Fl4m3Ph03n1x
Manage state in Elixir
Background
I have an application that upon start creates 100 processes. Now, every time I need to perform a specific operation (say, calculate the size of my ego 
) I pick one of those processes at random to perform the calculation.
So now I need to access those processes, which means I need to save them somewhere, aka, I need state.
State via named ETS tables
This solution advocates that when starting my app, I create all the processes and save their pids into an ETS table with a name (which is a singleton in the end).
This solution is simple, and works as a cache (so far so good), but I really don’t like singletons in my apps because they make for code poorly testable. I could create a mock of the singleton and use it for tests, but I wonder if there is simpler way.
State via GenServer
After reading pragmatic’s Dave approach to components, I understand that he (and some erlangers) prefer to manage state via GenServers. This would mean I need processes to communicate with this GenServer and would add a lot of boiler plate code to my app, not to mention I believe this is quite overkill for the problem at hand - I just want a table of pids after all.
Questions
So this brings me to a couple of questions:
- Are there other ways to manage State in Elixir?
- Which approach (ets or genserver) would you choose and why?
PS: the size of my ego is the same as the size of my intelligence: NaN (so small doesn’t even qualify 
)
Most Liked
shanesveller
I would say that this isn’t a question of state so much as of process registration. The workers themselves sound stateless in your description. Any one of them is capable of fulfilling a request, and none of the persist or share anything between subsequent requests.
Read up on how GenServer’s allow various forms of name registration. Next, take a look at :global from Erlang and Registry from the Elixir stdlib. If you just need a constant-sized worker pool where any of them are used to handle a given single invocation, look at the :poolboy Erlang library. One of these should fit your use-case.
benwilson512
How would the process get a command if not by receiving a message? Notably if they’re inside a registry you don’t also need pg2, you can use Registry to broadcast, there are examples in the registry docs.
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bottlenecked
This still sounds like poolboy to me- unless each connection is to a different endpoint, in which case process registration like other people mentioned here would work better. But if you connect to the same (or just a couple) different endpoints and do not wish to pay upfront the cost of opening 10000 connections, you can do that lazily with poolboy using a small size with a large max overflow
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