[erlang-questions] Stopping gen_server during processing

[Tony Rogvall]

Maybe you just want to kill it ?

exit(Pid, die_now). 

or if the little bugger is trapping exit you may have to be brutal.

exit(Pid, kill).

http://www.erlang.org/doc/man/erlang.html#exit-2


You can send the process normal messages:

Pid ! stop_processing_now.

Then while doing processing loop:

check_records(State) ->
	do some work...
	receive 
		stop_processing_now -> {stop, normal, State};
	after 0 ->
		check_records(State)
	end

The after 0 make sure that the process will not wait for messages, also
the selective receive approach here will guarantee that messages to
the gen_server (call and casts etc) will stay where they are.

You may have to add a clause in handle_info to handle the case
where the message is receive by the gen_server dispatcher.

handle_info(stop_processing_now, State) ->
	Stop? or something


/Tony



On 8 nov 2013, at 10:43, Janos Hary <janos.n.hary@REDACTED> wrote:

> Sorry, I cannot see how could it work in Erlang.
> 
> I have a handle_info processing a large number of records:
> handle_info(check, State) ->
> 	check_records(State).
> 
> check_records(State) ->
> 	do some work...
> 	case State#stop_flag of
> 		true ->
> 			{stop, normal, State};
> 		_ ->
> 			check_records(State)
> 	end.
> 
> The State in check_records cannot changed from another cast. I'm not even
> sure that the cast will execute before check_records finishes.
> 
> Janos
> 
> 
> -----Original Message-----
> From: erlang-questions-bounces@REDACTED
> [mailto:erlang-questions-bounces@REDACTED] On Behalf Of Bengt Kleberg
> Sent: Friday, November 08, 2013 9:28 AM
> To: undisclosed-recipients:
> Cc: erlang-questions@REDACTED
> Subject: Re: [erlang-questions] Stopping gen_server during processing
> 
> These are my opinions, not hard facts.
> 
> Add a member to the gen_server state record that says that you are going to
> stop when possible. Use a cast to set it to true when you want to stop. If
> it is true and you can stop the gen_server, stop it.
> 
> 
> bengt
> 
> On Fri, 2013-11-08 at 08:55 +0100, Janos Hary wrote:
>> All,
>> 
>> 
>> 
>> I have a gen_server process which periodically processes new records 
>> from a database. I use timer:send_after to schedule gathering and 
>> processing new records. I can gracefully stop the gen_server when it 
>> is waiting, but I need a way to stop it during processing. Of cause I 
>> only want to stop it at certain points of the processing, for example 
>> before starting to process the next record. I need to group the 
>> records, so I cannot ask them one by one from the db.
>> 
>> 
>> 
>> What is the preferred way of doing this?
>> 
>> 
>> 
>> Thanks for your answers in advance.
>> 
>> Janos
>> 
>> 
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