Operating System Concepts
Chapter 3 { Processes
Based on the 9th Edition of:
Abraham Silberschatz, Peter B. Galvin and Jreg Gagne:. Operating System
Concepts
Department of Information Technology, College of Business, Law & Governance
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Learning Objectives
To introduce the notion of a process { a program in
execution, which forms the basis of all computation
To describe the various features of processes, including
scheduling, creation and termination, and communication
To explore interprocess communication using shared memory
and message passing
To describe communication in client-server systems
Chapter 3 { Processes Operating System Concepts 2
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Outline
1 Process Concept
2 Process Scheduling
3 Operations on Processes
4 Interprocess Communication
5 Communications in Client-Server Systems
Chapter 3 { Processes Operating System Concepts 3
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
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 interchangeably
Process { a program in execution; has following parts:
The program code, also called text section
Current activity including program counter, processor registers
Stack containing temporary data, such as function parameters,
return addresses, local variables
Data section containing global variables
Heap containing memory dynamically allocated during run time
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Concept
Program is passive entity stored on disk
(executable file), process is active
Program becomes process when
executable file loaded into memory
Execution of program started via GUI
mouse clicks, command line entry of its
name, etc.
One program can be several processes
Consider multiple users executing the
same program
text
0
max
data
heap
stack
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Concept
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 processor
terminated: The process has finished execution
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Concept
Diagram of process state
new terminated
ready running
admitted interrupt
scheduler dispatch
I/O or event completion I/O or event wait
exit
waiting
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Concept
Process Control Block {information associated with each process:
Process state { running, waiting, etc
Program counter { location of instruction to next execute
CPU registers { contents of all process-centric registers
CPU scheduling information { priorities, scheduling queue
pointers
Memory-management information { memory allocated to the
process
Accounting information { CPU used, clock time elapsed since
start, time limits
I/O status information { I/O devices allocated to process, list
of open files
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Concept
Process Control Block (PCB)
process state
process number
program counter
memory limits
list of open files
registers
•••
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Concept
CPU switch from process to process
process P0 process P1
save state into PCB0
save state into PCB1
reload state from PCB1
reload state from PCB0
operating system
idle
idle
idle executing
executing
executing
interrupt or system call
interrupt or system call
••• •••
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Concept
Threads
So far, process has a single thread of execution
Consider having multiple program counters per process
Multiple locations can execute at once
Multiple threads of control ! threads
Must then have storage for thread details, multiple program
counters in PCB
See next chapter
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Concept
Process representation in Linux
pid t pid; /* process identifier */
long state; /* state of the process */
unsigned int time slice; /* scheduling information */
struct task struct *parent; /* this processs parent */
struct list head children; /* this processs children */
struct files struct *files; /* list of open files */
struct mm struct *mm; /* address space of this process */
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Scheduling
Maximize CPU use, quickly switch processes onto CPU for
time sharing
Process scheduler selects among available processes for next
execution on CPU
Maintains scheduling queues of processes
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
Processes migrate among the various queues
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Scheduling
The ready queue and various I/O device queues
queue header PCB7
PCB3
PCB5
PCB14 PCB6
PCB2
head
head
head
head
head
ready
queue
disk
unit 0
terminal
unit 0
mag
tape
unit 0
mag
tape
unit 1
tail registers registers
tail
tail
tail
tail
•••
•••
•••
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Scheduling
Queuing-diagram representation of process scheduling
ready queue CPU
I/O I/O queue I/O request
time slice
expired
fork a
child
wait for an
interrupt
interrupt
occurs
child
executes
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Scheduling
Schedulers
Short-term scheduler (or CPU scheduler) { selects which
process should be executed next and allocates CPU
invoked frequently (milliseconds) ) (must be fast)
Long-term scheduler (or job scheduler) { selects which
processes should be brought into the ready queue
invoked infrequently (seconds, minutes) ) (may be slow)
controls the degree of multiprogramming
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Scheduling
Schedulers (Cont.)
