DLPack.jl

Julia wrapper for DLPack.

This module provides a Julia interface to facilitate bidirectional data exchange of tensor objects between Julia and Python libraries such as JAX, CuPy, PyTorch, among others (all python libraries supporting the DLPack protocol).

It can share and wrap CPU and CUDA arrays, and supports interfacing through both PyCall and PythonCall.

Installation

From the Julia REPL activate the package manager (type ]) and run:

pkg> add DLPack

Usage

As an example, let us wrap a JAX array instantiated via the PyCall package:

using DLPack
using PyCall

np = pyimport("jax.numpy")
dl = pyimport("jax.dlpack")

pyv = np.arange(10)
v = from_dlpack(pyv)
# For older jax version use:
# v = DLPack.wrap(pyv, o -> @pycall dl.to_dlpack(o)::PyObject)

(pyv[1] == 1).item()  # This is false since the first element is 0

# Let's mutate an immutable jax DeviceArray
v[1] = 1

(pyv[1] == 1).item()  # true

If the python tensor has more than one dimension and the memory layout is row-major the array returned by DLPack.from_dlpack has its dimensions reversed. Let us illustrate this now by importing a torch.Tensor via the PythonCall package:

using DLPack
using PythonCall

torch = pyimport("torch")

pyv = torch.arange(1, 5).reshape(2, 2)
v = from_dlpack(pyv)
# For older torch releases use:
# v = DLPack.wrap(pyv, torch.to_dlpack)

Bool(v[2, 1] == 2 == pyv[0, 1])  # dimensions are reversed

Likewise, we can share Julia arrays to python:

using DLPack
using PythonCall

torch = pyimport("torch")

v = rand(3, 2)
pyv = DLPack.share(v, torch.from_dlpack)

Bool(pyv.shape == torch.Size((2, 3)))  # again, the dimensions are reversed.

Do you want to exchange CUDA tensors? Worry not:

using DLPack
using CUDA
using PyCall

cupy = pyimport("cupy")

pyv = cupy.arange(6).reshape(2, 3)
v = from_dlpack(pyv)
# For older versions of cupy use:
# v = DLPack.wrap(pyv, o -> pycall(o.toDlpack, PyObject))

v .= 1
pyv.sum().item() == 6  # true

pyw = DLPack.share(v, cupy.from_dlpack)  # new cupy ndarray holding the same data

[!WARNING]

Whenever a Python function allocates a lot of intermediate Python objects, Julia has no way of knowing when it should garbage collect such objects, and in some cases the allocated memory may grow too large. In such a case, it might be important to manually call GC.gc(false) from time to time. See https://github.com/pabloferz/DLPack.jl/issues/26 for an example of this issue.