[erlang-questions] supervising applications

Moe Aboulkheir <>
Wed Sep 20 03:10:01 CEST 2006



On Tue, 19 Sep 2006 17:43:56 -0700, Bob Ippolito <> wrote:
>On 9/19/06, Moe Aboulkheir <> wrote:
>>
>>
>>On Tue, 19 Sep 2006 17:12:10 -0700, Bob Ippolito <> wrote:
>> >On 9/19/06, Moe Aboulkheir <> wrote:
>> >>Hi,
>> >>
>> >>I'm very new to this.  I've written a trivial Erlang application, and i 
>>am
>> >>trying to write a second one which provides a superset of the 
>>functionality
>> >>of the first.  The supervisor that is started from start/2 in the second
>> >>application tries to start the first application by including an entry 
>>for
>> >>it in the list returned from init/1.  I tried the following two methods,
>> >>but neither works:
>> >>
>> >>1) Having StartFunc (in the init/1 term) as {application, start, [app1]}.
>> >>This doesn't work because application:start/1 returns ok instead of {ok,
>> >>Pid} like the supervisor interface wants.  Ideally i'd have liked to be
>> >>able to this, because app1:start/2 passes some stuff from its environment
>> >>as the argument to app1_supervisor:start_link/1, but i guess i could move
>> >>that stuff further into app1, though i saw an example that did the setup
>> >>here, and it makes sense to me
>> >>
>> >>2) Having StartFunc as {app1_supervisor, start_link, ...}.  This doesn't
>> >>work because some code inside app1 depends on things in the environment 
>>of
>> >>app1's .app file - things that don't seem to be available when i start it
>> >>like this.  Again, i could move these variables into app2's environment,
>> >>but i'd like to be able to use app1 without using app2, and would rather
>> >>not maintain the information in two places.
>> >>
>> >>Any ideas?
>> >
>> >Isn't this what you'd use the {applications, [app1, ...]} list for in
>> >the .app file?
>> >
>> >-bob
>> >
>>
>>I tried that before (putting app1 in app2's "applications" list and 
>>starting its supervisor directly from app2), but I get an 
>>{error,{not_started,app1}} when starting app2.  the docs say:
>>
>>"""
>>[when starting an application]
>>The application controller checks the value of the application 
>>specification key applications, to ensure that all applications that should 
>>be started before this application are running. If not, 
>>{error,{not_started,App}} is returned, where App is the name of the missing 
>>application.
>>"""
>>
>>Which seems to indicate that as long as app1 is in app2's applications 
>>list, it won't be possible to start it from app2's start() - and cursory 
>>examination (an erlang:display() in start()) indicates that it doesn't even 
>>get that far.
>
>I think that's taken care of when you create a boot script from the
>.app, though...
>

Thanks, I'll look into that further

--
Moe Aboulkheir



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