[erlang-questions] Custom supervisor

Paul Guyot <>
Sat Jan 17 12:27:51 CET 2009


Le 17 janv. 09 à 10:52, Dominic Williams a écrit :

> Hi Paul,
>
> Paul Guyot a écrit :
> > [...]
>> Is there a more OTP-way to perform this, i.e. to track the death/  
>> restarts of the children of a supervisor?
>
> In the OTP approach, you should not mix supervision with work. Your  
> manager is doing work, so it should not be a supervisor as well.
>
> One solution would be for the manager to attach the workers as  
> dynamic childs to its own supervisor. This would be if the number of  
> workers is variable.
>
> If the number of workers is fixed, everyone (manager and workers)  
> could be declared as fixed children in the same supervisor.
>
> Both of the above approaches are right if the restart strategies are  
> the same for manager and workers, though, which is rarely the case.  
> The "standard" solution in your kind of case is to have a top  
> supervisor that supervises the manager and another supervisor. The  
> sub-supervisor supervises all the workers. You'd probably need to  
> have the workers register themselves with the manager when they  
> start or restart.


Hello Dominic,

Thank you for your reply.

What you describe is what we did at first, i.e. a tree with a  
manager_sup that has the manager and a worker_sup as its children, the  
worker_sup having a simple_one_for_one strategy (we have a variable  
number of workers). We abandoned this approach because the worker  
needs to know when its started or restarted. Hence the idea of a  
custom supervisor that would change a parameter to start_link whenever  
the process is started or restarted. But maybe we outlook the standard  
supervisor and there is a way to figure out if a worker is started or  
restarted by the supervisor?

I also realize that having a supervisor doing some work is a very bad  
idea as it implies that the workers are killed if the manager dies,  
which might not be desirable.

Regards,

Paul




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