OpenAcc笔记——update

        program main
        use omp_lib
        use openacc
        implicit none
        
        real,allocatable:: v1(:)
        integer length, idx
        
        call acc_set_device_num(2,acc_device_nvidia)
        length = 1024!*1024!*1024
        allocate(v1(length))
        v1(1:length) = 0.0
        !使用data语句，将数据copy到device上
        !$acc data copy(v1(1: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(1:5))
        print*, "v1(1) = ", v1(1:5)
        !下面是在cpu上执行
        do idx = 1,length
        v1(idx) = v1(idx) + 10
        enddo
        print*, "v1(1) = ", v1(1:5) !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(1:5))
        call add1(v1, length)
        
        !上面子程序在device上执行完，update到本地输出
        !$acc update host(v1(1:5))
        print*, "v1(1) = ", v1(1:5)
        !结束
        !$acc end data
        
        deallocate(v1)

        end program 
        
        subroutine add1(vec, length)
        use openacc
        implicit none
        integer, intent(in)::length
        real, intent(inout) :: vec(1:length)
        integer idx
        !$acc parallel loop present(vec(1:length))
        do idx = 1, length
            vec(idx) = vec(idx) + idx
        enddo
        end subroutine