DynamicSupervisor: the option "max_restarts" only work if provided as initial argument
JoeZ99 opened this issue · comments
Elixir and Erlang/OTP versions
elixir 15.4
otp 26
Operating system
linux
Current behavior
When specifying the "max_restarts" option as a regular when using DynamicSupervisor, it doesn't work.
How to check?
Have this two modules:
defmodule Test2 do
use GenServer
def start_link(_opts \\ []) do
GenServer.start_link(__MODULE__, [])
end
def init(_opts \\ []) do
Process.send_after(self(), :boom, 2000)
{:ok, :ok}
end
def handle_info(:boom, _), do: raise "Boom!"
end and
defmodule Pipo do
def start(options_mr, args_mr) do
do_start(options_mr, args_mr)
end
@impl true
def init(args_mr) do
DynamicSupervisor.init(max_restarts: args_mr, strategy: :one_for_one, max_seconds: 10)
end
def add_children do
DynamicSupervisor.start_child(__MODULE__, Test2)
end
defp do_start(options_mr, args_mr) do
DynamicSupervisor.start_link(__MODULE__, args_mr, name: __MODULE__, max_restarts: options_mr)
end
end an then on a shell, do:
iex> Pipo.start(100,3)
iex> Pipo.add_childrenand you'll see how it explodes only three times (because after 3 restarts, the dynamicsupervisor dies), in spite of you specifying "100" restarts in the options
however, if you do:
iex> Pipo.start(3, 100)
iex> Pipo.add_childrenyou'll see it restarts the children more than three times.
Expected behavior
Based on documentation, I expect that providing max_restarts as regular option:
DynamicSupervisor.start_link(__MODULE__, _init_args, max_restarts: 100)would work
But only work if provided as initial option:
DynamicSupervisor.init(max_restarts: 100)
For clarity, Can you please link to the documentation that implied max_restarts work on start_link/3? Thank you!
@josevalim, I think it comes from
@spec start_link([option() | init_option()]) :: Supervisor.on_start()where :max_restarts is indeed seen as an init_option() element: https://hexdocs.pm/elixir/1.17.1/DynamicSupervisor.html#start_link/1
But that’s start_link/1, right?
But that’s start_link/1, right?
You're right. I mis-read it 😄 Maybe the OP did too 🤷 😄 Sorry for the noise.
Well, it's not so much a bug or a bad doc, but more like it's easy to confuse option with init_option in the docs, and the confusion of @paulo-ferraz-oliveira is a perfect example of that...
First and foremost, the people from https://github.com/arjan/singleton has suffered the same confusion (in fact, that's how I got -after 2 weeks- to nail this 😄 ), if you look at https://github.com/arjan/singleton/blob/master/lib/singleton/supervisor.ex#L25 and https://github.com/arjan/singleton/blob/master/lib/singleton/supervisor.ex#L25, you'll see that they intend to use max_restarts as an option to be passed to start_link/3
I've tried to read about it in the docs, and I find it at least slightly misleading...
- They talk about in https://hexdocs.pm/elixir/1.15.4/DynamicSupervisor.html#start_link/1 the
max_restarts. And in the spec of that function, they state:
So there are "init_options" and "options" (max_restartwould be an "init_option" only). If you click on the "init_option" and "option" links provided in that spec, you can see howmax_restartsbelongs only to the "init_option" group - On the other hand, in https://hexdocs.pm/elixir/1.15.4/DynamicSupervisor.html#start_link/3 they don't say anything about the
optionsthird argument
So, in a nutshell, I can't exactly "blame" the doc, but I think it's very easy to get confused and assume option and init_option are the same, and I'd rather be more explicit about the difference on init_option and option, which now can only be perceived if you link in the specs ....
Hi @JoeZ99! No worries, we can totally blame the docs! They can always improve and that's the biggest question: how could we improve them? Would you like to try a PR? I would be glad to review it.
hey @josevalim , txs!!!
I've made a PR: #13678, but I don't know what else to do ... Another thing is that this "doc improvement" is to be read at least since version 1.15.4 of elixir, I don't know if I should make a PR for that tag and every subsequent one ...
But that’s start_link/1, right?
You're right. I mis-read it 😄 Maybe the OP did too 🤷 😄 Sorry for the noise.
what does "OP" mean 😄 ????
I believe it means "Original Poster", so it was referring to you. :)