Passing of Parameters As A Table

1
Passing of Parameters As A Table
2
System Call Memory Map
3
Types of System Calls

• Process control
• File management
• Device management
• Information maintenance
• Communications

4
Types of System Calls

• Process control
• Call Description
• pidfork() Create a child process
  identical to parent
• pidwaitpid(pid, statloc, options) Wait for
  child to terminate
• sexecve(name, argv, environp) Replace a
  process core image
• exit(status) Terminate proc execution
  return status

5
Types of System Calls

• File Management
• Call Description
• fdopen(file, .) Open file for read,
  write, or both
• sclose(fd) Close an open file
• nread(fd, buf, nbytes) Read
  data from file to buffer
• nwrite(fd, buf, nbytes) Write
  data from buffer to file
• poslseek(fd, offset, whence) Move
  file pointer to .
• sstat(name, buf) Write data
  from buffer to file

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Types of System Calls

• Directory and File System Management
• Call Description
• smkdir(name, mode) Create a new
  directory
• srmdir(name, mode) Remove an empty
  directory
• slink(name1, name2) Create new
  entry name2, pointing to name1
• sunlink(name)
  Remove a directory entry
• smount(special, name, flag) Mount a
  file system
• sumount(special)
  Unmount a file system

7
UNIX vs Win System Calls

• UNIX
• - One-to-one relationship between system calls
  (e.g., read)
• and library procedures (e.g., read) to invoke
  system calls.
• i.e., for each syscall ? roughly one library
  procedure that is
• called to execute it.
• Windows
• - radically different.
• - library calls and syscalls are highly
  decoupled.
• - Win32 API defined for programmers to use to
  get OS services.
• - Supported on all versions of Windows since
  Win95.
• - Difficult to distinguish kernel syscall and
  user(-space) library
• calls

8
UNIX vs Win System Calls
9
MS-DOS Execution
At System Start-up
Running a Program
10
UNIX Running Multiple Programs
11
Communication Models

• Communication may take place using either message
  passing or shared memory.

Shared Memory
Msg Passing
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System Programs

• provide a convenient environment for program
  development and execution. The can be divided
  into
• File manipulation
• Status information
• File modification
• Programming language support
• Program loading and execution
• Communications
• Application programs
• Most users view of the operation system is
  defined by system programs, not the actual system
  calls.

13
MS-DOS System Structure

• MS-DOS written to provide the most
  functionality in the least space
• not divided into modules
• Although MS-DOS has some structure, its
  interfaces and levels of functionality are not
  well-separated

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MS-DOS Layer Structure
15
UNIX System Structure

• UNIX
• limited by hardware functionality
• - the original UNIX operating system had
  limited
• structuring.
• - the UNIX OS consists of two separable parts.
• ? Systems programs

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UNIX System Structure

• ? The kernel
• Consists of everything below the system-call
  interface and above the physical hardware
• Provides the file system, CPU scheduling, memory
  management, and other operating-system functions
  a large number of functions for one level.

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UNIX System Structure
18
Layered Approach

• the OS is divided into a number of layers
  (levels), each built on top of lower layers.
• - the bottom layer (layer 0) is the hardware
• - the highest (layer N) is the user interface.
• With modularity, layers are selected such that
  each uses functions (operations) and services of
  only lower-level layers.

19
An Operating System Layer
20
OS/2 Layer Structure
21
Microkernel System Structure

• Moves as much from the kernel into user space.
• Communication takes place between user modules
  using message passing.
• Benefits
• - easier to extend a microkernel
• - easier to port the operating system to new
  architectures
• - more reliable (less code is running in kernel
  mode)
• - more secure

22
Windows NT Client-Server Structure
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Virtual Machines

• A virtual machine takes the layered approach to
  its logical conclusion.
• It treats hardware and the operating system
  kernel as though they were all hardware.
• It provides an interface identical to the
  underlying bare hardware.
• The OS creates the illusion of multiple
  processes, each executing on its own processor
  with its own (virtual) memory.

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Virtual Machines (Cont.)

• The resources of the physical computer are shared
  to create the virtual machines.
• CPU scheduling can create the appearance that
  users have their own processor.
• Spooling and a file system can provide virtual
  card readers and virtual line printers.
• A normal user time-sharing terminal serves as the
  virtual machine operators console.

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System Models
Non-virtual Machine
Virtual Machine
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VM Advantages/Disadvantages

• provides complete protection of system resources
  since each VM is isolated from all other VMs.
• ? isolation permits no direct sharing of
  resources.
• perfect vehicle for OS RD. System development
  is done on the VM, instead of on a physical
  machine
• ? does not disrupt normal system operation.

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VM Advantages/Disadvantages

• VM concept is difficult to implement due to the
  effort required to provide an exact duplicate to
  the underlying machine.

