[erlang-questions] gen_server and init

[Éric Pailleau]

Hi,
To see this,  do a sync call to your gen server in the init function. Your process will stuck forever, by launching observer, on your process detail, you will see your message waiting in its process message queue,  until process is killed. 

Le 27 juil. 2015 16:44, Matthew Evans <mattevans123@REDACTED> a écrit :
>
> Thanks guys,
>
> I guess I was under the assumption that a process could not even get any messages until init had returned and the pid was registered.
>
> > Date: Mon, 27 Jul 2015 16:40:30 +0200
> > From: essen@REDACTED
> > To: mattevans123@REDACTED; erlang-questions@REDACTED
> > Subject: Re: [erlang-questions] gen_server and init
> > 
> > This and sending yourself a message is a bad idea. It will usually work, 
> > until it doesn't, and you will have a very hard time figuring out why.
> > 
> > Instead, start the process using proc_lib:spawn_link or 
> > proc_lib:start_link (depending on whether it needs to be synchronous or 
> > not), then perform your initialization (calling proc_lib:init_ack where 
> > appropriate), and finally calling gen_server:enter_loop.
> > 
> > What this gives you is pretty much the ability to customize the 
> > initialization of your gen_server process.
> > 
> > This is the correct way to do it. Your solution can fail if you receive 
> > a message. Sending yourself a message is subject to race conditions 
> > where you receive a message before you could init.
> > 
> > On 07/27/2015 04:25 PM, Matthew Evans wrote:
> > > Hi,
> > >
> > > We have used this pattern in gen_servers for a long time now:
> > >
> > > init(_) ->
> > > %% Some stuff
> > > {ok, #state{}, 0}.
> > >
> > > %%%
> > > %%%
> > >
> > > handle_info(timeout, State) ->
> > > %% Init stuff
> > > {noreply,State}
> > >
> > > Basically the idea is to prevent init from blocking and to have init/1
> > > return with a timeout of 0 causing an immediate timeout message to be
> > > invoked in the handle_info.
> > >
> > > Here's what's odd. Sometimes this timeout does not fire. It doesn't
> > > appear that any message is getting sent, but I would imagine that since
> > > it's a registered gen_server there is no way that can happen.
> > >
> > > Does anyone have any ideas?
> > >
> > > We are running vsn 17.1, and ntp is enabled on the host (Linux).
> > >
> > > Thanks
> > >
> > >
> > > _______________________________________________
> > > erlang-questions mailing list
> > > erlang-questions@REDACTED
> > > http://erlang.org/mailman/listinfo/erlang-questions
> > >
> > 
> > -- 
> > Loïc Hoguin
> > http://ninenines.eu
> > Author of The Erlanger Playbook,
> > A book about software development using Erlang