OpenAcc笔记——update

         program main
         use omp_lib
         use openacc
         implicit none

         real,allocatable:: v1(:)
         integer length, idx

         call acc_set_device_num(,acc_device_nvidia)
         length = !*!*
         allocate(v1(length))
         v1(:length) = 0.0
         !使用data语句，将数据copy到device上
         !$acc data copy(v1(:length))
         call add1(v1, length) !子程序在device上执行

         !print只能cpu实行，所以讲数据update到cpu上
         !$acc update host(v1(:))
         print*, "v1(1) = ", v1(:)
         !下面是在cpu上执行
         do idx = ,length
         v1(idx) = v1(idx) +
         enddo
         print*, "v1(1) = ", v1(:) !直接打印出cpu上的结果

         !将cpu上的执行结果update到device上
         !$acc update device(v1(:))
         call add1(v1, length)

         !上面子程序在device上执行完，update到本地输出
         !$acc update host(v1(:))
         print*, "v1(1) = ", v1(:)
         !结束
         !$acc end data

         deallocate(v1)

         end program 

         subroutine add1(vec, length)
         use openacc
         implicit none
         integer, intent(in)::length
         real, intent(inout) :: vec(:length)
         integer idx
         !$acc parallel loop present(vec(:length))
         do idx = , length
             vec(idx) = vec(idx) + idx
         enddo
         end subroutine