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Multiprocessing software

In this section, we explore how programs access multiprocessing features. These examples are written in C using the POSIX 1003.1 application programming interface. This example runs on most UNIX systems and on other POSIX-compliant systems including OpenNT, Open- VMS, and many others. In this example, the program creates a new process using the fork( ) function. The new process (child) prints some messages and then changes its identity using exec( ) by loading a new program. The original process (parent) prints some messages and then waits for the child process to complete:


int globvar; /* A global variable */ main () {int pid,status,retval; int stackvar; /* A stack variable */globvar = 1; stackvar = 1;printf("Main - calling fork globvar=%d stackvar=%d\n",globvar,stackvar); pid = fork();printf("Main - fork returned pid=%d\n",pid); if ( pid == 0 ) {printf("Child - globvar=%d stackvar=%d\n",globvar,stackvar); sleep(1);printf("Child - woke up globvar=%d stackvar=%d\n",globvar,stackvar); globvar = 100;stackvar = 100; printf("Child - modified globvar=%d stackvar=%d\n",globvar,stackvar);retval = execl("/bin/date", (char *) 0 ); printf("Child - WHY ARE WE HERE retval=%d\n",retval);} else { printf("Parent - globvar=%d stackvar=%d\n",globvar,stackvar);globvar = 5; stackvar = 5;printf("Parent - sleeping globvar=%d stackvar=%d\n",globvar,stackvar); sleep(2);printf("Parent - woke up globvar=%d stackvar=%d\n",globvar,stackvar); printf("Parent - waiting for pid=%d\n",pid);retval = wait(&status); status = status>>8; /* Return code in bits 15-8 */ printf("Parent - status=%d retval=%d\n",status,retval);} }

The key to understanding this code is to understand how the fork( ) function operates. The simple summary is that the fork( ) function is called once in a process and returns twice, once in the original process and once in a newly created process. The newly created process is an identical copy of the original process. All the variables (local and global) have been duplicated. Both processes have access to all of the open files of the original process. [link] shows how the fork operation creates a new process.

The only difference between the processes is that the return value from the fork( ) function call is 0 in the new (child) process and the process identifier (shown by the ps command) in the original (parent) process. This is the program output:


recs % cc -o fork fork.crecs % fork Main - calling fork globvar=1 stackvar=1Main - fork returned pid=19336 Main - fork returned pid=0Parent - globvar=1 stackvar=1 Parent - sleeping globvar=5 stackvar=5Child - globvar=1 stackvar=1 Child - woke up globvar=1 stackvar=1Child - modified globvar=100 stackvar=100 Thu Nov 6 22:40:33Parent - woke up globvar=5 stackvar=5 Parent - waiting for pid=19336Parent - status=0 retval=19336 recs %

Tracing this through, first the program sets the global and stack variable to one and then calls fork( ) . During the fork( ) call, the operating system suspends the process, makes an exact duplicate of the process, and then restarts both processes. You can see two messages from the statement immediately after the fork. The first line is coming from the original process, and the second line is coming from the new process. If you were to execute a ps command at this moment in time, you would see two processes running called “fork.” One would have a process identifier of 19336.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, High performance computing. OpenStax CNX. Aug 25, 2010 Download for free at http://cnx.org/content/col11136/1.5
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