Libtask

C shim for task copying in Turing

Getting Started

using Libtask

# Stack allocated objects are deep copied.
function f_ct()
  t = 0;
  while true
    produce(t)
    t = 1 + t
  end
end

t = CTask(f_ct)

consume(t) == 0
consume(t) == 1
a = copy(t);
consume(a) == 2
consume(a) == 3
consume(t) == 2
consume(t) == 3

# Heap allocated objects are shallow copied.

function f_ct2()
  t = [0 1 2];
  while true
    produce(t[1])
    t[1] = 1 + t[1]
  end
end

t = CTask(f_ct2)

consume(t) == 0
consume(t) == 1
a = copy(t);
consume(a) == 2
consume(a) == 3
consume(t) == 4
consume(t) == 5

# `TArray` implements a copy-on-write array. This is useful for task copying.
#  In constrast to standard arrays, which are only shallow copied during task copying,
#  `TArray` are deep copied after task copying.

function f_cta()
  t = TArray(Int, 1);
  t[1] = 0;
  while true
    produce(t[1])
    t[1] = 1 + t[1]
  end
end

t = CTask(f_cta)

consume(t) == 0
consume(t) == 1
a = copy(t);
consume(a) == 2
consume(a) == 3
consume(t) == 2
consume(t) == 3

Note: The Turing probabilistic programming language uses this task copying feature in an efficient implementation of the particle filtering sampling algorithm for arbitary order Markov processes.

Disclaimer: This feature is still experimental and should only be used with caution. Some discussions on its potential caveats can be found here.

For Developer

Release a new version

- If you have updates of the binary dylib (files under the `deps`
  directory), you should:
  - Update the version/commit information in [this
    file](https://github.com/JuliaPackaging/Yggdrasil/blob/master/L/Libtask/build_tarballs.jl)
    by a pull request
  - Wait for that PR being merged, then you will find a new
    release of the dylib
    [here](https://github.com/JuliaBinaryWrappers/Libtask_jll.jl/releases)
  - Then, in the root directory of the Yggdrasil project, run
    `https://github.com/JuliaBinaryWrappers/Libtask_jll.jl/releases`,
    you will get a build file like
    `build/build_Libtask.v0.3.1.jl`. Copy the binary download
    information (the variables `bin_prefix` and `download_info`)
    from that generated file to `deps/build.jl` in our repo and
    commit the changes.
- If you don't make any changes about the dylib, just ignore the
  first step and go to next one.
- Update the new version number in `Project.toml`, ping
  @JuliaRegistrator with `@JuliaRegistrator register` in a
  comment.