[Gomp-discuss] A Simple PThread Example of OpenMP

[Scott Robert Ladd]

Here's an example of how a simple OpenMP program can be implemented 
using pthreads. In toher words, GOMP should convert:

    #include <stdio.h>

    int main(void)
    {
        #pragma omp parallel
        puts("Hello, World!\n");

        return 0;
    }

into this code that uses pthreads:

    #include <stdio.h>
    #include <pthread.h>
    #include <unistd.h>

    // this function encapsulates the paralle region defined
    // by the OpenMP pragma
    void * par_proc(void * arg)
    {
        puts("Hello, World!\n");
        return NULL;
    }

    int main(void)
    {
        // what we'd do in a real OpenMP program
        // #pragma omp parallel
        // puts("Hello, World!\n");

        // Linux-specific; OpenMP would also check environment settings
        long num_procs = sysconf(_SC_NPROCESSORS_CONF);
        int n;

        // an array of thread ids
        pthread_t * thread_ids = (pthread_t *)malloc(sizeof(pthread_t)
                                                          * num_procs);

        // for each processor...
        for (n = 0; n < num_procs; ++n)
        {
            // launch a thread, storing its id in the list
            pthread_create(&thread_ids[n],NULL,par_proc,NULL);
        }

        // wait for threads to finish
        for (n = 0; n < num_procs; ++n)
        {
            // wait for each thread in succession
            pthread_join(thread_ids[n],NULL);
        }

        // clean up and exit
        free(thread_ids);
        return 0;
    }

Does this make sense to everyone?

The example is Linux-specific; however, I think that only the sysconf 
call might need to be replaced on other pthread-enabled OSs.

--
Scott Robert Ladd
Coyote Gulch Productions (http://www.coyotegulch.com)
Software Invention for High-Performance Computing