not open, create process for it
• Pass document as argument to application
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Creating and Deleting Processes
A process is created …
– … at system boot time
• The first process
• Built-in processes – e.g., in embedded systems
OR
– … by another process
• Possibly in response to an action by a (human) user
A process is deleted …
– When its program exits
– By another process – killed or paused (by debugger)
– When system crashes or shuts down
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Questions about Processes?
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Systems
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Four Fundamental Abstractions
• Processes & threads
• Multiplexing of processor(s) to create the illusion of
many of them
• Virtual memory
• Multiplexing of physical memory and disk blocks to
create illusion of separate memory per process
• Files – i.e., persistent storage
• Organizing principles about long-term data storage
• Sockets & Connections
• Organizing principles about network communication
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Systems
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Virtual Memory
• Definition:– the illusion that a process has
its own, independent memory
• (Often) more memory than machine has installed
• May be implemented using interrupts,
pages, and disk blocks
• Swapping fast enough so process is unaware
• May be implemented by partitioning
• Swapping not necessary for real-time activities
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Independence of Virtual Memories
• A process cannot even see the virtual memory of
another process
• A process cannot even see the memory used by the
OS
• I.e., no possible pointer value can point to
something in a different virtual memory
• Separate, parallel universes
• Except where explicitly linked together
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Typical Virtual Memory for Process
(Windows & Linux)
0xFFFFFFFF
stack
(dynamically allocated)
SP
address space
heap
(dynamically allocated)
static data
0x00000000
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program code
(text)
Introduction to Operating
Systems
PC
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Typical Virtual Memory for Process
(Windows & Linux)
0xFFFFFFFF
stack
(dynamically allocated)
SP
address space
heap
(dynamically allocated)
static data
0x00000000
CS-2301, B-Term 2009
program code
(text)
Introduction to Operating
Systems
PC
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Virtual Memory (continued)
• Typical virtual memory size – 4 GBytes
• Per process — even in a 1 GByte computer!
• “Inactive” pages are not resident in RAM
• Reference results in interrupt called a page fault
• OS brings in page from disk, (maybe) swaps one out
• Unused pages not filled in by OS
• Dereferencing pointer results in Segmentation Fault
• New pages created by OS as needed
• When stack or heap grows or programs are loaded
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Virtual Memory in Embedded Systems
• Implemented by partitioning RAM
• No swapping in or out
• May not even have a disk!
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Introduction to Operating
Systems
Also in smart-phone
operating systems
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Virtual Memories in Embedded System
0x0000FFFF
stack
Process 3
stack
Physical
Process 2
memory
stack
Process 1
OS Kernel
0x00000000
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Systems
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Questions about Processes
or Virtual Memory?
Not in Kernighan & Ritchie
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Systems
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Threads
• A refinement of concept of process
• Short for “thread of control”
• Concurrent execution of a function within
the context of a process
• Needs own stack in order to call other functions
• Shares heap, static data, and code with other threads
of same process
• Reason
• Application may need to manage concurrency of its
own computation with external events
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Systems
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Virtual Memory for Multiple Threads
0xFFFFFFFF
thread 1 stack
SP (T1)
thread 2 stack
SP (T2)
thread 3 stack
SP (T3)
Virtual
address space
heap
static data
0x00000000
CS-2301, B-Term 2009
PC (T2)
PC (T1)
PC (T3)
code
(text)
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Systems
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Why Threads?
• To enable development of applications with
concurrent activities inside them
• Need to share data (difficult with separate processes)
• Examples
•
•
•
•
•
Web server over common data pages
Transaction processor over common data base
Applications within a mobile phone or PDA
Applications with different speeds of devices
…
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Systems
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Thread Interface – POSIX standard
#include <pthread.h>
• int pthread_create(pthread_t *thread, const
pthread_attr_t *attr, void*(*start_routine) (void),
void *arg)
– creates a new thread of control
– new thread begins executing at start_routine
• pthread_exit(void *value_ptr)
– terminates the calling thread
• pthread_join(pthread_t thread, void **value_ptr)
– blocks the calling thread until the thread specified terminates
• pthread_t pthread_self()
– Returns the calling thread's identifier
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Systems
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Thread Interface – POSIX standard
#include <pthread.h>
• int pthread_create(pthread_t *thread, const
pthread_attr_t *attr, void*(*start_routine) (void),
void *arg)
– creates a new thread of control
– new thread begins executing at start_routine
• pthread_exit(void *value_ptr)
– terminates the calling thread
• pthread_join(pthread_t thread, void **value_ptr)
– blocks the calling thread until the thread specified terminates
• pthread_t pthread_self()
– Returns the calling thread's identifier
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Thread Interface – POSIX standard
#include <pthread.h>
• int pthread_create(pthread_t *thread, const
pthread_attr_t *attr, void*(*start_routine) (void),
void *arg)
– creates a new thread of control
– new thread begins executing at start_routine
• pthread_exit(void *value_ptr)
– terminates the calling thread
• pthread_join(pthread_t thread, void **value_ptr)
– blocks the calling thread until the thread specified terminates
• pthread_t pthread_self()
– Returns the calling thread's identifier
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Systems
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Thread Example
pthread_create(tp, &f, &args)
f
main function
g
main function
f
h
main function
f
pthread_join(tp)
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Systems
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Thread Example
pthread_create(tp, &f, &args)
Two threads run
at the same time
f
main function
g
main function
f
h
main function
f
pthread_join(tp)
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Systems
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Why Threads?
