Operating system Process Management

7/30/2019 Operating system Process Management

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Chapter 2: Process Management

2. Process Management


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Process Management

2.1 Process Concept

2.2 Process Control Block

2.3 Process operations :

Create

Kill

suspend

resume

wakeup,

2.4 Interprocess Communication IPC types

2.5 IPC in Client-Server RTOS (Real Time Operating System)



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Process Concept An operating system executes a variety of programs:

Batch system jobs Time-shared systems user programs or tasks

Textbook uses the termsjob andprocess almost

interchangeably

Process

a program in execution; A process includes:

Heap: Dynamic Storage allocation.

program counter :Next instruction to execute

Stack: Temporary data( Function, Parameters, localvariables)

data sect (Global variable)

Text: Process is more than program code which called

as text 2. Process Management


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Process in Memory



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Diagram of Process State

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Process State

As a process executes, it changes state

New: The process is being created

Ready: The process is waiting to be assigned to a processor

Running: Instructions are being executed

Waiting: The process is waiting for some event to occur

Terminated: The process has finished execution At one time only one process can be runnning on a single

processor



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The dynamic state of a process.

Example process life cycle PROCESS

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Five-State Process Model



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Process Scheduling Queues

A. Job queue set of all processes in the system

B. Ready queue set of all processes residing in main

memory, ready and waiting to execute

C. Device queues set of processes waiting for an I/O

device

Processes migrate among the various queues


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Ready Queue And

Various I/O Device Queues


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Representation of Process Scheduling


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Schedulers

Long-term scheduler (or job scheduler) selects which processesshould be brought into the ready queue

Short-term scheduler (or CPU scheduler) selects which process

should be executed next and allocates CPU


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Addition of Medium Term Scheduling


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Addition of Medium Term Scheduling

Execute

Wait for i/o

Suspend


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Frequency of calling 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


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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 processvia a context switch

Contextof a process represented in the PCB

Context-switch time is overhead; the system does no useful work

while switching

Time dependent on hardware support
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CPU Switch From Process to Process
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Process Control Block

Identifier

Figure 3.1 Simplified Process Control Block

State

Priority

Program counter

Memory pointers

Context data

I/O status

information

Accounting

information



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Process Control Block (PCB)

Information associated with each process

Process state: New, Ready, Running waiting

Program counter: Address of next instruction to execute

CPU registers: accumulators, index registers, stack pointers and general

purpose register plus condition code information. In case of interrupt

Process start continuously correct from last state

CPU scheduling information: Process priority pointers to scheduling

queues and any other scheduling information

Memory-management information: value of base and limit registers,

page table or segment table.

Accounting information:CPUusedtime, used time limit, accountnumbers, job or process numbers and so on.

I/O status information: list of I/O devices allocated to the processes, a

list of open files and so on.

Process Management 2. Process Management


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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

Processes migrate among the various queues



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Ready Queue And

Various I/O Device Queues



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Representation of Process Scheduling



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Process Operations

Process operations :

Create(New)

Kill(Terminate)

Suspend(When blocked process swapped out from main memory)

resume: Restart from previous wait state wakeup: Give signal that process has to make alive which is stopped

previously(Notify and Notify all)



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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 Parent and children share all resources

Children share subset of parents resources

Parent and child share no resources(directly taking from o.s.)

Restricting a child process to a subset of the parentsresources

Execution

Parent and children execute concurrently

Parent waits until children terminate



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A tree of processes on a typical Solaris


Pageout and flsflush: Memory

Management

Init: Parent process for all child

processinetdand : Networking

services such as t e l n e t and

ftp;

Dtlogin:login screen.

Xsession :- Creating usersession

sdt_shel : command-line shell

the C-shell or commandline

Interface invokes various child

processes, such as theI s and cat commands.


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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 forkto replace the process memory

space with a new program



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Process Creation


Fork(): Create new process parent/child

Return value: Null to child and return pid ofchild to parent

Exec () : system call loads a binary file into

memory and starts its execution.