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
Long-term scheduler strives for good process mix
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Scheduling
Schedulers (Cont.)
Medium-term scheduler can be added if degree of multiple
programming needs to decrease
Remove process from memory, store on disk, bring back in
from disk to continue execution: swapping
swap in swap out
CPU end
I/O I/O waiting
queues
ready queue
partially executed
swapped-out processes
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Multitasking in Mobile Systems
Some mobile systems (e.g., early version of iOS) allow only
one process to run, others suspended
Due to screen real estate, user interface limits iOS provides
for a
Single foreground process { controlled via user interface
Multiple background processes { in memory, running, but not
on the display, and with limits
Android runs foreground and background, with fewer limits
Background process uses a service to perform tasks
Service can keep running even if background process is
suspended
Service has no user interface, small memory use
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Process Scheduling
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 via a context switch
Context of a process represented in the PCB
Context-switch time is overhead; the system does no useful
work while switching
The more complex the OS and the PCB ) the longer the
context switch
Time dependent on hardware support
Some hardware provides multiple sets of registers per CPU )
multiple contexts loaded at once
Chapter 3 { Processes Operating System Concepts 20
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 The of a process contains temporary data such as
function parameters, return addresses, and local variables.
A. text section
B. data section
C. program counter
D. stack
Answer:
Chapter 3 { Processes Operating System Concepts 21
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 The of a process contains temporary data such as
function parameters, return addresses, and local variables.
A. text section
B. data section
C. program counter
D. stack
Answer: D
Chapter 3 { Processes Operating System Concepts 21
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 The of a process contains temporary data such as
function parameters, return addresses, and local variables.
A. text section
B. data section
C. program counter
D. stack
Answer: D
2 A process control block .
A. includes information on the process’s state
B. stores the address of the next instruction to be processed by a
different process
C. determines which process is to be executed next
D. is an example of a process queue
Answer:
Chapter 3 { Processes Operating System Concepts 21
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 The of a process contains temporary data such as
function parameters, return addresses, and local variables.
A. text section
B. data section
C. program counter
D. stack
Answer: D
2 A process control block .
A. includes information on the process’s state
B. stores the address of the next instruction to be processed by a
different process
C. determines which process is to be executed next
D. is an example of a process queue
Answer: A
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 . The refers to the number of processes in memory.
A. process count
B. long-term scheduler
C. degree of multiprogramming
D. CPU scheduler
Answer:
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 . The refers to the number of processes in memory.
A. process count
B. long-term scheduler
C. degree of multiprogramming
D. CPU scheduler
Answer: C
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 . The refers to the number of processes in memory.
A. process count
B. long-term scheduler
C. degree of multiprogramming
D. CPU scheduler
Answer: C
2 True or False { The difference between a program and a
process is that a program is an active entity while a process is
a passive entity.
Answer:
Chapter 3 { Processes Operating System Concepts 22
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 . The refers to the number of processes in memory.
A. process count
B. long-term scheduler
C. degree of multiprogramming
D. CPU scheduler
Answer: C
2 True or False { The difference between a program and a
process is that a program is an active entity while a process is
a passive entity.
Answer: False
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 . The refers to the number of processes in memory.
A. process count
B. long-term scheduler
C. degree of multiprogramming
D. CPU scheduler
Answer: C
2 True or False { The difference between a program and a
process is that a program is an active entity while a process is
a passive entity.
Answer: False
3 True or False { For a single-processor system, there will
never be more than one process in the Running state.
Answer:
Chapter 3 { Processes Operating System Concepts 22
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 . The refers to the number of processes in memory.
A. process count
B. long-term scheduler
C. degree of multiprogramming
D. CPU scheduler
Answer: C
2 True or False { The difference between a program and a
process is that a program is an active entity while a process is
a passive entity.
Answer: False
3 True or False { For a single-processor system, there will
never be more than one process in the Running state.
