Example Code

Try out my simple openMP examples, you can copy them over from here:

cp -r ~newhall/public/openMP_examples .

Include the opm.h file and then add in #pragma and other constructs. Here is a simple example:

#include <stdio.h>
#include <stdlib.h>
#ifdef _OPENMP
#include <omp.h>
#endif

int main() {
   int tid = -1;
#pragma omp parallel private(tid) // Start of parallel region: forks threads
   {
     tid = omp_get_thread_num();  // default is number of CPUs on machine
     printf("Hello from Thread %d\n",tid);
     if(tid ==0) {
        printf("Number of threads = %d\n", omp_get_num_threads());
     }
   }  // ** end of the the parallel: joins threads
   return 0;
}

• In your C source file #include <omp.h>

• Then compile with -f openmp:

  gcc -Wall -g -o hello hello.c -f openmp
  

• Then just run the executable from the command line:

  ./hello
  

  If you run top -H in another terminal you can see the multiple threads running (for something that runs longer than the hello example)

• OpenMPlinks The tutorial is a good place to start.

• top -H get system usage info on a per-thread basis

• Lab Machine specs page contains information about most of the lab machines, including number of cores.
• My help pages