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Processes - Operating Systems - Lecture Slides | CS 543, Study notes of Operating Systems

Drexel UniversityOperating Systems

Material Type: Notes; Class: Operating Systems; Subject: Computer Science; University: Drexel University; Term: Unknown 1989;

Typology: Study notes

Pre 2010

Uploaded on 08/19/2009

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CS370 - Operating Systems
Process Concept
Process Scheduling
Operations on Processes
Cooperating Processes
Interprocess Communication
Communication in Client-Server Systems
Slides derived from material in “Operating System Concepts,”
by Silberschatz, Galvin, and Gagne
Processes
2
Process Concept
• An operating system executes a variety of programs:
– Batch system – jobs
– Time-shared systems – user programs or tasks
• Textbook uses the terms job and process almost
interchangeably.
• Process – a program in execution; process execution must
progress in sequential fashion.
• A process includes:
– program counter
– stack
– data section
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CS370 - Operating Systems

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

Slides derived from material in “Operating System Concepts,” by Silberschatz, Galvin, and Gagne

Processes

Process Concept

  • An operating system executes a variety of programs:
    • Batch system – jobs
    • Time-shared systems – user programs or tasks
  • Textbook uses the terms job and process almost

interchangeably.

  • Process – a program in execution; process execution must

progress in sequential fashion.

  • A process includes:
    • program counter
    • stack
    • data section

3

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 process.
    • terminated: The process has finished execution.

Diagram of Process State

new interrupt^ terminated

waiting

ready running

admitted exit

I/O or event completion

scheduler dispatch (^) I/O or event wait

7

CPU Switch From Process to Process

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.

9

Ready Queue And Various I/O

Device Queues

interupt occurs

child executes

I/O queue

Representation of Process

Scheduling

ready queue CPU

I/O

time slice expired

I/O request

fork a child

wait for an interrupt

13

Schedulers (Cont.)

  • Short-term scheduler is invoked very frequently

(milliseconds) ⇒ (must be fast).

  • Long-term scheduler is invoked very infrequently

(seconds, minutes) ⇒ (may be slow).

  • 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.

Context Switch

  • When CPU switches to another process, the system must

save the state of the old process and 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.

15

Process Creation

  • Parent process creates 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 parent’ s resources.
    • Parent and child share no resources.
  • Execution
    • Parent and children execute concurrently.
    • Parent waits until children terminate.

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.

19

Supplemental: Threads

  • Light version of processes.
  • Not the same as fork and exec
  • Benefits:
    • Responsiveness: Continual response past a block
    • Resource sharing: Saves on memory
    • Economy: Less costly than process creation (if OS supports that)
    • Utilization of multiprocessors: Allows for hyperthreading

Supplemental: Threads

  • Interface
    • Logical threads (user threads)
    • Physical threads (kernel threads)
  • Types
    • Many to one model (Green threads in Solaris)
    • One to one model (Windows family and all modern OS)
    • Many to many model (older UNIX based OS uses this)
  • API
    • System: usually system calls
    • Libraries

21

Supplemental: Threads

  • API Libraries
    • POSIX Pthreads
      • Specification, not implementation (OS may implement threads as processes)
      • Based in C
    • Win
      • Part of the Win32 API
      • Based in C
    • Java
      • Native in JVM
      • Implements the Runnable class or extends the Thread class

Supplemental: Threads

  • Considerations
    • Cancellation: Asynchronous (one kills all) vs. Deferred (each check for termination)
    • Signal handling (refer to the book)
    • Thread pools: Limit thread creation and prevent CPU exhaustion
    • Scheduling: Using Lightweight Processes (LWP) to create virtual processors, which interfaces the kernel thread for the user thread

25

Bounded Buffer

Shared-Memory Solution

  • Shared data

#define BUFFER_SIZE 10 typedef struct {

... } item; item buffer[BUFFER_SIZE]; int counter = 0;

  • Non Shared data int in = 0; int out = 0;

Bounded Buffer

  • Producer Process item nextProduced; while (1) { while (counter == BUFFER_SIZEcounter == BUFFER_SIZE) ; /* do nothing */ buffer[in] = nextProduced; in = (in + 1) % BUFFER_SIZE; counter++;counter++; }
  • Consumer Process item nextConsumed; while (1) { while (counter == 0counter == 0) ; /* do nothing */ nextConsumed = buffer[out]; out = (out + 1) % BUFFER_SIZE; countercounter----;; }

27

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)
  • 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)

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?

31

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

Indirect Communication

  • Mailbox sharing
    • P 1 , P 2 , and P 3 share mailbox A.
    • P 1 , sends; P 2 and P 3 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.

33

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.

Buffering

  • Queue of messages attached to the link; implemented in

one of three ways.

  1. Zero capacity – 0 messages Sender must wait for receiver (rendezvous).
  2. Bounded capacity – finite length of n messages Sender must wait if link full.
  3. Unbounded capacity – infinite length Sender never waits.

37

Socket Communication

  • If the endpoint on the

web server is addr:80,

how can more than one

clients connect?

host X (192.168.10.1) socket (192.168.10.123:1625)

web server (192.168.10.123) socket (192.168.10.1.1:80)

Remote Procedure Calls

  • Remote procedure call (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 peforms the procedure on the

server.

Execution of RPC