ArrayAllocators

Introduction

This Julia package provides mechanisms to allocate arrays beyond that provided in the Base module of Julia.

The instances of the sub types of AbstractArrayAllocator take the place of undef in the Array{T}(undef, dims) invocation. This allows us to take advantage of alternative ways of allocating memory. The allocators take advantage of Base.unsafe_wrap in order to create arrays from pointers. A finalizer is also added for allocators that do not use Libc.free.

In the base ArrayAllocators package, the following allocators are provided.

An extension for use with Non-Uniform Memory Access allocations is available via the subpackage NumaAllocators.jl.

Example Basic Usage

Each of the methods below allocate 1 MiB of memory. Using undef as the first argument allocate uninitialized memory. The values are not guaranteed to be 0 or any other value.

In Base, the method zeros can be used to explicitly fill the memory with zeros. This is equivalent to using fill!(..., 0). Using calloc guarantees the values will be 0, yet is often as fast as using undef initialization.

julia> using ArrayAllocators

julia> @time U = Array{Int8}(undef, 1024, 1024);
  0.000019 seconds (2 allocations: 1.000 MiB)

julia> @time Z1 = zeros(Int8, 1024, 1024);
  0.000327 seconds (2 allocations: 1.000 MiB)

julia> @time Z2 = fill!(Array{UInt8}(undef, 1024, 1024), 0);
  0.000301 seconds (2 allocations: 1.000 MiB)

julia> @time C = Array{Int8}(calloc, 1024, 1024);
  0.000020 seconds (4 allocations: 1.000 MiB)

julia> sum(C)
0

Caveats

Above calloc appears to be much faster than zeros at generating an array full of 0s. However, some of the array created with zeros has already been fully allocated. The array allocated with calloc take longer to initialize since the operating system may have deferred the actual allocation of memory.

julia> @time Z = zeros(Int8, 1024, 1024);
  0.000324 seconds (2 allocations: 1.000 MiB)

julia> @time fill!(Z, 1);
  0.000138 seconds

julia> @time fill!(Z, 2);
  0.000136 seconds

julia> @time U = Array{Int8}(calloc, 1024, 1024);
  0.000020 seconds (4 allocations: 1.000 MiB)

julia> @time fill!(U, 1);
  0.000349 seconds

julia> @time fill!(U, 2);
  0.000136 seconds