<< Chapter < Page Chapter >> Page >

Multiple threads are also used in high performance database and Internet servers to improve the overall throughput of the server. With a single thread, the program can either be waiting for the next network request or reading the disk to satisfy the previous request. With multiple threads, one thread can be waiting for the next network transaction while several other threads are waiting for disk I/O to complete.

The following is an example of a simple multithreaded application. This example uses the IEEE POSIX standard interface for a thread library. If your system supports POSIX threads, this example should work. If not, there should be similar routines on your system for each of the thread functions. It begins with a single master thread that creates three additional threads. Each thread prints some messages, accesses some global and local variables, and then terminates:


#define_REENTRANT /* basic lines for threads */ #include<stdio.h>#include<pthread.h>#define THREAD_COUNT 3 void *TestFunc(void *);int globvar; /* A global variable */ int index[THREAD_COUNT]/* Local zero-based thread index */ pthread_t thread_id[THREAD_COUNT]; /* POSIX Thread IDs */ main() {int i,retval; pthread_t tid;globvar = 0;printf("Main - globvar=%d\n",globvar); for(i=0;i<THREAD_COUNT;i++) { index[i]= i; retval = pthread_create(&tid,NULL,TestFunc,(void *) index[i]);printf("Main - creating i=%d tid=%d retval=%d\n",i,tid,retval); thread_id[i]= tid; }printf("Main thread - threads started globvar=%d\n",globvar); for(i=0;i<THREAD_COUNT;i++) { printf("Main - waiting for join %d\n",thread_id[i]); retval = pthread_join( thread_id[i], NULL ) ; printf("Main - back from join %d retval=%d\n",i,retval);} printf("Main thread - threads completed globvar=%d\n",globvar);}void *TestFunc(void *parm) { int me,self;me = (int) parm; /* My own assigned thread ordinal */self = pthread_self(); /* The POSIX Thread library thread number */ printf("TestFunc me=%d - self=%d globvar=%d\n",me,self,globvar);globvar = me + 15; printf("TestFunc me=%d - sleeping globvar=%d\n",me,globvar);sleep(2); printf("TestFunc me=%d - done param=%d globvar=%d\n",me,self,globvar);}

Creating a thread

This figure shows a number of groupings of boxes, labeled global data, code, and stack. A couple discriptions and arrows labeled, executing, are arranged around the boxes.

The global shared areas in this case are those variables declared in the static area outside the main( ) code. The local variables are any variables declared within a routine. When threads are added, each thread gets its own function call stack. In C, the automatic variables that are declared at the beginning of each routine are allocated on the stack. As each thread enters a function, these variables are separately allocated on that particular thread’s stack. So these are the thread-local variables.

Unlike the fork( ) function, the pthread_create( ) function creates a new thread, and then control is returned to the calling thread. One of the parameters of the pthread_create( ) is the name of a function.

New threads begin execution in the function TestFunc( ) and the thread finishes when it returns from this function. When this program is executed, it produces the following output:

Questions & Answers

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
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
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
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
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