Answer: True
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Operations on Processes
System must provide mechanisms for:
process creation,
process termination,
and so on as detailed next
Chapter 3 { Processes Operating System Concepts 23
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Operations on Processes
Process Creation
Parent process create children processes, which, in turn create
other processes, forming a tree of processes
Generally, process identified and managed via a process
identifier (pid)
Resource sharing options
Parent and children share all resources
Children share subset of parent’s resources
Parent and child share no resources
Execution options
Parent and children execute concurrently
Parent waits until children terminate
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Operations on Processes
A tree of processes on a typical Solaris system
init
pid = 1
sshd
pid = 3028
login
pid = 8415
kthreadd
pid = 2
sshd
pid = 3610
pdflush
pid = 200
khelper
pid = 6
tcsch
pid = 4005
emacs
pid = 9204
bash
pid = 8416
ps
pid = 9298
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Operations on Processes
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
pid = fork()
exec()
parent
parent (pid > 0)
child (pid = 0)
wait()
exit()
parent resumes
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Operations on Processes
Process Termination
Process executes last statement and then asks the operating
system to delete it using the exit() system call.
Returns status data from child to parent (via wait())
Process’ resources are deallocated by operating system
Parent may terminate the execution of children processes
using the abort() system call. Some reasons for doing so:
Child has exceeded allocated resources
Task assigned to child is no longer required
The parent is exiting and the operating systems does not allow
a child to continue if its parent terminates
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Operations on Processes
Process Termination (Cont.)
Some operating systems do not allow child to exists if its
parent has terminated. If a process terminates, then all its
children must also be terminated ) cascading termination
The parent process may wait for termination of a child process
by using the wait() system call. The call returns status
information and the pid of the terminated process
pid = wait(&status);
If no parent waiting (did not invoke wait()) process is a
zombie
If parent terminated without invoking wait(), process is an
orphan
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Operations on Processes
Multiprocess Architecture { Chrome Browser
Many web browsers ran as single process (some still do)
If one web site causes trouble, entire browser can hang or crash
Google Chrome Browser is multiprocess with 3 different types
of processes:
Browser process manages user interface, disk and network I/O
Renderer process renders web pages, deals with HTML,
Javascript. A new renderer created for each website opened
Runs in sandbox restricting disk and network I/O, minimizing
effect of security exploits
Plug-in process for each type of plug-in
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Operations on Processes
Multiprocess Architecture { Chrome Browser
Chapter 3 { Processes Operating System Concepts 30
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 When a child process is created, which of the following is a
possibility in terms of the execution or address space of the
child process?
A. The child process runs concurrently with the parent.
B. The child process has a new program loaded into it.
C. The child is a duplicate of the parent.
D. All of the above
Answer:
Chapter 3 { Processes Operating System Concepts 31
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 When a child process is created, which of the following is a
possibility in terms of the execution or address space of the
child process?
A. The child process runs concurrently with the parent.
B. The child process has a new program loaded into it.
C. The child is a duplicate of the parent.
D. All of the above
Answer: D
Chapter 3 { Processes Operating System Concepts 31
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 When a child process is created, which of the following is a
possibility in terms of the execution or address space of the
child process?
A. The child process runs concurrently with the parent.
B. The child process has a new program loaded into it.
C. The child is a duplicate of the parent.
D. All of the above
Answer: D
2 A saves the state of the currently running process and
restores the state of the next process to run.
A. save-and-restore
B. state switch
C. context switch
D. none of the above
Answer:
Chapter 3 { Processes Operating System Concepts 31
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 When a child process is created, which of the following is a
possibility in terms of the execution or address space of the
child process?
A. The child process runs concurrently with the parent.
B. The child process has a new program loaded into it.
C. The child is a duplicate of the parent.
D. All of the above
Answer: D
2 A saves the state of the currently running process and
restores the state of the next process to run.