28
Java Virtual Machine

• Compiled Java programs are platform-neutral
  bytecodes executed by a Java Virtual Machine
  (JVM).
• JVM consists of
• - class loader
• - class verifier
• - runtime interpreter
• Just-In-Time (JIT) compilers increase performance

29
Java Virtual Machine
30
System Design Goals

• User goals
• OS should be convenient to use, easy to
• learn, reliable, safe, and fast.
• System goals
• OS should be easy to design, implement, and
• maintain, as well as flexible, reliable,
  error-
• free, and efficient.

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Mechanisms and Policies

• Mechanisms determine how to do something,
  policies decide what will be done.
• The separation of policy from mechanism is a very
  important principle
• ? allows maximum flexibility if policy
• decisions are to be changed later.

32
System Implementation

• Traditionally written in assembly language.
• OS can now be written in higher-level languages.
• Code written in a high-level language
• can be written faster.
• is more compact.
• is easier to understand and debug.
• An operating system is far easier to port (move
  to some other hardware) if it is written in a
  high-level language.

33
System Generation (SYSGEN)

• OSs are designed to run on any of a class of
  machines ? system must be configured for each
  specific computer
• site.
• SYSGEN program obtains information concerning the
  specific configuration of the hardware system.
• Booting starting a computer by loading the
  kernel.
• Bootstrap program code stored in ROM that is
  able to locate the kernel, load it into memory,
  and start its execution.

34
Units - Orders of Magnitude

• kilo (103) milli (10-3)
• mega (106) micro (10-6)
• giga (109) nano (10-9)
• tera (1012) pico (10-12)
• peta (1015) femto (10-15)
• exa (1018) atto (10-18)

35
Units - Orders of Magnitude
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Units - Orders of Magnitude
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Units - Orders of Magnitude
38
Processes

• Process Concept
• Process Scheduling
• Operations on Processes
• Cooperating Processes
• Interprocess Communication
• Communication in Client-Server Systems

39
Process Concept

• An OS executes a variety of programs
• Batch system jobs
• Time-shared systems user programs or tasks
• Terms job and process interchangeably.
• Process a program in execution process
  execution must progress in sequential fashion.
• A process includes
• program counter
• stack
• data section

40
Process State

• As a process executes, it changes state
• new The process is being created.
• running Instructions are being executed.
• waiting The process is waiting for some event
  to occur.
• ready The process is waiting to be assigned to
  a CPU.
• terminated The process has finished execution.

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Diagram of Process State
42
Process Control Block (PCB)

• Information associated with each process.
• Process state
• Program counter
• CPU registers
• CPU scheduling information
• Memory-management information
• Accounting information
• I/O status information

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Process Control Block (PCB)
44
CPU Switch From Process to Process
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Process Scheduling Queues

• Job queue
• set of all processes in the system.
• Ready queue
• set of all processes residing in main memory,
• ready and waiting to execute.
• Device queues
• set of processes waiting for an I/O device.
• Process migration between the various queues.

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Ready Various I/O Device Queues
47
Process Scheduling
48
Schedulers

• Long-term scheduler (or job scheduler)
• selects which processes should be brought
• into the ready queue.
• Short-term scheduler (or CPU scheduler)
• selects which process should be executed
• next and allocates CPU.

49
Addition of Medium Term Scheduling
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Schedulers (Cont.)

• Short-term scheduler is invoked frequently (ms)
• ? (must be fast).
• Long-term scheduler is invoked infrequently
  (seconds, minutes)
• ? (may be slow).

51
Schedulers (Cont.)

• The long-term scheduler controls the degree of
  multiprogramming.
• Processes can be described as either
• ?I/O-bound process
• spends more time doing I/O than computations,
  
• many short CPU bursts.
• ? CPU-bound process
• spends more time doing computations few very
• long CPU bursts.

52
Context Switch

• When CPU switches to another process
• - must save the state of the old process
• - load the saved state for the new process.
• Context-switch time is overhead the system does
  no useful work while switching.
• Time dependent on hardware support.

53
Process Creation

• Parent process create children processes, which,
  in turn create other processes, forming a tree of
  processes.
• Resource sharing
• Parent and children share all resources.
• Children share subset of parents resources.
• Parent and child share no resources.
• Execution
• Parent and children execute concurrently.
• Parent waits until children terminate.

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Process Creation (Cont.)

• Address space
• Child duplicate of parent.
• Child has a program loaded into it.
• UNIX examples
• fork system call creates new process
• exec system call used after a fork to replace the
  process memory space with a new program.

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Processes Tree on UNIX
56
Process Termination

• Process executes last statement and asks the
• to decide it (exit).
• Output data from child to parent (via wait).
• Process resources are deallocated by operating
  system.

57
Process Termination

• Parent may terminate execution of children
• processes (abort).
• Child has exceeded allocated resources.
• Task assigned to child is no longer required.
• Parent is exiting.
• OS does not allow child to continue if its parent
  terminates.
• Cascading termination.

