Hello!
I am writing my thesis application. I need linear programming, but my app is written in Elixir, which is really not the language for such operations. That is why I decided to use Erlport as the Elixir dependency, which is capable of connecting Python code with Elixir. I’m also using Pulp as the python library for the optimization.
Elixir version: 1.10.4,
Erlport version: 0.10.1,
Python version: 3.8.5,
PuLP version: 2.3
I’ve written such a module for Elixir-Python communication, which leverages the GenServer as the main ‘communication hub’ between Elixir and Python:
defmodule MyApp.PythonHub do
use GenServer
def start_link(_) do
GenServer.start_link(__MODULE__, nil, name: __MODULE__)
end
def init(_opts) do
path = [:code.priv_dir(:feed), "python"]
|> Path.join() |> to_charlist()
{:ok, pid} = :python.start([{ :python_path, path }, { :python, 'python3' }])
{:ok, pid}
end
def handle_call({:call_function, module, function_name, arguments}, _sender, pid) do
result = :python.call(pid, module, function_name, arguments)
{:reply, result, pid}
end
def call_python_function(file_name, function_name, arguments) do
GenServer.call(__MODULE__, {:call_function, file_name, function_name, arguments}, 10_000)
end
end
The GenServer module is calling python file, which contains such a function:
def calculate_meal_4(products_json, diet_json, lower_boundary, upper_boundary, enhance):
from pulp import LpMinimize, LpProblem, LpStatus, lpSum, LpVariable, value
import json
products_dictionary = json.loads(products_json)
print(products_dictionary)
diets_dictionary = json.loads(diet_json)
print(diets_dictionary)
model = LpProblem(name="diet-minimization", sense=LpMinimize)
# ... products setup ...
x = LpVariable("prod_1_100g", lower_boundary, upper_boundary)
y = LpVariable("prod_2_100g", lower_boundary, upper_boundary)
z = LpVariable("prod_3_100g", lower_boundary, upper_boundary)
w = LpVariable("prod_4_100g", lower_boundary, upper_boundary)
optimization_function = # ... optimization function setup ...
model += # ... optimization boundary function setup ...
model += optimization_function
print(model)
solved_model = model.solve()
print(value(model.objective))
return [value(x), value(y), value(z), value(w)]
The call to the GenServer itself looks like that:
PythonHub.call_python_function(:diets, python_function, [products_json, meal_statistics_json, @min_portion, @max_portion, @macro_enhancement])
where python_function is :calculate_meal_4 and products_json and meal_statistic_json are jsons containing required data.
While calling calculate_meal_4 via python3 diets.py, which launches the python script above with some example, but real (taken from the app), data everything works fine - I’ve got the minimized result in almost no time. The problem occurs while calling the python script via Elixir Erlport. Looking at the printed outputs I can tell that it seems working until
solved_model = model.solve()
is called. Then the script seems to freeze and GenServer finally reaches the timeout on GenServer.call function.
I’ve tested also the call on a simple python test file:
def pass_var(a):
print(a)
return [a, a, a]
and it worked fine.
That is why I am really consterned right now and I am looking for any advices. Shamefully I found nothing yet.
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