A. save-and-restore
B. state switch
C. context switch
D. none of the above
Answer: C
Chapter 3 { Processes Operating System Concepts 31
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Processes within a system may be independent or cooperating
Cooperating process can affect or be affected by other
processes, including sharing data
Reasons for cooperating processes:
Information sharing
Computation speedup
Modularity
Convenience
Cooperating processes need interprocess communication (IPC)
Two models of IPC
1 Shared memory
2 Message passing
Chapter 3 { Processes Operating System Concepts 32
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Communications models. (a) Message passing. (b) Shared memory
process A
message queue
kernel
(a) (b)
process A
shared memory
kernel
process B
m0 m1 m2 m3 … mn
process B
Chapter 3 { Processes Operating System Concepts 33
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Cooperating Processes { Producer-Consumer Problem
Paradigm for cooperating processes, producer process
produces information that is consumed by a consumer process
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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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Bounded-Buffer { Shared-Memory Solution
Shared data
#define BUFFER SIZE 10
typdef struct f
. . .
g item;
item buffer [BUFFER SIZE]
int in = 0;
int out = 0;
Solution is correct, but can only use BUFFER SIZE-1 elements
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Bounded-Buffer { Producer
item next prodced;
while (true) f
/* produce an item in next produced */
while (((in + 1) % BUFFER SIZE) == out)
; /* do nothing */
buffer[in] = next produced;
in = (in + 1) % BUFFER SIZE;
g
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Bounded-Buffer { Consumer
item next consumed;
while (true) f
while (in == out)
; /* do nothing */
next consumed = buffer[out];
out = (out + 1) % BUFFER SIZE;
/* consume the item in next consumed */
g
Chapter 3 { Processes Operating System Concepts 37
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Shared Memory
An area of memory shared among the processes that wish to
communicate
The communication is under the control of the users processes
not the operating system.
Major issues is to provide mechanism that will allow the user
processes to synchronize their actions when they access shared
memory.
Synchronization is discussed in great details in Chapter 5.
Chapter 3 { Processes Operating System Concepts 38
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Message Passing
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:
1 send(message)
2 receive(message)
The message size is either fixed or variable
Chapter 3 { Processes Operating System Concepts 39
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Message Passing (Cont.)
If processes P and Q wish to communicate, they need to:
Establish a communication link between them Exchange
messages via send/receive
Implementation issues:
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?
Chapter 3 { Processes Operating System Concepts 40
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Message Passing (Cont.)
Implementation of communication link
Physical:
Shared memory
Hardware bus
Network
Logical:
Direct or indirect
Synchronous or asynchronous
Automatic or explicit buffering
Chapter 3 { Processes Operating System Concepts 41
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
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
Chapter 3 { Processes Operating System Concepts 42
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
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
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
Chapter 3 { Processes Operating System Concepts 43
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Indirect Communication (Cont.)
Operations
create a new mailbox (port)
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
Chapter 3 { Processes Operating System Concepts 44
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Indirect Communication (Cont.)
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.
Chapter 3 { Processes Operating System Concepts 45
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Synchronization
Message passing may be either blocking or non-blocking
Blocking is considered synchronous
Blocking send { the sender is blocked until the message is
received
Blocking receive { the receiver is blocked until a message is
available
Non-blocking is considered asynchronous
Non-blocking send { the sender sends the message and
continue
Non-blocking receive { the receiver receives:
A valid message, or
Null message
Chapter 3 { Processes Operating System Concepts 46
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Synchronization (Cont.)
Producer-consumer becomes trivial
message next produced;
while (true) f
/* produce an item in next produced */
send(next produced);
g
message next consumed;
while (true) f
receive(next consumed);
/* consume the item in next consumed */
g
Chapter 3 { Processes Operating System Concepts 47
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Buffering
Queue of messages attached to the link.
implemented in one of three ways
1 Zero capacity { no messages are queued on a link. 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
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Example of IPC Sysems { Windows
Message-passing centric via advanced local procedure call
(LPC) facility
Only works between processes on the same system
Uses ports (like mailboxes) to establish and maintain
communication channels as follows:
The client opens a handle to the subsystem’s connection port
object.
The client sends a connection request.
The server creates two private communication ports and
returns the handle to one of them to the client.