Wait(): parent calls wait if it has not any

operation and wait for child to terminate

When the child process completes

the parent process resumes from the call to

wait (),

e x i t () :completes using the system call.


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C Program Forking Separate Process

int main()

{pid_t pid;

/* fork another process */

pid = fork();

if (pid < 0) { /* error occurred */

fprintf(stderr, "Fork Failed");

exit(-1);

}

else if (pid == 0) { /* child process */execlp("/bin/ls", "ls", NULL);

}

else { /* parent process */

/* parent will wait for the child to complete */

wait (NULL);

printf ("Child Complete");

exit(0);}

}



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Process Creation in Java



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Kill(Process Termination) Process executes last statement and asks the operating system to

delete it

Unix: exit()

TerminateProcess() in Win32

Output data from child to parent (via wait)

Process resources are deallocated by operating system

Only Parent may terminate execution of children processes (abort)

Child has exceeded allocated resources

Task assigned to child is no longer required

If parent is exiting

Some operating system do not allow child to continue if its

parent terminates

All children terminated - cascading termination(Defining

on delete cascade)2. Process Management


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If parent terminates child how child will resume further:

The wait () system call returns the process identifier of a terminated child

Assigned as new parent to terminate process defined in the init process.

Thus, the children still have a parent to collect their status and execution

statistics


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Process Termination


Read only

O.S. Area


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Process Termination


Not responding End now

User Mode and kernel mode

Cursoponding

s/w not available


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Suspended Processes

Swap processes to disk to free up more memory

Blocked or Wait state becomes suspend state when swapped to disk

again Activating into ready state and go on,

Two new states

Blocked/Suspend

Ready/Suspend



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Ready-suspendedfor those suspended process whose restarting conditionhas occurred.

Blocked-suspendedfor those who must still wait instead.



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Reasons for Process Suspension


If resource unavailable

Alarm ,Burst time


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Suspending, Resuming, and Stopping Threads

Display the time of day. If the user doesnt want a clock, then its thread

can be suspended. Once suspended, restarting the thread is also a simple

matter.



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Resume, Wakeup

wait( ) tells the calling thread to give up the monitor and go to sleep

by giving sleeep() until some other process enters the same monitor

and calls notify( ).

notify( ) wakes up the first process that called wait( ) on the same

object.

notifyAll( ) wakes up all the processes that called wait( ) on the same

object.

Notifications affect only threads that have been waiting ahead of the

notification

The highest priority process will run first.



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The run( ) method contains a block thatchecks suspendFlag.

IfsuspendFlag. is true, the wait( )

method is invoked to suspend the

execution of the process.

sets suspendFlag to false and invokes

notify( ) to wake up the thread.Sleep() : Pausing Execution with Sleep()

Thread.sleep causes the current thread

to suspend execution for a specified

period

Suspend(): causes any execution to be

suspend


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The notification methods :(Telling wait process to

resume operation) notify(): and notifyAll()notifyAll(): wake up all waitin process

notify() : picks one of the waiting process wakes up.

( )


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Interprocess Communication(IPC)

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

Shared Memory

Message Passing System


C i


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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 (share resource)

Computation speed-up: Process divide into sub -processes(pipelining)

Modularity(Problem in one sub process will not or less affect on the

processes) Convenience( User can perform more than one operations open file,

edit file, print file, Check grammar)



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Communications Models

A:Message Passing

B: Shared Memory2. Process Management

Sh d M i J


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Shared Memory in Java


Shared memory approach


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Shared memory approachProducer-Consumer Problem

Allow producer and consumer processes to run concurrently Paradigm for cooperating processes,producerprocess produces

information that is consumed by a consumerprocess

The producer and consumer must be synchronized,

unbounded-bufferplaces no practical limit on the size of the

buffer

bounded-bufferassumes 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 buffer[BUFFER_SIZE];

int in = 0;

int out = 0;

