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
