Weird behaviour in Task.start Elixir - erlang

Question

I am trying to write a Gossip Simulator in Elixir using GenServer. I have a main() method which acts as a client creating a network topology and starts all the actors (GenServer's). It then sends a Genserver.cast() to an Actor to initiate the gossip. The Actor in its handle_cast() starts a Task.start() to start gossiping with other actors. Looks like I am not using Task.start() (line 16 in actor.ex) in the right way as the called task startGossiping() is never executed nor the statements after Task.start(). Mix just exits without giving any error. The shortened program is given below.
actor.ex -
defmodule Actor do
use GenServer
def init([nodeId, neighborList, algorithm]) do
inspect "#{nodeId}"
recCount = 1
gossipingTask = 0
{:ok, {nodeId, neighborList, algorithm, recCount, gossipingTask}}#nodeId, neighborList, algorithm, receivedCount
end
def handle_cast({:message, rumour}, state) do
{nodeId, neighborList, algorithm, recCount, gossipingTask} = state
IO.puts "nodeId - #{nodeId} recCount - #{recCount} handle_cast: #{rumour} gossipingTask - #{gossipingTask}"
nL = elem(state, 1)
IO.puts "here #{rumour}"
gossipingTask = Task.start(fn -> startGossiping(nL, rumour) end)
IO.puts "Now again - #{rumour}"
{:noreply, {nodeId, neighborList, algorithm, recCount + 1, gossipingTask}}
end
def startGossiping(nL, rumour) do
IO.puts "In startGossiping "
#{Enum.random(nL)}"
# GenServer.cast(Proj2.intToAtom(Enum.random(nL)), {:message, rumour})
end
end
proj2.ex -
defmodule Proj2 do
# Instructions to run the project
# 1) $mix escript.build
# 2) $escript proj2 100 full gossip
def main(args) do
# Receive total number of nodes, topology, algorithm, triggerNodes(optional), threshold(optional) from user.
# Read README.md for more details
numOfNodes = String.to_integer(Enum.at(args, 0))
topology = Enum.at(args, 1)
algorithm = Enum.at(args, 2)
numOfNodes = if String.contains?(topology, "2d"), do: round(:math.pow(round(:math.sqrt(numOfNodes)), 2)), else: numOfNodes
case topology do
"full" ->
Enum.each 1..numOfNodes, fn nodeId ->
neighborList = getNeighborsFull(nodeId, numOfNodes)
inspect neighborList
nodeId_atom = intToAtom(nodeId)
GenServer.start_link(Actor, [nodeId, neighborList, algorithm], name: nodeId_atom)
# IO.puts "In main, nodeId = #{nodeId}"
end
end
GenServer.cast(intToAtom(2), {:message, "This is Elixir Gossip Simulator"})
end
def getNeighborsFull(nodeId,numOfNodes) do
range = 1..numOfNodes
range
|> Enum.filter(fn(value) -> value != nodeId end)
|> Enum.map(fn(filtered_value) -> filtered_value * 1 end)
# IO.inspect Neighboringlist
end
def intToAtom(integer) do
integer |> Integer.to_string() |> String.to_atom()
end
end
UPDATE :
Haven't figured out the problem still. I am not able to start any concurrent process actually. spawn, start_link, Task none of them are starting an asynchronous task.

Answer 1

Neither GenServer.cast/3 nor Task.start/1 would prevent your application from exiting.
I am unsure why would you build an escript to test the code. You have the following options to wait until the execution finishes before exiting (including but not limited to):
• use mix run --no-halt
• create an Application
• start the task linked and use Task.await/2 somewhere in your code to wait while the task is finished.