• To enable development of applications with
concurrent activities inside them
• Need to share data (difficult with separate virtual
memories)
• Examples
•
•
•
•
•
Web server over common data pages
Transaction processor over common data base
Applications within a mobile phone or PDA
Applications with different speeds of devices
…
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Systems
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Example Thread Application
• One or more threads to get data from sensor
• 1000 times per second; cannot afford to miss a
reading
• Places data on queue
• Another thread processes and displays data
• Removes and processes each data item from queue
• Displays system state on control panel
• User thread
• Allows operator to adjust system parameters
• While other threads are still running
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Additional Functions & Data Required
• pthread_mutex_t — mutual exclusion lock
– Enables a thread to “lock” some data so that
other threads do not touch in mid-operation
• pthread_cond_t — condition variable
– Enables a thread to wait for an event to happen
– Signaled by another thread
• See man pages for details
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Questions about Threads?
Not in Kernighan & Ritchie
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Systems
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Four fundamental Abstractions
• Processes & threads
• Multiplexing of processor(s) to create the illusion of
many of them
• Virtual memory
• Multiplexing of physical memory and disk blocks to
create illusion of own memory per process
• Files & persistent storage
• Organizing principles about long-term data storage
• Sockets & connections
• Organizing principles about network communication
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Introduction to Operating
Systems
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Definition – File
• A (potentially) large amount of information or data
that lives a (potentially) very long time
• Often much larger than the memory of the computer
• Often much longer than any computation
• Sometimes longer than life of machine itself
• (Usually) organized as a linear array of bytes or
blocks
• Internal structure is imposed by application
• (Occasionally) blocks may be variable length
• (Often) requiring concurrent access by multiple
threads or processes
• Even by processes on different machines!
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Systems
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Implementations of Files
• Usually on disks (or devices that mimic disks)
• Magnetic – hard drive or floppy
• Optical – CD, DVD
• Flash drives – electronic memory, organized as disks
• Requirement
• Preserve data contents during power-off or disasters
• Directory / Folder
• Special kind of file that contains links pointing to other files
• Associates names with files
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Implementations of Files
• Usually on disks (or devices that mimic disks)
• Magnetic – hard drive or floppy
• Optical – CD, DVD
• Flash drives – electronic memory, organized as disks
• Requirement
• Preserve data contents during power-off or disasters
• Directory / Folder
• Special kind of file that contains links pointing to other files
• Associates names with files
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File Access in C
• See Kernighan & Ritchie, Chapter 8
• Raw file access
• Without simplifying stream functions – e.g.,
– scanf, fscanf, printf, fprintf, fgetc, etc.
• read and write raw disk blocks
• Seek to a file position
– lseek, fseek — sets file pointer to specified
location
– Subsequent read, write, etc., start there
– ftell – returns file pointer
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Organizations of Files
• Contiguous
• Blocks stored contiguously on storage medium
• E.g., CD, DVD, some large database systems
• Access time to any block is O(1)
• Linked
• Blocks linked together – File Allocation Table (FAT)
• Access time is O(n)
• Indexed
• Blocks accessed via tree of index blocks (i-nodes)
• Access time is O(log n)
• However, base of logarithm may be very large (>100)
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Systems
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Organizations of Files
• Contiguous
• Blocks stored contiguously on storage medium
• E.g., CD, DVD, some large database systems
• Access time to any block is O(1)
• Linked
• Blocks linked together – File Allocation Table (FAT)
• Access time is O(n)
• Indexed
• Blocks accessed via tree of index blocks (i-nodes)
• Access time is O(log n)
• However, base of logarithm may be very large (>100)
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Systems
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Organizations of Files
• Contiguous
• Blocks stored contiguously on storage medium
• E.g., CD, DVD, some large database systems
• Access time to any block is O(1)
• Linked
• Blocks linked together – File Allocation Table (FAT)
• Access time is O(n)
• Indexed
• Blocks accessed via tree of index blocks (i-nodes)
• Access time is O(log n)
• However, base of logarithm may be very large (>100)
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Systems
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Questions about Files?
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Systems
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Four fundamental Abstractions
• Processes & threads
• Multiplexing of processor(s) to create the illusion of
many of them
• Virtual memory
• Multiplexing of physical memory and disk blocks to
create illusion of own memory per process
• Files & persistent storage
• Organizing principles about long-term data storage
• Sockets & connections
• Organizing principles about network communication
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Systems
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Sockets and Connections
• Connection:
– a serial conversation over a network between two end
points
• e.g., processes, threads, tasks on different computers
– organized as a sequence of messages or datagrams
– distinct from all other connections
• Socket:
– An end point of a connection
– An abstraction that allows a process to send or receive
only the information of that connection
– Multiplexed on network with all other connections
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Sockets and Connections
• Defer to another course
– CS-4513, Distributed Systems
– CS-4514, Computer Networks
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General Questions?
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