Parallel Programming - Hello World

Many computer science/engineering students learn to write Hello World program at their first programming lecture. What's your first parallel program? What about Hello World program in OpenMP, MPI, Cilk++, TBB, Ruby thread, PThread?

Hello World in C

/* hello.c */
#include <stdio.h>

int main()
{
    printf("hello world\n");
    return 0;
}

$ gcc hello.c -o hello
$ ./hello
hello world

Hello World in OpenMP

/* hello-omp.c */
#include <stdio.h>
#include <omp.h>

int main()
{
    #pragma omp parallel
    {   
        int n = omp_get_num_threads();
        int id = omp_get_thread_num();

        printf("hello world %d/%d\n", n, id);
    }   
    return 0;
}

$ gcc -fopenmp hello-omp.c -o hello-omp
$ ./hello-omp
hello world 1/2
hello world 0/2
$ ./hello-omp
hello world 0/2
hello world 1/2

Hello World in MPI

/* hello-mpi.c */
#include <stdio.h>
#include <mpi.h>

int main(int argc, char* argv[])
{
    int n, id; 
    MPI_Init(&argc, &argv);
    MPI_Comm_size(MPI_COMM_WORLD, &n);
    MPI_Comm_rank(MPI_COMM_WORLD, &id);

    printf("hello world %d/%d\n", id, n); 

    MPI_Finalize();
    return 0;
}

$ mpicc hello-mpi.c -o hello-mpi
$ mpirun -np 2 ./hello-mpi
hello world 0/2
hello world 1/2
$ mpirun -np 2 ./hello-mpi
hello world 1/2
hello world 0/2

Hello World in Cilk++

/* hello.cilk */
#include <stdio.h>

void hello()
{
    printf("hello world\n");
}

int cilk_main()
{
    cilk_spawn hello();
    cilk_spawn hello();
    cilk_sync;
    return 0;
}

$ cilk++ hello.cilk -o hello-cilk
$ ./hello-cilk
hello world
hello world

Hello World in TBB

/* hello-tbb.cpp */
#include <iostream>
#include <tbb/parallel_for.h>

using namespace tbb;

class Hello
{
public:
    void operator()(int x) const {
        std::cout << "Hello world\n";
    }
};

int main()
{
    // parallelizing:
    // for(int i = 0; i < 2; ++i) { ... }
    parallel_for(0, 2, 1, Hello());

    return 0;
}

$ g++ hello-tbb.cpp -ltbb -o hello-tbb
$ ./hello-tbb 
Hello world
Hello world

Hello World in Ruby Thread

/* hello.rb */
#!/usr/bin/ruby

def hello
    id = Thread.current.object_id
    puts "hello world #{id}"
end

t1 = Thread.new do
    hello
end
t2 = Thread.new do
    hello
end

t1.join
t2.join

$ ./hello.rb
hello world 69858970515620
hello world 69858970515540

Hello World in PThread

/* hello-pthread.c */
#include <stdio.h>
#include <pthread.h>

void* hello(void* arg)
{
    long id = (long)pthread_self();
    printf("hello world %ld\n", id);
    pthread_exit(NULL);
}

int main()
{
    pthread_t tid1, tid2;
    pthread_attr_t attr;

    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr,
                                PTHREAD_CREATE_JOINABLE);

    pthread_create(&tid1, &attr, hello, NULL);
    pthread_create(&tid2, &attr, hello, NULL);

    pthread_join(tid1, NULL);
    pthread_join(tid2, NULL);

    pthread_attr_destroy(&attr);
    pthread_exit(NULL);

    return 0;
}

$ gcc hello-pthread.c -lpthread -o hello-pthread
$ ./hello-pthread 
hello world 139999688689424
hello world 139999680296720