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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

can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
ninjadapaul
20/(×-6^2)
Salomon
okay, so you have 6 raised to the power of 2. what is that part of your answer
ninjadapaul
I don't understand what the A with approx sign and the boxed x mean
ninjadapaul
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
Salomon
I'm not sure why it wrote it the other way
Salomon
I got X =-6
Salomon
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
ninjadapaul
oops. ignore that.
ninjadapaul
so you not have an equal sign anywhere in the original equation?
ninjadapaul
Commplementary angles
Idrissa Reply
hello
Sherica
im all ears I need to learn
Sherica
right! what he said ⤴⤴⤴
Tamia
what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
Kevin Reply
a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
Kim
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Al
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
yes
Asali
I'm not good at math so would you help me
Samantha
what is the problem that i will help you to self with?
Asali
how do you translate this in Algebraic Expressions
linda Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
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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