Parallel Programming in Fortran 95 using OpenMP - People

18 2. OpenMP constructs
thread 0 thread 1 thread N p
!$OMP SINGLE
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E xecution
parallel region
write(*,*) "Hello"
...
!$OMP END SINGLE
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Figure 2.3: Graphical representation of the example explaining the working principle of the
!$OMP SINGLE/!$OMP END SINGLE directive-pair.
be parallelized with the aid of the !$OMP WORKSHARE/!$OMP END WORKSHARE directive-pair:
matmul, dot product, sum, product, maxval, minval, count, any, all, spread, pack, unpack,
reshape, transpose, eoshift, cshift, minloc and maxloc. The syntax to be used is the
following one:
!$OMP WORKSHARE
...
!$OMP END WORKSHARE end_clause
where an implied synchronization exists in the closing-directive !$OMP END WORKSHARE,
if the NOWAIT clause is not specified on the closing-directive.
In contrast to the previously presented work-sharing constructs, the block of code
enclosed inside the present directive-pair is executed in such a way, that each statement
is completed before the next statement is started. The result is that the block of code
behaves exactly in the same way as if it would be executed in serial. For example,
the effects of one statement within the enclosed code must appear to occur before the
execution of the following statements, and the evaluation of the right hand side of an
assignment must appear to have been completed prior to the effects of assigning to the
left hand side. This means that the following example
real(8) :: A(1000), B(1000)