coarray fortran 数组没有得到更新

Question

我刚开始学习使用 Coarry 和 Fortran。我有一个非常简单的程序。我有一个长度为 9 的数组，我想将其分配给 3 个进程，进行一些计算，然后将它们合并回单个数组（基本 MPI_scatter/MPI_gather 之类的问题）。

program name
   implicit none
   integer:: arr(9), local(3)[*]
   integer:: i, j, k, iz

   arr = [(i, i = 1, 9)]

   local(:)[1] = arr(1:3)
   local(:)[2] = arr(4:6)
   local(:)[3] = arr(7:9)

   iz = this_image()
   local = local*iz

   sync all
    
   if(iz == 1) then
      arr(1:3) = local(:)[1]
      arr(4:6) = local(:)[2]
      arr(7:9) = local(:)[3]
      write(*,'(*(i3))')arr
   endif

end program name

我正在用

编译这个

gfortran -fcorray=lib -lcaf_mpi

并以此执行

mpirun -np 3 ./a.out

这应该是这样的打印输出

 1 2 3 8 10 12 21 24 27

但是，如果我多次运行可执行文件（无需重新编译），有时它会显示多个结果，例如 1 2 3 4 5 6 21 24 27 等。这些值不会随着计算而更新。

我做错了什么？如何解决这个问题

Answer 1

欢迎来到共享内存编程的精彩世界！

您有竞争条件。有可能其中一个图像远远落后于其他图像，以至于它在另一个图像执行 local = local*iz 后重置（远程）数据。这是一种修复它的方法，要格外小心，只有一个进程会设置数据的给定部分：

ijb@ijb-Latitude-5410:~/work/stack$ cat caf.f90
program name
   implicit none
   integer:: arr(9), local(3)[*]
   integer:: i, j, k, iz

   iz = this_image()

   ! Only one image should ever write to a given memory location
   ! between synchronisation points. In a real code each different image
   ! would set up different parts of the array
   If( iz == 1 ) Then
      arr = [(i, i = 1, 9)]
      local(:)[1] = arr(1:3)
      local(:)[2] = arr(4:6)
      local(:)[3] = arr(7:9)
   End If

   ! Make sure the array is fully set up before you use it
   sync all

   local = local*iz

   sync all
    
   if(iz == 1) then
      arr(1:3) = local(:)[1]
      arr(4:6) = local(:)[2]
      arr(7:9) = local(:)[3]
      write(*,'(*(i3))')arr
   endif

end program name
ijb@ijb-Latitude-5410:~/work/stack$ mpif90 -std=f2018 -fcheck=all -Wall -Wextra -O -g -fcoarray=lib  caf.f90 -lcaf_openmpi
caf.f90:4:17:

    4 |    integer:: i, j, k, iz
      |                 1
Warning: Unused variable ‘j’ declared at (1) [-Wunused-variable]
caf.f90:4:20:

    4 |    integer:: i, j, k, iz
      |                    1
Warning: Unused variable ‘k’ declared at (1) [-Wunused-variable]
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27
ijb@ijb-Latitude-5410:~/work/stack$ mpirun -np 3 ./a.out
  1  2  3  8 10 12 21 24 27

coarray fortran 数组没有得到更新

coarray fortran array doesn't get updated

fortran

fortran-coarrays