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How a fork operates

This figure consists of a number of groupings of boxes, which are aligned in a column and labeled from top to bottom, global data, code, and stack. The figure shows the boxes in light grey with the label, before fork, and an arrow pointing at code titled, executing. It then shows two groupings of the boxes together, labeled, during fork, parent is suspended and cloned. The grouping on the left is light grey, and large arrows point to the right from this grouping to the second, darker grey grouping. Below this is another grouping of light and dark grey boxes, labeled, after fork, processes execute independently. to the side of the light grey and dark grey boxes labeled, Code, an arrow labeled Executing points at the box.

As both processes start, they execute an IF-THEN-ELSE and begin to perform different actions in the parent and child. Notice that globvar and stackvar are set to 5 in the parent, and then the parent sleeps for two seconds. At this point, the child begins executing. The values for globvar and stackvar are unchanged in the child process. This is because these two processes are operating in completely independent memory spaces. The child process sleeps for one second and sets its copies of the variables to 100. Next, the child process calls the execl( ) function to overwrite its memory space with the UNIX date program. Note that the execl( ) never returns; the date program takes over all of the resources of the child process. If you were to do a ps at this moment in time, you still see two processes on the system but process 19336 would be called “date.” The date command executes, and you can see its output. It’s not uncommon for a human parent process to “fork” and create a human child process that initially seems to have the same identity as the parent. It’s also not uncommon for the child process to change its overall identity to be something very different from the parent at some later point. Usually human children wait 13 years or so before this change occurs, but in UNIX, this happens in a few microseconds. So, in some ways, in UNIX, there are many parent processes that are “disappointed” because their children did not turn out like them!

The parent wakes up after a brief two-second sleep and notices that its copies of global and local variables have not been changed by the action of the child process. The parent then calls the wait( ) function to determine if any of its children exited. The wait( ) function returns which child has exited and the status code returned by that child process (in this case, process 19336).

User space multithreading

A thread is different from a process. When you add threads, they are added to the existing process rather than starting in a new process. Processes start with a single thread of execution and can add or remove threads throughout the duration of the program. Unlike processes, which operate in different memory spaces, all threads in a process share the same memory space. [link] shows how the creation of a thread differs from the creation of a process. Not all of the memory space in a process is shared between all threads. In addition to the global area that is shared across all threads, each thread has a thread private area for its own local variables. It’s important for programmers to know when they are working with shared variables and when they are working with local variables.

When attempting to speed up high performance computing applications, threads have the advantage over processes in that multiple threads can cooperate and work on a shared data structure to hasten the computation. By dividing the work into smaller portions and assigning each smaller portion to a separate thread, the total work can be completed more quickly.

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket 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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