Examples_workshare.tex

\pagebreak
\chapter{The \code{workshare} Construct}
\fortranspecificstart
\label{chap:workshare}

The following are examples of the \code{workshare} construct. 

In the following example, \code{workshare} spreads work across the threads executing 
the \code{parallel} region, and there is a barrier after the last statement. 
Implementations must enforce Fortran execution rules inside of the \code{workshare} 
block.

\fnexample{workshare}{1f}

In the following example, the barrier at the end of the first \code{workshare} 
region is eliminated with a \code{nowait} clause. Threads doing \code{CC = 
DD} immediately begin work on \code{EE = FF} when they are done with \code{CC 
= DD}.

\fnexample{workshare}{2f}
% blue line floater at top of this page for "Fortran, cont."
\begin{figure}[t!]
\linewitharrows{-1}{dashed}{Fortran (cont.)}{8em}
\end{figure}

The following example shows the use of an \code{atomic} directive inside a \code{workshare} 
construct. The computation of \code{SUM(AA)} is workshared, but the update to 
\code{R} is atomic.

\fnexample{workshare}{3f}

Fortran \code{WHERE} and \code{FORALL} statements are \emph{compound statements}, 
made up of a \emph{control} part and a \emph{statement} part. When \code{workshare} 
is applied to one of these compound statements, both the control and the statement 
parts are workshared. The following example shows the use of a \code{WHERE} statement 
in a \code{workshare} construct.

Each task gets worked on in order by the threads:

\code{AA = BB} then
\\
\code{CC = DD} then
\\
\code{EE .ne. 0} then
\\
\code{FF = 1 / EE} then
\\
\code{GG = HH}

\fnexample{workshare}{4f}
% blue line floater at top of this page for "Fortran, cont."
\begin{figure}[t!]
\linewitharrows{-1}{dashed}{Fortran (cont.)}{8em}
\end{figure}

In the following example, an assignment to a shared scalar variable is performed 
by one thread in a \code{workshare} while all other threads in the team wait.

\fnexample{workshare}{5f}

The following example contains an assignment to a private scalar variable, which 
is performed by one thread in a \code{workshare} while all other threads wait. 
It is non-conforming because the private scalar variable is undefined after the 
assignment statement. 

\fnexample{workshare}{6f}

Fortran execution rules must be enforced inside a \code{workshare} construct. 
In the following example, the same result is produced in the following program 
fragment regardless of whether the code is executed sequentially or inside an OpenMP 
program with multiple threads:

\fnexample{workshare}{7f}
\fortranspecificend