How to perform actions periodically with Erlang's gen_server?

Question

I want to start a gen_server that additionally, will perform one action every minute.

What is the best way to schedule that?

Answer 1

There is actually a built-in mechanism within gen_server to accomplish the same thing. If the third element of response tuple of the init, handle_call, handle_cast or handle_info methods in the gen_server is an integer, a timeout message wil be sent to the process after that period of time in millisecs... which should be handled using handle_info. For eg :

init(Args) ->
   ... % Start first timer
   {ok, SomeState, 20000}. %% 20000 is the timeout interval

handle_call(Input, From, State) ->
   ... % Do something
   ... % Do something else
   {reply, SomeState, 20000}. %% 20000 is the timeout interval

handle_cast(Input, State) ->
   ... % Do something
   ... % Do something else
   {noreply, SomeState, 20000}. %% 20000 is the timeout interval


%% A timeout message is sent to the gen_server to be handled in handle_info %%
handle_info(timeout, State) ->
   ... % Do the action
   ... % Start new timer
   {noreply, SomeState, 20000}. %% "timeout" can be sent again after 20000 ms