58
Cooperating Processes

• Independent process cannot affect or be affected
  by the execution of another process.
• Cooperating process can affect or be affected by
  the execution of another process
• Advantages of process cooperation
• Information sharing
• Computation speed-up
• Modularity
• Convenience

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Producer-Consumer Problem

• Paradigm for cooperating processes
• - producer process produces information
• - consumed by a consumer process.
• Cases
• unbounded-buffer places no practical limit on the
  size of the buffer.
• bounded-buffer assumes that there is a fixed
  buffer size.

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Bounded-Buffer Shared-Memory Solution

• Shared data
• define BUFFER_SIZE 10
• Typedef struct
• . . .
• item
• item bufferBUFFER_SIZE
• int in 0
• int out 0
• Solution is correct, but can only use
  BUFFER_SIZE-1 elements

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Bounded-Buffer Producer Process

• item nextProduced
• while (1)
• while (((in 1) BUFFER_SIZE) out) / do
  nothing /
• bufferin nextProduced
• in (in 1) BUFFER_SIZE

62
Bounded-Buffer Consumer Process

• item nextConsumed
• while (1)
• while (in out) / do nothing /
• nextConsumed bufferout
• out (out 1) BUFFER_SIZE

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Interprocess Communication (IPC)

• Mechanism for processes to communicate and to
  synchronize their actions.
• Message system
• processes communicate with each other
• without resorting to shared variables.
• IPC facility provides two operations
• send(message) message size fixed or variable
• receive(message)

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Interprocess Communication (IPC)

• If P and Q wish to communicate, they need to
• establish a communication link between them
• exchange messages via send/receive
• Implementation of communication link
• physical (e.g., shared memory, hardware bus)
• logical (e.g., logical properties)

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Implementation Questions

• How are links established?
• Can a link be associated with more than two
  processes?
• How many links can there be between every pair of
  communicating processes?
• What is the capacity of a link?
• Is the size of a message that the link can
  accommodate fixed or variable?
• Is a link unidirectional or bi-directional?

66
Direct Communication

• Processes must name each other explicitly
• send (P, message) send a message to process P
• receive(Q, message) receive a message from
  process Q
• Properties of communication link
• Links are established automatically.
• A link is associated with exactly one pair of
  communicating processes.
• Between each pair there exists exactly one link.
• The link may be unidirectional, but is usually
  bi-directional.

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Indirect Communication

• Messages are directed and received from mailboxes
  (also referred to as ports).
• Each mailbox has a unique id.
• Processes can communicate only if they share a
  mailbox.

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Indirect Communication

• Properties of communication link
• Link established only if processes share a common
  mailbox
• A link may be associated with many processes.
• Each pair of processes may share several
  communication links.
• Link may be unidirectional or bi-directional.

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Indirect Communication

• Operations
• create a new mailbox
• send and receive messages through mailbox
• destroy a mailbox
• Primitives are defined as
• send(A, message)
• send a message to mailbox A
• receive(A, message)
• receive a message from mailbox A

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Indirect Communication

• Mailbox sharing
• P1, P2, and P3 share mailbox A.
• P1, sends P2 and P3 receive.
• Who gets the message?
• Solutions
• Allow a link to be associated with at most two
  processes.
• Allow only one process at a time to execute a
  receive operation.
• Allow the system to select arbitrarily the
  receiver. Sender is notified who the receiver
  was.

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Synchronization

• Message passing may be either blocking or
  non-blocking.
• Blocking is considered synchronous
• Non-blocking is considered asynchronous
• send and receive primitives may be either
  blocking or non-blocking.

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Buffering

• Queue of messages attached to the link
  implemented in one of three ways.
• 1. Zero capacity 0 messagesSender must wait
  for receiver (rendezvous).
• 2. Bounded capacity finite length of n
  messagesSender must wait if link full.
• 3. Unbounded capacity infinite length Sender
  never waits.

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Client-Server Communication

• Sockets
• Remote Procedure Calls
• Remote Method Invocation (Java)

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Sockets

• A socket is defined as an endpoint for
  communication.
• Concatenation of IP address and port
• The socket 161.25.19.81625 refers to port 1625
  on host 161.25.19.8
• Communication consists between a pair of sockets.

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Socket Communication
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Remote Procedure Calls (RPC)

• RPC abstracts procedure calls between processes
  on networked systems.
• Stubs client-side proxy for the actual
  procedure on the server.
• The client-side stub locates the server and
  marshalls the parameters.
• The server-side stub receives this message,
  unpacks the marshalled parameters, and performs
  the procedure on the server.

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Marshalling Parameters
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Execution of RPC
79
Remote Method Invocation (RMI)

• Remote Method Invocation (RMI) is a Java
  mechanism similar to RPCs.
• RMI allows a Java program on one machine to
  invoke a method on a remote object.

80
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