sync call from process with many incoming msgs

Need to implement sync call from proces which receives many incoming messages from other processes. Problem in distinguish - when msg in return to call arrived. Do i need to spawn additional process for extracting msgs from queue into buffer while r开发者_开发问答eturn msg not encountered and then send it to main process and after it every else accepted.

The trick is to use a reference as a token for replication:

 replicate() ->
    {ok, Token} = db:ask_replicate(...),
    receive
       {replication_completed, Token} ->
             ok
    end

where Token is created with a call to make_ref(). Since no other message will match Token, you are safe. Other messages will be placed in the mailbox for later scrutiny.

However, the above solution does not take process crashes into account. You need a monitor on the DB server as well. The simplest way to get the pattern right is to let the mediator be a gen_server. Alternatively, you can read a chapter in LearnYouSomeErlang: http://learnyousomeerlang.com/what-is-otp#the-basic-server look at the synchronous call in the kitty_server.