<< Chapter < Page Chapter >> Page >

recs % cc -o create1 -lpthread -lposix4 create1.c recs % create1Main - globvar=0 Main - creating i=0 tid=4 retval=0Main - creating i=1 tid=5 retval=0 Main - creating i=2 tid=6 retval=0Main thread - threads started globvar=0 Main - waiting for join 4TestFunc me=0 - self=4 globvar=0 TestFunc me=0 - sleeping globvar=15TestFunc me=1 - self=5 globvar=15 TestFunc me=1 - sleeping globvar=16TestFunc me=2 - self=6 globvar=16 TestFunc me=2 - sleeping globvar=17TestFunc me=2 - done param=6 globvar=17 TestFunc me=1 - done param=5 globvar=17TestFunc me=0 - done param=4 globvar=17 Main - back from join 0 retval=0Main - waiting for join 5 Main - back from join 1 retval=0Main - waiting for join 6 Main - back from join 2 retval=0Main thread – threads completed globvar=17 recs %

You can see the threads getting created in the loop. The master thread completes the pthread_create( ) loop, executes the second loop, and calls the pthread_join( ) function. This function suspends the master thread until the specified thread completes. The master thread is waiting for Thread 4 to complete. Once the master thread suspends, one of the new threads is started. Thread 4 starts executing. Initially the variable globvar is set to 0 from the main program. The self, me , and param variables are thread-local variables, so each thread has its own copy. Thread 4 sets globvar to 15 and goes to sleep. Then Thread 5 begins to execute and sees globvar set to 15 from Thread 4; Thread 5 sets globvar to 16, and goes to sleep. This activates Thread 6, which sees the current value for globvar and sets it to 17. Then Threads 6, 5, and 4 wake up from their sleep, all notice the latest value of 17 in globvar , and return from the TestFunc( ) routine, ending the threads.

All this time, the master thread is in the middle of a pthread_join( ) waiting for Thread 4 to complete. As Thread 4 completes, the pthread_join( ) returns. The master thread then calls pthread_join( ) repeatedly to ensure that all three threads have been completed. Finally, the master thread prints out the value for globvar that contains the latest value of 17.

To summarize, when an application is executing with more than one thread, there are shared global areas and thread private areas. Different threads execute at different times, and they can easily work together in shared areas.

Limitations of user space multithreading

Multithreaded applications were around long before multiprocessors existed. It is quite practical to have multiple threads with a single CPU. As a matter of fact, the previous example would run on a system with any number of processors, including one. If you look closely at the code, it performs a sleep operation at each critical point in the code. One reason to add the sleep calls is to slow the program down enough that you can actually see what is going on. However, these sleep calls also have another effect. When one thread enters the sleep routine, it causes the thread library to search for other “runnable” threads. If a runnable thread is found, it begins executing immediately while the calling thread is “sleeping.” This is called a user-space thread context switch. The process actually has one operating system thread shared among several logical user threads. When library routines (such as sleep ) are called, the thread library The pthreads library supports both user-space threads and operating-system threads, as we shall soon see. Another popular early threads package was called cthreads . jumps in and reschedules threads.

Questions & Answers

anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
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.
Bharti
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
Daniel
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
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
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
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
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.
Tarell
what is the actual application of fullerenes nowadays?
Damian
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.
Tarell
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.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
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.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket 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
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Berger describes sociologists as concerned with
Mueller Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!





Source:  OpenStax, High performance computing. OpenStax CNX. Aug 25, 2010 Download for free at http://cnx.org/content/col11136/1.5
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'High performance computing' conversation and receive update notifications?

Ask