Is there a way to access the state of a GenServer?

Question

Is there a built in way to see the current state of a GenServer? You can always implement a simple call to return the state, but is there a more generic way?

When I run :observer.start I can look at the running applications and see their state, so it seems possible. But it may be doing some double-secret Erlang voodoo to get that.

Answer 1

It depends on how you're going to use it.

If obtaining the state is part of your business logic, then yes - this should be properly modelled in your application with GenServer.call to return the state.

If you need this only in terms of debugging/insights of your application, you could use :sys.get_state like this:

iex> :sys.get_state(pid)
# some state printed

Please be aware of that :sys.get_state will accept either pid or the name of the server (if it is registered under one).

Also, please take a look at this section about debugging with :sys module in Elixir's GenServer documentation as it is very useful.

Hope that helps!