The client and server use the corresponding port handle to
send messages or callbacks and to listen for replies.
Chapter 3 { Processes Operating System Concepts 49
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Interprocess Communication
Local Procedure Calls (LPC) in Windows
Connection
Port
Connection
request Handle
Handle
Handle
Client
Communication Port
Server
Communication Port
Shared
Section Object
(> 256 bytes)
Client Server
Chapter 3 { Processes Operating System Concepts 50
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Communications in Client-Server Systems
Sockets
Remote Procedure Calls
Pipes
Remote Method Invocation (Java)
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Communications in Client-Server Systems
Socket Communication
A socket is defined as an endpoint for communication
Concatenation of IP address and port { a number included at
start of message packet to differentiate network services on a
host
The socket 161.25.19.8:1625 refers to port 1625 on host
161.25.19.8
Communication consists between a pair of sockets
All ports below 1024 are well known, used for standard
services
Special IP address 127.0.0.1 (loopback) to refer to system on
which process is running
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Communications in Client-Server Systems
Socket Communication
socket
(146.86.5.20:1625)
host X
(146.86.5.20)
socket
(161.25.19.8:80)
web server
(161.25.19.8)
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Communications in Client-Server Systems
Remote Procedure Calls (RPC)
Remote procedure call (RPC) abstracts procedure calls
between processes on networked systems
Again uses ports for service differentiation
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
On Windows, stub code compile from specification written in
Microsoft Interface Definition Language (MIDL)
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Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Communications in Client-Server Systems
Execution of a remote procedure calls (RPC)
client
user calls kernel
to send RPC
message to
procedure X
matchmaker
receives
message, looks
up answer
matchmaker
replies to client
with port P
daemon
listening to
port P receives
message
daemon
processes
request and
processes send
output
kernel sends
message to
matchmaker to
find port number
From: client
To: server
Port: matchmaker
Re: address
for RPC X
From: client
To: server
Port: port P
<contents>
From: RPC
Port: P
To: client
Port: kernel
<output>
From: server
To: client
Port: kernel
Re: RPC X
Port: P
kernel places
port P in user
RPC message
kernel sends
RPC
kernel receives
reply, passes
it to user
messages server
Chapter 3 { Processes Operating System Concepts 55
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Communications in Client-Server Systems
Pipes
Acts as a conduit allowing two processes to communicate
Issues:
Is communication unidirectional or bidirectional?
In the case of two-way communication, is it half or full-duplex?
Must there exist a relationship (i.e., parent-child) between the
communicating processes?
Can the pipes be used over a network?
Ordinary pipes cannot be accessed from outside the process
that created it. Typically, a parent process creates a pipe and
uses it to communicate with a child process that it created.
Named pipes { can be accessed without a parent-child
relationship.
Chapter 3 { Processes Operating System Concepts 56
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Communications in Client-Server Systems
Ordinary Pipes
Ordinary Pipes allow communication in standard
producer-consumer style
Producer writes to one end (the write-end of the pipe)
Consumer reads from the other end (the read-end of the pipe)
Ordinary pipes are therefore unidirectional
Require parent-child relationship between communicating
processes
Windows calls these anonymous pipes
Chapter 3 { Processes Operating System Concepts 57
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Communications in Client-Server Systems
Ordinary Pipe
Chapter 3 { Processes Operating System Concepts 58
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Communications in Client-Server Systems
Named Pipes
Named Pipes are more powerful than ordinary pipes
Communication is bidirectional
No parent-child relationship is necessary between the
communicating processes
Several processes can use the named pipe for communication
Provided on both UNIX and Windows systems
Chapter 3 { Processes Operating System Concepts 59
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 A blocking send() and blocking receive() is known as a(n)
.
A. synchronized message
B. rendezvous
C. blocked message
D. asynchronous message
Answer:
Chapter 3 { Processes Operating System Concepts 60
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 A blocking send() and blocking receive() is known as a(n)
.
