Re: OpenMP: data scoping and modules

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Hello Joaquin,

The short answer to your question: Yes.

However, in general it is recommended to keep the usage of global
variables to a minimum, since the "non-locality" in programming style
is error-prone. In your example, just assume that "sub" is called within
a threaded region. Then, at the very least, you need to put updates
to shared_data into a critical region. Even so, your algorithm may
not work as intended.

Regards

joaquin.casanova@xxxxxxxxx wrote:
I'm getting confused by OpenMP behaviour for shared/private. I can't
find a definitive answer about the rules for shared-ness of variables
defined in modules. Let's say I have a program like this:

PROGRAM test

use omp_lib
use utils

implicit none

real::out,x

call sub

call omp_set_num_threads(4)

!$omp parallel private(out,x)
x = ...
out = func(x)
print*,x,out,omp_get_num_thread()
!$omp end parallel

END PROGRAM test

MODULE utils

use data
implicit none

contains

FUNCTION func(x) result(y)
...
private_data = x
...
END FUNCTION func

SUBROUTINE sub
...
shared_data = ...
...
END SUBROUTINE sub

END MODULE utils

MODULE data

implicit none

real::shared_data
real::private_data

!$omp threadprivate(private_data)

END MODULE data

My question is this: with the omp directives in this example, is
shared_data shared, and is private_data private? Thanks for your help.


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