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37 lines
1.6 KiB
TeX
37 lines
1.6 KiB
TeX
%\pagebreak
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\section{\kcode{requires} Directive}
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\label{sec:requires}
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\index{directives!requires@\kcode{requires}}
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\index{requires directive@\kcode{requires} directive}
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The declarative \kcode{requires} directive can be used to
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specify features that an implementation must provide to compile and
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execute correctly.
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\index{requires directive@\kcode{requires} directive!unified_shared_memory clause@\kcode{unified_shared_memory} clause}
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\index{clauses!unified_shared_memory@\kcode{unified_shared_memory}}
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\index{unified_shared_memory clause@\kcode{unified_shared_memory} clause}
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In the following example the \kcode{unified_shared_memory} clause
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of the \kcode{requires} directive ensures that the host and all
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devices accessible through OpenMP provide a \plc{unified address} space
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for memory that is shared by all devices.
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The example illustrates the use of the \kcode{requires} directive specifying
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\plc{unified shared memory} in file scope, before any device
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directives or device routines. No \kcode{map} clause is needed for
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the \ucode{p} structure on the device (and its address \ucode{\&p}, for the C++ code,
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is the same address on the host and device).
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However, scalar variables referenced within the \kcode{target}
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construct still have a default data-sharing attribute of \kcode{firstprivate}.
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The \ucode{q} scalar is incremented on the device, and its change is
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not updated on the host.
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% will defaultmap(toform:scalar) make q use shared address space?
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%Or will it be ignored at this point.
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% Does before device routines also mean before prototype?
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%\pagebreak
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\cppexample[5.0]{requires}{1}
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\ffreeexample[5.0]{requires}{1}
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