\section{Task Affinity}

\label{sec: task_affinity}

The next example illustrates the use of the \code{affinity}

clause with a \code{task} construct.

The variables in the \code{affinity} clause provide a

hint to the runtime that the task should execute

"close" to the physical storage location of the variables. For example,

on a two-socket platform with a local memory component

close to each processor socket, the runtime will attempt to

schedule the task execution on the socket where the storage is located.

Because the C/C++ code employs a pointer, an array section is used in

the \code{affinity} clause.

Fortran code can use an array reference to specify the storage, as

shown here.

Note, in the second task of the C/C++ code the \plc{B} pointer is declared

shared. Otherwise, by default, it would be firstprivate since it is a local

variable, and would probably be saved for the second task before being assigned

a storage address by the first task. Also, one might think it reasonable to use

the \code{affinity} clause \plc{affinity(B[:N])} on the second \code{task} construct.

However, the storage behind \plc{B} is created in the first task, and the

array section reference may not be valid when the second task is generated.

The use of the \plc{A} array is sufficient for this case, because one

would expect the storage for \plc{A} and \plc{B} would be physically "close"

(as provided by the hint in the first task).

\cexample{affinity}{6}

\ffreeexample{affinity}{6}