Intel C++ 10, OpenMP & OpenSuSE Linux
Friday, August 31st, 2007
As promised yesterday, I’ll try the OpenMP features of Intel C++ 10.0 for Linux today. Cause I’m lazy, I use a wide spread “Hello World” for OpenMP example, it is very simple and it’s only purpose is to demonstrate the basics of how to parallelize a code with OpenMP.
/***********************************************************
* FILE: omp_hello.c
* DESCRIPTION:
* OpenMP Example - Hello World - C/C++ Version
* In this simple example, the master thread
* forks a parallel region. All threads in the team obtain
* their unique thread number and print it. The master
* thread only prints the total number of threads. Two OpenMP
* library routines are used to obtain the number of threads
* and each thread's number.
* AUTHOR: Blaise Barney 5/99
* LAST REVISED: 04/06/05
************************************************************/
#include <omp.h>
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char **argv) {
int nthreads, tid;
/* Fork a team of threads giving them their own copies of variables */
#pragma omp parallel private(nthreads, tid)
{
/* Obtain thread number */
tid = omp_get_thread_num();
printf("Hello World from thread = %dn", tid);
/* Only master thread does this */
if (tid == 0)
{
nthreads = omp_get_num_threads();
printf("Number of threads = %dn", nthreads);
}
} /* All threads join master thread and disband */
}
To compile this example with icc you need the OpenMP switch turned on:
rainer@novotop:/tmp> icc -openmp omp_hello.c
omp_hello.c(22): (col. 1) remark: OpenMP DEFINED REGION
WAS PARALLELIZED.
rainer@novotop:/tmp> ./a.out
Hello World from thread = 0
Number of threads = 2
Hello World from thread = 1
Ok, that’s pretty cool. We saw how to parallelize a region and giving private variables to it. By the way, you can specify the number of threads OpenMP starts with the OMP_NUM_THREADS environment variable (export OMP_NUM_THREADS=4, then start a.out -> you get four thread outputs).
Next post will handle mutexes, semaphores, thread shared memory etc. in more depth.
About installing Intel C++ 10.0 on OpenSuSE 10.2
A good tutorial
