Can a gen_server receive messages from two different client processes?

Question

• I have a gen_server (my_gen_server.erl) that is started by another server (i.e. ejabberd)

• Inside my_gen_server.erl, I start another server which handles HTTP2 calls like this:

  {ok, ServerPid} = apns:connect(cert, my_first_connection).
  

• Now, my_gen_server is receiving messages both from ejabberd and ServerPid which I handle as follows:

  1. handle_info({reconnecting, ServerPid}=Msg, State) -> %% do Something
  2. handle_info({connection_up, ServerPid}=Msg, State) -> %% do Something
  
  3. handle_info(#offline_msg{...} = _Msg, State) -> %% do Something
  

So 1 & 2 are sent by ServerPid and 3 is sent by ejabberd. This is working but I am not sure about the correct behavior. So,

My question is:

• Is this correct gen_server behavior to receive/handle messages from multiple client processes?

Please help.

Answer 1

Any process that has the gen_server's pid can send the gen_server a message using !, which will be handled by the gen_server's function:

handl_info()

Any process that has the gen_server's pid can call the functions:

call(GenServerPid, Msg) 
cast(GenServerPid, Msg)

which will be handled by the gen_server functions:

handle_call() 
handle_cast() 

In elixir, there is a module called Agent, which is just a gen_server that stores State, like a counter. Multiple processes can update the counter and retrieve the current count. Of course, some process has to start the gen_server, then pass the pid to the other processes that want to update/retrieve the count.