A. synchronized message
B. rendezvous
C. blocked message
D. asynchronous message
Answer: B
Chapter 3 { Processes Operating System Concepts 60
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 A blocking send() and blocking receive() is known as a(n)
.
A. synchronized message
B. rendezvous
C. blocked message
D. asynchronous message
Answer: B
2 Which of the following statements is true?
A. Shared memory is typically faster than message passing.
B. Message passing is typically faster than shared memory.
C. Message passing is most useful for exchanging large amounts
of data.
D. Shared memory is far more common in operating systems than
message passing.
Answer:
Chapter 3 { Processes Operating System Concepts 60
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 A blocking send() and blocking receive() is known as a(n)
.
A. synchronized message
B. rendezvous
C. blocked message
D. asynchronous message
Answer: B
2 Which of the following statements is true?
A. Shared memory is typically faster than message passing.
B. Message passing is typically faster than shared memory.
C. Message passing is most useful for exchanging large amounts
of data.
D. Shared memory is far more common in operating systems than
message passing.
Answer: A
Chapter 3 { Processes Operating System Concepts 60
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 Which of the following statements is true?
A. Named pipes do not allow bi-directional communication.
B. Only the parent and child processes can use named pipes for
communication.
C. Reading and writing to ordinary pipes on both UNIX and
Windows systems can be performed like ordinary file I/O.
D. Named pipes can only be used by communicating processes on
the same machine.
Answer:
Chapter 3 { Processes Operating System Concepts 61
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 Which of the following statements is true?
A. Named pipes do not allow bi-directional communication.
B. Only the parent and child processes can use named pipes for
communication.
C. Reading and writing to ordinary pipes on both UNIX and
Windows systems can be performed like ordinary file I/O.
D. Named pipes can only be used by communicating processes on
the same machine.
Answer: C
Chapter 3 { Processes Operating System Concepts 61
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 Which of the following statements is true?
A. Named pipes do not allow bi-directional communication.
B. Only the parent and child processes can use named pipes for
communication.
C. Reading and writing to ordinary pipes on both UNIX and
Windows systems can be performed like ordinary file I/O.
D. Named pipes can only be used by communicating processes on
the same machine.
Answer: C
2 True or False { The exec() system call creates a new
process.
Answer:
Chapter 3 { Processes Operating System Concepts 61
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 Which of the following statements is true?
A. Named pipes do not allow bi-directional communication.
B. Only the parent and child processes can use named pipes for
communication.
C. Reading and writing to ordinary pipes on both UNIX and
Windows systems can be performed like ordinary file I/O.
D. Named pipes can only be used by communicating processes on
the same machine.
Answer: C
2 True or False { The exec() system call creates a new
process.
Answer: False
Chapter 3 { Processes Operating System Concepts 61
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 Which of the following statements is true?
A. Named pipes do not allow bi-directional communication.
B. Only the parent and child processes can use named pipes for
communication.
C. Reading and writing to ordinary pipes on both UNIX and
Windows systems can be performed like ordinary file I/O.
D. Named pipes can only be used by communicating processes on
the same machine.
Answer: C
2 True or False { The exec() system call creates a new
process.
Answer: False
3 True or False { Ordinary pipes in Windows require a
parent-child relationship between the communicating
processes.
Answer:
Chapter 3 { Processes Operating System Concepts 61
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
Quick Quiz
1 Which of the following statements is true?
A. Named pipes do not allow bi-directional communication.
B. Only the parent and child processes can use named pipes for
communication.
C. Reading and writing to ordinary pipes on both UNIX and
Windows systems can be performed like ordinary file I/O.
D. Named pipes can only be used by communicating processes on
the same machine.
Answer: C
2 True or False { The exec() system call creates a new
process.
Answer: False
3 True or False { Ordinary pipes in Windows require a
parent-child relationship between the communicating
processes.
Answer: True
Chapter 3 { Processes Operating System Concepts 61
Concept Scheduling Operations Interprocess Communication Communications in Client-Server
End of Chapter 3
Chapter 3 { Processes Operating System Concepts 62