Solution is correct, but can only use BUFFER_SIZE-1 elements


B d d B ff P d


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Bounded-Buffer Producer

The buffer is full when ((in + 1) % BUFFER_SIZE) == out.

while (true) {/* Produce an item */

while (((in = (in + 1) % BUFFER SIZE count) == out)

; /* do nothing -- no free buffers */

buffer[in] = item;

in = (in + 1) % BUFFER SIZE;}

Throuout: Out=0

First in=0

Last before in=8

Last in=9 which makes condition false so no add item in buffer



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Bounded Buffer ConsumerThe buffer is empty when in == out;

while (true) {while (in == out)

; // do nothing -- nothing to consume

// remove an item from the bufferitem = buffer[out];

out = (out + 1) % BUFFER SIZE;

return item;

}

Throuout: Out=9

First out=0

Last before out=8

Last out=9 which makes condition false so no

retreival of items.2. Process Management


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Interprocess Communication Message Passing Without sharing address space provide Mechanism for processes to

communicate and to synchronize their actions

Message system processes communicate with each other without resortingto shared variables

IPC facility provides two operations:

send(message) message size fixed or variable

receive(message)

IfP and Q wish to communicate, they need to:

establish a communicationlinkbetween them

exchange messages via send/receive

Implementation of communication link

physical (e.g., shared memory, hardware bus)

logical (e.g., logical properties)

Direct communication Indirect Communication

Synchronization

Buffering


I l t ti Q ti


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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?


Di t C i ti


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Direct Communication Symmetric direct communication:both the senderprocess and the receiver

process must name the other to communicate.

Processes must name each other explicitly: send (P, message) send a message to process P(P Is receiver)

receive(Q, message) receive a message from process Q(Q is sender)

ASymmetric direct communication: only the sender names the recipient; the

recipient is not required to name the sender

send(P, message)Send a message to process P. receive(id, message)-Receive a message from any process; the variable

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

Disavantage: In general, any such hard-coding techniques, where identifiers must

be explicitly stated, are less desirable than techniques involving

indirection, as described next.(indirect communication)


Indirect Communication


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Instead of sending message to receiver send message to mailbox

Messages are directed and received from mailboxes (also referredto 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




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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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Mailbox sharing

P1, P2, and P3 share mailbox A

P1, sends; P2and 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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Mailbox ownership

Process:

When a process that owns a mailbox terminates, the mailbox disappearsOperating system:

Mailbox is independent and not atttahced to partiular proces.

Steps for message passing

Initially, the owneris the only process that can receive messages through

this mailbox. However, the ownership and receiving privilege may bepassed to other processes through appropriate system calls. Of course,

this provision

could result in multiple receivers for each mailbox.


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Synchronization Message passing may be either blocking or non-blocking

Blocking is considered synchronous

Blocking send has the sender block until the message is received

Blocking receive has the receiver block until a message is

available

Non-blocking is considered asynchronous

Non-blocking send has the sender send the message and

continue

Non-blocking receive has the receiver receive a valid message or

null



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Buffering Queue of messages attached to the link; implemented in one

of three ways1. Zero capacity 0 messages

Sender must wait for receiver (rendezvous)

2. Bounded capacity finite length ofn messages Sender

must wait if link full

3. Unbounded capacity infinite lengthSender never waits


Process Management

Local Proced re Calls in Windo s XP


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Local Procedure Calls in Windows XP


Process Management

Communications in Client Server Systems


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Communications in Client-Server Systems

Sockets

Remote Procedure Calls

Remote Method Invocation (Java)


Sockets


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Sockets

A socket is defined as an endpoint for communication

Concatenation of IP address and port

The socket 161.25.19.8:1625 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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Socket Communication in Java


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Remote Procedure Calls

Remote procedure call (RPC) abstracts procedure calls between processeson 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



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Execution of RPC



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Remote Method Invocation Remote Method Invocation (RMI) is a Java mechanism similar to RPCs

