[erlang-questions] puzzle about gen_server:call/2

Ulf Wiger <>
Mon Sep 22 16:44:01 CEST 2008


It is possible to return {noreply, NewState} in cases when
e.g. the request triggers a background job. The server can
then reply later with gen_server:reply(From, Reply), and
be free to handle other requests in the meantime.

BR,
Ulf W

2008/9/22 litao cheng <>:
> Greetings !
> I read the codes of gen_server.erl and gen.erl in stdlib, the
> gen_server:call/3 invoke process is illustrated as follows:
>
> gen_server:call/3 ->
> gen:call/3 ->
> gen:call/4 ->
> gen:do_call/4
>
> in the gen:do_call/4, first check if the target Process is exist by invoke
> erlang:monitor/2, if the process is alive then send the message,
> after the messge is sended, invoke the  wait_resp_mon/3 to wait the
> response, if the Mod:handle_call return {reply, Reply, State}, then in
> wait_resp_mon/3, we can receive the message and return the Reply to the
> gen_server:call/2 caller. My Question is: If the Mod:handle_call return
> {noreply, State}, then I see the gen_server continue the loop, not send any
> message to caller, in that case I think the wait_resp_mon/3 will be blocked,
> Factually I know the caller not block! Anyone can give me a explain?
>
> thanks!
> Best Regards!
>
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