Concurrent Image Processing

Mix.install([
  {:kino, github: "livebook-dev/kino", override: true},
  {:kino_lab, "~> 0.1.0-dev", github: "jonatanklosko/kino_lab"},
  {:vega_lite, "~> 0.1.4"},
  {:kino_vega_lite, "~> 0.1.1"},
  {:benchee, "~> 0.1"},
  {:ecto, "~> 3.7"},
  {:math, "~> 0.7.0"},
  {:faker, "~> 0.17.0"},
  {:utils, path: "#{__DIR__}/../utils"},
  {:tested_cell, git: "https://github.com/BrooklinJazz/tested_cell"}
])

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Concurrent Image Processing

You have built an image processing app which helps users by converting image files from png time to jpeg.

We’ve provided an Image module which simulates this process.

defmodule Image do
  def convert(file) do
    # simulating expensive processing
    Process.sleep(2000)
    [file_name, _ext] = String.split(file, ".")
    file_name <> ".jpeg"
  end
end

Image.convert("a.png")

This process is very slow, and images take an average of 2 seconds to complete processing. Users with many files complain and ask that you improve performance.

Unfortunately, there is no way to improve the performance of processing an individual file, however you can leverage concurrency process many files at once.

Write a MutliImage converter module which takes in many files, and concurrently calls Image.convert/1 on each file.

MultiImage.convert(["a.png", "b.png", "c.png"])
["a.jpeg", "b.jpeg", "c.jpeg"]

When complete, rather than taking 8 seconds to convert 4 files, it should take approximately 2 seconds in the best case.

> This is for a computer with 4 or more cores. A computer with 2 cores would take 4 seconds, and a computer with a single core would still take 8 seconds.

defmodule MultiImage do
  # Optimize the function below using concurrency. Notice that it currently takes 8 seconds to run.
  def convert(files) do
    Enum.map(files, &Image.convert/1)
  end
end

# Ensure the result matches the following
MultiImage.convert(["a.png", "b.png", "c.png", "d.png"]) == [
  "a.jpeg",
  "b.jpeg",
  "c.jpeg",
  "d.jpeg"
]

Commit Your Progress

Run the following in your command line from the project folder to track and save your progress in a Git commit.

$ git add .
$ git commit -m "finish concurrent image processing exercise"