RMI allows a Java program on one machine to invoke a method on aremote object



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MatchmakeRequested

Procedure


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Socket flow of events -- synchronous

Await client message

Receive client messageDecode client message (Unmarshaling)

Perform action

Create client message

Send to client

Get user input

Decode user input(Marshaling)

Create server message

Send message to server

Await server response

Receive server message

Decode reply

Send output to user

Client Server

Method call on standalone object


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Socket flow - asynchronous

Wait

Receive client msgDecode client msg

Perform action

Create client message

Send to client1

Send to client2

User input (UI)

Decode UI

Create srvr msg

Send srvr msgAwait srvr reply

Receive server

messageDecode reply

Output to user

Client1 Server

User input (UI)

Decode UI

Create srvr msg

Send srvr msgAwait srvr reply

Receive server

messageDecode reply

Output to user

Client2


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RMI Example

Stub is generated which then sends marshalled data to receiver

x = remoteObj.MethodA(param); Remote Object

Stub

Remote Reference Layer

Transport Layer

Receiver



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RMI Example

Receiver unmarshals, or decodes, parameters, locatesobject and calls the method specified by the stub


Stub


Transport Layer

Receiver



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RMI Example

Receiver retrieves and marshals return value and sendsback the encoded info to the stub


Stub


Transport Layer

Receiver



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Marshalling Parameters


RMI Example


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RMI Example


RMI Example


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RMI Example


RMI Example


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a p e


Chapter Index: 2 Process Management


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Pi


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Pipes

Pipes: Pipes are used to allow one or more processes to have informationflow between



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Reading from pipesread() will return 0 (end of file) when the write end of the pipe is closed. if

write end of the is still open and there is no data, read() will sleep until

input become available.

if a read() tries to get more data than is currently in pipe, read() will only

contain the number of bytes actually read. Subsequent reads will sleepuntil more data is available.

Writing to pipes

When writing to a pipe:

If read end of pipe is closes, a write() will fail and process will be sent

SIGPIPE signal. Default SIGPIPE handler terminates.



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There are 2 types of pipes:unnamed pipesnamed pipes

Unnamed/Anonymous pipes:They are created, used and destroyed within thelife a set of processes. Each end of the pipe has its own file descriptor. Oneend is for reading and one end is for writing. When you are done with a pipe,it is closed like any other file.

#include int pipe(int fd[2]);Returns 2 file descriptors in the fd array.fd[0] is for readfd[1] write

Returns 0 on successful creation of pipe, 1 otherwise.Each end of the pipe is closed individually using normal close() system call.Pipes are only available the process that creates the pipe and its descendants.



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Named pipesNamed pipes are also called FIFOs (first in first out). They have names

and exist as special files within a file system. (file type p) They exist until

they are removed with rm or unlink()

They can be used with unrelated process not just descendants of the pipe

creator. i.e. accessing by process from outside of pipe Created with:

mknod utility

mknod() system call



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Reading from pipes

When reading from a pipe:

read() will return 0 (end of file) when the write end of the pipe is closed. if

write end of the is still open and there is no data, read() will sleep until

input become available. if a read() tries to get more data than is currentlyin pipe, read() will only contain the number of bytes actually read.

Subsequent reads will sleep until more data is available.

Writing to pipes

When writing to a pipe:

If read end of pipe is closes, a write() will fail and process will be sent

SIGPIPE signal. Default SIGPIPE handler terminates.


T f P


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Trace of Processes


P St t


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Process States

Process Management



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RTOS


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RTOS


Real-time operating system 1

Real-time operating system

A real-time operating system (RTOS) is an operating system (OS)

intended to serve real-time application requests.

It must be able to process data as it comes in, typically without

buffering delays.

jitter.: amount of time it takes to accept and complete an application's

task;

A hard real-time operating system has less jitter than a

softreal-time operating system.

minimal interrupt latency and minimal thread switching latency;

a real-time OS is valued more for how quickly or how predictably it

can respond than for the amount of work it can perform in a givenperiod of time.[3]


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