(OpenMP) How to start each function 1 time in 1 thread

Question

I have 4 threads and I want to start in one time 3 functions. Each function takes one thread.
But this code is starting every function 4 times

#pragma omp parallel
    {
        Func1();
        Func2();
        Func3();
    }

and I have this result:

Func* 1 * started

Func* 1 * started

Func* 1 * started

Func* 1 * started

Func* 1 * finished

Func* 1 * finished

Func* 1 * finished

Func* 1 * finished

Func* 2 * started

Func* 2 * started

Func* 2 * started

Func* 2 * started

Func* 2 * finished

Func* 2 * finished

Func* 2 * finished

Func* 2 * finished

...

How should I change the code to display some like this:

Func* 1 * started

Func* 2 * started

Func* 3 * started

Func* 2 * finished

Func* 1 * finished

Func* 3 * finished

Answer 1

What you are searching for is the sections worksharing construct. The syntax should be the following:

#pragma omp parallel
{
#pragma omp sections
  {
#pragma omp section
    Func1();
#pragma omp section
    Func2();
#pragma omp section
    Func3();
  }
}

I suggest you to refer to the specifications and the examples therein for more information on how this construct works.

Answer 2

As already answered by Massimiliano, the easiest way to achieve what you want is to use the sections construct:

#pragma omp parallel sections
{
    #pragma omp section
    Func1();
    #pragma omp section
    Func2();
    #pragma omp section
    Func3();
}

(when the sections construct is the only thing nested inside a parallel region, both pragmas can be combined as shown)

Each section scopes the statement or block immediately following it. Eg if you'd like to include some more code in a section, you should put it inside a block:

#pragma omp section
{
    Func1();
    SomeOtherFunc1();
}

A more general way to control what each thread does is to examine the thread ID as returned by omp_get_thread_num() and to branch in accordance. This resembles the way MPI programs are written:

#pragma omp parallel
{
    switch (omp_get_thread_num())
    {
        case 0:
            Func1();
            break;
        case 1:
            Func2();
            break;
        case 2:
            Func3();
            break;
        default:
            // Do nothing
     }
}

One obvious disadvantage is that it would only work unless there are at least 3 threads in the team that executes the parallel region, ie code that relies on thread IDs becomes somewhat non-portable. In contrast, the sections directive works with any number of threads, eg if there is only one thread, all sections would be executed sequentially.