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77 lines
2.5 KiB
TeX
77 lines
2.5 KiB
TeX
\pagebreak
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\chapter{The \code{workshare} Construct}
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\fortranspecificstart
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\label{chap:workshare}
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The following are examples of the \code{workshare} construct.
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In the following example, \code{workshare} spreads work across the threads executing
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the \code{parallel} region, and there is a barrier after the last statement.
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Implementations must enforce Fortran execution rules inside of the \code{workshare}
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block.
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\fnexample{workshare}{1f}
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In the following example, the barrier at the end of the first \code{workshare}
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region is eliminated with a \code{nowait} clause. Threads doing \code{CC =
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DD} immediately begin work on \code{EE = FF} when they are done with \code{CC
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= DD}.
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\fnexample{workshare}{2f}
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% blue line floater at top of this page for "Fortran, cont."
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\begin{figure}[t!]
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\linewitharrows{-1}{dashed}{Fortran (cont.)}{8em}
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\end{figure}
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The following example shows the use of an \code{atomic} directive inside a \code{workshare}
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construct. The computation of \code{SUM(AA)} is workshared, but the update to
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\code{R} is atomic.
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\fnexample{workshare}{3f}
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Fortran \code{WHERE} and \code{FORALL} statements are \emph{compound statements},
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made up of a \emph{control} part and a \emph{statement} part. When \code{workshare}
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is applied to one of these compound statements, both the control and the statement
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parts are workshared. The following example shows the use of a \code{WHERE} statement
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in a \code{workshare} construct.
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Each task gets worked on in order by the threads:
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\code{AA = BB} then
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\\
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\code{CC = DD} then
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\\
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\code{EE .ne. 0} then
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\\
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\code{FF = 1 / EE} then
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\\
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\code{GG = HH}
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\fnexample{workshare}{4f}
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% blue line floater at top of this page for "Fortran, cont."
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\begin{figure}[t!]
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\linewitharrows{-1}{dashed}{Fortran (cont.)}{8em}
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\end{figure}
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In the following example, an assignment to a shared scalar variable is performed
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by one thread in a \code{workshare} while all other threads in the team wait.
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\fnexample{workshare}{5f}
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The following example contains an assignment to a private scalar variable, which
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is performed by one thread in a \code{workshare} while all other threads wait.
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It is non-conforming because the private scalar variable is undefined after the
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assignment statement.
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\fnexample{workshare}{6f}
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Fortran execution rules must be enforced inside a \code{workshare} construct.
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In the following example, the same result is produced in the following program
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fragment regardless of whether the code is executed sequentially or inside an OpenMP
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program with multiple threads:
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\fnexample{workshare}{7f}
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\fortranspecificend
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