Fortran中自定义类型的嵌套数据结构

Question

我正在寻找一种在 Fortran 2008 中使用用户定义类型构建树结构的方法。虽然我可以使一些基本代码正常工作，但我遇到了无法查明的内存泄漏。

树结构不必过于通用，因为它被用作一次性插入和多次读取的存储类型，这就是我决定使用可分配表的原因。由于 Fortran 不允许将可分配类型用作其自身成员之一，因此我使用由指针引用的中间结构来存储可分配。因此，以下是我想使用但不允许使用的内容：

type :: invalid_section
  type(invalid_section), dimension(:), allocatable :: subsections
end type

在下面的示例中，我使用了指向持有可分配类型的指针的惰性分配（仅当有子节点指向 add/present 时才分配它）。

module sectiontest

   type :: section
      type(subsections), pointer :: subsections_ => null()

      contains
         procedure, pass(self) :: section_assign
         generic :: assignment(=) => section_assign

         final :: section_cleanup, section_cleanup_arr
   end type

   type :: subsections
      type(section), dimension(:), allocatable :: arr
   end type

   interface section
      module procedure constructor
   end interface

contains

   type(section) function constructor(subsections)
      type(section), optional, intent(in) :: subsections(:)
      integer :: idx

      print *, "constructor"

      if (present(subsections)) then
         print *, "allocating subsection"
         allocate(constructor%subsections_)
         allocate(constructor%subsections_%arr(size(subsections)))
         do idx=1,size(subsections)
            ! make sure we recursively copy everything
            constructor%subsections_%arr(idx) = subsections(idx)
         enddo
      endif
   end function

   recursive subroutine section_assign(self, rhs)
      class(section), intent(inout) :: self
      type(section), intent(in) :: rhs
      integer :: idx

      print *, "assign"
      if (associated(self%subsections_)) then
         deallocate(self%subsections_)
      endif

      if (associated(rhs%subsections_)) then
         print *, "allocation subsection"
         allocate(self%subsections_)
         allocate(self%subsections_%arr(size(rhs%subsections_%arr)))

         do idx=1,size(rhs%subsections_%arr)
            self%subsections_%arr(idx) = rhs%subsections_%arr(idx)
         enddo
      endif
   end subroutine

   recursive subroutine section_cleanup(sec)
      type(section), intent(inout) :: sec

      print *, "section_cleanup"
      if (associated(sec%subsections_)) then
         print *, "  deallocated a subsection"
         deallocate(sec%subsections_)
      endif
   end subroutine

   recursive subroutine section_cleanup_arr(arr)
      type(section), dimension(:), intent(inout) :: arr
      integer :: idx

      print *, "deallocating array of sections of size:", size(arr)

      do idx=1,size(arr)
         print *, "deallocating subsection array index", idx
         if (associated(arr(idx)%subsections_)) then
            print *, "  deallocated a subsection"
            deallocate(arr(idx)%subsections_)
         endif
      end do
   end subroutine

   subroutine demo()
      type(section) :: root

      root = section(subsections=[ &
         section(subsections=[section(), section(), section()]), &
         section() &
         ])
   end subroutine
end module sectiontest

program main
   use sectiontest
   implicit none

   call demo()
end program

从 gfortran（7 和 9）、flang 和 nagfor 我得到来自 constructor 中的 allocate(constructor%subsections_) 的直接内存泄漏。

来自 gfortran-7 并使用 -fsanitize=address 构建：

==26536==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 48 byte(s) in 1 object(s) allocated from:
    #0 0x7f965539c510 in malloc (/usr/lib64/libasan.so.4+0xdc510)
    #1 0x407e35 in __sectiontest_MOD_constructor /users/tiziano/work/tests/fortran/cp2k_input_parser/recursive_mwe.f90:31
    #2 0x40432a in __sectiontest_MOD_demo /users/tiziano/work/tests/fortran/cp2k_input_parser/recursive_mwe.f90:92
    #3 0x4090d9 in MAIN__ /users/tiziano/work/tests/fortran/cp2k_input_parser/recursive_mwe_prog.f90:5
    #4 0x409119 in main /users/tiziano/work/tests/fortran/cp2k_input_parser/recursive_mwe_prog.f90:2
    #5 0x7f96543c2f89 in __libc_start_main (/lib64/libc.so.6+0x20f89)

我正在寻找替代实现（但最好是类似的优雅初始化）或内存泄漏的解释和可能的解决方案。

Answer 1

Fortran 2008 支持包含所定义类型的可分配组件的类型。这将代码简化为：

module sectiontest
   type :: section
      type(section), allocatable :: subsections(:)
   end type
contains
   subroutine demo()
      type(section) :: root

      root = section( subsections=[ &
         section(subsections=[section(), section(), section()]), &
         section() ])
   end subroutine
end module sectiontest

program main
   use sectiontest
   implicit none

   call demo()
end program

最新版本的 gfortran 支持此语言功能。

对于不能充分支持 Fortran 2008 的编译器，问题中的代码是一种合理的解决方法，并且可以在正确实现 Fortran 2003 的编译器上运行。

但是，gfortran（至少达到 9.1.1）没有正确实现函数结果的最终确定 - 因此观察到内存泄漏。

Fortran中自定义类型的嵌套数据结构

Nested data structure of User-Defined Type in Fortran

pointers

memory-leaks

fortran

user-defined-types

allocatable-array