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58 lines
2.4 KiB
TeX
58 lines
2.4 KiB
TeX
\pagebreak
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\section{\code{copyprivate} Clause}
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\label{sec:copyprivate}
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\index{clauses!copyprivate@\code{copyprivate}}
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\index{copyprivate clause@\code{copyprivate} clause}
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The \code{copyprivate} clause can be used to broadcast values acquired by a single
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thread directly to all instances of the private variables in the other threads.
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In this example, if the routine is called from the sequential part, its behavior
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is not affected by the presence of the directives. If it is called from a \code{parallel}
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region, then the actual arguments with which \code{a} and \code{b} are associated
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must be private.
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\index{constructs!single@\code{single}}
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\index{single construct@\code{single} construct}
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The thread that executes the structured block associated with the \code{single}
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construct broadcasts the values of the private variables \code{a}, \code{b},
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\code{x}, and
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\code{y} from its implicit task's data environment to the data environments
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of the other implicit tasks in the thread team. The broadcast completes before
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any of the threads have left the barrier at the end of the construct.
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\cexample{copyprivate}{1}
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\fexample{copyprivate}{1}
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\index{constructs!masked@\code{masked}}
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\index{masked construct@\code{masked} construct}
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In this example, assume that the input must be performed by the primary thread.
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Since the \code{masked} construct does not support the \code{copyprivate} clause,
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it cannot broadcast the input value that is read. However, \code{copyprivate}
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is used to broadcast an address where the input value is stored.
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\cexample[5.1]{copyprivate}{2}
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\fexample[5.1]{copyprivate}{2}
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Suppose that the number of lock variables required within a \code{parallel} region
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cannot easily be determined prior to entering it. The \code{copyprivate} clause
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can be used to provide access to shared lock variables that are allocated within
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that \code{parallel} region.
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\cexample{copyprivate}{3}
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\fortranspecificstart
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\fnexample{copyprivate}{3}
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Note that the effect of the \code{copyprivate} clause on a variable with the
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\code{allocatable} attribute is different than on a variable with the \code{pointer}
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attribute. The value of \code{A} is copied (as if by intrinsic assignment) and
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the pointer \code{B} is copied (as if by pointer assignment) to the corresponding
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list items in the other implicit tasks belonging to the \code{parallel} region.
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\fnexample{copyprivate}{4}
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\fortranspecificend
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