I) definitions of vars & linear code, setting up some vars for later usage
II) a while loop which works like that in pseudocode:
nr=1
while(true)
{
filename='result'//nr//'.bin' (nr converted to string)
if(!file_exists(filename))
goto 100
// file exists... so do something with it
// calculations, read/write...
nr=nr+1
}
100 continue
III) some more linear code...
现在我想用openmpi进行并行计算。来自I)和III)的线性代码应该只计算一次,而while循环应该在几个处理器上运行......如何最好地实现它? 我的问题是while循环是如何工作的:例如当处理器1计算result1.bin时,如何直接告诉处理器2计算result2.bin?如果有30个文件,我将如何使用
mpirun -n 10 my_program
? MPI如何“知道”在完成计算一个文件之后,有更多文件“等待”处理:一个处理器处理完一个文件后,该处理器应该直接重新开始处理队列中的下一个文件。
到目前为止感谢!
#编辑:
#嘿那里,又是我了......我也想尝试OpenMP,所以我使用了一大块代码来读取现有文件,然后循环它们(并处理它们):
nfiles = 0
do
write(filename,FMT='(A,I0,A)'), prefix, nfiles+1, suffix
inquire(file=trim(filename),exist=exists)
if (not(exists)) exit
nfiles = nfiles + 1
enddo
现在我尝试了以下代码:
call omp_set_num_threads(2)
!$OMP PARALLEL
!$OMP DO
do i=startnum, endnum
write(filename,FMT='(A,I0,A)'), prefix, i, suffix
...CODE DIRECTLY HERE TO PROCESS THE FILE...
enddo
!$OMP END DO
!$OMP END PARALLEL
但它总是给我这样的错误: “分支出与Open MP DO或PARALLEL DO指令相关的DO循环是非法的。”
总是关于这类代码的代码行:
read (F_RESULT,*,ERR=1) variable
F_RESULT是一个文件句柄......有什么可能是错的? 变量是在循环块之外定义的,我已经尝试将OpenMP指令设置为
private(variable)
这样每个帖子都有自己的副本,但是没有用完! 非常感谢您的帮助!
答案 0 :(得分:5)
执行此操作的最明智的方法可能是让其中一个进程预先计算文件总数,广播该文件,然后让每个人都执行“他们的”文件:
program processfiles
use mpi
implicit none
integer :: rank, comsize, ierr
integer :: nfiles
character(len=6) :: prefix="result"
character(len=4) :: suffix=".bin"
character(len=50) :: filename
integer :: i
integer :: locnumfiles, startnum, endnum
logical :: exists
call MPI_Init(ierr)
call MPI_Comm_size(MPI_COMM_WORLD, comsize, ierr)
call MPI_Comm_rank(MPI_COMM_WORLD, rank, ierr)
! rank zero finds number of files
if (rank == 0) then
nfiles = 0
do
write(filename,FMT='(A,I0,A)'), prefix, nfiles+1, suffix
inquire(file=trim(filename),exist=exists)
if (not(exists)) exit
nfiles = nfiles + 1
enddo
endif
! make sure everyone knows
call MPI_Bcast(nfiles, 1, MPI_INTEGER, 0, MPI_COMM_WORLD, ierr)
if (nfiles /= 0) then
! calculate who gets what file
locnumfiles = nfiles/comsize
if (locnumfiles * comsize /= nfiles) locnumfiles = locnumfiles + 1
startnum = locnumfiles * rank + 1
endnum = startnum + locnumfiles - 1
if (rank == comsize-1) endnum = nfiles
do i=startnum, endnum
write(filename,FMT='(A,I0,A)'), prefix, i, suffix
call processfile(rank,filename)
enddo
else
if (rank == 0) then
print *,'No files found; exiting.'
endif
endif
call MPI_Finalize(ierr)
contains
subroutine processfile(rank,filename)
implicit none
integer, intent(in) :: rank
character(len=*), intent(in) :: filename
integer :: unitno
open(newunit=unitno, file=trim(filename))
print '(I4,A,A)',rank,': Processing file ', filename
close(unitno)
end subroutine processfile
end program processfiles
然后进行简单的测试:
$ seq 1 33 | xargs -I num touch "result"num".bin"
$ mpirun -np 2 ./processfiles
0: Processing file result1.bin
0: Processing file result2.bin
0: Processing file result3.bin
0: Processing file result4.bin
0: Processing file result5.bin
0: Processing file result6.bin
1: Processing file result18.bin
0: Processing file result7.bin
0: Processing file result8.bin
1: Processing file result19.bin
0: Processing file result9.bin
1: Processing file result20.bin
0: Processing file result10.bin
1: Processing file result21.bin
1: Processing file result22.bin
0: Processing file result11.bin
1: Processing file result23.bin
0: Processing file result12.bin
1: Processing file result24.bin
1: Processing file result25.bin
0: Processing file result13.bin
0: Processing file result14.bin
1: Processing file result26.bin
1: Processing file result27.bin
0: Processing file result15.bin
0: Processing file result16.bin
1: Processing file result28.bin
1: Processing file result29.bin
1: Processing file result30.bin
0: Processing file result17.bin
1: Processing file result31.bin
1: Processing file result32.bin
1: Processing file result33.bin
更新了以添加补充的OpenMP问题:
因此,在文件的并行处理开始之前,第一个循环是计算文件数的位置。在文件的并行处理发生之前,需要对文件进行计数,否则就不可能在处理器之间划分工作;你需要知道在分割工作之前会有多少“工作单位”。 (这不是绝对唯一的做事方式,但它是最直接的方式)。
类似地,OMP DO
循环需要非常结构化的循环 - 需要有一个简单的循环,如do i=1,n
,然后可以在线程之间轻松分解。 n
不需要编译,并且增量甚至不需要是1,但它必须是在实际执行循环之前可以确定的那种事情。因此,例如,由于某些外部原因(如不存在文件),您无法退出循环。
所以你想用OpenMP做的是做同样的文件计数,然后单独留下,但是在处理循环中,使用并行的do构造。因此,在删除MPI之后,你会看到类似的内容:
do
write(filename,FMT='(A,I0,A)'), prefix, nfiles+1, suffix
inquire(file=trim(filename),exist=exists)
if (.not.exists) exit
nfiles = nfiles + 1
enddo
if (nfiles /= 0) then
!$OMP PARALLEL SHARED(nfiles,prefix,suffix) PRIVATE(i,thread,filename)
thread = omp_get_thread_num()
!$OMP DO
do i=1, nfiles
write(filename,FMT='(A,I0,A)'), prefix, i, suffix
call processfile(thread,filename)
enddo
!$OMP END DO
!$OMP END PARALLEL
else
print *,'No files found; exiting.'
endif
但其他一切都是一样的。而且,如果你想处理文件“内联”(例如,不在sburoutine中),你可以将文件处理代码放在'call processfile()'行的位置。