'after' in gen_server

Fri Mar 24 02:59:45 CET 2006

The only problem I have with that is it sounds very error prone.  What 
if I forget a timeout?  The more callbacks i implement the uglier it'll 
get, won't it?

On Mar 23, 2006, at 4:35 PM, Rick Pettit wrote:

> On Thu, Mar 23, 2006 at 04:26:22PM -0500, orbitz@REDACTED wrote:
>> I want to do it from all callbacks.  Basically I want to make it so if
>> the server is idle for X amount of time, then that means something is
>> wrong and I need to do something to figure out what is wrong.
> Then have your callbacks set a gen_server "idle timeout" by way of the
> gen_server timeout mechanism, and service timeouts in handle_info/2.
> It is as simple as passing a timeout value in the return value from 
> your
> callbacks--Module:init/1, Module:handle_call/3, Module:handle_cast/2, 
> etc.
> -Rick
>> On Mar 23, 2006, at 11:04 AM, Rick Pettit wrote:
>>> On Thu, Mar 23, 2006 at 10:42:04AM -0500, orbitz@REDACTED wrote:
>>>> I am reworking a bit of code into gen_server pattern.  In this code 
>>>> I
>>>> have a typical loop construct.  In this I want to perform an action 
>>>> if
>>>> no messages have been receive in a certain amount of time, to do 
>>>> this
>>>> I
>>>> simply have after sometimeout ->.  Is there any equivalence of this 
>>>> in
>>>> gen_server?
>>> If I understand you correctly, all you need to do is set a timeout 
>>> when
>>> returning from one of the gen_server callback functions.
>>> For example, instead of returning {ok,State} from Module:init/1, 
>>> return
>>> {ok,State,TimeoutMs}. You can do this for all the gen_server callback
>>> routines (at least handle_call/handle_cast, etc).
>>> This effectively sets a timer which will expire if no message is
>>> received
>>> by the gen_server before TimeoutMs has elapsed. If/when the timer 
>>> does
>>> expire, you receive a 'timeout' message in Module:handle_info/2.
>>> -Rick
>>> P.S. Since gen_server abstracts the server receive loop, I (as a
>>> general rule
>>>     of thumb) *never* call receive in a gen_server callback module.
>>>> It has been suggested that I use a timer and record when the last
>>>> message has come in and when the timer signals check against that
>>>> message.  This seems a poor solution.  Another suggestions was to 
>>>> use
>>>> a
>>>> gen_fsm with a timeout, but this seem a bit much just to get an
>>>> 'after'
>>>> mechanism. Any other suggestions?  Perhaps my disregard of gen_fsm 
>>>> is
>>>> a
>>>> bit hasty?

More information about the erlang-questions mailing list