How to restart a supervised task that crashes

Question

{:ok, tas} = Task.Supervisor.start_link(restart: :transient, max_restarts: 4)
a = 1
Task.Supervisor.async_nolink(tas, fn -> IO.puts "#{a}..." end)
Task.Supervisor.async_nolink(tas, fn ->
  IO.puts "Not Restarting :( "
  1 = 2
end)
a =  a + 1
Task.Supervisor.async_nolink(tas, fn -> IO.puts "#{a}.." end)
a =  a + 1
Task.Supervisor.async_nolink(tas, fn -> IO.puts "#{a}.." end)

The option restart: :transient does not seem to have any effect.

I've few tasks Task.async(fn(x) -> fetch_info(x) end that make an http request to get multiple resources, and has timeout error. It would be nice to retry those failing tasks, instead of using try, rescue.

I think async_nolink is the closest I got without crashing the process. If there is no way using Task, do we have a simpler approach using Supervisor that starts multiple process which exists once their job is done and restart them if they fail?

Answer 1

You just have to use Task.Supervisor.start_child instead of Task.Supervisor.async_nolink to have the children properly restarted:

{:ok, tas} = Task.Supervisor.start_link(restart: :transient, max_restarts: 4)

Task.Supervisor.start_child(tas, fn -> 1 = 2 end)