stdx.allocator.building_blocks.affix_allocator

  • AffixAllocator

    Declaration

    struct AffixAllocator(Allocator, Prefix, Suffix = void);

    Allocator that adds some extra data before (of type ) and/or after (of type ) any allocation made with its parent allocator. This is useful for uses where additional allocation-related information is needed, such as mutexes, reference counts, or walls for debugging memory corruption errors.

    Discussion

    If is not , must guarantee an alignment at least as large as .

    Suffixes are slower to get at because of alignment rounding, so prefixes should be preferred. However, small prefixes blunt the alignment so if a large alignment with a small affix is needed, suffixes should be chosen.

    The following methods are defined if defines them, and forward to it: , , .

    Examples

    1. import stdx.allocator.mallocator : Mallocator; // One word before and after each allocation. alias A = AffixAllocator!(Mallocator, size_t, size_t); auto b = A.instance.allocate(11); A.instance.prefix(b) = 0xCAFE_BABE; A.instance.suffix(b) = 0xDEAD_BEEF; assert(A.instance.prefix(b) == 0xCAFE_BABE && A.instance.suffix(b) == 0xDEAD_BEEF);

    • alignment

      Declaration

      enum uint alignment;

      If is , the alignment is that of the parent. Otherwise, the alignment is the same as the 's alignment.

    • _parent

      Declaration

      Allocator _parent;

      If the parent allocator is stateful, an instance of it is stored as a member. Otherwise, uses Allocator.instance. In either case, the name is uniformly used for accessing the parent allocator.

    • parent

      Declaration

      Allocator parent();

      If the parent allocator is stateful, an instance of it is stored as a member. Otherwise, uses Allocator.instance. In either case, the name is uniformly used for accessing the parent allocator.

    • goodAllocSize

      Declaration

      size_t goodAllocSize(size_t);
      void[] allocate(size_t);
      Ternary owns(void[]);
      bool expand(ref void[] b, size_t delta);
      bool reallocate(ref void[] b, size_t s);
      bool deallocate(void[] b);
      bool deallocateAll();
      Ternary empty();

      Standard allocator methods. Each is defined if and only if the parent allocator defines the homonym method (except for , which may use the global default). Also, the methods will be if the parent allocator defines them as such.

    • instance

      Declaration

      static AffixAllocator instance;

      The instance singleton is defined if and only if the parent allocator has no state and defines its own it object.

    • prefix

      Declaration

      ref auto prefix(T)(T[] b);
      ref auto suffix(T)(T[] b);

      Affix access functions offering references to the affixes of a block b previously allocated with this allocator. b may not be null. They are defined if and only if the corresponding affix is not void.

      Discussion

      The qualifiers of the affix are not always the same as the qualifiers of the argument. This is because the affixes are not part of the data itself, but instead are just associated with the data and known to the allocator. The table below documents the type of preffix(b) and affix(b) depending on the type of b.

      Precondition: b !is null and b must have been allocated with this allocator.