[erlang-questions] supervisor started from gen_server

Kannan <>
Fri May 20 13:52:54 CEST 2011


Mazen,

You can do the same thing with simple_one_for_one supervisors, one_for_all
supervisors and one_for_one supervisors stacked in different levels.





On Fri, May 20, 2011 at 2:55 PM, Mazen Harake <>wrote:

> I don't agree with the "never" part. There are corner cases and I would, in
> general, absolutely agree with what you wrote but here is one example of an
> exception.
>
> In my IRC library (https://github.com/mazenharake/eirc) I have the
> following scenario:
>
> One can create 1..n clients. Each client is a process (running a gen_server
> in eirc_cl.erl). A client can have many processes associated with it, in my
> case these are called Bots. Each bot is started and supervised by a client.
> A bot shall not terminate unless told to do so (gracefully) or if the parent
> dies (i.e the client). Now if I manually start a supervisor instance inside
> the gen_server I can simply make use of the supervisor functionality without
> handling any of that in my gen_server. I can add and remove children (bots)
> dynamically from my supervisor I.e. I don't have to maintain my own list of
> them and when I (the client) exits my children (I.e. the supervisor) will
> exit and thus my bots will exit... all according to OTP principals and I
> don't need to catch exit signals. This makes it REALLY easy to clean up
> things since all I have to do is to close the client process, the client
> process doesn't even need logic in the terminate callback since the children
> will exit with the same reason. If my supervisor was "on the outside" (like
> you suggest and which it normally is) I would have to make sure to clean up
> after myself with the supervisor.
>
> So it is much simpler (from an isolation point of view) to (in my case)
> start a supervisor Inside the gen_server.
>
> never say never ;)
>
> /M
>
>
>
>
>
> On 18 May 2011 14:13, Vance Shipley <> wrote:
>
>> On Wed, May 18, 2011 at 11:38:50AM +0200, Roberto Ostinelli wrote:
>> }  just a quick question: can you think of any case in which starting a
>> }  supervisor from a gen_server would actually be a perfectly fit idea?
>>
>> Never.
>>
>>                      +---------+
>>                      | foo_sup |
>>                      +-+-----+-+
>>                       /       \
>>           +----------+--+   +--+---------+
>>           | bar_sup_sup |   | foo_server |
>>           +---+---------+   +------------+
>>               |
>>          +----+----+
>>          | bar_sup |
>>          +---------+
>>
>> Start a supervisor for the new dynamic supervisor(s) and use
>> supervisor:start_child/2 from the gen_server to start it.
>>
>> --
>>         -Vance
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>
>
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