Programming/C
From HPC
Contents
Programming Details
C is a general-purpose, imperative computer programming language. There are some derivations of the language due to the modernisation of the original specification in the form of C++ and C#.
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There is direct support for openMP and openMPI. |
Programming example
#include <omp.h>
#include <stdio.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
{
/* Obtain thread number */
tid = omp_get_thread_num();
printf("Hello World from thread = %d\n", tid);
/* Only Master thread does this */
if(tid == 0)
{
nthreads = omp_get_num_threads();
printf("Number of threads = %d\n", nthreads);
}
} /* All threads join together and disband */
return (0);
}
Compilation
The program would be compiled in the following way, optional Intel compiler available too:
[username@login01 ~]$ module add gcc/4.9.3 [username@login01 ~]$ gcc -o test2 -fopenmp test2.c (openMP support) [username@login01 ~]$ ./test2 Hello World from thread = 0 Number of threads = 1
Modules Available
The following modules are available for C
- module add gcc/4.9.3 (GNU compiler)
- module add intel/compiler/64/2016.2.181 (Intel compiler)
Note: OpenMP is a library directive within the compiler and does not require any additional module to be loaded.
Usage Examples
Batch example
#!/bin/bash #SBATCH -J openmpi-single-node #SBATCH -N 1 #SBATCH --ntasks-per-node 28 #SBATCH -o %N.%j.%a.out #SBATCH -e %N.%j.%a.err #SBATCH -p compute #SBATCH --exclusive echo $SLURM_JOB_NODELIST module purge module add gcc/4.9.3 export I_MPI_DEBUG=5 export I_MPI_FABRICS=shm:tmi export I_MPI_FALLBACK=no /home/user/CODE_SAMPLES/OPENMP/demo
[username@login01 ~]$ sbatch demo.job Submitted batch job 289552