stdx.allocator.building_blocks.allocator_list

  • AllocatorList

    Declaration

    struct AllocatorList(Factory, BookkeepingAllocator = GCAllocator);
    template AllocatorList(alias factoryFunction, BookkeepingAllocator = GCAllocator)

    Given an object factory of type Factory or a factory function factoryFunction, and optionally also BookkeepingAllocator as a supplemental allocator for bookkeeping, AllocatorList creates an allocator that lazily creates as many allocators are needed for satisfying client allocation requests.

    Discussion

    An embedded list builds a most-recently-used strategy: the most recent allocators used in calls to either allocate, owns (successful calls only), or deallocate are tried for new allocations in order of their most recent use. Thus, although core operations take in theory time for allocators in current use, in many workloads the factor is sublinear. Details of the actual strategy may change in future releases.

    AllocatorList is primarily intended for coarse-grained handling of allocators, i.e. the number of allocators in the list is expected to be relatively small compared to the number of allocations handled by each allocator. However, the per-allocator overhead is small so using AllocatorList with a large number of allocators should be satisfactory as long as the most-recently-used strategy is fast enough for the application.

    AllocatorList makes an effort to return allocated memory back when no longer used. It does so by destroying empty allocators. However, in order to avoid thrashing (excessive creation/destruction of allocators under certain use patterns), it keeps unused allocators for a while.

    Parameters

    factoryFunction

    A function or template function (including function literals). New allocators are created by calling factoryFunction(n) with strictly positive numbers n. Delegates that capture their enviroment are not created amid concerns regarding garbage creation for the environment. When the factory needs state, a Factory object should be used.

    BookkeepingAllocator

    Allocator used for storing bookkeeping data. The size of bookkeeping data is proportional to the number of allocators. If is , then is "ouroboros-style", i.e. it keeps the bookkeeping data in memory obtained from the allocators themselves. Note that for ouroboros-style management, the size passed to will be occasionally different from the size requested by client code.

    Factory

    Type of a factory object that returns new allocators on a need basis. For an object of type , sweatshop(n) should return an allocator able to allocate at least n bytes (i.e. Factory must define opCall(size_t) to return an allocator object). Usually the capacity of allocators created should be much larger than such that an allocator can be used for many subsequent allocations. is passed only to ensure the minimum necessary for the next allocation. The factory object is allowed to hold state, which will be stored inside AllocatorList as a direct public member called factory.

    Examples

    1. import std.algorithm.comparison : max; import stdx.allocator.building_blocks.free_list : ContiguousFreeList; import stdx.allocator.building_blocks.null_allocator : NullAllocator; import stdx.allocator.building_blocks.region : Region; import stdx.allocator.building_blocks.segregator : Segregator; import stdx.allocator.gc_allocator : GCAllocator; import stdx.allocator.mmap_allocator : MmapAllocator; // Ouroboros allocator list based upon 4MB regions, fetched directly from // mmap. All memory is released upon destruction. alias A1 = AllocatorList!((n) => Region!MmapAllocator(max(n, 1024 * 4096)), NullAllocator); // Allocator list based upon 4MB regions, fetched from the garbage // collector. All memory is released upon destruction. alias A2 = AllocatorList!((n) => Region!GCAllocator(max(n, 1024 * 4096))); // Ouroboros allocator list based upon 4MB regions, fetched from the garbage // collector. Memory is left to the collector. alias A3 = AllocatorList!( (n) => Region!NullAllocator(new ubyte[max(n, 1024 * 4096)]), NullAllocator); // Allocator list that creates one freelist for all objects alias A4 = Segregator!( 64, AllocatorList!( (n) => ContiguousFreeList!(NullAllocator, 0, 64)( cast(ubyte[])(GCAllocator.instance.allocate(4096)))), GCAllocator); A4 a; auto small = a.allocate(64); assert(small); a.deallocate(small); auto b1 = a.allocate(1024 * 8192); assert(b1 !is null); // still works due to overdimensioning b1 = a.allocate(1024 * 10); assert(b1.length == 1024 * 10);

    • Allocator

      Declaration

      alias Allocator = typeof(Factory.init(1));

      Alias for typeof(Factory()(1)), i.e. the type of the individual allocators.

    • bkalloc

      Declaration

      BookkeepingAllocator bkalloc;

      If is not , is defined and accessible.

    • this

      Declaration

      this(ref Factory plant);
      this(Factory plant);

      Constructs an AllocatorList given a factory object. This constructor is defined only if Factory has state.

    • alignment

      Declaration

      enum uint alignment;

      The alignment offered.

    • allocate

      Declaration

      void[] allocate(size_t s);

      Allocate a block of size . First tries to allocate from the existing list of already-created allocators. If neither can satisfy the request, creates a new allocator by calling and delegates the request to it. However, if the allocation fresh off a newly created allocator fails, subsequent calls to will not cause more calls to .

    • owns

      Declaration

      Ternary owns(void[] b);

      Defined only if Allocator defines owns. Tries each allocator in turn, in most-recently-used order. If the owner is found, it is moved to the front of the list as a side effect under the assumption it will be used soon.

      Return Value

      Ternary.yes if one allocator was found to return Ternary.yes, Ternary.no if all component allocators returned Ternary.no, and Ternary.unknown if no allocator returned Ternary.yes and at least one returned Ternary.unknown.

    • expand

      Declaration

      bool expand(ref void[] b, size_t delta);

      Defined only if is defined. Finds the owner of and calls for it. The owner is not brought to the head of the list.

    • reallocate

      Declaration

      bool reallocate(ref void[] b, size_t s);

      Defined only if is defined. Finds the owner of and calls for it. If that fails, calls the global , which allocates a new block and moves memory.

    • deallocate

      Declaration

      bool deallocate(void[] b);

      Defined if and are defined.

    • deallocateAll

      Declaration

      bool deallocateAll();

      Defined only if and are defined.

    • empty

      Declaration

      const Ternary empty();

      Returns Ternary.yes if no allocators are currently active, Ternary.no otherwise. This methods never returns Ternary.unknown.